OCS Study 

MMS 2004-060 

 

Boundary Layer Study 

in the Western and Central Gulf of Mexico 

Final Report 

U.S. Department of the Interior

Minerals Management Service 

Gulf of Mexico OCS Region 
U.S. Department of the Interior

Minerals Management Service 

Gulf of Mexico OCS Region 

OCS Study 

MMS 2004-060 

Boundary Layer Study 

in the Western and Central Gulf of Mexico 

Final Report 

Authors 

Clinton P. MacDonald 

Paul T. Roberts 

Mark R. Lilly 

Charley A. Knoderer 

Dianne S. Miller 

Sonoma Technology, Inc. 

Petaluma, California 

Steven R. Hanna 

Hanna Consultants 

Kennebunkport, Maine 

Prepared under MMS Contract 

1435-01-99-CT-30919 

by 

Sonoma Technology, Inc. 

1360 Redwood Way, Suite C 

Petaluma, California 94954-1169 

Published by 

New Orleans

October 2004 
iii

DISCLAIMER 

This final report was prepared under contract between the Minerals Management Service (MMS) 

and Sonoma Technology, Inc. This Final Report has been technically reviewed by the MMS, 

and it has been approved for publication. Approval does not signify that the contents necessarily 

reflect the views and policies of the MMS, nor does mention of trade names or commercial 

products constitute endorsement or recommendation for use. It is, however, exempt from review 

and compliance with the MMS editorial standards. 

REPORT AVAILABILITY 

Extra copies of this report may be obtained from the Public Information Office (Mail Stop 5034) 

at the following address: 

U.S. Department of the Interior 

Minerals Management Service 

Gulf of Mexico OCS Region 

Public Information Office (MS 5034) 

1201 Elmwood Park Boulevard 

New Orleans, Louisiana 70123-2394 

Telephone: (504) 736-2519 or 

 1-800-200-GULF 

CITATION 

Suggested citation: 

MacDonald C.P., P.T. Roberts, M.R. Lilly, C.A. Knoderer, D.S. Miller, and S.R. Hanna. 2004. 

Boundary layer study in the western and central Gulf of Mexico: final report. 

U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, 

New Orleans, LA. OCS Study MMS 2004-060. 606 pp.
ACKNOWLEDGMENTS 

This research was sponsored by the Minerals Management Service of the 

U.S. Department of Interior. We thank the current Contracting Officer’s Technical 

Representative (COTR), Dr. C.H. Huang, and Dr. Alexis Lugo-Fernandez the COTR early in the 

study, for their support and technical advice. We appreciate the technical advice from the 

Scientific Review Board, Dr. Stephen Burk, Dr. S.A. Hsu, and Dr. Richard McNider, and one of 

the developers of the COARE model, Dr. Christopher Fairall. We acknowledge the hard work 

and assistance given by numerous persons responsible for meteorological data collection, 

validation, and processing. We thank Lisa DiStefano, Jana Schwartz, and Sandy Smethurst of 

STI for editing and producing this report, and Jeffrey Prouty, Timothy Dye, and Eric Gray of STI 

for their invaluable role in designing the database and the data visualization tool. 

v 
vii 

TABLE OF CONTENTS 

Section Page

ACKNOWLEDGMENTS ...............................................................................................................v

LIST OF FIGURES ....................................................................................................................... xi 

LIST OF TABLES.................................................................................................................... xxvii 

LIST OF VARIABLES.............................................................................................................. xxix 

EXTENDED ABSTRACT .......................................................................................................EA-1 

EA.1 Deliverables and Conclusions...........................................................................EA-1 

EA.2 Recommendations.............................................................................................EA-3 

1. INTRODUCTION ........................................................................................................... 1-1 

2. DATA AVAILABILITY AND VISUALIZATION TOOL............................................ 2-1 

2.1 Available Data ..................................................................................................... 2-1 

2.1.1 Aloft Meteorological Measurements ....................................................... 2-1 

2.1.2 Surface Meteorological Measurements.................................................... 2-2 

2.1.3 Model Simulations................................................................................... 2-2 

2.1.4 Derived Data ............................................................................................ 2-2 

2.1.5 Data Classifications ................................................................................. 2-3 

2.1.6 Averaged Aloft Data................................................................................ 2-3 

2.2 Data Validation Objectives and Results .............................................................. 2-3 

2.3 Environmental Data Analysis Tool (EDAT) ....................................................... 2-4 

3. GENERAL METEOROLOGY ....................................................................................... 3-1 

3.1 Introduction.......................................................................................................... 3-1 

3.2 Upper-air patterns ................................................................................................ 3-1 

3.2.1 Methods of Obtaining and Classifying Data............................................ 3-1 

3.2.2 Data Classification Results ...................................................................... 3-3 

3.3 Surface Flow Characteristics ............................................................................... 3-5 

3.3.1 Methods of Determining Surface Flow Characteristics........................... 3-5 

3.3.2 Results of Determining Surface Flow Characteristics............................. 3-6 

4. UPPER-AIR WINDS AND VIRTUAL TEMPERATURES .......................................... 4-1 

4.1 RWP and RASS Data........................................................................................... 4-1 

4.2 Profiler Results and Interpretations ..................................................................... 4-1 

4.2.1 Overall Average Wind Profiles................................................................ 4-2 

4.2.2 Yearly Wind Profiles ............................................................................... 4-2 

4.2.3 Seasonal Wind Profiles............................................................................ 4-3 

4.2.4 Monthly Wind Profiles ............................................................................ 4-3 

4.2.5 Wind Profiles by Upper-air Classification............................................... 4-4 
TABLE OF CONTENTS (Continued) 

Section Page

4.3 RASS Results and Interpretations........................................................................ 4-5 

4.3.1 Overall Average Temperature Profiles.................................................... 4-5 

4.3.2 Yearly Average Virtual Temperature Profiles......................................... 4-6 

4.3.3 Seasonal Virtual Temperature Profiles.................................................... 4-7 

4.3.4 Virtual Temperature Profiles by Upper-air Classification....................... 4-7 

4.3.5 Caveats..................................................................................................... 4-8 

5. CHARACTERIZATION OF THE SURFACE FLUXES AND OTHER

PARAMETERS IN THE ATMOSPHERIC BOUNDARY LAYER USING 

THE COARE ALGORITHM .......................................................................................... 5-1 

5.1 Summary of COARE Program Versions and Modifications............................... 5-1 

5.2 Background on the COARE Model..................................................................... 5-2 

5.3 Implementation of the COARE Program............................................................. 5-6 

5.4 Comparison of COARE Measurements with TOGA-COARE 

Measurements...................................................................................................... 5-6 

5.5 Application of the COARE Program to Data Collected in the Gulf of 

Mexico ................................................................................................................. 5-7 

5.6 Climatological Results......................................................................................... 5-9 

5.6.1 COARE Results Grouped by Monthly Averages.................................... 5-9 

5.6.2 COARE Results Grouped by Synoptic Class and General 

Flow Direction ....................................................................................... 5-12 

5.6.3 Diurnal Variations by Month................................................................. 5-16 

5.7 Case Study Analyses.......................................................................................... 5-18 

5.7.1 Analysis of January 20-25, 2000 ........................................................... 5-19 

5.7.2 Analysis of January 4-6, 2001 ............................................................... 5-21 

5.7.3 Analysis of July 30-August 1, 1999....................................................... 5-23 

5.7.4 Analysis of September 18-20, 2001....................................................... 5-25 

5.7.5 Summary of Results of Four Case Studies ............................................ 5-27 

6. METEOROLOGICAL AND AIR QUALITY MODELING.......................................... 6-1 

6.1 Radar Wind Profiler – EDAS Comparison.......................................................... 6-1 

6.1.1 Method ..................................................................................................... 6-1 

6.1.2 Results...................................................................................................... 6-3 

6.1.3 Conclusions.............................................................................................. 6-4 

6.2 CALMET Meteorological Modeling ................................................................... 6-4 

6.2.1 High Frequency RWP and RASS Measurements and Data 

Manipulation for Input to CALMET ....................................................... 6-6 

6.3 CALPUFF Dispersion Modeling ......................................................................... 6-8 

6.4 Transport Analysis............................................................................................... 6-9 

viii 
TABLE OF CONTENTS (Concluded) 

Section Page

6.5 Case Studies......................................................................................................... 6-9 

6.5.1 July 30–August 1, 1999: Summer Period with Strong 

Upper-Level Ridge and Surface High Causing Weak Winds................ 6-10 

6.5.2 January 20-25, 2000: Winter Case Study with Shift in 

Wind Direction....................................................................................... 6-11 

6.5.3 January 4-6, 2001: Winter Period Post Upper-level Trough 

Transitioning into Weak Upper-level Ridge.......................................... 6-13 

6.5.4 January 29, 2001: Winter Case with Strong Southerly Winds ............. 6-14 

6.5.5 April 14-15, 2001: Onshore Wind Case Study ..................................... 6-15 

6.5.6 May 14-15, 2001: Spring Case Study with Light Winds 

and Regional High Ozone...................................................................... 6-16 

6.5.7 September 18-20, 2001: Nearly Stationary Front Along the 

Gulf Coast .............................................................................................. 6-17 

6.6 Conclusions........................................................................................................ 6-19 

7. SUMMARY OF MAJOR FINDINGS AND RECOMMENDATIONS ......................... 7-1 

7.1 Summary of Findings........................................................................................... 7-1 

7.1.1 Data and Data Viewer (Section 2) ........................................................... 7-1 

7.1.2 Atmospheric Boundary Layer Characteristics (Sections 3-5) ................. 7-2 

7.1.3 Wind Fields, Transport, and Dispersion (Section 6)................................ 7-9 

7.2 Recommendations.............................................................................................. 7-11 

8. REFERENCES ................................................................................................................ 8-1 

APPENDIX A: EDAT DATABASE FORMAT....................................................................... A-1 

APPENDIX B: COARE DOCUMENTATION FROM NOAA’S FTP SITE ...........................B-1 

APPENDIX C: COARE FORTRAN CODE..............................................................................C-1 

APPENDIX D: BOUNDARY LAYER STUDY IN THE WESTERN AND CENTRAL 

GULF OF MEXICO FINAL MEETING, OCTOBER 15-16, 2003 ............... D-1 

ix 
LIST OF FIGURES 

Figure Page

2-1. Map of the MMS study region depicting locations of C-MAN, buoy, and 

RWP platform monitors................................................................................................... 2-6 

2-2. SMI offshore oil platform showing the RWP and RASS upper-air measurement 

systems............................................................................................................................. 2-7 

2-3. EDAT screen shot showing a spatial plot, time series plots, the time-height 

cross-section, and the vertical profile .............................................................................. 2-8 

2-4. Sequence of events for creating a time series plot in EDAT: open a new time series 

graph, select data to be displayed, and create the plot..................................................... 2-9 

3-1. An upper-level high pressure system with ridge axis...................................................... 3-8 

3-2. Example of an upper-air ridge pattern for the Gulf of Mexico region for 

March 22, 2000, at 1200 UTC (0600 CST) ..................................................................... 3-9 

3-3. Example of an upper-air weak ridge pattern for the Gulf of Mexico region for 

July 30, 1998, at 1200 UTC (0600) CST)...................................................................... 3-10 

3-4. Example of an upper-air trough pattern for the Gulf of Mexico region for 

January 5, 1999, at 0000 UTC (January 4, 1999, at 1800 CST).................................... 3-11 

3-5. Example of an upper-air weak trough pattern for the Gulf of Mexico region for 

May 31, 1999, at 0000 UTC (May 30, 1999, at 1800 CST).......................................... 3-12 

3-6. Example of an upper-air cut-off low pattern for the Gulf of Mexico region for 

March 30, 1999, at 0000 UTC (March 29, 1999, at 1800 CST).................................... 3-13 

3-7. Example of an upper-air post-trough pattern for the Gulf of Mexico region for 

December 18, 1998, at 0000 UTC (December 17, 1998, at 1800 CST)........................ 3-14 

3-8. Example of an upper-air flat pattern for the Gulf of Mexico region for 

October 1, 2000, at 1200 UTC (0600 CST)................................................................... 3-15 

3-9. Example of an upper-air zonal pattern for the Gulf of Mexico region for 

November 15, 2000, at 0000 UTC (November 14, 2000, at 1800 CST)....................... 3-16 

3-10. Example of an upper-air hurricane pattern for the Gulf of Mexico region for 

August 23, 1999, at 0000 UTC (August 22, 1999, at 1800 CST).................................. 3-17 

3-11. Overall frequency distribution of grouped upper-air patterns observed for the 

study period.................................................................................................................... 3-18 

3-12. Frequency distribution of upper-air patterns observed for the study period.................. 3-18 

3-13. Frequency distribution of grouped upper-air patterns observed for each MMS year, 

June through May, during the study period ................................................................... 3-19 

3-14. Frequency distribution of nine upper-air patterns observed for each MMS year 

during the study period .................................................................................................. 3-20 

xi 
LIST OF FIGURES (Continued) 

Figure Page

3-15. Frequency distribution of grouped upper-air patterns observed for each season 

for all years during the MMS study period.................................................................... 3-21 

3-16. Frequency distribution of nine upper-air patterns observed for each season for 

all years during the MMS study period.......................................................................... 3-22 

3-17. Frequency distribution of grouped upper-air patterns observed for each month 

for all years during the MMS study period.................................................................... 3-22 

3-18. Wind rose plot for the SMI platform for the study period............................................. 3-23 

3-19. Monitoring sites in the Gulf of Mexico region .............................................................. 3-24 

3-20. Yearly frequency distributions of surface wind direction and surface wind speed 

and for the near-shore site, buoy 42035, and the offshore site, SMI............................. 3-24 

3-21. Frequency distribution of seasonal surface flow directions for near-shore and 

offshore sites.................................................................................................................. 3-25 

3-22. Frequency distribution of surface flow typing for upper-air ridge, upper-air 

trough, and other upper-air patterns at the four selected sites during the MMS 

study period.................................................................................................................... 3-26 

3-23a. Wind rose for VRM ....................................................................................................... 3-27 

3-23b. Wind rose for buoy 42040 ............................................................................................. 3-28 

3-24. Spatial plot depicting wind roses for Group A and Group B for the fall season ........... 3-29 

3-25. Spatial plot depicting wind roses for Group A and Group B for the winter season ...... 3-30 

3-26. Spatial plot depicting wind roses for Group A and Group B for the spring season ...... 3-31 

3-27. Spatial plot depicting wind roses for Group A and Group B for the summer season.... 3-32 

4-1. Overall average winds at SMI from 0000 to 2300 CST, June 1, 1998, to 

May 31, 2001 ................................................................................................................... 4-9 

4-2. Overall average winds at VRM from 0000 to 2300 CST, June 1, 1998, to 

May 31, 2001 ................................................................................................................... 4-9 

4-3. 1998 year average winds at SMI from 0000 to 2300 CST, June 1, 1998, to 

May 31, 1999 ................................................................................................................. 4-10 

4-4. 1998 year average winds at VRM from 0000 to 2300 CST, June 1, 1998, to 

May 31, 1999 ................................................................................................................. 4-10 

4-5. 1999 year average winds at SMI from 0000 to 2300 CST, June 1, 1999, to 

May 31, 2000 ................................................................................................................. 4-11 

4-6. 1999 year average winds at VRM from 0000 to 2300 CST, June 1, 1999, to 

May 31, 2000 ................................................................................................................. 4-11 

xii 
LIST OF FIGURES (Continued) 

Figure Page

4-7. 2000 year average winds at SMI from 0000 to 2300 CST, June 1, 2000, to 

May 31, 2001 ................................................................................................................. 4-12 

4-8. 2000 year average winds at VRM from 0000 to 2300 CST, June 1, 2000, to 

May 31, 2001 ................................................................................................................. 4-12 

4-9. Fall average winds at SMI from 0000 to 2300 CST, September 24 to December 22, 

for all study years........................................................................................................... 4-13 

4-10. Fall average winds at VRM from 0000 to 2300 CST, September 24 to December 22, 

for all study years........................................................................................................... 4-13 

4-11. Winter average winds at SMI from 0000 to 2300 CST, December 23 to March 21, 

for all study years........................................................................................................... 4-14 

4-12. Winter average winds at VRM from 0000 to 2300 CST, December 23 to March 21, 

for all study years........................................................................................................... 4-14 

4-13. Spring average winds at SMI from 0000 to 2300 CST, March 22 to June 22, for 

all study years ................................................................................................................ 4-15 

4-14. Spring average winds at VRM from 0000 to 2300 CST, March 22 to June 22, 

for all study years........................................................................................................... 4-15 

4-15. Summer average winds at SMI from 0000 to 2300 CST, June 23 to September 23, 

for all study years........................................................................................................... 4-16 

4-16. Summer average winds at VRM from 0000 to 2300 CST, June 23 to September 23, 

for all study years........................................................................................................... 4-16 

4-17. Ridge pattern average winds at SMI from 0000 to 2300 CST, for all study years........ 4-17 

4-18. Ridge pattern average winds at VRM from 0000 to 2300 CST, for all study years...... 4-17 

4-19. Weak ridge average winds at SMI, 0000 to 2300 CST, for all study years................... 4-18 

4-20. Weak ridge average winds at VRM, 0000 to 2300 CST, for all study years................. 4-18 

4-21. Weak trough average winds at SMI, 0000 to 2300 CST, for all study years................. 4-19 

4-22. Weak trough average winds at VRM, 0000 to 2300 CST, for all study years............... 4-19 

4-23. Trough average winds at SMI, 0000 to 2300 CST, for all study years.......................... 4-20 

4-24. Cut-off low average winds at SMI, 0000 to 2300 CST, for all study years................... 4-20 

4-25. Trough average winds at VRM, 0000 to 2300 CST, for all study years........................ 4-21 

4-26. Cut-off low average winds at VRM, 0000 to 2300 CST, for all study years ................ 4-21 

4-27. Flat average winds at SMI, 0000 to 2300 CST, for all study years............................... 4-22 

4-28. Flat average winds at VRM, 0000 to 2300 CST, for all study years............................. 4-22 

4-29. Zonal average winds at SMI, 0000 to 2300 CST for all study years............................. 4-23 

xiii 
xiv 

LIST OF FIGURES (Continued) 

Figure Page

4-30. Zonal average winds at VRM, 0000 to 2300 CST, for all study years.......................... 4-23 

4-31. Post-trough average winds at SMI, 0000 to 2300 CST, for all study years................... 4-24 

4-32. Post-trough average winds at VRM, 0000 to 2300 CST, for all study years................. 4-24 

4-33. Tropical storm average winds at SMI, 0000 to 2300 CST, for all study years.............. 4-25 

4-34. Tropical storm average winds at VRM, 0000 to 2300 CST, for all study years............ 4-25 

4-35. Average overall daytime and nighttime Tv profiles at SMI, June 1, 1998, to 

May 31, 2001 ................................................................................................................. 4-26 

4-36. Average overall daytime and nighttime Tv profiles at VRM, June 1, 1998, to 

May 31, 2001 ................................................................................................................. 4-26 

4-37. 1998 year average daytime and nighttime Tv profiles at SMI, June 1, 1998, to 

May 31, 1999 ................................................................................................................. 4-27 

4-38. 1998 year average daytime and nighttime Tv profiles at VRM, June 1, 1998, to 

May 31, 1999 ................................................................................................................. 4-27 

4-39. 1999 year average daytime and nighttime Tv profiles at SMI, June 1, 1999, to 

May 31, 2000 ................................................................................................................. 4-28 

4-40. 1999 year average daytime and nighttime Tv profiles at VRM, June 1, 1999, to 

May 31, 2000 ................................................................................................................. 4-28 

4-41. 2000 year average daytime and nighttime Tv profiles at SMI, June 1, 2000, to 

May 31, 2001 ................................................................................................................. 4-29 

4-42. 2000 year average daytime and nighttime Tv profiles at VRM, June 1, 2000, to 

May 31, 2001 ................................................................................................................. 4-29 

4-43. Fall average daytime and nighttime Tv profiles at SMI, September 24 to 

December 22 .................................................................................................................. 4-30 

4-44. Fall average daytime and nighttime Tv profiles at VRM, September 24 to 

December 22 .................................................................................................................. 4-30 

4-45. Winter average daytime and nighttime Tv profiles at SMI, December 23 to 

March 21 ........................................................................................................................ 4-31 

4-46. Winter average daytime and nighttime Tv profiles at VRM, December 23 to 

March 21 ........................................................................................................................ 4-31 

4-47. Spring average daytime and nighttime Tv profiles at SMI, March 22 to June 22.......... 4-32 

4-48. Spring average daytime and nighttime Tv profiles at VRM, March 22 to June 22........ 4-32 

4-49. Summer average daytime and nighttime Tv profiles at SMI, June 23 to 

September 23 ................................................................................................................. 4-33 
LIST OF FIGURES (Continued) 

Figure Page

4-50. Summer average daytime and nighttime Tv profiles at VRM, June 23 to 

September 23 ................................................................................................................. 4-33 

4-51. Ridge average daytime and nighttime Tv profiles at SMI.............................................. 4-34 

4-52. Ridge average daytime and nighttime Tv profiles at VRM............................................ 4-34 

4-53. Weak ridge average daytime and nighttime Tv profiles at SMI..................................... 4-35 

4-54. Weak ridge average daytime and nighttime Tv profiles at VRM................................... 4-35 

4-55. Weak trough average daytime and nighttime Tv profiles at SMI .................................. 4-36 

4-56. Weak trough average daytime and nighttime Tv profiles at VRM ................................ 4-36 

4-57. Trough average daytime and nighttime Tv profiles at SMI ........................................... 4-37 

4-58. Trough average daytime and nighttime Tv profiles at VRM ......................................... 4-37 

4-59. Cut-off low average daytime and nighttime Tv profiles at VRM .................................. 4-38 

4-60. Flat average daytime and nighttime Tv profiles at SMI................................................. 4-38 

4-61. Flat average daytime and nighttime Tv profiles at VRM............................................... 4-39 

4-62. Zonal average daytime and nighttime Tv profiles at SMI.............................................. 4-39 

4-63. Zonal average daytime and nighttime Tv profiles at VRM............................................ 4-40 

4-64. Post-trough average daytime and nighttime Tv profiles at SMI .................................... 4-40 

4-65. Post-trough average daytime and nighttime Tv profiles at VRM .................................. 4-41 

4-66. Tropical storm average daytime and nighttime Tv profiles at VRM ............................. 4-41 

5-1a. COARE monthly average sensible heat fluxes by site for May 1998 through 

October 2001.................................................................................................................. 5-31 

5-1b. COARE monthly average sensible heat fluxes by BAMP site for September 2000 

through September 2001................................................................................................ 5-32 

5-2a. COARE monthly average latent heat fluxes by site for May 1998 through 

October 2001.................................................................................................................. 5-33 

5-2b. COARE monthly average latent heat fluxes by BAMP site for September 2000 

through September 2001................................................................................................ 5-34 

5-3a. Observed monthly average wind speed by site for May 1998 through 

October 2001.................................................................................................................. 5-35 

5-3b. Observed monthly average wind speed by BAMP site for September 2000 

through September 2001................................................................................................ 5-36 

5-4a. Monthly average skin temperature minus air temperature by site for May 1998 

through October 2001 .................................................................................................... 5-37 

xv 
LIST OF FIGURES (Continued) 

Figure Page

5-4b. COARE monthly average skin temperature minus air temperature by BAMP site 

for September 2000 through September 2001 ............................................................... 5-38 

5-5a. COARE monthly average of total heat fluxes by site for May 1998 through 

October 2001.................................................................................................................. 5-39 

5-5b. COARE monthly average total heat fluxes by BAMP site for September 2000 

through September 2001................................................................................................ 5-40 

5-6. Eta monthly average latent heat fluxes by site for May 1998 through 

October 2001, for the 6- to 12-hr forecast ..................................................................... 5-41 

5-7. Eta monthly average sensible heat fluxes by site for May 1998 through 

October 2001, for the 6- to 12-hr forecast ..................................................................... 5-42 

5-8a. COARE monthly average friction velocity by site for May 1998 through 

October 2001.................................................................................................................. 5-43 

5-8b. COARE monthly average friction velocity by BAMP site for September 2000 

through September 2001................................................................................................ 5-44 

5-9. Eta monthly average friction velocity by site for May 1998 through October 2001, 

for the 6- to 12-hr forecast ............................................................................................. 5-45 

5-10a. COARE calculated monthly average temperature scaling parameter by site for 

May 1998 through October 2001................................................................................... 5-46 

5-10b. COARE calculated monthly average temperature scaling parameter by BAMP site 

for September 2000 through September 2001 ............................................................... 5-47 

5-11a. COARE calculated monthly average humidity scaling parameter by site for 

May 1998 through October 2001................................................................................... 5-48 

5-11b. COARE calculated monthly average humidity scaling parameter by BAMP site 

for September 2000 through September 2001 ............................................................... 5-49 

5-12a. Observed monthly average air temperature by site for May 1998 through 

October 2001.................................................................................................................. 5-50 

5-12b. Observed monthly average air temperature by BAMP site for September 2000 

through September 2001................................................................................................ 5-51 

5-13a. Observed monthly average skin temperature by site for May 1998 through 

October 2001.................................................................................................................. 5-52 

5-13b. Observed monthly average skin temperature by BAMP site for September 2000 

through September 2001................................................................................................ 5-53 

5-14. Eta average downwelling longwave radiation by synoptic class by site for 

May 1998 through October 2001, for the 6- to 12-hr forecast....................................... 5-54 

5-15. Eta average shortwave radiation by synoptic class by site for May 1998 through 

October 2001, for the 6-to 12-hr forecast ...................................................................... 5-55 

xvi 
LIST OF FIGURES (Continued) 

Figure Page

5-16a. COARE average humidity scaling parameter by synoptic class by site for 

May 1998 through October 2001................................................................................... 5-56 

5-16b. COARE average humidity scaling parameter by synoptic class by BAMP site for 

September 2000 through September 2001..................................................................... 5-57 

5-17a. COARE average temperature scaling parameter by synoptic class by site for 

May 1998 through October 2001................................................................................... 5-58 

5-17b. COARE average temperature scaling parameter by synoptic class by BAMP site 

for September 2000 through September 2001 ............................................................... 5-59 

5-18a. COARE surface roughness by synoptic class by site for May 1998 through 

October 2001.................................................................................................................. 5-60 

5-18b. COARE surface roughness by synoptic class by BAMP site for September 2000 

through September 2001................................................................................................ 5-61 

5-19a. COARE average sensible heat fluxes by synoptic class by site for May 1998 

through October 2001 .................................................................................................... 5-62 

5-19b. COARE average sensible heat fluxes by synoptic class by BAMP site for 

September 2000 through September 2001..................................................................... 5-63 

5-20a. COARE average latent heat fluxes by synoptic class by site for May 1998 through 

October 2001.................................................................................................................. 5-64 

5-20b. COARE average latent heat fluxes by synoptic class by BAMP site for 

September 2000 through September 2001..................................................................... 5-65 

5-21a. COARE average friction velocity by synoptic class by site for May 1998 through 

October 2001.................................................................................................................. 5-66 

5-21b. COARE average friction velocity by synoptic class by BAMP site for 

September 2000 through September 2001..................................................................... 5-67 

5-22. Observed average wind speed by synoptic class by site for May 1998 through 

October 2001.................................................................................................................. 5-68 

5-23. Eta average downwelling longwave radiation by general flow direction by site 

for May 1998 through October 2001, for the 6-to 12-hr forecast.................................. 5-69 

5-24. Eta average shortwave radiation by general flow direction by site for May 1998 

through October 2001, for the 6-to 12-hr forecast......................................................... 5-70 

5-25a. COARE average humidity scaling parameter by general flow direction by site 

for May 1998 through October 2001 ............................................................................. 5-71 

5-25b. COARE average humidity scaling parameter by general flow direction by 

BAMP site for September 2000 through September 2001 ............................................ 5-72 

5-26a. COARE average temperature scaling parameter by general flow direction by 

site for May 1998 through October 2001....................................................................... 5-73 

xvii 
LIST OF FIGURES (Continued) 

Figure Page

5-26b. COARE average temperature scaling parameter by general flow direction by 

BAMP site for September 2000 through September 2001 ............................................ 5-74 

5-27a. COARE average surface roughness by general flow direction by site for May 1998 

through October 2001 .................................................................................................... 5-75 

5-27b. COARE average surface roughness by general flow direction by BAMP site for 

September 2000 through September 2001..................................................................... 5-76 

5-28a. COARE average sensible heat fluxes by general flow direction by site for May 1998 

through October 2001 .................................................................................................... 5-77 

5-28b. COARE average sensible heat fluxes by general flow direction by BAMP site for 

September 2000 through September 2001..................................................................... 5-78 

5-29a. COARE average latent heat fluxes by general flow direction by site for May 1998 

through October 2001 .................................................................................................... 5-79 

5-29b. COARE average latent heat fluxes by general flow direction by BAMP site for 

September 2000 through September 2001..................................................................... 5-80 

5-30a. COARE average friction velocity by general flow direction by site for 

May 1998 through October 2001................................................................................... 5-81 

5-30b. COARE average friction velocity by general flow direction by BAMP site 

for September 2000 through September 2001 ............................................................... 5-82 

5-31. Observed average wind speed by general flow direction by site for May 1998 

through October 2001 .................................................................................................... 5-83 

5-32. COARE hourly average sensible heat fluxes over buoy 42001 for May 1998 

through October 2001 .................................................................................................... 5-84 

5-33. COARE hourly average sensible heat fluxes over SMI for May 1998 through 

October 2001.................................................................................................................. 5-85 

5-34. COARE hourly average friction velocity over SMI for May 1998 through 

October 2001.................................................................................................................. 5-86 

5-35. COARE hourly average latent heat fluxes over VRM for May 1998 through 

October 2001.................................................................................................................. 5-87 

5-36. COARE hourly average sensible heat fluxes over VRM for May 1998 through 

October 2001.................................................................................................................. 5-88 

5-37. Hourly average skin temperature minus air temperature over VRM for May 1998 

through October 2001 .................................................................................................... 5-89 

5-38. COARE hourly average sensible heat fluxes over buoy 42040 for May 1998 

through October 2001 .................................................................................................... 5-90 

5-39. COARE hourly average latent heat fluxes over buoy 42040 for May 1998 

through October 2001 .................................................................................................... 5-91 

xviii 
LIST OF FIGURES (Continued) 

Figure Page

5-40. COARE hourly average sensible heat fluxes over GDIL1 for May 1998 through 

October 2001.................................................................................................................. 5-92 

5-41. Hourly skin temperature minus air temperature over GDIL1 for May 1998 

through October 2001 .................................................................................................... 5-93 

5-42. COARE hourly friction velocity over GDIL1 for May 1998 through 

October 2001.................................................................................................................. 5-94 

5-43. COARE hourly average latent heat fluxes over GDIL1 for May 1998 through 

October 2001.................................................................................................................. 5-95 

5-44. COARE hourly average sensible heat fluxes over BIP for September 2000 

through September 2001................................................................................................ 5-96 

5-45. COARE hourly average latent heat fluxes over BIP for September 2000 

through September 2001................................................................................................ 5-97 

5-46. COARE hourly average friction velocity over BIP for September 2000 

through September 2001................................................................................................ 5-98 

5-47. Hourly skin temperature minus air temperature over BIP for September 2000 

through September 2001................................................................................................ 5-99 

5-48. Observed hourly average wind speed over BIP for September 2000 through 

September 2001 ........................................................................................................... 5-100 

5-49. Observed hourly average wind speed over DWP for September 2000 through 

September 2001 ........................................................................................................... 5-101 

5-50. COARE hourly average sensible heat fluxes over DWP for September 2000 

through September 2001.............................................................................................. 5-102 

5-51. COARE hourly average latent heat fluxes over DWP for September 2000 

through September 2001.............................................................................................. 5-103 

5-52. COARE hourly average friction velocity over DWP for September 2000 

through September 2001.............................................................................................. 5-104 

5-53. Hourly skin temperature minus air temperature over DWP for September 2000 

through September 2001.............................................................................................. 5-105 

5-54. Air and skin temperatures and wind speed at buoy 42040 for January 20 

through 25, 2000 .......................................................................................................... 5-106

5-55. COARE and Eta hourly sensible heat fluxes at buoy 42040 for January 20 

through 25, 2000 .......................................................................................................... 5-107

5-56. COARE and Eta hourly latent heat fluxes at buoy 42040 for January 20 

through 25, 2000 .......................................................................................................... 5-108

5-57. Hourly air and skin temperatures, wind speed, and relative humidity at VRM for 

January 4 through 6, 2001............................................................................................ 5-109 

xix 
LIST OF FIGURES (Continued) 

Figure Page

5-58. COARE hourly average latent and sensible heat fluxes and friction velocity 

at VRM for January 4 through 6, 2001........................................................................ 5-110 

5-59. Estimated wave height and period, wind speed, and surface roughness length 

at VRM for January 4 through 6, 2001........................................................................ 5-111 

5-60. COARE and Eta latent and sensible heat fluxes at VRM for January 4 

through 6, 2001 ............................................................................................................ 5-112 

5-61. COARE and Eta friction velocity and z/L at VRM for January 4 through 

January 6, 2001 ............................................................................................................ 5-113 

5-62a. Hourly air and skin temperatures, wind speed, and relative humidity at VRM 

for July 30 through August 1, 1999 ............................................................................. 5-114 

5-62b. Hourly air and skin temperatures, wind speed, and relative humidity at SMI for 

July 30 through August 1, 1999................................................................................... 5-115 

5-63a. COARE latent and sensible heat fluxes and friction velocity at VRM for July 30 

through August 1, 1999................................................................................................ 5-116 

5-63b. COARE latent and sensible heat fluxes and friction velocity at SMI for July 30 

through August 1, 1999................................................................................................ 5-117 

5-64a. Estimated wave height and period, and surface roughness length and wind speed 

at VRM for July 30 through August 1, 1999 .............................................................. 5-118 

5-64b. Estimated wave height and period, and surface roughness length and wind speed 

at SMI for July 30 through August 1, 1999 ................................................................ 5-119 

5-65a. COARE and Eta latent and sensible heat fluxes at VRM for July 30 through 

August 1, 1999............................................................................................................. 5-120 

5-65b. COARE and Eta latent and sensible heat fluxes at SMI for July 30 through 

August 1, 1999............................................................................................................. 5-121 

5-66a. COARE and Eta friction velocity and z/L at VRM for July 30 through 

August 1, 1999............................................................................................................. 5-122 

5-66b. COARE and Eta friction velocity and z/L at SMI for July 30 through 

August 1, 1999............................................................................................................. 5-123 

5-67a. Hourly air and skin temperatures, wind speed, and relative humidity at VRM for 

September 18 through 20, 2001................................................................................... 5-124 

5-67b. Hourly air and skin temperatures, wind speed, and relative humidity at SMI for 

September 18 through 20, 2001................................................................................... 5-125 

5-68a. COARE latent and sensible heat fluxes and friction velocity at VRM for 

September 18 through 20, 2001................................................................................... 5-126 

5-68b. COARE latent and sensible heat fluxes and friction velocity at SMI for 

September 18 through 20, 2001................................................................................... 5-127 

xx 
LIST OF FIGURES (Continued) 

Figure Page

5-69a. Estimated wave height and period, wind speed, and surface roughness length 

at VRM for September 18 through 20, 2001 ............................................................... 5-128 

5-69b. Estimated wave height and period, wind speed, and surface roughness length 

at SMI for September 18 through 20, 2001 ................................................................. 5-129 

5-70a. COARE and Eta latent and sensible heat fluxes at VRM for September 18 

through 20, 2001 .......................................................................................................... 5-130

5-70b. COARE and Eta latent and sensible heat fluxes at SMI for September 18 

through 20, 2001 .......................................................................................................... 5-131

5-71a. COARE and Eta friction velocity and z/L at VRM for September 18 

through 20, 2001 .......................................................................................................... 5-132

5-71b. COARE and Eta friction velocity and z/L at SMI for September 18 

through 20, 2001 .......................................................................................................... 5-133

6-1. Gulf of Mexico study region with site locations for the six RWPs............................... 6-21 

6-2. Comparison of RWP wind speeds and directions with EDAS simulations: 

wind speed and direction mean bias, mean standard deviation, and mean 

absolute error for all RWP sites shown in Figure 6.1.................................................... 6-22 

6-3. Locations of meteorological stations used to provide inputs to the CALMET 

diagnostic meteorological model to derive three-dimensional wind fields and 

other ABL parameters.................................................................................................... 6-23 

6-4. CALMET modeling domain for the Gulf of Mexico coastal region from 

mid-Texas to western Florida; 860 X 560 km; 5-km horizontal grid resolution........... 6-24 

6-5. EDAS modeling domain using a horizontal resolution of 40 km.................................. 6-24 

6-6. Standard options for incorporating gridded model output into a CALMET analysis.... 6-25 

6-7. Locations oil platform where the arbitrary hypothetical tracers were assumed to be 

emitted for the air quality modeling exercise ................................................................ 6-26 

6-8. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for July 29 at 0000 CST through August 1, 1999, at 0800 CST.......................... 6-27 

6-9. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for July 29 

at 0000 CST through August 1, 1999, at 0800 CST...................................................... 6-27 

6-10. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic 

wind fields for July 29 at 0000 CST through August 1, 1999, at 0800 CST................. 6-28 

6-11. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for July 29 

at 0000 CST through August 1, 1999, at 0800 CST...................................................... 6-28 

6-12. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic 

wind fields for July 29 at 0000 CST through August 1, 1999, at 0800 CST................. 6-29 

xxi 
LIST OF FIGURES (Continued) 

Figure Page

6-13. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

July 29 at 0000 CST through August 1, 1999, at 0800 CST ......................................... 6-29 

6-14. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on July 30, 1999, at 2200 CST.................................................. 6-30 

6-15. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on July 31, 1999, at 1600 CST.................................................. 6-30 

6-16. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on August 1 at 1700 CST.......................................................... 6-31 

6-17. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic 

wind fields for January 19 at 0000 CST through January 22, 2000, at 1600 CST ........ 6-31 

6-18. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 19 at 0000 CST through January 22, 2000, at 1600 CST................................. 6-32 

6-19. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for January 19 at 0000 CST through January 22, 2000 at 1600 CST .................. 6-32 

6-20. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 19 at 0000 CST through January 22, 2000 at 1600 CST.................................. 6-33 

6-21. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic 

wind fields for January 19 at 0000 CST through January 22, 2000, at 1600 CST ........ 6-33 

6-22. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 19 at 0000 CST through January 22, 2000, at 1600 CST................................. 6-34 

6-23. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic 

wind fields for January 22 at 0000 CST through January 25, 2000, at 0800 CST ........ 6-34 

6-24. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 22 at 0000 CST through January 25, 2000, at 0800 CST................................. 6-35 

6-25. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic 

wind fields for January 22 at 0000 CST through January 25, 2000, at 0800 CST ........ 6-35 

6-26. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 22 at 0000 CST through January 25, 2000, at 0800 CST................................. 6-36 

6-27. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic 

wind fields for January 22 at 0000 CST through January 25, 2000, at 0800 CST ........ 6-36 

6-28. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 22 at 0000 CST through January 25, 2000, at 0800 CST................................. 6-37 

6-29. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 20, 2000, at 1600 CST............................................ 6-37 

6-30. CALMET-derived mixing heights for January 20, 2000, at 1400 CST......................... 6-38 

xxii 
LIST OF FIGURES (Continued) 

Figure Page

6-31. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 21, 2000, at 1600 CST............................................ 6-38 

6-32. CALMET-derived mixing heights for January 21, 2000, at 1400 CST......................... 6-39 

6-33. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 22, 2000, at 1900 CST............................................ 6-39 

6-34. CALMET-derived mixing heights for January 22, 2000, at 1400 CST......................... 6-40 

6-35. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 23, 2000, at 1200 CST............................................ 6-40 

6-36. CALMET-derived mixing heights for January 23, 2000, at 1400 CST......................... 6-41 

6-37. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 24, 2000, at 1200 CST............................................ 6-41 

6-38. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 25, 2000, at 1400 CST............................................ 6-42 

6-39. CALMET-derived mixing heights for January 24, 2000, at 1400 CST......................... 6-42 

6-40. CALMET-derived mixing heights for January 25, 2000, at 1400 CST......................... 6-43 

6-41. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic 

wind fields for January 3, at 0000 CST through January 6, 2001, at 0000 CST ........... 6-43 

6-42. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 3 at 0000 CST through January 6, 2001, at 0000 CST..................................... 6-44 

6-43. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic 

wind fields for January 3 at 0000 CST through January 6, 2001, at 0000 CST ............ 6-44 

6-44. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 3 at 0000 CST through January 6, 2001, at 0000 at 0800 CST........................ 6-45 

6-45. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic 

wind fields for January 3 at 0000 CST through January 6, 2001, at 0000 CST ............ 6-45 

6-46. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 3 at 0000 CST through January 6, 2001, at 0000 CST..................................... 6-46 

6-47. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 4, 2001, at 0800 CST.............................................. 6-46 

6-48. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 5, 2001, at 0300 CST.............................................. 6-47 

6-49. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 5, 2001, at 1700 CST.............................................. 6-47 

6-50. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 6, 2001, at 1000 CST.............................................. 6-48 

xxiii 
LIST OF FIGURES (Continued) 

Figure Page

6-51. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic 

wind fields for January 27 at 0000 CST through January 30, 2001, at 0000 CST ........ 6-48 

6-52. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 27 at 0000 CST through January 30, 2001, at 0000 CST................................. 6-49 

6-53. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic 

wind fields for January 27 at 0000 CST through January 30, 2001, at 0000 CST ........ 6-49 

6-54. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 27 at 0000 CST through January 30, 2001, at 0000 CST................................. 6-50 

6-55. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic 

wind fields for January 27 at 0000 CST through January 30, 2001, at 0000 CST ........ 6-50 

6-56. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 27 at 0000 CST through January 30, 2001, at 0000 CST................................. 6-51 

6-57. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 29, 2001, at 1200 CST............................................ 6-51 

6-58. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic 

wind fields for April 13 at 0000 CST through April 16, 2001, at 0000 CST ................ 6-52 

6-59. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

April 13 at 0000 CST through April 16, 2001, at 0000 CST......................................... 6-52 

6-60. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic 

wind fields for April 13 at 0000 CST through April 16, 2001, at 0000 CST ................ 6-53 

6-61. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

April 13 at 0000 CST through April 16, 2001, at 0000 CST......................................... 6-53 

6-62. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic 

wind fields for April 13 at 0000 CST through April 16, 2001, at 0000 CST ................ 6-54 

6-63. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

April 13 at 0000 CST through April 16, 2001, at 0000 CST......................................... 6-54 

6-64. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on April 14, 2001, at 1900 CST................................................ 6-55 

6-65. CALMET-derived mixing heights for April 14, 2001, at 1400 CST............................. 6-55 

6-66. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on April 15, 2001, at 1100 CST................................................ 6-56 

6-67. CALMET-derived mixing heights for April 15, 2001, at 1400 CST............................. 6-56 

6-68. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic 

wind fields for May 13 at 0000 CST through May 16, 2001, at 0000 CST .................. 6-57 

xxiv 
LIST OF FIGURES (Continued) 

Figure Page

6-69. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

May 13 at 0000 CST through May 16, 2001, at 0000 CST........................................... 6-57 

6-70. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic 

wind fields for May 13 at 0000 CST through May 16, 2001, at 0000 CST .................. 6-58 

6-71. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

May 13 at 0000 CST through May 16, 2001, at 0000 CST........................................... 6-58 

6-72. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic 

wind fields for May 13 at 0000 CST through May 16, 2001, at 0000 CST .................. 6-59 

6-73. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

May 13 at 0000 CST through May 16, 2001, at 0000 CST........................................... 6-59 

6-74. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on May 14, 2001, at 0600 CST ................................................. 6-60 

6-75. CALMET-derived mixing heights for May 14, 2001, at 1400 CST.............................. 6-60 

6-76. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on May 15, 2001, at 2200 CST ................................................. 6-61 

6-77. CALMET-derived mixing heights for May 15, 2001, at 1400 CST.............................. 6-61 

6-78. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for September 17 at 0000 CST through September 21, 2001, at 0000 CST........ 6-62 

6-79. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

September 17 at 0000 CST through September 21, 2001, at 0000 CST ....................... 6-62 

6-80. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for September 17 at 0000 CST through September 21, 2001, at 0000 CST........ 6-63 

6-81. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

September 17 at 0000 CST through September 21, 2001, at 0000 CST ....................... 6-63 

6-82. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for September 17 at 0000 CST through September 21, 2001, at 0000 CST........ 6-64 

6-83. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

September 17 at 0000 CST through September 21, 2001, at 0000 CST ....................... 6-64 

6-84. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on September 18, 2001, at 2200 CST ....................................... 6-65 

6-85. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on September 19, 2001, at 1900 CST ....................................... 6-65 

6-86. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on September 20, 2001, at 1300 CST ....................................... 6-66 

xxv 
LIST OF TABLES 

Table Page

2-1. C-MAN, buoy, and RWP platform sites........................................................................ 2-10 

2-2. C-MAN, buoy, and RWP platform sites and their available surface 

meteorological data........................................................................................................ 2-11

2-3. Derived COARE parameters.......................................................................................... 2-12 

2-4. Aloft synoptic classifications used in the 1998-2001 MMS Boundary Layer Study .... 2-12 

2-5. Surface wind flow speed and direction classification used in the 1998-2001 MMS 

Boundary Layer Study ................................................................................................... 2-12 

3-1. Speed classifications........................................................................................................ 3-6 

5-1. Number of occurrences of each synoptic classification by year for the 

MMS Boundary Layer Study......................................................................................... 5-12 

xxvii 
LIST OF VARIABLES 

θ Potential temperature 

h or Zi Mixing depth 

Hs Sensible heat flux 

L Monin-Obukhov length

Le or He or H1 Latent heat flux 

q* Humidity scaling parameter 

qr Water vapor mixing ratio 

RH Relative humidity 

T Air temperature 

T* Temperature scaling parameter 

Ts Sea Skin temperature or sea surface temperature 

Tv Virtual temperature 

u Wind speed

u* Friction velocity 

us Water current speed 

xr Any variable measured at the reference height

zo Surface roughness length 

zr Standard reference height or observing height 

xxix
EA-1

EXTENDED ABSTRACT 

This report presents the results from the U.S. Department of the Interior, Minerals 

Management Service (MMS) atmospheric boundary layer (ABL) study. Observations and model 

predictions from the Gulf of Mexico were analyzed with a focus on better parameterizing the 

over-water ABL. In addition, the ABL results were used to calculate the transport and dispersion 

of pollutants in the western and central Gulf of Mexico. 

The analysis incorporated new observations of vertical profiles in the ABL from six 

meteorological stations in the Gulf of Mexico. These stations include 915-MHz radar wind 

profilers (RWP), 2-KHz Radio Acoustic Sounding Systems (RASS), and surface meteorological 

stations. Two stations collected ABL data for three years from May 1998 through October 2001, 

and four stations collected data from September 2000 through October 2001. The RWPs and 

RASS measure winds and virtual temperatures (Tv), respectively, from near the surface to 

heights of a few kilometers, and the surface stations measure skin temperature as well as wind 

speed, wind direction, air temperature, and water vapor mixing ratio at an elevation of about 

25 m on an oil platform. In addition to the new data from the vertical profilers, routine 

meteorological observations from buoys and from shoreline stations were included in the 

analysis. 

The new and routine data collected were analyzed to investigate the over-water surface 

energy balance, the climatology of latent heat versus sensible heat fluxes, mixing depths, the 

frequency of occurrence of very stable conditions, and the horizontal spatial variability of wind 

speed and direction. Estimates of the scaling velocity (u*) and scaling temperature (T*) were 

studied. Three-dimensional prediction fields of surface winds, heat and momentum fluxes, and 

wind profiles from the National Center for Environmental Protection’s (NCEP) Eta model were 

compared with the observations from the RWPs and buoys. The annual, seasonal, and diurnal 

variations of the ABL characteristics were determined. Using the new data as inputs, test runs 

with CALMET and CALPUFF were made for several case study periods to determine typical 

plume trajectories and relative dispersion rates. The various data sets described above were 

collected and quality assurance/quality control (QA/QC) procedures were applied to produce a 

single, user-friendly database. 

EA.1 DELIVERABLES AND CONCLUSIONS 

• Data collected as part of this study, as well as other relevant data, were placed in a 

common Microsoft SQL Server database and are also contained in quarterly Microsoft 

Access databases. These data sets, which were delivered to MMS, are generally available 

from May 1998 through September 2001; RWP, RASS, and rawinsonde data, over-water 

and land-surface data, over-water boundary layer parameters using the Coupled OceanAtmosphere Response Experiment (COARE) model, Eta forecast model data, and daily 

synoptic weather classifications and surface flow classifications are included in the data 

sets. In addition, external to the database, CALMET gridded wind fields were generated 

for selected case studies. To effectively display this diverse set of data for use in data 

analysis, the Environmental Data Analysis Tool (EDAT) was developed and delivered to 
EA-2

MMS. EDAT can produce four types of plots—time series, time-height cross-sections, 

vertical profiles, and spatial plots—and can display images. 

• To assist in characterizing ABL surface fluxes and scaling parameters, the COARE 

algorithm was modified and used to estimate hourly surface fluxes of momentum, 

sensible heat, and latent heat, based on observations of wind speed, air temperature, and 

water vapor mixing ratio at a standard reference height near the water surface and the 

skin temperature at the water surface. The COARE algorithm was originally derived 

from the Tropical Ocean-Global Atmosphere (TOGA)-COARE research project. The 

COARE algorithm has proved to be a useful tool to parameterize boundary layer 

characteristics in the western and central Gulf of Mexico and is recommended for use in 

future studies. 

• The Eta Data Assimilation System (EDAS)-simulated wind fields and the observed RWP 

winds from six sites were compared. EDAS is based on a combination of Eta model 

forecast winds and diagnostic interpolations of observed winds but does not include RWP 

data. The mean wind speed (WS) bias was near zero close to the shore but increased with 

offshore distance, so that the EDAS mean WS exceeded the RWP mean WS by 1 to 2 m/s 

at 50 km offshore and by 2 to 6 m/s at 100 to 200 km offshore. Mean wind direction 

(WD) bias was small, a difference of about 10° to 20° (e.g., if the RWP WD was 180°, 

then the EDAS WD would be 160°). Standard deviations of the differences (with mean 

bias removed) were 1 to 2 m/s for WS and 20° to 40° for WD, in agreement with findings 

for other domains and models. This analysis indicates that the EDAS wind field can be 

improved if it ingests offshore measurements of aloft wind data; such data can be 

obtained from offshore RWPs. 

• The fluxes and scaling parameters calculated by the COARE algorithm in the Gulf of 

Mexico are physically consistent with expectations and are similar in magnitude to the 

observations and COARE calculations for TOGA, which took place in the warm western 

Pacific Ocean near the equator. Calculated monthly average sensible heat fluxes in the 

Gulf of Mexico ranged from 5 to 30 W/m2

, typical of other over-water areas. Similarly, 

calculated monthly average latent heat fluxes ranged from 50 to 150 W/m2

, also typical 

of other over-water areas. Both the latent and sensible heat fluxes were highest in the late 

fall and early winter and lowest in the late spring and summer. Sensible heat flux is 

maximized for post-trough synoptic conditions, which are likely to be marked by above 

average wind speeds and by low air temperature. The latent heat flux is consistently 

large during the post-trough synoptic condition, due to higher wind speeds and low dew 

points that follow a cold front. The calculated fluxes are generally in good agreement 

with the monthly average Eta model latent and sensible heat fluxes. 

• The COARE-calculated monthly average friction velocity (u*) using data from the buoys, 

the C-MAN sites at the shoreline, and the South Marsh Island (SMI) platform near shore 

shows agreement among these sites well within a factor of two and often within 20%. 

This agreement is important because the monthly average friction velocity is the key 

scaling velocity for estimating transport speeds and dispersion rates. However the 

COARE-calculated monthly average friction velocities using data from the platform sites 

further from shore are 30% to 40% less than at the other sites. These platforms (the 

Vermillion offshore oil platform [VRM], the Breton Island Platform [BIP], the Deep 
EA-3

Water Platform [DWP], the Mid Buoy Platform [MBP], the Shallow Water Platform 

[SWP], and the West Delta Platform [WDP] are typically in deeper water. A possible 

explanation is that the wave height and frequency are estimated from empirical relations 

given observations of wind speed at the platforms, whereas they are directly measured at 

the buoys. The monthly average Eta model friction velocity was usually within about 

10% to 20% of the COARE-calculated friction velocity. 

• The differences between the observed water “skin” and air temperatures were, on 

average, +1 to +3°C at most sites all year. The differences were lower in late spring and 

greater in late fall and early winter. This persistent positive temperature difference 

suggests that the ABL is usually well-mixed and unstable. 

• For seven multi-day case studies, the CALPUFF transport and dispersion model was 

applied using arbitrary assumptions for hypothetical tracer releases from three oil 

platforms, BIP, SMI, and SWP. Twenty-four-hour trajectories were calculated for 

releases at heights of 10 m, 75 m, and 350 m using (1) CALMET wind fields and an inhouse STI trajectory model (TRAJMOD) and (2) EDAS wind fields and the NOAA 

HYSPLIT trajectory model. The seven case study periods covered a range of 

representative synoptic conditions and seasons, such as strong-wind January days and 

light-wind July days. The CALMET and EDAS-HYSPLIT trajectories agree within 

20° to 30° most of the time, although the speeds of the EDAS trajectories are larger by as 

much as a factor of two (due to the mean bias discussed above). The CALPUFFsimulated plumes from the three oil platforms sometimes impact the shoreline or offshore 

islands, depending on wind direction. The concentrations are higher during light winds, 

when dilution is less. It is fortunate that the most persistent winds, associated with 

onshore impact near the same location for several hours, are nearly always marked by 

high winds and consequently lower concentrations. When winds are light and variable, 

the local centerline concentration may be higher, but the plume does not remain for long 

over a specific point. 

• The CALMET-CALPUFF estimates of over-water mixing depth were low, about 100 to 

200 m, in contrast to observed mixing depths of about 600 m. This factor of three to six 

difference causes model overpredictions in concentrations, since the plume is constricted 

to the mixing layer. The underpredictions of mixing depth appear to be due to the neglect 

of convective mixing processes offshore, where CALMET currently assumes that the 

mixing depth is due solely to mechanical mixing and is therefore proportional to wind 

speed. 

EA.2 RECOMMENDATIONS 

Based on our analysis and modeling results, and our interactions with other researchers, 

we have prepared a number of recommendations that, if implemented, will further advance the 

current scientific understanding of the ABL in the central and western Gulf of Mexico and 

further develop and improve the tools available to understand the ABL in the central and western 

Gulf of Mexico. Thus, these activities will improve future estimates of the transport and 

dispersion of pollutants in the central and western Gulf of Mexico. The recommendations are 

arranged into groups with other similar recommendations. Some recommendations involve 
EA-4

interaction among various researchers and the publication of research results, others involve 

additional analysis and modeling efforts using existing data, while others involve the collection 

of new data. 

Collaborations 

• Work with NCEP to better understand over-water wind differences between the Eta 

model and observed RWP winds. Analysis has shown that Eta model winds are biased 

high compared to RWP winds away from shore. 

• Work with National Oceanic and Atmospheric Administration’s (NOAA) Environmental 

Technology Laboratory (ETL) to design a scheme to remove sea-clutter from profiler 

data so that mixing heights can be automatically estimated for data from the ABL study 

and future studies using existing mixing-height algorithms. 

• Work with NOAA to improve COARE predictions of large surface roughness. 

Roughness increases under very low wind speeds, which influences estimations of the 

ABL parameters. Conduct a joint meeting on COARE to further improve the model for 

use in the Gulf of Mexico. 

• Make better use of ABL measurements and analyses in other MMS-sponsored projects by 

reviewing plans and progress and recommending ways to incorporate ABL data and 

analysis and modeling results. 

Publication 

• Plan a special journal issue (e.g., Journal of Applied Meteorology, Journal of 

Geophysical Research, Boundary Layer Meteorology) on ABL issues in the Gulf of 

Mexico and prepare specific papers on, for example, the following topics: Eta/RWP 

wind comparisons, climatology of surface ABL parameters calculated using COARE in a 

shallow-water ocean and modifications made to COARE, modeled and estimated mixing 

heights in the Gulf of Mexico, and results from related MMS-sponsored projects. 

Analysis 

• Compare satellite-derived sea-surface temperatures to radiometer temperatures and buoy 

temperatures measured during this study. Compare estimates of sea-surface temperatures 

to the radiometer temperatures when clouds obscure the satellite’s view of the Gulf 

(currently estimated using hole-filling techniques). Comparison results and the 

subsequent improvements in predictions of spatial sea-surface temperatures will improve 

model results. 

• Identify several additional periods of super-stable conditions in the existing data set (i.e., 

a period of southerly flow occurring immediately after a cold outbreak has cooled the 

water in the shallow portion of the Gulf) and perform an ABL case study similar to other 

case studies. 
EA-5

• Determine the best method for estimating wave height and frequency as a function of 

water depth from wind speed alone. When wave data are not available at the platforms, 

inaccurate knowledge of wave characteristics can result in inaccurate estimates of surface 

roughness, which influence ABL parameterizations. 

• Determine the relationship between wind speed and RWP sea-clutter. 

• Use buoyancy flux to estimate mixing heights when winds are less than 6 m/sec and 

compare to RWP-derived mixing heights. 

Modeling 

• Update the CALMET model to correct the large underestimates of over-water mixing 

heights due to the neglect of the buoyant heat flux; perform additional comparisons of 

observation-based estimations of mixing heights to model mixing heights. 

• Update the CALPUFF dispersion runs using new CALMET output created with an 

improved mixing-height scheme. Compare results from the new runs to those created as 

part of the current project. 

• Compare CALMET diagnostic model runs to MM5 prognostic model runs (from a 

separate MMS project) and observational data and create best estimates of gridded 

mixing heights and winds. 

• Modify the way diagnostic and prognostic models treat the diffuse shoreline of the Gulf 

of Mexico; operate the models and compare results with observations. 

• Quantify the differences between the CALMET and HYSPLIT trajectories. For example, 

two trajectories can be compared by calculating the difference in the two positions after 

certain travel times. The differences can then be expressed as function of time for that 

trajectory and a root mean square error (rmse) calculated for a group of trajectories. The 

difference can be categorized by its components (e.g., radial distance and angular 

distance). 

• Compare CALPUFF concentration predictions quantitatively because the same amount of 

tracer was released in each case. For example the following outputs could be compared: 

− Maximum concentration at the point the shoreline is hit. 

− Maximum (centerline) concentration at specific downwind times (e.g., 3 hrs, 6 hrs, 

etc.) and distances (50 km, 100 km, etc.) 

− Penetration distance (downwind distance) for a given concentration. 

− Width of plume for a given concentration contour at a given travel time or distance. 

• Develop an alternative procedure within CALMET to handle missing upper-air 

measurements. 
EA-6

Measurements 

• Conduct continuous meteorological (aloft and surface) and air quality measurements in 

offshore and coastal areas to (1) support routine source-based modeling for lessees and 

special-research MMS objectives; (2) provide long-term information on spatial and 

temporal ABL characteristics; and (3) support routine comparisons with Eta model 

predictions for routine estimates of ABL characteristics, for real-time modeling, and for 

special research studies. 

• Collocate a radiometer and underwater temperature sensor to better determine the 

relationship and accuracy of the COARE-estimated warm-layer and cool-skin effects. 

• Routinely operate a measurement system on an offshore platform that measures a range 

of meteorological parameters at several depths of the surface layer and boundary layer. 

Such a system could include a mini-Sodar, an RWP/RASS system, and a surface 

meteorological monitoring system on a platform to obtain wind and temperature 

measurements. The addition of the mini-Sodar would fill the measurement void that 

exists from 30 m to 200 m; this hole is often the location of plumes. 

• Improve the RWP and RASS sounders so that they are not so susceptible to interferences 

due to objects on the platform and to sea-surface (wave) characteristics. 
1-1

1. INTRODUCTION 

This report presents the results from the U.S. Department of the Interior, Minerals 

Management Service (MMS) atmospheric boundary layer (ABL) study. Sonoma Technology, 

Inc. (STI) and Hanna Consultants analyzed ABL observations and investigated how the ABL 

structure influences the transport and dispersion of pollutants in the western and central Gulf of 

Mexico. The results of this study will be used by the MMS to support techniques for evaluating 

the effects of oil and gas exploration, development, and production activities in the Outer 

Continental Shelf (OCS) on air quality over coastal areas. 

The vertical and horizontal variability of the ABL in the Gulf of Mexico has been an 

uncertainty. For example, the depth of the ABL and its vertical stability and wind and turbulence 

structure can vary greatly in OCS zones due to horizontal variations in water skin temperature 

and the overlying air mass. The MMS now has available new observations of vertical profiles in 

the ABL for the OCS in the Gulf of Mexico from six meteorological stations. These 

meteorological stations include 915-MHz radar wind profilers (RWP), 2-KHz Radio Acoustic 

Sounding Systems (RASS), and surface meteorological stations. Two stations collected ABL 

observations for three years from May 1998 through October 2001, and four stations collected 

observations from September 2000 through October 2001. The RWPs and RASS measure winds 

and virtual temperatures (Tv), respectively, from near the surface to heights of a few kilometers, 

and the surface stations measure skin temperature as well as wind speed, wind direction, air 

temperature, and water vapor mixing ratio at an elevation of about 25 m on an oil platform. In 

addition to the vertical profilers, routine meteorological observations from buoys and from 

shoreline stations are available. For the first time in the Gulf of Mexico region, we are able to 

input the full vertical profiles of meteorological variables that are required by transport and 

dispersion models. 

There are several similarities between over-land and over-water boundary layers. The 

basic boundary layer theories and equations apply over any surface, as long as care is taken to 

correctly apply definitions (i.e., the heat flux used in calculating L, the Monin-Obukhov length, 

must include the effects of the latent heat flux). Mesoscale eddies, with time scales from one 

minute to one hour, are present over both land and water and are not observed to diminish even 

over the open ocean. Over both surfaces, it is possible to parameterize the entire ABL based on 

simple observations of wind speed near the surface, air-skin temperature differences, and relative 

humidity. However, there is no substitute for observations through the entire depth of the ABL 

because elevated inversion layers and shear layers are unpredictable. 

Some fundamental differences between over-land and over-water boundary layers need to 

be accounted for. For example, roughness length, zo, is a strong function of wind speed over 

water. In addition, because water has high thermal conductivity and there is mixing in the ABL, 

the surface temperature of water slowly reacts to changes in air temperature. Consequently, the 

atmospheric stability over water does not follow the typical diurnal cycle characteristic of the 

atmospheric stability over land. In fact, the atmosphere can be stable during the day and unstable 

at night, or it can be stable or unstable for weeks at a time. Strong stability (positive or negative) 

occurs over water only when there is advection of a warm air mass over cold water or a cold air 

mass over warm water. Most of the time, the latent heat flux over water is larger than the 
1-2

sensible heat flux. It is essential that the calculation of any stability parameter, such as the 

Monin-Obukhov length, includes the vertical gradient of water vapor along with the vertical 

gradient of temperature. It is possible to have a temperature inversion and still have unstable 

conditions, due to a decrease of specific humidity with height. 

The new and routine data collected have been analyzed to investigate the following 

technical issues: 

1. The over-water surface energy balance was studied using near-surface observations for 

both steady-state, horizontally homogeneous conditions and for conditions variable in 

time and space. A climatology of latent heat versus sensible heat fluxes has been 

developed for both situations. 

2. The extensive virtual temperature profiles from RASS were studied in order to estimate 

the mixing depths. 

3. The frequency of occurrence of very stable conditions near the surface and in layers aloft 

was investigated because these layers are important for defining worst-case conditions for 

air pollutants. 

4. The horizontal spatial variability of wind speed and direction was studied to identify the 

fraction of time that wind directions and speeds persist over several hours in the Gulf of 

Mexico, thus causing straight-line transport of pollutants towards receptors on the 

shoreline. 

5. Estimates of the scaling velocity (u*) and scaling temperature (T*) were created and 

studied. These scaling parameters are directly related to surface momentum and heat 

fluxes. Because turbulent velocities (important to dispersion) are directly proportional to 

u*, it should be possible to derive improved parameterizations for the dispersion 

coefficients σy and σz. 

6. Three-dimensional prediction fields of surface winds, heat and momentum fluxes, and 

wind profiles—from the National Center for Environmental Protection’s (NCEP’s) Eta 

Model—are available for the Gulf of Mexico and were compared with the observations 

from the RFPs and buoys. 

7. The annual, seasonal, and diurnal variations of the ABL characteristics (item 5) were 

determined. 

8. Synoptic (regional) classification schemes were developed so that meteorological 

characteristics of the ABL and pollutant transport and dispersion can be estimated by 

synoptic class. 

9. Using the new data as inputs, test runs with CALMET and CALPUFF were made for 

several case study periods to determine typical plume trajectories and relative dispersion 

rates. 

10. The various data sets described above were collected and quality assurance/quality 

control (QA/QC) procedures were applied to produce a single, user-friendly database. 

The database includes statistical summaries of the data and derived ABL parameters, as 

well as all of the observed data. 
1-3

This report describes the results of the study and demonstrates that the technical issues 

listed above have been addressed. Section 2 describes the data and how they were collected into 

a comprehensive database. It also describes specialized software that allows the data to be 

extracted and visualized. The database and software were delivered to MMS at the final project 

meeting on October 15, 2003, in New Orleans. Section 3 describes the general meteorology and 

the synoptic classification results. Section 4 summarizes the characteristics of the ABL as 

determined by the RWP and RASS data. Section 5 describes additional characteristics of the 

ABL, including application of the Coupled Ocean-Atmosphere Response Experiment (COARE) 

algorithm to estimate the terms of the surface energy balance and comparisons of these terms 

with Eta model simulations. Section 6 discusses the CALMET wind field modeling and 

transport and dispersion analyses. Section 7 presents a summary of the important findings and 

recommendations. Appendix A contains information on the format and structure of the MMS 

EDAT database, which is discussed in Section 2. Appendix B contains additional information 

about the COARE program, which is discussed in Section 5. Appendix C contains FORTRAN 

code of the COARE program that was modified for use in this project. Appendix D contains the 

final presentation delivered to MMS on October 15, 2003, in which there are many additional 

data plots. 
2-1

2. DATA AVAILABILITY AND VISUALIZATION TOOL 

This section presents the data availability, sources, quality control (QC), and display tool 

used for this study. 

2.1 AVAILABLE DATA 

The measurements collected during the June 1998-October 2001 MMS Boundary Layer 

Study include data from continuous surface and aloft monitoring of meteorological conditions on 

two oil platforms; standard surface data collected at buoy and Coastal Marine Automated 

Network (C-MAN) stations; rawinsonde data; and data from surface land sites. For September 

2000 through October 2001, continuous surface and aloft monitoring of meteorological 

conditions were collected from three additional oil platforms and a land-base site as part of the 

Breton Island Aerometric Program (BAMP). Model simulations include three-dimensional Eta 

model simulations and the Eta’s four-dimensional data assimilation system, EDAS (Eta Data 

Assimilation System). The three-dimensional Eta model simulations and surface observations 

were used to create derived data of boundary layer parameters using the Coupled OceanAtmosphere Response Experiment (COARE) computer program. The COARE program is 

described in Section 5. 

All observational and derived data and selected Eta model simulations were reviewed for 

accuracy, completeness, and internal consistency and were imported into a Microsoft SQL 

Server database. Figure 2-1 shows the locations of the buoy, C-MAN, and platform monitoring 

sites. 

In addition to the data contained in the database, CALMET wind fields for seven selected 

case studies are available in their native binary format. 

2.1.1 Aloft Meteorological Measurements 

Aloft (non-surface) meteorological measurements were collected as part of the 

1998-2001 MMS Boundary Layer Study. In addition, aloft data collected from the September 

2000 through October 2001 BAMP study were also integrated into this project. For the MMS 

study, the RWP and RASS Tv data were collected at the Vermillion offshore oil platform (VRM) 

and the South Marsh Island offshore oil platform (SMI) (Figure 2-2). For the BAMP study, the 

RWP and RASS Tv data were collected at the West Delta Platform (WDP), the Deep Water 

Platform (DWP), the Breton Island Platform (BIP), and Fort Morgan (FTM). All RWP and 

RASS data were quality-controlled and are considered Level 1 validated as discussed in 

Section 2.2. See Lindsey et al. (1997b) for more details about the RWP and RASS data. 

Rawinsonde data were collected from Lake Charles and Slidell, Louisiana, at 0000 UTC 

and 1200 UTC for each day during the study. These data were not quality controlled; however, 

they are available in the Microsoft SQL Server database and will be utilized for case study 

analyses and modeling. 
2-2

2.1.2 Surface Meteorological Measurements 

Surface meteorological data were collected at the VRM and SMI sites for the 1998-2001 

MMS study period and at six sites as part of the BAMP study (See Figure 2-2). In addition, 

surface data were obtained from buoy and C-MAN sites located in the MMS study region 

through the National Buoy Data Center. Table 2-1 lists buoy, C-MAN, and platform sites and 

their locations. Table 2-2 lists the parameters available for the C-MAN, buoy, and platform 

sites. The routine data collected at most sites include wind speed and direction, temperature, 

relative humidity, station pressure, and skin temperature. The buoy sites also collect wave height 

and wave period data. 

Surface data collected at the platform sites were quality-controlled and are considered 

Level 1 validated (discussed in Section 2.2). In addition, all other surface data listed in Table 2-1 

were reviewed for reasonableness. 

Additional hourly surface data were obtained through The National Climatic Data Center 

(NCDC) for land-based surface sites throughout the Gulf of Mexico region. These data were 

input into a Microsoft SQL Server database; however, they were not quality-controlled. 

2.1.3 Model Simulations 

Three-dimensional Eta model simulations and the EDAS were obtained from the 

University Corporation for Atmospheric Research (UCAR) for the entire study period. The Eta 

forecast model contains forecast fields out to 48 hours from initial states at 0000 UTC and 

1200 UTC. The EDAS generates eight 3-hourly initial states or analyses during each 24-hr 

period, utilizing a vast set of observed data. From the Eta forecast model, geopotential height, 

friction velocity, latent heat flux, sensible heat flux, low cloud cover, middle cloud cover, and 

high cloud cover were extracted for each over-water site and placed in the database. Wind speed 

and wind direction were extracted from the EDAS model simulations. The Eta model 

simulations, along with the surface observations, were placed in the database. 

Both Eta and EDAS utilize the AWIPS Grid 212 as their standard output grid. This grid 

is defined on a Lambert Conformal projection with a spatial resolution of 40 km by 40 km. Both 

Eta and EDAS contain 38 vertical levels and cover most of North America and the surrounding 

oceans. 

In addition to the Eta and EDAS predictions, CALMET wind fields for seven selected 

case studies are available in their native binary format. Section 7 discusses the CALMET 

modeling. 

2.1.4 Derived Data 

Three-dimensional model simulations and surface observations at the sites listed in 

Table 2-2 were used to create the derived COARE data set. The derived data were created for 

the entire 1998-2001 MMS study period. Table 2-3 shows the derived variables. These derived 

variables were placed in the database for analysis. 
2-3

2.1.5 Data Classifications 

Aloft synoptic weather maps were reviewed and nine classifications were created based 

on the review. The classifications are discussed in Section 3. The classification of each hourly 

period was imported into the database as a derived data set. These data are different from other 

data sources because they refer to the Gulf of Mexico region as a whole and not to a single point 

location. Table 2-4 shows the aloft classifications that were used for this study. 

Surface flow classifications were created using a simple set of queries to determine the 

wind direction and observed wind speeds. These surface flow classifications are contained in the 

database. Details of how the classifications were created are provided in Section 3. Table 2-5

lists the classifications. 

2.1.6 Averaged Aloft Data 

In addition to the data discussed above, the database also contains averages of RWP wind 

and RASS Tv data. Averages were created for the entire 1998-2001 study period by year, 

season, month, and aloft classification. 

2.2 DATA VALIDATION OBJECTIVES AND RESULTS 

Data validation is the process of evaluating the data quality through objective and 

subjective comparisons with other data sets, such as those from rawinsondes or model 

simulations. The data validation process was a necessary component of this project because it 

allowed us to identify data with errors, biases, and physically unrealistic values before they were 

used for analysis and modeling. The objectives of the data validation process were to 

• produce a working database with values that are validated and of a known quality; 

• evaluate the internal, spatial, temporal, and physical consistency of the data; and 

• determine the suitability of the data for analysis and modeling. 

To indicate the validity of a data point, we used QC flags that are stored with the data in 

the database. The following QC flags were used: 

• Valid data (QC flag = 0). Observations that were judged accurate within the performance 

limits of the instruments. 

• Invalid data (QC flag = 8). Observations that were judged inaccurate or in error. 

• Missing data (QC flag = 9). Observations that were not collected. In addition to a QC 

flag signifying missing data, the data values were assigned a missing value indicator 

(-999.0). 

All platform data were previously validated by STI as part of the data collection process. 

Details of the data collection and validation process can be found in Vaisala Meteorological 

Systems, Inc. and Sonoma Technology, Inc. (2002). Visual comparisons of the spatial and 

temporal variability of all buoy and C-MAN surface meteorological data were performed. This 

was accomplished by reviewing time series and spatial plots for consistency in time and space. 
2-4

Outliers were removed and flagged as invalid. Very few changes to the data validity were 

necessary. 

In addition to these QC flags, QC “out flags” were created for the derived COARE data 

set. The following out flags were used: 

• Out flag = 0 indicates that radiation from Eta model cloud data and all observations 

needed by COARE exist. 

• Out flag = 3 indicates that the observations were interpolated in time, and radiation data 

exist from Eta model cloud data. 

• Out flag = 6 indicates that the observations were interpolated in time. The radiation was 

estimated by time of year, day, and latitude. 

• Out flag = 7 indicates that the observations exist. The radiation was estimated by time of 

year, day, and latitude. 

• Out flag = 9 indicates no observations were available. 

Most derived data for this study have out flags of 0 or 3. 

2.3 ENVIRONMENTAL DATA ANALYSIS TOOL (EDAT) 

To effectively display the diverse set of MMS data for use in data analysis, the 

Environmental Data Analysis Tool (EDAT) was developed. EDAT is designed to work with 

environmental data sets such as RWP, RASS, rawindsonde, air quality, surface meteorological, 

and modeling data sets. EDAT reads from a Microsoft Access or Microsoft SQL Server 

database. Details about the structure of the database can be found in Appendix A. This section 

discusses the EDAT features. 

EDAT can produce four types of plots—time series, time-height cross-sections, vertical 

profiles, and spatial plots—and can display images. In addition, these plots can be displayed all 

at once, simplifying visual comparison of several different data types (see Figure 2-3). 

EDAT can plot two time series plots on a single graph and the variables do not have to be 

the same. For example, one can plot wind speed versus time as one time series and temperature 

as a separate time series on the same graph. In addition, these two variables may be from 

different sites. It is also possible to plot wind barbs as a time series. Figure 2-3 shows three 

examples of time series plots. Time series plots provide a means for the data analyst to look at 

trends within the data and evaluate how they might relate to other variables. 

Time-height cross-sections are designed to plot either wind barbs or wind vectors. An 

example of a wind barb time-height cross-section is shown in Figure 2-3(c). Time-height crosssections are important for looking at how winds vary with height and time. For example, winds 

that change direction rapidly with height may indicate a shear layer, which may be important for 

determining the source of air pollutants. 
2-5

Vertical profile plots are plots of a particular variable versus height. Vertical profiles are 

useful for examining the vertical structure of the atmosphere. For example, Tv profiles are useful 

for determining the mixing height. EDAT can display one or more profiles on the same graph; 

however, it is limited to one variable at one site. 

Spatial plots are plots of a variable at a site displayed in map view. Multiple sites are 

normally displayed, and up to two types of data may be displayed on one spatial plot. An 

example plot of wind barbs and ozone bars is shown in Figure 2-3(a). EDAT allows a base map 

of the user’s choice to be displayed in the background and referenced using latitude and 

longitude coordinates. Data can be displayed in the spatial plot with barbs, vectors, scalar 

values, and/or bars. EDAT also allows the user to change altitude by using the up/down cursor 

keys or the height toolbar. 

EDAT has an interactive screen that allows the user to create the graph displays discussed 

above. Once a graph type is selected, a new screen pops up requesting additional information to 

be used for creating the graph. Figure 2-4 illustrates how the user creates a time series plot. The 

first step is to select “New Time Series Graph” under the “Window” menu option. A selection 

screen pops up that requests the site name, data class, parameter, and height. A feature called 

Auto Scale then searches the database for maximum and minimum values. Once the search is 

completed, it is possible to change the scales by unchecking the “Auto Scale” boxes and typing 

the desired scales into the minimum and maximum value boxes. The “Time Window” feature 

allows the user to choose to plot one day, one week, one month, or all available data. 

EDAT can also link all of the resulting graphs in time and height (when applicable). This 

allows an analyst to scroll through a large set of data values as all the graphs scroll at the same 

time. This facilitates spatial and temporal analyses. In addition, the user can click on any point 

on any plot to see the data value, QC code, and height at any time. 

EDAT can save graph layouts to a configuration file. Layouts are a type of template that 

allows the user to make the same plots at a later time. These layouts are not to be confused with 

saving a file. In EDAT, graphs can be saved as bitmap (.bmp) images and/or printed. 

EDAT can also save data in formats used by other programs. In particular, EDAT allows 

users to save data for plotting by the U.S. Environmental Protection Agency’s (EPA) WRLPlot 

wind rose program. In addition, wind fields can be created for use in the CALMET diagnostic 

meteorological model. This is useful since any set of data in the database can be converted to 

either of these two formats for plotting in other programs. 

EDAT users can create a subset of data. This feature is useful for large databases that 

may take too long to create displays. 
2-6

Figure 2-1. Map of the MMS study region depicting locations of C-MAN, buoy, and RWP platform 

The water depths are provided in parenthesis. 
2-7

MeteorolTower

Radar Wind Profiler and RASS

Figure 2-2. SMI offshore oil platform showing the RWP and RASS upper-air measurement sys
2-8

Figure 2-3. EDAT screen shot showing (a) a spatial plot, (b) time series plots, 

(c) the time-height cross-section, and (d) the vertical profile. 

(a)

(c) 

(b)

(d) 
2-9

Figure 2-4. Sequence of events for creating a time series plot in EDAT: (a) open a new time 

series graph, (b) select data to be displayed, and (c) create the plot. 

(a)

(b) 

(c) 
2-10 

Table 2-1. C-MAN (five-character alphabetic), buoy (five-character numeric), and RWP 

platform sites. Included are the air temperature, anemometer, and sea 

temperature sensor heights. Sensor heights are in m above the site’s elevation. 

Site Name Site 

Latitude 

(degrees N)

Longitude 

(degrees W) 

Elevation 

(m msl) 

Air Temperature 

Height Above 

Site (m) 

Anemometer 

Height Above 

Site (m) 

Sea 

Temperature 

Height (m) 

Mid Gulf 180 nm South of 

Southwest Pass LA 

42001 25.93 89.65 0.0 10.0 10.0 -1.0 

West Gulf 240 nm SouthSoutheast of Sabine TX 42002 25.89 93.57 0.0 10.0 10.0 -1.0 

Biloxi 22 nm South-Southeast of 

Biloxi MS 

42007 30.10 88.78 0.0 4.0 5.0 -0.6 

Freeport TX. 60 nm South of 

Freeport TX 

42019 27.92 95.35 0.0 4.0 5.0 -0.6 

Corpus Christi TX 50 nm 

Southeast of Corpus Christi 

42020 26.92 96.70 0.0 4.0 5.0 -0.6 

Galveston 22 nm East of 

Galveston TX 

42035 29.25 94.41 0.0 4.0 5.0 -0.6 

Mobile South 64 nm South of 

Dauphin Island AL 

42040 29.18 88.30 0.0 4.0 5.0 -0.6 

Southwest Pass LA BURL1 28.90 89.43 0.0 11.9 30.5 -0.5 

Dauphin Island AL DPIA1 30.25 88.07 0.0 9.1 17.4 -0.5 

Grand Isle LA GDIL1 29.27 89.96 1.8 15.2 15.8 -0.5 

Port Arkansas TX PTAT2 27.83 97.05 0.0 9.1 14.9 -0.5 

Sabine TX SRST2 29.67 94.05 0.9 11.9 12.5 -0.5 

Breton Island Platform BIP 29.77 88.71 20.0 2.0 3.0 0.0 

Deep Water Platform DWP 28.15 89.10 41.0 2.0 3.0 0.0 

Shallow Water Platform SWP 29.98 88.60 20.0 2.0 2.0 0.0 

Mid Buoy Platform MBP 29.62 88.57 20.0 2.0 3.0 0.0 

West Delta Platform WDP 28.83 89.78 20.0 2.0 3.0 0.0 

Vermillion Gulf of Mexico VRM 29.47 92.55 21.0 2.0 3.0 0.0 

South Marsh Gulf of Mexico SMI 28.15 91.91 25.0 2.0 3.0 0.0 
2-11

Table 2-2. C-MAN (alphabetic), buoy (numeric), and RWP platform sites and their available surface meteor

Checkmarks indicate data were available. 

Site Site ID 

Air 

Temperature 

Near-Sea 

Surface 

Temperature Skin Temperature 

Relative 

Humidity Wind Pre

Mid Gulf 180 nm South of Southwest Pass LA 

42001 9 9 9 9 

West Gulf 240 nm SouthSoutheast of Sabine TX 42002 9 9 9 9 Biloxi 22 nm SouthSoutheast of Biloxi MS 42007 9 9 9 9 Freeport TX. 60 nm South of Freeport TX 

42019 9 9 9 

Corpus Christi TX 50 nm Southeast of Corpus Christi 

42020 9 9 9 9 

Galveston 22 nm East of Galveston TX 

42035 9 9 9 9 

Mobile South 64 nm South of Dauphin Island AL 

42040 9 9 9 9 

Southwest Pass LA BURL11 9 9 9 Dauphin Island AL DPIA11 9 9 9 9 Grand Isle LA GDIL11 9 9 9 9 Port Aransas TX PTAT21 9 9 9 9 South Marsh Gulf of Mexico 

SMI 9 9 9 9 

Sabine TX SRST21 9 9 9 Vermillion Gulf of Mexico VRM 9 9 9 9 Breton Island Platform BIP 9 9 9 9 Deep Water Platform DWP 9 9 9 9 Shallow Water Platform SWP 9 9 9 9 Mid Buoy Platform MBP 9 9 9 9 West Delta Platform WDP 9 9 9 9 
2-12

Table 2-3. Derived COARE parameters. 

Description 

Sensible heat flux 

Latent heat flux 

Wind stress 

Velocity scaling parameter (friction velocity) 

Humidity scaling parameter 

Temperature scaling parameter 

Roughness Reynolds number 

Height/Monin-Obukhov length 

Roughness length 

Total warm layer temperature difference 

Thickness of warm layer 

Cool skin temperature difference 

Skin temperature 

Table 2-4. Aloft synoptic classifications used in the 1998-2001 MMS Boundary Layer Study. 

Classifications 

Ridge 

Weak Ridge 

Flat 

Zonal 

Post-trough 

Weak Trough 

Trough 

Cut-off Low 

Tropical Storm 

Table 2-5. Surface wind flow speed and direction classification used in the 1998-2001 

MMS Boundary Layer Study. 

Flow Direction Flow Speed 

Onshore Light 

Offshore Moderate 

Parallel east Strong 

Parallel west 
3-1

3. GENERAL METEOROLOGY 

3.1 INTRODUCTION 

This section defines the upper-air and surface patterns observed in the Gulf of Mexico for 

the study period from June 1, 1998, to October 2, 2001, and describes the climatology of the 

upper-air and surface wind flow patterns. The results from this work were used to understand 

how the upper-air and surface wind flow patterns influence ABL characteristics, transport, and 

dispersion. 

3.2 UPPER-AIR PATTERNS 

Upper-level synoptic-scale weather features are large-scale (1000 km or more) weather 

circulations that produce regional meteorological conditions. It is necessary to analyze these 

patterns because they have a direct influence on the production, accumulation, and transport of 

pollutants. For example, an upper-level trough is an area of generally lower pressure in the 

upper levels of the troposphere. These troughs are typically associated with lifting of air, cloudy 

skies, and cooler temperatures. These weather conditions result in more vertical mixing of air, 

which tends to cause the ABL to grow quite large, increasing the vertical dispersion of 

pollutants. Upper-level troughs are often associated with surface weather systems that result in 

stronger winds and hence more horizontal dispersion. Another example of a general pattern is an 

upper-level ridge. The upper-level ridge is a region of generally higher pressure in the upper 

levels of the troposphere. These ridges are typically associated with sinking air, clear skies, and 

warm temperatures. These weather conditions result in decreased vertical mixing of air, which 

tends to suppress the growth of the ABL, which leads to less vertical dispersion of pollutants. 

Upper-level ridges also tend to result in surface-based highs downstream of the upper-level ridge 

axis. These surface highs can either lead to transport by influencing the wind directions or they 

can lead to light winds (and hence less horizontal dispersion). They may also allow mesoscale 

circulations to dominate the local flows, such as the sea breeze. 

3.2.1 Methods of Obtaining and Classifying Data 

To determine the upper-air meteorological patterns for the Gulf of Mexico region, we 

obtained EDAS meteorological plots of the 500-mb geopotential height pattern for the United 

States twice per day, once at 0000 UTC and once at 1200 UTC. We also obtained National 

Oceanic and Atmospheric Administration (NOAA)/National Weather Service (NWS)/National 

Center for Environmental Prediction (NCEP) Daily Weather Maps, which provide 500-mb 

geopotential height patterns and winds for the entire United States once per day at 0600 CST. 

The 500-mb geopotential height patterns depict the large-scale weather patterns across a region. 

The upper-level patterns were classified based on observations of the 500-mb 

geopotential height pattern, locations of ridge and trough axes, and circulations apparent in the 

500-mb winds. Anti-cyclonic circulations (clockwise in the northern hemisphere) indicate high 

pressure while cyclonic circulations (counterclockwise in the northern hemisphere) represent low 
3-2

pressure. All classifications were compiled based on the positions of weather systems with 

respect to the study region over the Gulf of Mexico. 

Figure 3-1 shows an example of an upper-level ridge over the Gulf of Mexico region. 

The ridge axis is defined by connecting the peak amplitude of each line into a single line, or axis. 

The weather patterns associated with the upper-level ridge are likely to be strongest near the axis. 

Transitions between upper-level patterns were observed in this study; therefore, it was 

necessary to determine the average daily pattern based on the pattern that was observed for a 

majority of that day. 

We looked at the upper-level synoptic pattern at 500 mb for every day, twice per day, 

during the study period and determined a dominant set of upper-air patterns. We then assigned a 

pattern to each day. These patterns were put into the database. Figure 3-2 shows the 500-mb 

heights on March 22, 2000, at 1200 UTC generated by the EDAS model output. This particular 

day was classified as a ridge pattern (see below) for the study area. 

In our statistical review of the upper-level synoptic patterns, the frequency of occurrence 

of each upper-air pattern was determined using queries of the daily data available in the database. 

Queries were used to group each upper-air pattern by the entire study period, by year, by month, 

and by season. 

The following upper-level synoptic classifications were used: 

• Ridge: An example of a ridge is shown in Figure 3-2. A ridge pattern usually leads to 

high pollution levels as a result of conditions such as subsidence of air, clear skies, and 

warming of surface and aloft temperatures. These weather conditions decrease the height 

of the ABL and often allow mesoscale circulations, such as the sea breeze/land breeze 

circulation, to dominate the boundary layer winds. 

• Weak Ridge: An example of a weak ridge is shown in Figure 3-3. A weak ridge 

pattern can lead to high pollution levels as a result of subsidence of air, clear skies, and 

warming of surface and aloft temperatures. However, weak ridges tend to result in 

weaker subsidence, which may allow the ABL to grow vertically more than it can under a 

ridge pattern. 

• Trough: An example of a trough is shown in Figure 3-4. A trough pattern is associated 

with rising air, cloudy skies, strong winds, and cool aloft temperatures. All of these 

weather conditions tend to result in more vertical mixing and horizontal dispersion. In 

addition, the mixing height of the ABL may be very high under these conditions.

• Weak Trough: An example of a weak trough is shown in Figure 3-5. A weak trough 

may be associated with rising air, cloudy skies, stronger winds, and cooler temperatures; 

however, not all conditions may occur. Weak troughs are typically associated with the 

same dispersion characteristics as troughs; however, these characteristics may not be as 

strong so the mixing height of the ABL may not be as large.
3-3

• Cut-off Low: An example of a cut-off low is shown in Figure 3-6. A cut-off low is 

similar to a trough; however, cut-off lows tend to move more slowly than troughs. 

Sometimes, cut-off lows may be too weak to produce much vertical mixing; therefore, it 

may be possible to see higher pollution levels and less dispersion than expected under a 

trough pattern.

• Post Trough: A post trough is typically found after a trough has passed through a 

region, but prior to a ridge building in. Figure 3-7 shows an example of this pattern over 

southern Louisiana. A post trough typically indicates clearing skies and northerly surface 

winds. Since a post trough immediately follows a trough, background pollution levels 

are typically low.

• Flat: A flat upper-air pattern is typically found when neither a ridge nor a trough is near 

the region. Figure 3-8 shows an example of this pattern over the Gulf of Mexico. In this 

case, winds were driven by mesoscale meteorological conditions, such as a sea breeze. 

For this pattern, ABL characteristics are strongly dependent on the mesoscale 

meteorological conditions. 

• Zonal: A zonal weather pattern is depicted in Figure 3-9 over the Gulf Coast states. 

Zonal weather patterns typically do not last long and are often replaced by ridges and 

troughs. The ABL characteristics are once again dependent on mesoscale meteorological 

conditions, such as the sea breeze.

• Tropical Storm: Tropical storms occur on only a few days of a year, at most, in the Gulf 

region. Figure 3-10 depicts hurricane Bret over southeast Texas, extending into the 

eastern Gulf of Mexico. A tropical storm is typically associated with cloudy skies, strong 

winds, and low air pollution levels; however, it is possible for these patterns to introduce 

subsidence in nearby regions as a result of outflow at the upper levels. This increased 

subsidence away from the storm center may decrease winds, warm temperatures, and 

enhance pollutant levels. 

To simplify some of the analyses, it was necessary to group similar patterns into broader 

categories. Therefore, we combined the ridge and weak ridge into the “grouped ridge” category. 

We grouped the trough, weak trough, and cut-off low into the “grouped trough” category, and 

the remaining patterns, post-trough, flat, zonal, and tropical storm, were grouped into the 

“grouped others” category. 

3.2.2 Data Classification Results 

Figure 3-11 shows the grouped upper-air synoptic pattern for the three general groups for 

the study period and shows an almost equal representation of both ridges and troughs. Other 

patterns (the post trough, flat, zonal, and tropical storm patterns) were observed less than 20% of 

the time. 

Figure 3-12 shows the frequency of occurrence of each of the nine upper-air patterns 

during the study period. Note that the ridge pattern was the dominant upper-air pattern, 
3-4

occurring approximately one-third of the time. This is important because the ridge pattern is 

often associated with ABL characteristics that lead to high pollutant concentrations. The trough 

was the second-most predominant upper-air feature, which was observed about a quarter of the 

time. This is important because the ABL characteristics under trough scenarios typically lead to 

low pollution episodes. Weak troughs occurred less frequently and were observed on about one 

out of every six days. The other patterns were found to occur far less frequently, with tropical 

storms being rare. 

Figure 3-13 shows the frequency distribution of the grouped upper-air patterns observed 

during the study period by “MMS year”. Since the study began in June 1998 and ended in 

October 2001, an MMS year is defined as June 1 through May 31. Thus, the year 1998 refers to 

the period from June 1, 1998, through May 31, 1999. MMS year 2001 contains June 1, 2001, 

through October 1, 2001, data. Therefore, the results for 2001 are biased because they contain 

only four months of data. As shown in Figure 3-13, the frequency of occurrence of each pattern 

did not vary significantly from year to year with the exception of 1998. During 1998, the trough 

pattern was observed approximately 10% more often than the ridge pattern. This is important 

because the ABL characteristics may have been significantly affected by the presence of more 

troughs during that year. Fewer troughs occurred in 2001 than in other years; however, since 

most of the 2001 data came from the summer months, this observation is biased. 

Figure 3-14 shows the frequency distribution of the individual upper-air patterns 

observed during the study period by MMS year. Although the frequency of occurrence of 

grouped trough and ridge patterns were generally similar, further examination of the upper-air 

patterns show that the ridge pattern dominated followed by the trough pattern, but the weak 

ridges occurred less frequently than the weak troughs. 

In 2000, a ridge pattern occurred almost 10% more often than during the other years. The 

other five patterns occurred far less frequently, and tropical storms were a rare occurrence. An 

anomalously high percentage of flat pattern days occurred in 2001, probably due to bias in the 

data for that shortened year. 

Figure 3-15 shows the frequency distribution of the grouped upper-air patterns by season 

for all years during the study period. Although there was a relatively even distribution in the 

annual upper-air characteristics between the trough and ridge patterns, seasonal breakdowns 

show that both the fall and winter seasons are dominated by a trough pattern, while spring is 

equally distributed between troughs and ridges, and summer is dominated by a ridge pattern. 

These seasonal variations imply that the ABL characteristics will also be different as the seasons 

change. For example, in the winter, with more troughs, we would expect vertical mixing and 

horizontal dispersion to be high, leading to lower pollutant concentrations than during the 

summer. 

Figure 3-16 shows the frequency distribution of the individual upper-air patterns for all 

years by season. Recall that the summer season was dominated by the grouped ridge pattern 

while fall and winter were predominantly characterized by the grouped trough pattern. The 

refined classifications show that the ridges that are not weak account for about 45% of the 

summer days; whereas, the weak ridges account for less than 10% of summer days. In the fall 

and winter months, the troughs account for approximately one-third of the days; whereas, the 
3-5

weak troughs account for about 15% of the days. These facts are important because strong 

patterns will have a stronger impact on the ABL characteristics and, therefore, a stronger impact 

on air pollution. 

Analysis shows that during the spring, a majority of the troughs were actually weak 

troughs. Weak troughs have a different impact on the ABL characteristics than strong troughs. 

While the impact on the ABL is significant when tropical storms are present, they occur only 

during the summer months. 

Figure 3-17 shows the monthly frequency distribution of the grouped upper-air patterns. 

June, July, August, and September produced more days of data because the study period ran 

from June 1, 1998, through October 2, 2001. The ridge pattern dominated from June through 

October, as expected for this region. However, September had significantly more troughs 

compared to the other months. This implies that the ABL characteristics may differ during 

September in contrast to other summer months. November through March was dominated by a 

trough pattern. 

3.3 SURFACE FLOW CHARACTERISTICS 

Surface wind speed and direction data collected at the C-MAN, buoy, and platform 

surface monitors were analyzed to characterize the surface flow patterns in the Gulf of Mexico. 

The analysis involved creating wind rose plots for all sites to characterize surface flows and 

classifying the flow at selected sites on each day of the study period as onshore, offshore, parallel 

west, or parallel east. The daily surface speed and direction flow classifications are included in 

the database. The buoy and platform sites are separated by large distances, stretching from buoy 

42019 a few hundred km southwest of Houston, to buoy 42040 near southern Alabama, to as far 

as 100 km offshore. These distances alone provide expected variability in the nature of the 

onshore and offshore flow characteristics. 

3.3.1 Methods of Determining Surface Flow Characteristics 

To determine the onshore/offshore surface flow patterns and the wind roses, we obtained 

hourly surface wind speed and wind direction data from the MMS platform sites at VRM and 

SMI. We also obtained surface wind speed and wind direction data for several C-MAN and 

buoy sites located in the Gulf of Mexico, as shown in Figure 2-1. 

Daily Flow Characteristic Analysis 

Two buoy sites and two platform sites were chosen to characterize the surface flows on 

each day. Buoy 42035 (15 km offshore from Galveston, Texas) and the VRM platform site 

(10 km offshore from central Louisiana) were selected to represent the near-shore characteristics. 

Buoy 42019 (100 km offshore from Freeport, Texas) and the SMI platform site (about 100 km 

south of South Marsh Island) were selected to represent the offshore characteristics. Onshore 

flows were classified by wind directions between 100° and 260°. Offshore flows were classified 

by wind directions between 280° and 80°. Wind directions between 80° and 100° were 

designated “parallel east” and wind directions between 260° and 280° were designated “parallel 
3-6

west”. Note, since the parallel directions exist within a 40° range, an even distribution of winds 

would be eight times more likely to occur than wind directions parallel to the shore. Yearly, 

seasonal, and upper-air averages of the daily surface flow directions and speeds were created and 

analyzed. Flow types were classified by speed. Table 3-1 depicts the categories used for speed 

classifications. Three classifications were developed based on the Beaufort Wind Scale: light, 

moderate, and strong. 

Table 3-1. Speed classifications. 

Wind Speed > 10 m/s Strong 

Wind Speed > 5 m/s and ≤ 10 m/s Moderate 

Wind Speed ≤ 5 m/s Light 

Wind Rose Analysis 

Wind roses were created using the WRPLOT View wind rose program based on data 

collected from all of the buoy and platform monitors within the MMS study region. Wind roses 

are useful for determining surface flow speed and direction characteristics for the entire study 

period and by season. Wind roses provide a quick indication of the flow characteristics for 

individual sites. An example of a wind rose plot is given in Figure 3-18. The dashed circles 

indicate the percentage of time the winds are from a particular direction. The different colors 

within the bars indicate the percentage of time each range of wind speeds was observed. 

The wind rose data results were grouped based on initial comparisons of all of the sites. 

Figure 3-19 shows the site groupings. Group A sites represent the western Gulf of Mexico. 

Group B sites represent the eastern portion of the study region. 

3.3.2 Results of Determining Surface Flow Characteristics 

Daily Flow Characteristic Analyses 

A predominant onshore flow that was light to moderate in speed was observed for the 

entire study period at the four sites used for analyzing the daily flow characteristics. Figure 3-20

shows the frequency distribution of surface flow types by year for the near-shore buoy site 

(42035) and the offshore site (SMI). All four sites show onshore flow about twice as often as 

offshore flow. The flow is rarely parallel to the coastline, and when it is, it is predominantly 

from the east. In 1999, less onshore flow was observed at buoy 42019 and VRM compared to 

1998 and 2000. This pattern was not observed at buoy 42035 or SMI. This is important because 

these differences may impact the characteristics of the ABL. 

Figure 3-21 shows the seasonal frequency distribution of surface flow directions. Once 

again the onshore flow direction clearly dominates during all seasons, except for one notable 

exception. For the buoy 42035, VRM, and SMI sites, surface flow during the fall is 

predominantly offshore (occurring approximately half of the time). Summer and spring at all 
3-7

sites are characterized by onshore flow between 70% and 80% of the time. Winter and fall tend 

to have a more even distribution of offshore and onshore days, with each occurring 40% to 50% 

of the time. These observations are important to the transport and dispersion characteristics as 

well as the ABL structure. For example, the onshore flow suggests that offshore sources may 

impact onshore areas more often in the spring and summer. The winds during all seasons were 

seldom strong. During fall, winter, and spring, moderate winds dominated, while during the 

summer, light winds dominated. 

Figure 3-22 shows the frequency distribution of flow speeds and directions based on 

upper-air synoptic pattern. For all of the upper-air patterns, light-to-moderate winds and 

offshore or onshore flow dominated. Annual and seasonal results were similar. Stronger winds 

were observed under the trough pattern as opposed to the ridge pattern, which is consistent with 

the fact that more horizontal dispersion is expected with a trough. In general, stronger winds 

were observed more often at the offshore sites. 

Onshore flow occurs 70% to 80% of the time a ridge is present; whereas, it occurs 50% to 

60% of the time for the other upper-air patterns. This shows that under a ridge pattern, the 

offshore flow occurrences are extremely low, especially when compared with the trough and 

other upper-air patterns. Consistent with the yearly and seasonal breakdowns, parallel flows 

were a rare occurrence no matter what upper-air pattern was present. 

Wind Rose Analysis 

The wind roses show that the dominant flow within the region was southeasterly, with a 

secondary, less predominant flow from the northeast. Westerly flow within the region was less 

predominant. 

For the wind rose analysis, the sites were divided into two groups: Group A and 

Group B. Group A sites were characterized by a strong southeasterly flow (as shown in 

Figure 3-23a at VRM) and very little southwest through northeast flow. The southeasterly flow 

is likely a reflection of the predominant weather feature, the Bermuda high, as well as the sea 

breeze. The northeasterly flow is likely a result of continental high pressure systems. The 

Group B sites, although dominated by a southeasterly flow, did not have a strong southeasterly 

flow (Figure 3-23b shows this for buoy 42040). In addition, winds were more evenly 

distributed in other directions. The strongest winds for the Group B sites occurred 

predominantly from the northeast. The Group A sites had an even distribution of strong winds. 

These differences are important as they suggest that different areas of the Gulf of Mexico region 

may experience different ABL characteristics. 

The seasonal wind rose patterns revealed general agreement with the overall patterns and 

have the following characteristics. 

• The fall wind rose plots (Figure 3-24) show that Group B sites had predominantly northnortheast flows and very little southwesterly flow. Group A sites had a predominantly 

southeasterly flow with secondary flows from the north-northeast, with the exception of 

buoy 42001, which was dominated by an easterly flow. 
3-8

• The winter wind rose plots (Figure 3-25) were similar to fall wind rose plots except for a 

stronger southeast flow at the Group B sites. Buoy 42007 had a more even peak 

distribution than the other Group B sites. 

• The flow in the spring (Figure 3-26) in both groups was very different than in the fall 

and winter. Spring is characterized by a predominant southeasterly flow with very little 

northerly flow at the Group A sites. Group B sites were dominated by a broad peak from 

the east-southeast to the southwest. 

• The summer wind rose plots with a dominant southeast peak show that the summer flow 

was similar to the spring flow for Group A sites (Figure 3-27). The near-shore sites 

show a more frequent southerly peak, likely due to the land/sea breeze circulation. Group 

B sites had an evenly distributed peak from east through south to west, with the exception 

of SMI, which only had a southwest peak. 

These seasonal differences indicate that seasonal variability in surface wind speeds and 

directions exist and that attention needs to be paid to these differences with respect to the ABL 

characteristics, case study analyses, and modeling. 

Figure 3-1. An upper-level high pressure system with ridge axis (dotted line). The contours 

represent geopotential heights, with the highest heights located near the “H” over 

the Gulf of Mexico. 

Ridge axis
3-9

 Figure 3-2. Example of an upper-air ridge pattern (box) for the Gulf of Mexico region for 

March 22, 2000, at 1200 UTC (0600 CST). Solid lines indicate height contours 

(decameters). 
3-10

Figure 3-3. Example of an upper-air weak ridge pattern (box) for the Gulf of Mexico region 

for July 30, 1998, at 1200 UTC (0600 CST). Solid lines indicate height contours 

(decameters). 
3-11

Figure 3-4. Example of an upper-air trough pattern (box) for the Gulf of Mexico region for 

January 5, 1999, at 0000 UTC (January 4, 1999, at 1800 CST). Solid lines indicate 

height contours (decameters). 
3-12

Figure 3-5. Example of an upper-air weak trough pattern (box) for the Gulf of Mexico region 

for May 31, 1999, at 0000 UTC (May 30, 1999, at 1800 CST). Solid lines 

indicate height contours (decameters). 
3-13

Figure 3-6. Example of an upper-air cut-off low pattern (box) for the Gulf of Mexico region 

for March 30, 1999, at 0000 UTC (March 29, 1999, at 1800 CST). Solid lines 

indicate height contours (decameters). 
3-14

Figure 3-7. Example of an upper-air post-trough pattern (box) for the Gulf of Mexico region 

for December 18, 1998, at 0000 UTC (December 17, 1998, at 1800 CST). Solid 

lines indicate height contours (decameters). 
3-15

Figure 3-8. Example of an upper-air flat pattern (box) for the Gulf of Mexico region for 

October 1, 2000, at 1200 UTC (0600 CST). Solid lines indicate height contours 

(decameters). 
3-16

Figure 3-9. Example of an upper-air zonal pattern (box) for the Gulf of Mexico region for 

November 15, 2000, at 0000 UTC (November 14, 2000, at 1800 CST). Solid 

lines indicate height contours (decameters). 
3-17

Figure 3-10. Example of an upper-air hurricane pattern (box) for the Gulf of Mexico region 

for August 23, 1999, at 0000 UTC (August 22, 1999, at 1800 CST). Solid lines 

indicate height contours (decameters). This upper-air pattern depicts hurricane 

Bret over southeast Texas, extending east into the western Gulf of Mexico. 
3-18

0

5

10

15

20

25

30

35

40

45

Grouped Ridge Pattern Grouped Trough Pattern Grouped Other

Percentages

Figure 3-11. Overall frequency distribution of grouped upper-air patterns observed for the 

study period. 

Percentages for Entire Study Period

0

5

10

15

20

25

30

35

Ridge

Weak Ridge

Trough

Weak Trough

Cut-off Low

Post Trough

Flat

Zonal

Tropical Storm

Percentage

Figure 3-12. Frequency distribution of upper-air patterns observed for the study period. 
3-19

0

5

10

15

20

25

30

35

40

45

50

Grouped Ridge

Pattern

Grouped Trough

Pattern

Grouped Other

Percentages

1998

1999

2000

2001

Figure 3-13. Frequency distribution of grouped upper-air patterns observed for each MMS 

year, June through May, during the study period. 
3-20

05

1015202530354045

Ridge Weak

Ridge

Trough Weak

Trough

Cut-off

Low

Post

Trough

Flat Z

Percentage

Figure 3-14. Frequency distribution of nine upper-air patterns observed for each MMS year during the 
3-21

Fall All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped trough Grouped Other

Percentage

Winter All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped trough Grouped Other

Percentage

Spring All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped trough Grouped Other

Percentage

Summer All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped trough Grouped Other

Percentage

 

Figure 3-15. Frequency distribution of grouped upper-air patterns observed for each season 

for all years during the MMS study period. 
3-22

Fall All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

trough Weak

trough

Cut-off

Low

Post

trough

Flat ZonalTropical

Storm

Percentage

Winter All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

trough Weak

trough

Cut-off

Low

Post

trough

Flat ZonalTropical

Storm

Percentage

Spring All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

trough Weak

trough

Cut-off

Low

Post

trough

Flat ZonalTropical

Storm

Percentage

Summer All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

trough Weak

trough

Cut-off

Low

Post

trough

Flat ZonalTropical

Storm

Percentage

Figure 3-16. Frequency distribution of nine upper-air patterns observed for each season for all 

years during the MMS study period. 

0

10

20

30

40

50

60

70

80

90

01 02 03 04 05 06 07 08 09 10 11 12

Month

Total Number of Days

Grouped Ridge Pattern Grouped Trough Pattern Grouped Other

Figure 3-17. Frequency distribution of grouped upper-air patterns observed for each month 

for all years during the MMS study period. 
3-23

Figure 3-18. Wind rose plot for the SMI platform for the study period. 

WIND ROSE PLOTStation #00001 - , 

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

Wind Spee

> 8.45.43.31.80.5

UNITm/sDISPLAYWind SpeedCALM WINDS0.61%MODELERDATE5/28/2002COMPANY NAMECOMMENTS

WRPLOT View 3.5 by Lakes Environmental Software - www.lakes-environmental.com

PLOT YEAR-DATE-TIME2000 Jan 1 - Dec 31Midnight - 11 PMAVG. WIND SPEED5.38 m/sORIENTATIONDirection(blowing from)PROJECT/PLOT NO.
3-24

Group A map

VRM

SRST2

42035

PTAT2 42019

42020

42002 42001

Louisiana Texas

MS

Group B map

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Mississippi

Alabama

Florida

Group A map

VRM

SRST2

42035

PTAT2 42019

42020

42002 42001

Louisiana Texas

MS

Group B map

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Mississippi

Alabama

Florida

Figure 3-19. Monitoring sites in the Gulf of Mexico region. Group A sites are shown on the 

left, Group B sites on the right. 

Yearly Surface Flow Direction (42035)

0

10

20

30

40

50

60

70

80

90

1998 1999 2000 2001

Percentage

offshore

onshore

parallel east

parallel west

Yearly Surface Flow Direction (SMI)

0

10

20

30

40

50

60

70

80

1998 1999 2000 2001

Percentage

offshore

onshore 

parallel east

parallel west

Yearly Surface Speed (42035)

0

10

20

30

40

50

60

70

80

90

1998 1999 2000 2001

Percentage

light

moderate

strong

Yearly Surface Speed (SMI)

0

10

20

30

40

50

60

70

80

90

1998 1999 2000 2001

Percentage

light

moderate

strong

Figure 3-20. Yearly frequency distributions of surface wind direction (top graphs) and surface 

wind speed (bottom graphs) and for the near-shore site, buoy 42035, and the 

offshore site, SMI. Recall that these two sites are separated by about 200 km. 
3-25

Seasonal Surface Direction (42019)

0

102030405060708090

Fall Spring Summer Winter

Percentage

offshoreonshoreparallel eastparallel west

Seasonal Surface Direction (42035)

0

102030405060708090

Fall Spring Summer Winter

Percentage

offshoreonshoreparallel eastparallel west

Seasonal Surface Direction (S

0

102030405060708090

Fall Spring Sum

Percentage

Seasonal Surface Direction (V

0

102030405060708090

Fall Spring Summ

Percentage

Figure 3-21. Frequency distribution of seasonal surface flow directions for near-shore and offsho
3-26

Percentage Flow Speeds for Upper-Air 

Ridge

0

20

40

60

80

100

42019 SMI 42035 VRM

Light Flow Speed

Moderate Flow

Speed

Strong Flow

Speed

Percentage Flow Directions for Upper-Air 

Ridge

0

20

40

60

80

100

42019 SMI 42035 VRM

Onshore Flow

Direction

Offshore Flow

Direction

Parallel to Shore

Flow Direction

Percentage Flow Speeds for Upper-Air 

Trough

0

20

40

60

80

100

42019 SMI 42035 VRM

Light Flow Speed

Moderate Flow

Speed

Strong Flow Speed

Percentage Flow Directions for Upper-Air 

Trough

0

20

40

60

80

100

42019 SMI 42035 VRM

Onshore Flow

Direction

Offshore Flow

Direction

Parallel to Shore

Flow Direction

Percentage Flow Speeds for Other UpperAir Patterns

0

20

40

60

80

100

42019 SMI 42035 VRM

Light Flow Speed

Moderate Flow

Speed

Strong Flow Speed

Percentage Flow Directions for Other 

Upper-Air Patterns

0

20

40

60

80

100

42019 SMI 42035 VRM

Onshore Flow

Direction

Offshore Flow

Direction

Parallel to Shore

Flow Direction

Figure 3-22. Frequency distribution of surface flow typing for upper-air ridge, upper-air 

trough, and other upper-air patterns at the four selected sites during the MMS 

study period. 
3-27

Figure 3-23a. Wind rose for VRM. This plot is representative of the wind rose plots for Group A 

WIND ROSE PLOTStation #00002 - , 

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

UNITm/sDISPLAYWind SpeedCALM WINDS4.52%MODELERDATE5/28/2002COMPANY NAMECOMMENTS

WRPLOT View 3.5 by Lakes Environmental Software - www.lakes-environmental.com

PLOT YEAR-DATE-TIME2000 Jan 1 - Dec 31Midnight - 11 PMAVG. WIND SPEED5.87 m/sORIENTATIONDirection(blowing from)PROJECT/PLOT NO.
3-28

Figure 3-23b. Wind rose for buoy 42040. This plot is representative of the wind rose plots for Grou

WIND ROSE PLOTStation #00017 - , 

NORTHSOUTH

WEST EAST

2%

4%

6%

8%

10%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

UNITm/sDISPLAYWind SpeedCALM WINDS2.67%MODELERDATE5/28/2002COMPANY NAMECOMMENTS

WRPLOT View 3.5 by Lakes Environmental Software - www.lakes-environmental.com

PLOT YEAR-DATE-TIME2000 Jan 1 - Dec 31Midnight - 11 PMAVG. WIND SPEED5.71 m/sORIENTATIONDirection(blowing from)PROJECT/PLOT NO.
3-29

Figure 3-24. Spatial plot depicting wind roses for Group A (left) and Group B (right) for the fall 

Group A -- Fall

VRM SRST2

PTAT2

42019

42020

42002

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20% 42001

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

42035

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group A -- Fall

VRM SRST2

PTAT2

42019

42020

42002

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20% 42001

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

42035

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Fall

GDIL1

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

WEST 

WEST 

BUR

SMI

Louisiana

Miss

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Fall

GDIL1

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

WEST 

WEST 

BUR

SMI

Louisiana

Miss

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80
3-30

Figure 3-25. Spatial plot depicting wind roses for Group A (left) and Group B (right) for the winte

Group A -- Winter

VRM SRST2 42035

PTAT2

42019

42020

42002 42001

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group A -- Winter

VRM SRST2 42035

PTAT2

42019

42020

42002 42001

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Winter

GDIL1

BUR

SMI

Louisiana

Missi

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

WEST 

NORTH SOUTH

WEST 

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Winter

GDIL1

BUR

SMI

Louisiana

Missi

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

WEST 

NORTH SOUTH

WEST 

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80
3-31

Figure 3-26. Spatial plot depicting wind roses for Group A (left) and Group B (right) for the sprin

Group A -- Spring

VRM 42035 SRST2

PTAT2

42019

42020

42002 42001

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group A -- Spring

VRM 42035 SRST2

PTAT2

42019

42020

42002 42001

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Spring

GDIL1

SMI

Louisiana

M

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

WEST 

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Spring

GDIL1

SMI

Louisiana

M

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

WEST 

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80
3-32

Figure 3-27. Spatial plot depicting wind roses for Group A (left) and Group B (right) for the summ

Group A -- Summer

VRM 42035 SRST2

PTAT2

42019

42020

42002 42001

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group A -- Summer

VRM 42035 SRST2

PTAT2

42019

42020

42002 42001

Louisiana Texas

MS

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTHSOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Summer

GDIL1

BUR

SMI

Louisiana

Missis

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

WEST 

NORTHSOUTH

WEST 

2%

NORTHSOUTH

WEST EAST

2%

4%

6%

8%

10%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80

Group B -- Summer

GDIL1

BUR

SMI

Louisiana

Missis

NORTHSOUTH

WEST EAST

4%

8%

12%

16%

20%

WEST 

NORTHSOUTH

WEST 

2%

NORTHSOUTH

WEST EAST

2%

4%

6%

8%

10%

Wind Speed (m/s)

> 11.068.49 - 11.065.40 - 8.493.34 - 5.401.80 - 3.340.51 - 1.80
4-1

4. UPPER-AIR WINDS AND VIRTUAL TEMPERATURES 

The MMS now has available new boundary layer observations for the OCS in the Gulf of 

Mexico from six meteorological stations. These meteorological stations contain 915-MHz 

RWPs, 2-KHz RASS, and surface meteorological stations. Two stations collected observations 

of the ABL for three years from May 1998 through October 2001 and four stations collected 

observations from September 2000 through October 2001 (as described in Section 1). 

This section presents an evaluation of the characteristics of the boundary layer winds and 

Tv profiles and how these characteristics change by year, by season, by month, by upper-air 

classification, and among sites. The analysis of the characteristics yields insight into the spatial 

and temporal processes that occur vertically in the atmosphere. This information was used to 

support modeling efforts discussed in Section 6. 

4.1 RWP AND RASS DATA 

Quality-controlled RWP and RASS data from the six profiler sites were averaged over 

several intervals to determine the characteristics and patterns in these data. Averaging was done 

by month, season, year, upper-air classification, and the 1998-2001 period (for VRM and SMI). 

Surface wind and Tv data were averaged and analyzed along with the aloft data to give a more 

complete picture of the atmospheric boundary layer. The winds were vector averaged, which 

inherently produces lighter wind speeds than are typically observed. Data from each of the six 

profiler and RASS sites were characterized both individually and comparatively for each 

averaging period. 

Wind data were grouped by hour and height prior to averaging, creating an average 

diurnal profile for the given interval. Tv data were grouped by height and also into day (0600 to 

1800 CST) and night (1800 to 0600 CST) categories prior to averaging, yielding a daytime and 

nighttime Tv profile for each averaging period. Averages were only calculated if at least 50% of 

the possible measurements contributing to that average were valid. 

Figures showing the results for the wind and temperature analyses for selected sites are 

contained in this section and figures for all sites can be found in the final project presentation 

(MacDonald et. al. 2003) delivered to MMS on October 15, 2003, and are included in 

Appendix D. 

4.2 PROFILER RESULTS AND INTERPRETATIONS 

RWP data showed several distinct patterns at various averaging intervals. The following 

is a description of those patterns, along with a basic interpretation of their causes. Note that 

averages above 3500 m are not available because the return signal was lost above that height on 

more than 50% of the days. Averages are also often not available from 131-500 m due to sea 

clutter. This analysis focuses on VRM and SMI but also includes information from the four 

BAMP sites. Data plots for the BAMP sites are included in Appendix D. 
4-2

In summary, the average wind profiles from the platform height of 25 m to the top of the 

RWP range (about 3500 m) show 

• Southwest through easterly flow throughout all seasons, years, and sites; southeasterly 

was the most frequent flow direction. 

• At WDP, more easterly winds in the lowest 500 m compared to southerly at the other 

sites.In the fall, easterly flow at lower levels and southwesterly flow aloft with the 

transition height near 1000 m. 

• In the winter, easterly surface flow very decoupled from south to southwesterly flow 

aloft. 

• In the spring, coupled surface and aloft flow with southerly winds up to 1000 m and 

southwesterly winds above 1000 m. 

• In the summer, winds ranging from easterly to southwesterly below 2000 m and the most 

diurnal variability at VRM. 

• With a ridge pattern, winds south to southeasterly below 1100 m, and southwest to 

easterly aloft. 

• With a trough pattern, mostly southwesterly flow aloft, with southeasterly to 

northeasterly flow in the low levels. Stronger troughs have a more defined shear layer. 

4.2.1 Overall Average Wind Profiles 

The wind profiles at each site showed a general pattern of light winds (1-3 m/s), 

transitioning from southeasterly to easterly winds at the surface, through southerly winds at the 

mid-levels, to southwesterly winds above 1500-1700 m. Below 1400 m, pre-dawn winds had a 

prominent southeasterly component, especially at SMI (Figure 4-1). The surface winds 

generally matched the aloft winds at both sites, except from 1100 to 1500 CST at VRM 

(Figure 4-2), when the surface winds were easterly. With the exception of these slight 

discrepancies, the overall wind averages at the two sites correlate well with each other. 

4.2.2 Yearly Wind Profiles 

The yearly patterns in the wind profiles generally followed the overall patterns, with light 

winds transitioning from southeasterly at the surface, through southerly, to southwesterly above 

approximately 1400-1700 m. In general, the 1998-1999 year appeared very similar to the overall 

average for both sites (Figures 4-3 and 4-4). The 1999-2000 year showed a more easterly 

component to the lower-level winds than the previous year and produced poorer data quality, but 

was otherwise similar to the previous year (Figures 4-5 and 4-6). The 2000-2001 year provided 

less data with no points above 1600 m meeting the 50% averaging criteria. Within the lower 

levels at SMI, this year showed light winds transitioning from easterly in the pre-dawn hours, 

through southerly in the early morning, to southwesterly in the afternoon and evening 

(Figure 4-7). In addition, the surface winds remained the same as the overall pattern, eastsoutheasterly all day. As a result, the surface winds were discontinuous from the winds at 500 m 

and differed by as much as 180°. This suggests that the mixing height is, on average, below 
4-3

500 m. The VRM profile matched well with the overall pattern, except for the lack of data aloft 

and the surface wind pattern, which showed northeasterly winds from 1100 to 1500 CST, leading 

to discontinuity with the aloft winds at 500 m (Figure 4-8). 

4.2.3 Seasonal Wind Profiles 

Fall profiles at both sites matched the overall pattern above 1700 m with light 

southwesterly winds. However, easterly winds dominated the lower levels. The height of the 

transition from east to south was the lowest in the middle of the day (500-800 m at VRM, 

900-1200 m at SMI) and the highest at night (1200-1500 m at VRM, 1700-2000 m at SMI). The 

surface winds at both sites were constant throughout the day, but at VRM, they were 

northeasterly while at SMI the winds were east to east-northeasterly. With the exception of the 

transition-height differences and the surface wind directions, the fall profiles at the two sites 

correlate well (Figures 4-9 and 4-10). 

Winter profiles had considerably fewer points meeting the 50% criteria, especially at 

VRM; this should be further investigated. The SMI winter profile appeared very similar to its 

overall average profile, with light winds from the south at 500 m transitioning into southwesterly 

winds above approximately 1500 m. There was no easterly component from 500 to 1000 m like 

the overall pattern had in the early morning hours. The few points available from VRM for the 

winter appear to correlate with the SMI profile. The surface winds at both sites were similar, 

with easterly flow all day, which was discontinuous from the aloft winds 

(Figures 4-11 and 4-12). 

Spring profiles were nearly identical to the overall averages for both sites, but with a less 

easterly component in the morning hours. Surface winds at SMI were stronger than at VRM in 

the pre-dawn hours, with speeds averaging 5 m/s. However, aloft winds were stronger at VRM, 

with wind speeds averaging 5 m/s from 0500 to 1800 CST, while the average speed of aloft 

winds at SMI never exceeded 3 m/s (Figures 4-13 and 4-14). 

The summer profile at SMI above 1500 m showed light, easterly winds through the early 

morning, becoming southeasterly from 0700 to 1600 CST before returning to easterly at night. 

Below 1500 m, the pattern was similar to the overall pattern below 1000 m (Figure 4-15). The 

summer pattern at VRM showed the most diurnal changes in any season at either site. There was 

little in common with the overall profile except for the southerly winds below 500 m from 

1800 to 0700 CST. The winds aloft became easterly to northeasterly with the transition height at 

about 800 m at night to 1800 m during the afternoon (Figure 4-16). 

4.2.4 Monthly Wind Profiles 

RWP wind data were inconsistent in the winter months, and a January profile could not 

be generated that met the 50% averaging criteria. February had a limited number of data points, 

but profiles could be generated that matched well with the winter profile at each site. The only 

notable difference between the February profiles and the overall winter profiles was that the SMI 

low-level winds in February were slightly more southwesterly than the winds of its winter 

profile. 
4-4

For March through May, monthly averages resembled seasonal averages at both sites 

aloft, with the same persistent pattern of light winds transitioning from southerly or southeasterly 

near the surface to southwesterly aloft. However, the surface winds at VRM in March were very 

different than those in February and April. During the day, winds were northeasterly, as opposed 

to east-southeasterly in February and south-southeasterly in April. The northerly flow did not 

show up at all in the aloft wind pattern. This may be due to the shallow nature of post-cold front 

northerly winds. At VRM in May, winds above 3000 m were westerly, but data at this height 

were not available from SMI for comparison. 

In June at SMI, the winds above 1500 m resembled the summer pattern more than the 

spring pattern. Winds were southeasterly in the early morning before shifting to southerly for the 

remainder of the day. The winds below 1500 m, however, more closely matched the spring 

pattern. At VRM, the June profile was similar to the spring profile. In July at SMI, the profile 

matched the summer profile fairly well except for southwesterly flow that developed during the 

daytime hours up to 1500 m, and light and variable winds aloft after sunset. At VRM, the July 

profile was similar to the summer pattern. The August profiles at both sites correlate well with 

the summer pattern. 

In September and October, at both sites, the profiles above 1000 m resembled the fall 

patterns, with southwesterly flow. Below 1000 m, the profiles at both sites resembled the 

summer patterns, with a southerly component to the winds. These months showed the transition 

from summer to fall. The November profiles at both sites correlate well with the fall profiles. 

In December at SMI, data were sparse, but December appeared to be a transition month 

from fall to winter. There was a mixture of easterly and southerly winds at low levels. At VRM, 

data were again sparse, but the pattern was similar to the winter profiles as the southwesterly 

flow aloft started at 600 m, while the fall profile had all southwesterly flow above 1200 m. 

4.2.5 Wind Profiles by Upper-air Classification 

Both the ridge and weak ridge patterns were similar to the overall patterns at both sites. 

Winds were east to southeasterly below 1100 m (1500 m at VRM) and south to southwesterly 

above 1100 m (Figures 4-17 to 4-20). The ridge pattern had more of an easterly component than 

the overall pattern. At VRM, the surface winds did not shift to easterly from 1100 to 1500 CST 

like the overall pattern. 

The weak trough patterns up to 1000 m at both sites were similar to the overall patterns at 

SMI (Figure 4-21), and throughout the profile at VRM (Figure 4-22). At SMI, winds were 

southwesterly aloft for weak trough, trough (Figure 4-23), and cut-off low patterns 

(Figure 4-24). At VRM, winds were southwest to westerly aloft for trough (Figure 4-25) and 

cut-off low patterns (Figure 4-26). At both sites, the trough pattern contained a shear layer 

between northerly flow at the surface and southwesterly flow aloft, with the transition height 

ranging from 300-700 m. Data were limited at SMI during cut-off low patterns, so little analysis 

could be done. 

The flat patterns below 1100 m at both sites were similar to the overall patterns. Above 

1100 m, winds were mostly easterly, except from 0700 to 1200 CST when they were southerly 
4-5

(Figures 4-27 and 4-28). Both sites had limited data for zonal patterns and showed mostly 

southwesterly winds (Figures 4-29 and 4-30). Winds were southerly below 700 m at SMI and 

surface winds at both sites were easterly (Figures 4-31). The post-trough patterns had northerly 

winds at all levels at both sites except from 300-900 m at VRM, where the winds were easterly 

in the afternoon and evening (Figure 4-32). Winds for the tropical storm pattern were more 

variable at both sites, but only three to six days of data went into the averages. Winds were 

constant out of the southeast at the surface, with mostly southerly to southeasterly winds aloft at 

both sites (Figures 4-33 and 4-34). The winds at VRM were stronger than those in any other 

pattern. 

4.3 RASS RESULTS AND INTERPRETATIONS 

This subsection presents observations of Tv observed by RASS at elevations ranging from 

131 m (above the level of the instrument on the oil platform) to about 700 m. The RASS data in 

the figures in this subsection are combined with Tv observations collected by thermometers on 

short towers on the oil platforms at heights of about 25 msl. 

It should be noted that errors or biases of about 1oC in RASS observations are expected. 

As a result, small discontinuities, shallow inversion, or superadiabatic layers in the plots may not 

be real. 

In summary, the average temperature profiles from the platform height of 25 m to the top 

of the profile (about 1500 m) show the following characteristics: 

• There is often a discontinuity in temperature gradient at the lower two or three RASS 

levels (e.g., 131 m), due to a known cold bias. 

• The surface temperature and the 131-m temperature are measured by two types of 

instruments, which may influence the diagnosis of stable or unstable temperature 

gradients. 

• The average profiles, which extend to about 700 m, do not show an elevated inversion or 

mixing height, despite the fact that a mixing depth of 500 to 700 m is expected and often 

observed in the RWP reflectivity data 

• VRM is more stable than other sites. 

• BIP has a strong stable inversion in the lowest layer; other sites do not. 

• In fall, FTM has surface inversion at night; others do not. 

• In winter, all sites have an inversion during the day and night except VRM and BIP. 

Inversion may be a result of platform radiational cooling. 

• In spring and summer, all sites are about adiabatic.

4.3.1 Overall Average Temperature Profiles 

The Tv data in this subsection are averaged over three years. Subsequent subsections 

describe single-year averages. 
4-6

At SMI, which is about 100 km offshore, the daytime and nighttime Tv profiles were very 

similar. The overall average daytime profile for SMI indicates an average lapse rate of about 

-6°C/km (Figure 4-35), which is close to the standard environmental lapse rate (-6.5°C/km). 

The average surface temperature was 26°C. The figure shows some cold bias in the RASS data 

at the lowest two range gates. The cold bias is an erroneous cold shift in the Tv profile due to 

non-coherent sound waves from the sound sources. The nighttime profile in Figure 4-35 also 

shows a lapse rate of about -6°C/km. The average surface temperature was nearly the same as 

the daytime temperature, but the nighttime profile was about 0.25°C warmer than the daytime 

profile. This 0.25°C difference is less than the accuracy in the RASS Tv measurement (±1°C). 

Again, there was some cold bias evident in the lowest two range gates at night. 

At VRM, which is much closer to shore than SMI (18 km versus 100 km), the daytime 

and nighttime profiles were very similar to each other and showed more stability than did the 

SMI profiles. The overall daytime profile at VRM shows a lapse rate of -2.3°C/km 

(Figure 4-36). The average surface temperature was 23.9°C. The nighttime profile shows a 

lapse rate of -0.7°C/km and an average surface temperature of 23.6°C. It is suggested that the 

VRM profile is more stable than the SMI profile because of its nearness to land, which tends to 

have a higher frequency of stable conditions. 

Note that there is no upper-level inversion marking the top of the mixing depth at either 

SMI or VRM. This suggests that the average mixing depth is at a level exceeding the 700 m 

upper range of the RASS profiles. 

4.3.2 Yearly Average Virtual Temperature Profiles 

This subsection presents the averaged Tv profiles for individual years at the SMI and 

VRM sites. 

For the 1998 MMS year (June 1, 1998, to May 31, 1999) at SMI, the Tv profiles were 

generally the same as the overall (three-year average) Tv profiles (Figure 4-37). However, the 

surface temperature was 0.5 to 1°C warmer in 1998 than the overall surface temperature. At 

VRM, the profiles were slightly warmer than the overall profiles up to 400 m and cooler above 

400 m. In addition, at VRM the day and night surface temperature was about 1.5°C warmer than 

the overall temperature. Cold bias was evident at the lowest range gate (131 m) aloft 

(Figure 4-38), and the observations at that level should be given less credibility. 

For the 1999 MMS year (June 1, 1999, to May 31, 2000) at SMI, both night and day Tv

profiles were about 0.5°C cooler than the overall (three-year average) aloft Tv profiles, and the 

surface temperature was slightly cooler (Figure 4-39). The lapse rate is slightly closer to 

adiabatic. At VRM, the Tv profile was 0.25 to 0.5°C cooler aloft, and 1 to 1.5°C cooler at the 

surface (Figure 4-40) than the overall profiles. However, the lapse rates were nearly identical to 

the overall (three-year average) lapse rates. 

For the 2000 MMS year (June 1, 2000, to May 31, 2001) at SMI, there were limited data. 

The existing data showed a slightly cooler Tv profile during the day and a slightly warmer Tv

profile at night compared to the overall (three-year average) profile. Surface temperatures were 

about 1°C cooler both day and night (Figure 4-41). At VRM, the daytime profile was 0.5 to 1°C 
4-7

warmer aloft during the day compared to the overall (three-year average) profile. The nighttime 

profile was up to 1°C warmer above 300 m compared to the overall profile and had an inversion 

layer. Surface temperatures were 1 to 2°C cooler (Figure 4-42). 

4.3.3 Seasonal Virtual Temperature Profiles 

In the fall, the Tv profiles at SMI were 1.5 to 2°C cooler than the overall (three-year 

average) profiles, but the lapse rates remained the same (Figure 4-43). At VRM, the Tv profiles 

were 2.5 to 3°C cooler than the overall profiles, with a slightly more unstable lapse rate 

(Figure 4-44). 

In the winter, the Tv profiles at SMI were 5° to 6°C cooler, with a more unstable lapse 

rate than the overall (three-year average) profiles (Figure 4-45). At VRM, there were very 

limited data for the winter season, but these data showed a Tv profile nearly 7°C cooler aloft and 

8°C cooler at the surface (Figure 4-46). 

In the spring, the Tv profiles at SMI were 0.5° to 1°C warmer than the overall (three-year 

average) profile and the lapse rate was the same (Figure 4-47). The surface temperatures were 

1 to 1.5°C warmer. At VRM, the Tv profiles were warmer up to 500 m and cooler above 500 m 

compared to the overall profiles (Figure 4-48). This resulted in a lapse rate of about -6°C/km. 

In the summer, at SMI, the Tv profiles were 4° to 6°C warmer than the overall Tv profiles, 

with less stable lapse rates (Figure 4-49). At VRM, the Tv profiles were 3° to 6°C warmer than 

the overall Tv profiles, and 9°C warmer at the surface, which resulted in an apparent 

superadiabatic layer. The lapse rate was more unstable than the overall three-year average, at 

nearly -6°C/km (Figure 4-50). 

4.3.4 Virtual Temperature Profiles by Upper-air Classification 

As expected, the Tv profiles at both sites for the ridge pattern were warmer than the 

overall profiles by 2° to 4°C (Figures 4-51 to 4-54). The lapse rates at SMI were the same as for 

the overall three-year average. 

The Tv profiles for the weak trough pattern were warmer than the overall three-year 

average profiles by 0.5° to 1°C (Figures 4-55 and 4-56). The Tv profiles for the trough pattern 

at both sites were 3° to 4°C cooler than the overall profiles (Figures 4-57 and 4-58). The Tv

profiles for the cut-off low pattern at VRM were cooler at the surface but were the same Tv aloft 

as the overall profile (Figure 4-59). There was no Tv profile for the cut-off low profile at SMI 

due to limited data. 

The profiles for flat synoptic conditions were 3° to 6°C warmer at both sites than the 

overall Tv profiles (Figures 4-60 and 4-61). At SMI, the lapse rate was the same but at VRM 

the lapse rate was less stable than the overall profile. The profiles for the zonal patterns were 

5°C cooler than the overall profiles at both sites, although data were limited at VRM 

(Figures 4-62 and 4-63). The profiles for the post-trough pattern at both sites were 6° to 7°C 

cooler than the overall average profiles (Figures 4-64 and 4-65). The profile for the tropical 
4-8

storm pattern at VRM was about 6°C warmer than the overall profile, due to the warm and moist 

characteristics of tropical storms (Figure 4-66). 

4.3.5 Caveats 

As mentioned earlier, more work is required to fully understand the observed Tv profiles. 

In particular, the following issues need to be resolved: 

1. There is often a discontinuity in Tv at the lower two or three RASS levels (e.g., 131 m) 

due to a cold bias. 

2. The surface temperature and the 131-m temperature are measured by two different 

instruments and an unexpected stable or unstable lapse rate often results. A nearly 

adiabatic gradient would be expected from theoretical arguments because water 

temperature is nearly always a few degrees warmer than air temperature, causing an 

upward heat flux and a well-mixed boundary layer that should extend to heights of 

several hundred meters. 

3. The average Tv profiles, which extend to about 700 m, never show an elevated inversion 

or mixing height, despite the fact that we expect a mixing depth of 500 to 700 m. 
4-9

00 12 06 18 23

Time CST

Figure 4-1. Overall average winds at SMI from 0000 to 2300 CST, June 1, 1998, to 

May 31, 2001. 

00 12 06 18 23

Time CST

Figure 4-2. Overall average winds at VRM from 0000 to 2300 CST, June 1, 1998, to 

May 31, 2001. 
4-10

Time CST

Figure 4-3. 1998 year average winds at SMI from 0000 to 2300 CST, June 1, 1998, to 

 May 31, 1999. 

Time CST

Figure 4-4. 1998 year average winds at VRM from 0000 to 2300 CST, June 1, 1998, to 

May 31, 1999. 
4-11

Time CST

Figure 4-5. 1999 year average winds at SMI from 0000 to 2300 CST, June 1, 1999, to 

 May 31, 2000. 

Time CST

Figure 4-6. 1999 year average winds at VRM from 0000 to 2300 CST, June 1, 1999, to 

May 31, 2000. 
4-12

Time CST

Figure 4-7. 2000 year average winds at SMI from 0000 to 2300 CST, June 1, 2000, to 

May 31, 2001. 

Time CST

Figure 4-8. 2000 year average winds at VRM from 0000 to 2300 CST, June 1, 2000, to 

 May 31, 2001. 
4-13

00 12 06 18 23

Time CST

Figure 4-9. Fall average winds at SMI from 0000 to 2300 CST, September 24 to December 22, 

 for all study years. 

00 12 06 18 23

Time CST

Figure 4-10. Fall average winds at VRM from 0000 to 2300 CST, September 24 to 

December 22, for all study years. 
4-14

00 12 06 18 23

Time CST

Figure 4-11. Winter average winds at SMI from 0000 to 2300 CST, December 23 to March 21, 

for all study years. 

00 12 06 18 23

Time CST

Figure 4-12. Winter average winds at VRM from 0000 to 2300 CST, December 23 to 

March 21, for all study years. 
4-15

00 12 06 18 23

Time CST

Figure 4-13. Spring average winds at SMI from 0000 to 2300 CST, March 22 to June 22, for all 

 study years. 

00 12 06 18 23

Time CST

Figure 4-14. Spring average winds at VRM from 0000 to 2300 CST, March 22 to June 22, for 

 all study years. 
4-16

00 12 06 18 23

Time CST

Figure 4-15. Summer average winds at SMI from 0000 to 2300 CST, June 23 to September 23, 

for all study years. 

00 12 06 18 23

Time CST

Figure 4-16. Summer average winds at VRM from 0000 to 2300 CST, June 23 to 

September 23, for all study years. 
4-17

00 12 06 18 23

Time CST

Figure 4-17. Ridge pattern average winds at SMI from 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-18. Ridge pattern average winds at VRM from 0000 to 2300 CST, for all study years. 
4-18

00 12 06 18 23

Time CST

Figure 4-19. Weak ridge average winds at SMI, 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-20. Weak ridge average winds at VRM, 0000 to 2300 CST, for all study years. 
4-19

00 12 06 18 23

Time CST

Figure 4-21. Weak trough average winds at SMI, 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-22. Weak trough average winds at VRM, 0000 to 2300 CST, for all study years. 
4-20

00 12 06 18 23

Time CST

Figure 4-23. Trough average winds at SMI, 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-24. Cut-off low average winds at SMI, 0000 to 2300 CST, for all study years. 
4-21

00 12 06 18 23

Time CST

Figure 4-25. Trough average winds at VRM, 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-26. Cut-off low average winds at VRM, 0000 to 2300 CST, for all study years. 
4-22

00 12 06 18 23

Time CST

Figure 4-27. Flat average winds at SMI, 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-28. Flat average winds at VRM, 0000 to 2300 CST, for all study years. 
4-23

00 12 06 18 23

Time CST

Figure 4-29. Zonal average winds at SMI, 0000 to 2300 CST for all study years. 

00 12 06 18 23

Time CST

Figure 4-30. Zonal average winds at VRM, 0000 to 2300 CST, for all study years. 
4-24

00 12 06 18 23

Time CST

Figure 4-31. Post-trough average winds at SMI, 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-32. Post-trough average winds at VRM, 0000 to 2300 CST, for all study years. 
4-25

00 12 06 18 23

Time CST

Figure 4-33. Tropical storm average winds at SMI, 0000 to 2300 CST, for all study years. 

00 12 06 18 23

Time CST

Figure 4-34. Tropical storm average winds at VRM, 0000 to 2300 CST, for all study years. 
4-26

Tv, oC

Figure 4-35. Average overall daytime and nighttime Tv profiles at SMI, June 1, 1998, 

to May 31, 2001. Hour 12 is the daytime profile and Hour 00 is the 

nighttime profile. 

Tv, oC

Figure 4-36. Average overall daytime and nighttime Tv profiles at VRM, June 1, 1998, 

to May 31, 2001. Hour 12 is the daytime profile and the Hour 00 is the 

nighttime profile. 
4-27

Tv, oC

Figure 4-37. 1998 year average daytime and nighttime Tv profiles at SMI, June 1, 1998, 

to May 31, 1999. Hour 12 is the daytime profile and the Hour 00 is the 

nighttime profile. 

Tv, oC

Figure 4-38. 1998 year average daytime and nighttime Tv profiles at VRM, June 1, 1998, 

to May 31, 1999. Hour 12 is the daytime profile and the Hour 00 is the 

nighttime profile. 
4-28

Tv, oC

Figure 4-39. 1999 year average daytime and nighttime Tv profiles at SMI, 

 June 1, 1999, to May 31, 2000. Hour 12 is the daytime profile and the Hour 00 is 

 the nighttime profile. 

Tv, oC

Figure 4-40. 1999 year average daytime and nighttime Tv profiles at VRM, June 1, 1999, to 

May 31, 2000. Hour 12 is the daytime profile and the Hour 00 is the nighttime 

profile. 
4-29

Tv, oC

Figure 4-41. 2000 year average daytime and nighttime Tv profiles at SMI, June 1, 2000, to 

May 31, 2001. Hour 12 is the daytime profile and the Hour 00 is the nighttime 

profile. 

Tv, oC

Figure 4-42. 2000 year average daytime and nighttime Tv profiles at VRM, June 1, 2000, to 

May 31, 2001. Hour 12 is the daytime profile and the Hour 00 is the nighttime 

profile. 
4-30

Tv, oC

Figure 4-43. Fall average daytime and nighttime Tv profiles at SMI, September 24 to 

December 22. Hour 12 is the daytime profile and the Hour 00 is the 

nighttime profile. 

Tv, oC

Figure 4-44. Fall average daytime and nighttime Tv profiles at VRM, September 24 to 

December 22. Hour 12 is the daytime profile and the Hour 00 is the 

nighttime profile. 
4-31

Tv, oC

Figure 4-45. Winter average daytime and nighttime Tv profiles at SMI, December 23 to 

March 21. Hour 12 is the daytime profile and the Hour 00 is the nighttime 

profile. 

Tv, oC

Figure 4-46. Winter average daytime and nighttime Tv profiles at VRM, December 23 to 

March 21. Hour 12 is the daytime profile and the Hour 00 is the nighttime 

profile. 
4-32

Tv, oC

Figure 4-47. Spring average daytime and nighttime Tv profiles at SMI, March 22 to 

June 22. Hour 12 is the daytime profile and the Hour 00 is the nighttime 

profile. 

Tv, oC

 Figure 4-48. Spring average daytime and nighttime Tv profiles at VRM, March 22 to 

June 22. Hour 12 is the daytime profile and the Hour 00 is the nighttime 

profile. 
4-33

Tv, oC

Figure 4-49. Summer average daytime and nighttime Tv profiles at SMI, June 23 to 

September 23. Hour 12 is the daytime profile and the Hour 00 is the 

nighttime profile. 

Tv, oC

 Figure 4-50. Summer average daytime and nighttime Tv profiles at VRM, June 23 to 

September 23. Hour 12 is the daytime profile and the Hour 00 is the 

nighttime profile. 
4-34

Tv, oC

Figure 4-51. Ridge average daytime and nighttime Tv profiles at SMI. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 

Tv, oC

 Figure 4-52. Ridge average daytime and nighttime Tv profiles at VRM. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 
4-35

Tv, oC

 Figure 4-53. Weak ridge average daytime and nighttime Tv profiles at SMI. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 

Tv, oC

Figure 4-54. Weak ridge average daytime and nighttime Tv profiles at VRM. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 
4-36

Tv, oC

Figure 4-55. Weak trough average daytime and nighttime Tv profiles at SMI. Hour 12 is the 

 daytime profile and the Hour 00 is the nighttime profile. 

Tv, oC

Figure 4-56. Weak trough average daytime and nighttime Tv profiles at VRM. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 
4-37

Tv, oC

Figure 4-57. Trough average daytime and nighttime Tv profiles at SMI. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 

Tv, oC

Figure 4-58. Trough average daytime and nighttime Tv profiles at VRM. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 
4-38

Tv, oC

Figure 4-59. Cut-off low average daytime and nighttime Tv profiles at VRM. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 

Tv, oC

Figure 4-60. Flat average daytime and nighttime Tv profiles at SMI. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 
4-39

Tv, oC

Figure 4-61. Flat average daytime and nighttime Tv profiles at VRM. Hour 12 is the daytime 

profile and the Hour 00 is the nighttime profile. 

Tv, oC

 Figure 4-62. Zonal average daytime and nighttime Tv profiles at SMI. Hour 12 is the daytime 

profile and the Hour 00 is the nighttime profile. 
4-40

Tv, oC

 Figure 4-63. Zonal average daytime and nighttime Tv profiles at VRM. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 

Tv, oC

Figure 4-64. Post-trough average daytime and nighttime Tv profiles at SMI. Hour 12 is the 

daytime profile and the Hour 00 is the nighttime profile. 
4-41

Tv, oC

Figure 4-65. Post-trough average daytime and nighttime Tv profiles at VRM. Hour 12 is the 

 daytime profile and the Hour 00 is the nighttime profile. 

Tv, oC

Figure 4-66. Tropical storm average daytime and nighttime Tv profiles at VRM. Hour 12 is 

the daytime profile and the Hour 00 is the nighttime profile. 
5-1

5. CHARACTERIZATION OF THE SURFACE FLUXES AND OTHER 

PARAMETERS IN THE ATMOSPHERIC BOUNDARY LAYER USING 

THE COARE ALGORITHM 

This section describes atmospheric boundary layer analyses performed for the western 

and central Gulf of Mexico. The results presented here are largely based on output from the 

COARE algorithm. COARE has been demonstrated to accurately parameterize surface fluxes of 

momentum, heat, and moisture, and various boundary layer scaling parameters over the ocean 

using routine observations (Fairall et al., 1996a). COARE was originally derived from the 

Tropical Ocean-Global Atmosphere Coupled-Ocean Atmosphere Response Experiment (TOGACOARE) research project. The TOGA program was intended to study the role of the tropical 

oceans in climate and annual climate variability (Webster and Lucas, 1992). The TOGACOARE experiment made use of an extensive array of meteorological instruments and 

platforms. Most of the fast-response turbulence data were taken from a research vessel, the R/V 

Moana Wave, over several weeks. The data were then analyzed and the COARE program was 

developed by an international team of boundary layer researchers. 

The basic structure of COARE is an outgrowth of the Liu-Katsaros-Businger (Liu et al., 

1979) method, sometimes referred to as the LKB method. The COARE program was designed 

to improve estimates of surface fluxes and scaling parameters in the surface boundary layer of 

the atmosphere over the deep ocean in tropical regions (Fairall et al., 1996a). This program 

estimates fundamental boundary layer scaling parameters such as the surface roughness length, 

the friction velocity, the scaling temperature, the scaling water vapor mixing ratio, and the 

Monin-Obukhov length (L). Standard boundary layer formulas can be used to estimate the 

mixing depth and the vertical profiles of wind speed, Tv, and water vapor mixing ratio (Stull, 

1988; Garratt, 1992). 

5.1 SUMMARY OF COARE PROGRAM VERSIONS AND MODIFICATIONS 

The COARE program was originally released in 1993, and three new versions have been 

used in the MMS Boundary Layer Study since it began in May 1998. Version 2.5b, released in 

May 1997, included updated transfer coefficients and was used for this study until January 2000, 

when version 2.6b was released. There were six minor differences between versions 2.5b and 

2.6b, including a change in the Charnock “constant” to a parameter based on wind speed data 

from Hare et al. (1999) and Yelland and Taylor (1996). Version 2.6b was used for this study 

until June 2000. An improved version of COARE (version 2.6bw) was released in June 2000 

and all COARE outputs presented in this report are from this latest version. An important 

difference between version 2.6bw and the prior versions is that version 2.6bw incorporates 

surface gravity wave information, based on wave height and period data. This change should 

increase the accuracy of the estimates of surface fluxes and scaling parameters over shallow 

areas, since the characteristics of waves differ from the deep ocean to the shallow coastal waters. 

Our comparisons between the outputs from the two versions show few differences, except in the 

derived roughness lengths, zo, for low-wind conditions. A consequence of the differences in 

roughness lengths is a difference in the derived friction velocities, u*. The two are directly 

related through the log wind profile relationship: u = (u*/0.4)ln(z/zo). 
5-2

In addition to the changes made to the COARE program by its authors, STI made some 

minor changes to the program, with guidance and approval from one of its authors, Dr. 

Christopher Fairall. For example, we found that there was an occasional problem with the 

evaporative cooling calculation due to unrealistically high amounts of solar energy estimated to 

reach the ocean surface. The representation in COARE follows from laboratory measurements 

with artificial light sources and ignores the fact that the solar flux reaching the surface of the 

ocean has been partially absorbed by the atmosphere. In the equation for the net absorption by 

the ocean (Equation 5-1), the leading coefficient was changed from 0.137 to 0.060, based on 

tests performed by Dr. Christopher Fairall. This change provided a more realistic representation 

of the actual absorption, which caused the evaporative cooling calculations to better agree with 

observations. The original formula, still using the 0.137 coefficient, is given below:

 Net = SW*(0.137+11*CST–6.6e-5/ CST*(1–exp(!CST/8.0e–4))) (5-1)

where: 

Net = Net absorption by the ocean (Watts/m2

) 

SW = Incoming short wave radiation (Watts/m2

) 

CST= Cool skin thickness (m) 

We discovered another problem in the COARE program: during early daylight hours, 

under light-wind conditions with the air temperature warmer than skin temperatures (i.e., a stable 

lapse rate), COARE calculated unrealistic skin temperature increases (up to 500oC). This was 

caused by a lack of heat removal due to very small accumulated stress (surface momentum flux) 

and a very thin (almost zero) warm layer thickness. To correct this problem, a minimum stress 

of .002 N/m2

 was imposed for this calculation. This value was chosen after analysis of measured 

stresses during TOGA-COARE (personal communication with Dr. Christopher Fairall, July 

2002). 

In addition to the changes to the basic calculations described above, the COARE program 

was modified so that it could incorporate Eta model analyzed fields and/or predictions. The 

capability to flag the COARE output based upon the validity of the incoming data was also 

incorporated. (See Section 2 for a discussion of the QC flags.) 

5.2 BACKGROUND ON THE COARE MODEL 

To characterize the ABL characteristics in the Gulf of Mexico, we use the COARE model 

to estimate the surface fluxes of momentum (also called the surface stress, τ), sensible heat (Hs), 

and latent heat (Hl) from observations of wind speed (u), air temperature (T), and water vapor 

mixing ratio (qr) at some standard reference height (z = zr) near the water surface, and the skin 

temperature (Ts) at the water surface. The standard height (zr) could be, for example, the height 

of the instruments on a buoy, a fixed tower (mounted on the sea floor), an oil platform, or a ship. 

However, zr must be within the surface boundary layer, which usually has a depth of about 50 m. 

The wind speed at the water surface is assumed to equal the water current speed (us) in the 

direction of the wind. The potential temperature (θ) at the height, zr, is assumed to equal 

T (zr) + (0.0098°C/m)zr. The skin temperature is defined as the temperature of the water that is 

in contact with the air. The water vapor mixing ratio (q) is calculated from measurements of 
5-3

temperature and relative humidity (RH) through the relation q = RH qsat(T). The water vapor 

mixing ratio at the surface (qsat) is an interfacial value that is computed from the saturation 

mixing ratio for pure water at the skin temperature: 

 qs = 0.98 qsat (Ts) (5-2) 

where the dimensionless constant, 0.98, accounts for the reduction in water vapor pressure 

caused by a typical salinity of 34 parts per thousand. 

With the above definitions, which are explained in more detail in boundary layer texts 

such as Garratt (1992) or Stull (1988), the standard bulk expressions for the surface fluxes 

(positive when directed upwards) are 

τ = –ρa Cd (us – ur)

2

 = ρa u*2 (5-3)

 Hs = ρa cpa Ch ur (Ts – θr) = ρa cpa u* T* (5-4)

 Hl = ρa Le Ce ur (qs – qr) = ρa Le u* q* (5-5)

where: 

ρa = air density 

cpa = specific heat of air at constant pressure 

Le = latent heat of water vapor 

In Equations 5-3 through 5-8, Cd, Ch, and Ce are known as the bulk transfer coefficients 

for stress or momentum, sensible heat, and latent heat, respectively. They are dimensionless 

quantities that have magnitudes of about 0.0011 when the reference height, zr, equals about 

10 m. These bulk transfer coefficients can be partitioned into coefficients cd, cT, and cq for 

individual variables u, θ, and q, respectively: 

 Cd = cd

1/2cd1/2 (5-6)

 Ch= cd

1/2cT1/2 (5-7)

 Ce = cd

1/2cq1/2 (5-8)

The coefficients cd, cT, and cq can be written (see equations 5-10 through 5-12) in terms of 

Monin-Obukhov similarity theory as functions of reference height, zr, surface roughness length 

(zo for momentum, zoT for heat, and zoq for water vapor), and Monin-Obukhov length, L, which 

is defined as 

 L = (u*2

/0.4)/((g/T)(T* + 0.61 Tq*)) (5-9)

The parameter, 0.4, in this equation is the von Karman constant. Note that L is defined so as to 

include the effects of the latent heat flux, which contributes to the flux of total buoyancy. The 

effects of water vapor (i.e., the second term in Equation 5-9) are usually ignored in calculations 

of L over land, but should be accounted for over warm ocean waters. Because water vapor is 
5-4

lighter than dry air (molecular weight of 18 for water vapor and 29 for dry air), it is possible to 

have an upward flux of buoyancy (and hence an unstable boundary layer) when there is an 

upward latent heat flux even though the flux of sensible heat (as determined by the dry bulb 

temperature) is downward. Such a situation might occur when a hot dry air mass occurs over a 

cool water surface. 

For nearly neutral conditions (n), when zr/L approaches 0.0, the coefficients cd, cT, and cq

in Equations 5-6 through 5-8 are given by the neutral profile equations: 

 u*/(ur – us) = cdn

1/2 = 0.4/ln(zr/zo) (5-10)

 T*/(θr – us) = cTn

1/2 = 0.4a/ln(zr/zoT) (5-11)

 q*/(qr – qs) = cqn

1/2 = 0.4a/ln(zr/zoq) (5-12)

where the constant “a” equals about 0.74, and the surface roughness lengths for heat and water 

vapor are not necessarily the same as the surface roughness length for momentum (Garratt, 

1992). These relationships lead to the following formulas for the scaling parameters: 

 u* = (Cd (ur – us)

2

)

1/2 (5-13)

 T* = cT

1/2 (Ts – θr) (5-14)

 Q* = cq

1/2 (qs – qr) (5-15)

For non-neutral conditions, when z/L is not zero, an additional term involving z/L has to 

be added to the ln(z/zo) term in Equations 5-10 through 5-12. In practice, an iterative procedure 

is followed where u*, T*, and q* are first estimated using the neutral Equations 5-10 through 

5-12, then L (proportional to u* and inversely proportional to T* and q*) is calculated and used 

to recalculate u* etc. This procedure continues until the solution converges according to a preset 

criterion. 

The TOGA-COARE experiments verified the result from previous studies that, with 

moderate to high wind speeds, the surface roughness length, zo, over the sea is proportional to 

the momentum flux or stress, and is given by the Charnock relation: 

 zo = α u*2 / g (5-16)

with a constant, α, equal to 0.011. For light wind speeds, the term 0.11 ν/u* should be added to 

the right side of Equation 5-16, where ν = 0.15 cm2

/s is the molecular viscosity of air. Of course, 

over the land, zo is independent of wind speed. For the latest version of COARE, there are 

options to replace the Charnock relation by 

 zo =1200. hw(hw/l)4.5+0.11 ν/u* (Taylor and Yelland, 2001) (5-17)

or 

 zo =50/2pi l (u*/c) 4.5+0.11 ν/u* (Oost et al., 2001) (5-18)
5-5

These equations use wave height (hw), wave length (l), phase speed (c), friction velocity 

(u*), and kinematic viscosity of dry air (ν) to calculate zo. 

The TOGA-COARE program also accounts for special situations such as periods with 

light winds, periods with rainfall, and periods with significant cooling of the surface by 

evaporation or warming of the near-surface layer by solar energy. 

During light wind conditions, the effective average wind speed in the boundary layer 

never truly drops to zero because of the presence of convective eddies and other turbulent 

phenomena with time scales ranging from about 10 to 1000 seconds. Even though the measured 

average wind speed may be near 0.0, that average is made up of several non-zero wind speeds 

blowing from one direction and then another. The TOGA-COARE program, like other 

meteorological boundary layer preprocessors (e.g., Hanna and Chang, 1992a) assumes that the 

effective reference wind speed, ur, during unstable conditions is given by two components: 

 ur

2

 = ur

2

 (observed) + (βw*)2 (5-19)

where w* is the convective scaling velocity, given by: 

 w*3 = (g/T) ((Hs/ρacpa) + 0.61 T (Hl/ρaLe)) h (5-20)

and h is the mixing height. Usually w* is about 1 m/s. The COARE data from TOGA suggest 

that the constant, β, equals 1.25.

A “Webb effect” correction is made by the COARE algorithm. This correction of about 

4 w/m2

 to the latent heat flux term assures mass continuity when the density differences between 

updrafts and downdrafts are considered. 

If the skin temperature is not observed at the surface (e.g., from a radiometer observation) 

but is observed by a sensor at some depth (say, 0.5 m to 1.0 m below the surface), the COARE 

program calculates the skin temperature from the observed near-skin temperature at that depth. 

The near-skin temperature is defined as the temperature of the water measured by the buoys at a 

depth of approximately .5 m. The COARE program contains an algorithm to account for the 

“cool skin” effect caused by evaporation of water from the surface, and also contains an 

algorithm to account for the “warm layer” effect caused by warming of the surface layer due to 

solar energy. The degree of surface warming is a function of the amount of vertical mixing in 

the water boundary layer, which is, in turn, a function of the wind speed. During light winds, the 

solar energy input can cause the water surface to warm by several degrees. 

Corrections are also made to the momentum flux term and the heat flux term to account 

for the effects of rain. For example, if the rain has a different temperature than the water surface, 

the rain will contribute heat to the surface if the rain is warmer and will remove heat from the 

surface if the rain is cooler. Also, the momentum carried by the rain as it strikes the surface will 

affect the surface momentum flux. The surface stress due to heavy rain can be twice the surface 

stress due to wind (Fairall et al., 1996a).
5-6

5.3 IMPLEMENTATION OF THE COARE PROGRAM 

The COARE program is being distributed by Fairall and his coauthors. The written 

material from the (NOAA’s FTP site is reproduced in Appendix B and our modified version of 

the FORTRAN code, cor2_6bfwMMS.for, is in Appendix C. 

The COARE program requires input of the atmospheric measurement heights (wind 

speed, air temperature, relative humidity) and the near-skin temperature sensor depth. The 

mixing depth, h, is required, and Fairall et al. set a default value of h = 600 m for their TOGACOARE study area. Hanna et al. (1985) note that the h = 600 m assumption is fairly good for 

most over-water boundary layers. The surface pressure and the approximate latitude and 

longitude are required as inputs to the program. All predetermined constants (e.g., von Karman 

constant) are automatically set to default values unless the user overrides them. 

Next, a line of data in the form of a time series is input to COARE. Each line should 

contain local time, ur, Ts, Tr, qr, R (precipitation in mm/hr), Rl (downwelling longwave radiation 

flux in w/m2

), and Rs (downwelling solar flux in w/m2). 

For each line of input data, representing an averaging time of, say, one hour, the code 

assigns a minimum wind speed of 0.5 m/s and neutral stability as a first guess and then calculates 

a first estimate of u*, T*, and q*. It computes all temperature-dependent constants such as Le 

and ν. Then the program iterates or loops through successive calculations of u*, T*, and q* until 

the solutions converge within stated limits. 

The COARE program is sufficiently general that it can be applied to a wide variety of 

platforms used for meteorological observations at sea. It has been tested with high-quality 

research ship observations, with routine ocean buoy observations, and with data from nonstandard sources such as oil platforms. However, the COARE program has not been thoroughly 

tested with data from shallow water, marsh, beach, or other coastal scenarios. 

5.4 COMPARISON OF COARE MEASUREMENTS WITH TOGA-COARE 

MEASUREMENTS 

Fairall et al. (1996a) describe the detailed observations taken during TOGA-COARE, the 

observations used to calibrate constants in the COARE algorithm, and the various modules of the 

program. Because of the requirement (for climate change studies) to resolve the surface energy 

balance with an accuracy of 10 W/m2

 or less, it was important to measure the many atmospheric 

variables with an unprecedented degree of accuracy. The goals for the instrument accuracies 

were 0.2 m/s for wind speed, 0.2 K for skin temperature and air temperature, and 0.2 g/kg for 

water vapor mixing ratio. These goals were met during TOGA-COARE. Several figures 

containing examples of observations and COARE model predictions of fluxes are given by 

Fairall et al. (1996), showing agreement usually within about plus or minus 10% for stress, and 

within roughly 5 W/m2

 for sensible heat flux and 25 W/m2 for latent heat flux. The covariance 

observations of fluxes have considerably more uncertainty than the inertial-dissipation 

observations, due to the difficulties in observing the turbulent fluctuations from moving 

platforms such as ships. In general, the relative uncertainties are largest for periods with light 
5-7

wind speeds. The results of sensitivity studies are also presented in the figures in Fairall et al. 

(1996a), illustrating how the choice of “constants” such as β can have a large effect on the flux 

calculations, especially at low wind speeds. 

Fairall et al. (1996a) also included comparisons of flux predictions by the COARE 

program with fluxes observed by the NCAR Electra Aircraft during flights at heights of 30 to 

60 m. This comparison represents a good test of the method with independent data. A 

comparison of the predictions and observations of latent heat flux, sensible heat flux, and stress 

show that there is typically a range of about a factor of two, although the overall means are 

predicted within plus or minus 5%. 

5.5 APPLICATION OF THE COARE PROGRAM TO DATA COLLECTED IN THE 

GULF OF MEXICO 

As stated in Section 5.3, the COARE program requires the following input data: time 

and site location; wind speed, air temperature, and relative humidity within the surface layer at 

reference height zr; skin temperature or near-skin temperature plus radiation estimates; and 

mixing height. If the near-skin temperature (i.e., observed at a depth of 0.5 to 1.0 m) is used 

(such as the data collected at buoys and C-MAN stations), then solar and downwelling longwave 

radiation fluxes need to be estimated from some alternate source in order to correct this observed 

temperature to a skin temperature. Precipitation data is not required but, if available, can be used 

by COARE to estimate the precipitation contribution to the energy balance equation. Wave 

height and period data are not required, but, if available, can be used with COARE version 2.6bw 

to account for the different wave structures and theoretically improve the accuracy of the 

estimates of surface fluxes and scaling parameters over shallow ocean areas, such as the Gulf of 

Mexico. For this application, the Taylor and Yelland (2001) method for calculating zo was used 

(see Equation 5-17). If wave data were not measured, they were calculated from wind speed (u) 

where wave height = 0.018*u2

*(1+0.15*u) and wave period = 0.729*u. 

• Data collected at offshore buoys and at the VRM, SMI, BIP, DWP, MBP, SWP, and 

WDP platforms meet the COARE input data requirements. 

• C-MAN stations collected all the required data except shortwave and longwave radiation. 

These sites are not located in deep water and sometimes are located in marshes or on 

beaches. The COARE program was “tuned” using deep-water data and may not 

adequately handle the sea-state at shallow-water sites such as C-MAN stations. 

However, based on discussions with Scientific Review Board members and Dr. 

Christopher Fairall, it was concluded that the error produced by inaccurate representation 

of the sea-state may be acceptable for the current study, where the emphasis is on flow 

patterns and dispersion of pollutant plume released over the Gulf of Mexico, and the 

accuracy requirements for surface fluxes are not as stringent as those for climate change 

studies. Therefore, data from C-MAN stations were included in the analysis, but we treat 

these COARE results with caution. 

• The offshore buoy sites did not measure skin temperature or solar and downwelling 

longwave radiation; thus, radiation fluxes were estimated using 6-hourly Eta model cloud 

simulations and sun elevation data to estimate the required radiation fluxes needed to 
5-8

calculate the skin temperatures from temperatures at depths of about 0.5 to 1.0 m. The 

6-hourly radiation flux estimates from the Eta outputs were interpolated to hourly data for 

each buoy location. 

The following data were acquired and processed for input to COARE for the period from 

May 1998 through October 2001: 

• Offshore buoy data from seven sites, 

• Shoreline C-MAN station data from three sites, 

• Data collected as part of this project on the VRM, SMI, BIP, DWP, MBP, SWP, and 

WDP oil platforms, and 

• Eta model predictions. 

Figure 2-1 is a map of the Gulf of Mexico region, showing the locations of the 

meteorological sites discussed above and in the following analyses. The analyses are intended to 

identify similarities and differences among the boundary layer parameters at the sites. It is 

anticipated that the boundary layer parameters at the farther offshore sites such as DWP and SMI 

are more characteristic of the open ocean, with fewer variations by season and by time of day, 

whereas the parameters at the sites closer to shore, such as VRM and BIP, show some influence 

of the nearby land surfaces. 

The latest version of COARE (cor2_6bfwMMS.for) was used to calculate hourly sensible 

heat flux, latent heat flux, friction velocity, temperature and relative humidity scaling parameters 

(zr/L), and roughness length using the three-plus years of hourly meteorological data from 

14 sites and one year of hourly data from the BIP, DWP, MBP, SWP, and WDP platform sites. 

Underwater temperature was corrected to skin temperature when no skin temperature was 

measured. An additional COARE sensitivity run for the buoy data was performed where 

underwater temperatures were used without correction to skin temperature. This was done to test 

the influence of this correction on the boundary layer parameters. 

Both statistical and case study analyses of the COARE input and output data were 

performed. For the statistical analyses the following averages were computed: 

• Monthly averages were calculated for the ABL observations and derived parameters at 

each site. Averages were not computed if more than 25% of the data in a given month 

were missing. 

• Hourly averages were calculated by month for the ABL observations and derived 

parameters at each site to investigate the diurnal cycles. The averages were not computed 

if more than 25% of the data in a given month and hour were missing. 

• Overall averages of the parameters were calculated for nine synoptic classes and for each 

site to investigate the relationship between the large-scale weather patterns that are 

characterized in Section 3 and the ABL parameters. No data availability criteria were 

applied. 
5-9

• Averages were calculated for four surface flow direction classes (onshore, offshore, 

parallel east, and parallel west) and for each site to investigate the relationship between 

the flow direction and the ABL parameters. No data availability criteria were applied. 

Four periods were selected for case study analysis. The periods selected capture a variety 

of meteorological conditions, especially conditions for which transport of materials from 

offshore areas is likely to impact onshore areas. The case study periods are 

• July 30 through August 1, 1999, 

• January 20 through 25, 2000, 

• January 4 through 6, 2001, and 

• September 18 through 20, 2001. 

5.6 CLIMATOLOGICAL RESULTS 

This section presents the results of the climatological analyses. Averages were reviewed 

by month, by synoptic class, by flow direction, and diurnally by month. The 14 stations that 

were analyzed are shown in Figure 2-1 and are denoted by the codes: 

Buoys – 42001, 42002, 42007, 42019, 42020, 42035, and 42040 

Oil Platforms – VRM, SMI, BIP, DWP, MBP, SWP, and WDP 

C-MAN (coastal) – DPIA1, GDIL1, PTAT2, BURL1, and SRST2 

Note that BURL1 and DPIA1 are missing data necessary for COARE but the available 

monthly average observations are described here. 

The following discussions and figures are grouped separately: (a) the buoys, the VRM 

and SMI platforms, and the C-MAN stations and (b) the BIP, DWP, MBP, SWP and WDP 

platforms. The latter sites are part of the BAMP study which took place over a one-year period 

near the end of the three-year study of the other sites. The figures described in the discussions 

reflect the two groups and are designated (a) and (b). 

5.6.1 COARE Results Grouped by Monthly Averages 

Fluxes. The fluxes and scalar parameters calculated by the COARE algorithm in the Gulf 

of Mexico are physically consistent with expectations and are similar to observations and 

COARE calculations for TOGA, which took place in the warm western Pacific Ocean near the 

equator. Calculated monthly average sensible heat fluxes (Figures 5-1a and 5-1b) in the Gulf of 

Mexico ranged from about 5 to 30 W/m2

, typical of other over-water areas. Similarly, calculated 

monthly average latent heat fluxes (Figures 5-2a and 5-2b) ranged from about 50 to 150 W/m2

, 

also typical of other over-water areas. Both the latent and sensible heat fluxes were highest in 

the late fall and early winter and lowest in the late spring and summer, although the yearly cycle 

in latent heat values is less pronounced than the seasonal cycle. The largest fluxes shown in 

Figures 5-1(a) and 5-2(a) occur at near-shore and/or the buoy sites, whereas the fluxes at the 

VRM and SMI platforms shown in Figures 5-1(a) and 5-2(a) are more moderate and are similar 

to the fluxes from the five platforms shown in Figures 5-1(b) and 5-2(b). 
5-10

These estimates of annual variations of latent and sensible heat fluxes are consistent with 

lighter winds (Figures 5-3a and 5-3b) and smaller skin-air temperature differences 

(Figures 5-4a and 5-4b) in the summer compared to other times of year. Calculated monthly 

average sensible heat fluxes were about one-fifth the calculated monthly average latent heat 

fluxes, and the differences between the two were generally greatest in the summer and smaller in 

the late fall and winter. 

The monthly average calculated total heat flux (sensible plus latent) is in fair agreement 

(generally within a factor of two) among the sites in the Gulf of Mexico (Figures 5-5a and 

5-5b). The largest relative variations (ranging from 20 to 170 W/m2

) occurred in February when 

the total heat flux was small due to the cool water temperatures and the small difference between 

the skin and air temperatures. The smallest relative variations (ranging from 110 to 235 W/m2

) 

occurred in September when the total heat flux was large due to the warm water temperatures 

and large difference between the skin and air temperature. 

Eta Fluxes. The monthly average Eta model latent and sensible heat fluxes (Figures 5-6 

and 5-7) were generally in good agreement with the calculated fluxes. However, the model 

fluxes did not show as great a variation between sites as the calculated fluxes. In addition, the 

model fluxes were about 20% greater than the calculated fluxes in the fall and early winter, but 

were very similar during the spring and summer. 

Friction Velocity. The COARE-calculated monthly average friction velocity, u*, shown 

in Figures 5-8a and 5-8b. Figure 5-8a (the buoys, the C-MAN sites, and the SMI platform) 

demonstrates agreement among the sites well within a factor of two and often within 20%. This 

agreement is important because the monthly average friction velocity is the key scaling velocity 

for estimating transport speeds and dispersion rates. However, Figure 5-8b (BIP, DWP, MBP, 

SWP, and WDP platforms) and Figure 5-8a (VRM only) show mean friction velocities that are 

about 30% to 40 % less than those in Figure 5-8a (for all other sites). Possible explanations are 

that the wave height and frequency are estimated from wind speed at the platforms, whereas they 

are measured at the buoys. Also, the platform wind observations are corrected from 20+ m to 10 

m and the wind speed is, on average, less than at the other non-platform sites. All data show that 

the calculated monthly average friction velocity was slightly lower from May through August 

and peaked in late fall and early winter. The monthly average Eta model friction velocity 

(Figure 5-9) showed the same yearly pattern as the calculated friction velocity. However, the Eta 

model friction velocity was about 10% to 20% higher than the calculated friction velocity in the 

fall and early winter. The difference in velocity likely explains why the Eta model fluxes were 

slightly high during the same period. 

Temperature and Humidity Scaling Parameter. The calculated monthly average 

temperature scaling parameter and humidity scaling parameter generally showed a factor of two 

or better agreement among sites (Figures 5-10a and 5-10b, and 5-11a and 5-11b, respectively). 

The monthly average temperature scaling parameter tended to be smaller in April and May, 

when the difference between the skin and air temperatures was at its minimum, and tended to be 

larger in November through January, when the difference between the skin and air temperatures 

was at its maximum. Conversely, the monthly average humidity scaling parameter tends to be 

largest during the warmest period of the year (July through September) because moisture content 

of the atmosphere is a strong function of temperature. 
5-11

Air Temperature. Monthly average air temperatures are plotted in Figures 5-12a and 

5-12b. Very close agreement is evidenced among the sites from May through September when it 

is hot (over 25°C) and the air temperature differences are minimal between near-shore and faroffshore sites. At all sites, the temperatures were warmest in July and August (ranging from 

24.5°C to 29°C) and coolest in winter (ranging from 11°C to 21°C). The difference in air 

temperature was much greater between near-shore and offshore sites in winter compared to 

summer (about 10°C in winter versus about 2°C in summer). This difference was probably due 

to wintertime cold fronts influencing near-shore sites more than offshore sites. For example, the 

average monthly air temperature at offshore buoys 42001 and 42002 was 21°C in January and 

28°C in August (a 7°C range). On the other hand, the average monthly temperatures at the nearshore sites, VRM, BIP, SWP, and SRST, were 12.5°C in January and 28.5°C in August (a 16°C 

range). 

Skin Temperature. Like the monthly average air temperatures, skin temperatures were 

warmest in July and August and coolest in January and showed a similar site grouping 

(Figures 5-13a and 5-13b). The far offshore near-skin temperatures at buoys 42001 and 42002 

and at platform DWP showed the least amount of seasonal variation (about 6° to 8°C) compared 

to the near-shore sites (about 17.5°C maximum at VRM and BWP between September and 

January). The magnitudes of the sum of the latent and sensible heat fluxes generally follow the 

annual variation of the skin temperature, with maxima in the late fall and minima in the late 

spring. 

Skin and Air Temperature Differences. The differences between the skin and air 

temperatures were, on average, about +1° to +3°C at most sites all year (Figures 5-4a and 5-4b). 

The differences were less in late spring and more in late fall and early winter. This persistent 

positive temperature difference has been noted by Dr. Christopher Fairall at most other sites 

located on warm water oceans. 

Surface Wind Speed. Scalar monthly average wind speed showed good agreement 

among sites (Figures 5-3a and 5-3b). The lowest speeds occurred in July and August and the 

highest in December and January. For some years, there was a transition from lower wind 

speeds in August to higher winds speeds in September and October. Weather maps indicate that 

the high wind speeds in September and October on some years were probably a result of tropical 

storms. 

Relative Humidity. Average relative humidity was similar among sites and was about 

75% in all months. 

5.6.2 COARE Results Grouped by Synoptic Class and General Flow Direction 

This section uses histograms to present information about the magnitudes of nine 

COARE parameters for 14 monitoring sites for nine classes of synoptic conditions and for the 

four general air flow directions (onshore, offshore, parallel east, and parallel west). 

The nine COARE parameters are downwelling longwave radiation, shortwave radiation, 

humidity scaling parameter, temperature scaling parameter, roughness, sensible heat flux, latent 

heat flux, friction velocity, and wind speed. 
5-12

The nine synoptic classes are discussed in Section 3 and are denoted by the terms ridge, 

weak ridge, flat, zonal, post-trough, trough, weak trough, cut-off low, and tropical storm. The 

occurrences of the nine synoptic classes are listed in the table below. The counts in some classes 

(Table 5-1), such as tropical storm and cut-off low, are quite low and, therefore, the numbers for 

the average COARE parameters in Figures 5-14, 5-15, 5-16 through 5-21(a and b), 5-22 

through 5-24, 5-25 through 5-30(a and b) and 5-31 have a broader confidence bound than the 

numbers for the more heavily populated classes such as ridge and trough. 

Table 5-1. Number of occurrences of each synoptic classification by year for the MMS 

Boundary Layer Study. 

MMS 

Year 

Cut-off 

Low Flat Posttrough Ridge Trough Tropical 

Storm 

Weak 

Ridge 

Weak 

Trough Zonal Total 

1998 2 31 11 104 94 3 35 76 9 365 

1999 6 30 18 107 85 0 36 61 23 366 

2000 11 10 17 142 82 0 20 53 30 365 

2001 6 24 7 36 10 3 16 20 2 124 

The discussions in this section focus on the typical magnitudes and on the reasons for 

differences that are observed. 

Synoptic Class 

Figures 5-14, 5-15, 5-16 through 5-21(a and b), and 5-22 contain histograms showing the 

results of the average COARE calculations, divided into nine synoptic classes, for nine COARE 

parameters and outputs. The wind speed data are observed rather than parameterized by 

COARE. The highlights of the results are discussed by COARE parameter. 

Downwelling Longwave Radiation – Longwave radiation is emitted in all directions by 

gases and aerosols in the atmosphere; however, the component being analyzed is longwave 

radiation directed down towards the water’s surface. Its magnitude is a function of temperature 

and humidity and of the amount of cloud and fog. Longwave radiation was not observed by 

on-site radiometers so it was parameterized based on cloudiness and temperature. Note that this 

parameter is a COARE input rather than an output, and, when observations are not available, it is 

based on estimates made by the Eta prognostic meteorological model. Figure 5-14 shows that 

the Eta-predicted longwave radiation, averaged over a year or more, had little variation by 

synoptic class or by site, ranging from about 290 to 420 W/m2

. The magnitude may be less for 

post-trough synoptic conditions since such periods are generally cool and clear. The magnitude 

of longwave radiation was largest for tropical storms, which are marked by warm temperatures, 

high humidity, and a maximum amount of aerosols (i.e., fog, clouds, and rain). Its magnitude 

may be less for the most northerly sites: the C-MAN sites on the coast or the buoys near the 

coast. 

Shortwave Radiation – The incoming solar radiation flux is mostly in the shortwave 

range, which is a strong function of cloud cover. Sometimes the shortwave radiation was 
5-13

observed by a solar radiometer, but usually it was parameterized based on time of day and year, 

latitude, and Eta model predictions of cloudiness and humidity. The range in Figure 5-15 is from 

80 to 280 W/m2

, which is a much larger range than for the longwave component. The 

distribution with synoptic class makes physical sense, with maximum amounts during ridge 

conditions which are known to be clear and sunny, and minimum amounts during weak troughs 

or tropical storms which are known to be cloudy. The figure suggests that there was little 

variation by monitoring site. 

Humidity Scaling Parameter – The humidity scaling parameter is defined by MoninObukhov similarity theory and is proportional to the latent heat flux divided by the friction 

velocity. This parameter is not observed but must be calculated by COARE and has a factor of 

seven variability, as shown in Figures 5-16a and b. Because the latent heat flux tends to be 

maximized during periods with a low dew point in the air and/or periods when the skin 

temperature is much higher than the air temperature, such as in the middle of a large high 

pressure system, we expect the humidity scaling parameter to be largest as well during low 

humidity periods or hot high pressure periods. This expectation is borne out in Figures 5-16a 

and b, since the humidity scaling factor is larger during flat and ridge periods. 

Temperature Scaling Parameter – The temperature scaling parameter is defined by 

Monin-Obukhov similarity theory and is proportional to the sensible heat flux divided by the 

friction velocity. It is calculated by COARE. This parameter has a large variability, from near 

zero to about –0.22°

C. Because the sensible heat flux tends to be maximized during periods 

when the air is cooler than the water, such as after a cold front passes, we expect the temperature 

scaling parameter to be largest during low temperature periods as well. This result is shown in 

Figure 5-17, since the temperature scaling factor is much larger during post-trough periods. It is 

smallest during tropical storms, when the air is likely to be at the same temperature as the water. 

This parameter is expected to be largest at sites near land, for example, the C-MAN sites; the 

sensible heat flux is larger over land than over water because land surface can heat up much 

more under the sun’s effect at midday. Figure 5-17 suggests that the SRST2 C-MAN site has a 

larger temperature scaling parameter; however, the PTAT2 and GDIL C-MAN sites did not 

support this trend. 

Roughness – The surface roughness over water is a function of wind speed. It is 

calculated by COARE based on the observed wind speed and the sea state. The Charnock 

relation used in COARE states that roughness is proportional to the square of friction velocity. 

Therefore, we would expect the roughness to be larger during synoptic periods with stronger 

winds. This is exemplified by the buoy 42002 and SMI sites in Figures 5-18a and 5-18b, since 

the largest roughness measurements occur during tropical storms; however, the opposite effect is 

shown at other sites. Part of the reason for this inconsistency may be the problem identified 

earlier, where a large roughness is calculated at small wind speeds (wind speed less than 2 m/s). 

This is due to a COARE algorithm that adjusts the wave period to be very short during low 

winds, but causes a large increase in roughness. 

The variation in roughness is less at the BAMP platform sites (Figure 5-18b) and at the 

VRM platform (Figure 5-18a), and the average magnitude of roughness is about 40% to 50% less 

than the site data shown Figure 5-18a (excluding VRM). Possible explanations are that the wave 

height and frequency are estimated from wind speed at the platforms, whereas, they are 
5-14

measured at the buoys. Also, the platform wind observations are corrected from 20+ m to 10 m 

and wind speeds are, on average, less than the other non-platform sites 

Sensible Heat Flux – The sensible heat flux is calculated by COARE using observations 

of wind speed and the skin-air temperature difference. It increases as the wind speed and the 

skin-air temperature difference increase. Figures 5-19a and 5-19b show that sensible heat flux is 

maximized for post-trough synoptic conditions, which are likely to be marked by above-average 

wind speeds and low air temperature. There is a factor of 10 variability across the nine synoptic 

classes. There are some differences among the sites, but they are not consistent and need further 

investigation. 

Latent Heat Flux – The average latent heat flux shown in Figures 5-20a and 5-20b is 

about an order of magnitude greater than the sensible heat flux shown in Figures 5-19a and 

5-19b. In addition, less variability exists in the latent heat flux, perhaps because the latent heat 

flux (calculated by COARE based on observations of wind speed, skin-air temperature 

difference, and relative humidity) is generally positive, while the sensible heat flux can be 

negative (when air temperature is greater than skin temperature). As noted, the latent heat flux is 

consistently large during the post-trough synoptic condition due to higher wind speeds and lower 

dew points that follow a cold front. It can also be large during tropical storms due to high 

temperatures and strong winds. 

Friction Velocity – The friction velocity is calculated by COARE using the log wind 

profile relation. Since that relation has friction velocity proportional to wind speed, the friction 

velocity values in Figures 5-21a and 5-21b are expected to be largest during high-wind periods. 

In fact, the figures show the highest friction velocity values at most sites during tropical storms. 

Aside from the anomaly during tropical storms, there is little variability in friction velocity from 

site to site or with synoptic class. The friction velocity averages 0.2 m/s in Figure 5-21a and 

0.12 in Figure 5-21b; the difference is due to the difference in estimated roughness, zo (see 

discussion of roughness and Figures 5-18a and 5-18b). 

Wind Speed – Wind speed is the only COARE parameter that is observed at all sites. It 

is not calculated by COARE. Wind speed averages 6 m/s at non-platform sites and 4 m/s at 

platform sites and varies in a manner similar to that of friction velocity. Figure 5-22 shows a 

wind speed range of 4 m/s for ridge and flat classes at GDIL to 11.5 m/s for the tropical storm 

class at buoys 42002 and 42035. Wind speeds shown are not corrected to a standard height. 

General Flow Direction 

Figures 5-23, 5-24, 5-25 through 5-30 (a and b), and 5-31 contain histograms showing the 

results of the average COARE calculations, grouped by the four general flow directions, for the 

nine COARE parameters. The highlights of the results are discussed by COARE parameter. 

Downwelling Longwave Radiation –Downwelling longwave radiation shows little 

variation by flow direction or by station, ranging from 340 to 390 W/m2

 (Figure 5-23) Note that 

this parameter is a COARE input rather than an output and, when observations are not available, 

it is based on estimates made by the Eta prognostic meteorological model. The magnitude may 

be less for offshore flow directions since such periods are generally associated with post-frontal 
5-15

northerly wind directions that would be cool and clear. The magnitude of longwave radiation is 

largest for tropical storms, which are marked by warm temperatures, high humidity and much 

cloud and rain. Its magnitude may be less for the most northerly sites, either the C-MAN sites on 

the coast or the buoys near the coast. 

Shortwave Radiation – The incoming solar radiation flux is mostly in the shortwave 

range. This component is a strong function of cloud cover. If observations were not available, 

Eta prognostic meteorological model predictions were used. Figure 5-24 suggests that there little 

variation with site and with flow direction since the minimum and maximum values in the figure 

are 170 and 290 W/m2

, respectively. The shortwave radiation behavior is consistent at the 

14 monitoring sites; the higher values averaged 240 W/m2

 for onshore and parallel west flow 

directions, and lower values averaged 190 W/m2

 for offshore and parallel east flow directions. 

There probably was slightly more cloud cover for offshore and parallel east flow directions. 

Humidity Scaling Parameter – This parameter has a small (factor of two) variability 

across the 14 sites and the four flow directions plotted in Figures 5-25a and 5-25b. Few obvious 

trends are apparent. The values appear to be slightly larger for offshore than for onshore flow 

directions, possibly reflecting drier air associated with offshore flows. 

Temperature Scaling Parameter – The sensible heat flux tends to be maximized during 

periods when the air is cooler than the water, such as for northerly offshore wind flow patterns. 

Therefore, we expect the temperature scaling parameter to be largest during offshore flow 

periods as well. This is shown in Figures 5-26a and 5-26b, since the temperature scaling factor 

is much larger (usually more than a factor of two) at all 14 sites for offshore flow directions. It is 

smallest during onshore flow periods at the buoy sites, when the air is likely to be at the same 

temperature as the water. At the oil platform and C-MAN sites, the temperature scaling 

parameter is smallest during either onshore or parallel west flow directions. 

Roughness – The surface roughness over water is a function of wind speed, wave height, 

and time period. Therefore, roughness is expected to be larger during flow directions with 

stronger winds. This effect is shown in Figure 5-27a for the seven buoy sites; the largest wind 

speeds and, therefore the largest roughness values, are found for offshore flow directions; 

however, there are no clear variations at the oil platform and C-MAN sites. Figure 5-27a 

illustrates more variability in roughness, and larger mean values (by almost a factor of two) than 

does Figure 5-27b (the BAMP platform sites). 

Sensible Heat Flux – The sensible heat flux increases as the wind speed and the skin-air 

temperature difference increase. Figures 5-28a and 5-28b show that sensible heat flux is 

maximized for northerly offshore flow directions, which are more likely to be marked by aboveaverage wind speeds and by low air temperatures. The sensible heat flux is lowest for onshore 

flow directions, when the boundary layer is in balance with the water surface. The average 

difference in sensible heat flux for offshore and onshore flow directions across the nine stations 

is about a factor of 10. Differences exist among the sites but they are not consistent and the 

reasons for the differences are not obvious. 
5-16

Latent Heat Flux – The average latent heat flux shows some differences between offshore 

and onshore wind directions at most sites. The latent heat flux is usually largest during offshore 

(northerly) flows, which tend to be associated with post-trough synoptic conditions—higher 

wind speeds and lower dew points that follow a cold front. With any offshore flow the dew 

point in the air is likely to be less than that usually found over the water. The minimum latent 

heat fluxes in Figures 5-29a and 5-29b occur with onshore flows, which would tend to be 

boundary layer flows in balance with the water surface. 

Friction Velocity – Fiction velocity is calculated by COARE using the log wind profile 

relation. Figures 5-30a and 5-30b show the results. Because the friction velocity of the log wind 

relation is proportional to wind speed, the largest friction velocity values were associated with 

high-wind periods, which tended to occur with offshore winds. Minimum friction velocity 

occurred during parallel west wind directions. There is little variability in friction velocity from 

site to site. The average friction velocity at non-platform sites (Figure 5-30a) is larger, by about 

50%, than the average friction velocity at the platforms (Figure 5-30b). As noted, the difference 

is probably due to differences in estimated roughness length, zo. 

Wind Speed – Wind speed, shown in Figure 5-31, ranges from 4 m/s for onshore flows at 

GDIL1 to 7.5 m/s for offshore flows at BURL1. At most sites, the maximum occurs during 

offshore flows, which may be associated with post-cold front conditions from the north quadrant. 

5.6.3 Diurnal Variations by Month 

Seven sites were selected to analyze the diurnal variations by month of latent and sensible 

heat fluxes, friction velocity, wind speed, and skin-air temperature differences. The sites include 

buoy 42001 (a deep-water buoy); the VRM (near shore) and SMI (far offshore) platforms; buoy 

42040 (a near-shore buoy site); a C-MAN site, GDIL; the BIP platform (in a shallows near 

Breton Island); and the DWP platform (the deepest water platform site). The highlights of the 

results are discussed below. 

Buoy 42001 – The sensible heat fluxes show almost no diurnal variation, which makes 

physical sense for an over-water site far from land (Figure 5-32). Maximum sensible heat fluxes 

occur in December and January, when the water-air temperature difference is the greatest. 

SMI – The sensible heat flux shows very little diurnal variation, but slightly more than at 

buoy 42001 (Figure 5-33). At SMI in December, the greatest diurnal variation in sensible heat 

flux is observed and is only about 20% (about 50 W/m2

 in the morning and 40 W/m2 in the 

afternoon). The variation is associated with a smaller friction velocity in the afternoon (see 

Figure 5-34) and not due to variations in the Tv profiles, which show almost no diurnal cycle in 

December. During May, sensible heat fluxes are near zero during most of the daylight hours 

because the water temperature is approximately equal to the air temperature. Figure 5-34 shows 

that the mean friction velocity is 2.5 times larger in December than in July, due to a combination 

of larger wind speeds and larger instabilities in December. 

VRM – In June, July, August, and September, the latent heat flux shows minor peaks in 

both the morning and afternoon (Figure 5-35). During the other months, the latent heat flux 

shows very little diurnal variation. The latent heat flux is smaller in December and January than 
5-17

in July through September (50 W/m2

 versus 180 W/m2) because there is more water vapor 

present in the atmosphere in the summer. In December, Figure 5-36 shows that the sensible heat 

flux has a factor of two diurnal cycle, peaking at sunrise. The morning peaks in the sensible heat 

flux are due to peaks in the difference between the skin and air temperatures (Figure 5-37). The 

sensible heat flux in December is much higher (50 W/m2

 versus 20 W/m2) than during other 

months. The high sensible heat flux in December is a result of a higher than average difference 

between the skin and air temperatures and higher than average friction velocity. The slight 

diurnal trend seen at VRM may be caused by its nearness to shore. 

Buoy 42040 – The diurnal monthly profiles of sensible heat flux, shown in Figure 5-38, 

are similar to those at SMI. They show a maximum diurnal variation of about 20% in December 

and January. The maximum sensible heat flux (65 to 70 W/m2

) occurs in December due to a 

combination of higher than average friction velocity and differences between the skin and air 

temperatures. Sensible heat fluxes in May and June drop to nearly zero due to the small waterair temperature differences. The latent heat flux at Buoy 42040 shows less diurnal variation and 

is also greatest in December (Figure 5-39). The December latent heat flux is about 230 W/m2

while the May latent heat flux is about 80 W/m2

. 

GDIL1 – The sensible heat flux curve indicates that GDIL1 is not strongly influenced by 

land—the sensible heat flux is lowest in mid-afternoon (the opposite of a land station) and 

highest in the early morning (Figure 5-40). Average sensible heat flux is also never negative at 

night (land stations have negative sensible heat flux at night). However, the sensible heat flux 

curve shows a diurnal cycle, ranging from 10 to 35 W/m2

 in the predawn hours to 4 to 12 W/m2

in the afternoon. The diurnal cycle closely follows the diurnal cycle of the difference between 

the skin and air temperatures (Figure 5-41). The friction velocity is nearly constant throughout 

the day (Figure 5-42). The latent heat flux curves are somewhat flatter than the sensible heat 

flux curves but show slight peaks in the afternoon during the summer months (Figure 5-43). 

The latent heat flux is not as sensitive as the sensible heat flux to water-air temperature 

difference. 

BIP – Figures 5-44 through 5-48 show diurnal curves, by month, for sensible heat flux, 

latent heat flux, friction velocity, skin minus air temperature, and wind speed for the Breton 

Island platform. Note that these data represent a shorter period (one year from September 2000 

through September 2001) than data in previous figures (May 1998 through October 2001). 

Figure 5-44 shows that the sensible heat flux has minimal diurnal variation and is largest (20 to 

30 W/m2

) in late fall and early winter when the water temperature is warmer than air 

temperature. During other months, the sensible heat flux is small (less than 10 W/m2

). 

Figure 5-45 shows that the latent heat flux also has minimal diurnal variation and is largest 

(150 to 200 W/m2

) in July through October when the water temperature is highest. In February, 

when water temperatures are cool, the latent heat flux drops to about 30 W/m2

. The COAREcalculated friction velocity, seen in Figure 5-46, shows minimal diurnal variation and varies by 

as much as a factor of two from month to month. However, the month-to-month variation 

appears random and no physical causes can be identified. The difference between skin and air 

temperature shows a 1° to 2°C diurnal variation in Figure 5-47, with maximum values occurring 

between 0800 and 0900 CST and minimum values between 2000 and 2400 CST. As noted for 

other sites, the temperature difference is greater (2°C or more) in the fall and is smaller (between 

–1° and 1°C in the late winter). The wind speeds, plotted in Figure 5-48, show little diurnal 
5-18

variation, and are about 30% less from July through September, when they are about 4 m/s 

versus 5 to 6 m/s for most other months. 

DWP – Figures 5-49 through 5-53 show diurnal curves, by month, for sensible heat 

flux, latent heat flux, friction velocity, skin minus air temperature, and wind speed for the Deep 

Water Platform. This site should be most representative of the “open ocean” for which the 

COARE algorithm was developed. As noted in the BIP discussion, these data represent a 

shorter period (one year from September 2000 through September 2001) than the data 

represented in Figures 5-32 through 5-43 (May 1998 through October 2001). The DWP wind 

speeds, plotted in Figure 5-49, show little diurnal variation and are about 30% less from July 

through October (behavior similar to the BIP wind speeds plotted in Figure 5-48), when they are 

about 3 m/s versus 4 to 5 m/s for most other months. Figure 5-50 shows that the sensible heat 

flux has very little diurnal variation and is largest (15 to 25 W/m2

) in late fall and early winter, 

when the water temperature is warm relative to the air temperature (this is behavior similar to 

that shown in the BIP data in Figure 5-44). During the other months, the sensible heat flux is 

small (less than 10 W/m2

, with the minimal average of 4 W/m2 in May). Diurnal variation of the 

latent heat flux, plotted in Figure 5-51, is also insignificant, and the latent heat flux is largest 

(about 120 W/m2

) in the fall, when the water temperature is greatest. In February, when water 

temperatures are cool, the latent heat flux drops to about 70 W/m2

. The COARE-calculated 

friction velocity, seen in Figure 5-52, shows some diurnal variations but the variations are not 

consistent from month to month. The average friction velocity varies by as much as a factor of 

two from month to month. However, the month-to-month variation appears random and no 

physical causes can be identified. The difference between skin and air temperature shows a 1° to 

2°C diurnal variation in Figure 5-53, with maximum values occurring between 0400 and 

0500 CST and minimum values at about noon. The plots of the same variable for BIP in 

Figure 5-47 show the same diurnal shape but offset by 5 to 8 hours later in the day. As noted for 

other sites, the temperature difference is greater (4°C or more) in the late fall and is smaller 

(between –1° and 1°C) in the spring (e.g., negative or stable temperature differences occur in 

May in the afternoon). A negative temperature difference will lead to a negative sensible heat 

flux. 

5.7 CASE STUDY ANALYSES 

This section presents case study analyses of COARE model output for selected days and 

comparisons to Eta model simulations. Case studies were performed for the following periods: 

• January 20 through 25, 2000 – a period characterized by post frontal offshore flow on 

January 20 and 21, followed by onshore flow on January 22 and 23, and strong offshore 

flow on January 24 and 25. 

• January 4 through 6, 2001 – a period of post upper-level trough (January 4 and 5) fading 

into weak ridge, and a period with air temperature much warmer than skin temperature. 

• July 30 through August 1, 1999 – a period with a strong upper-level ridge, surface high 

pressure, and light winds. 
5-19

• September 18 through 20, 2001 – a period of weak onshore flow with a weak cold front 

orientated west to east along the Gulf Coast from Houston, Texas, to Mobile, Alabama, 

on September 20. 

Time series of hourly-averaged observations, COARE-model outputs, and Eta-model 

simulations of surface boundary layer fluxes at the sites in the Gulf of Mexico were analyzed for 

several short (multi-day) time periods during different seasons and for different synoptic 

scenarios. Analyses were performed to explain the physical relationships between the observed 

variables and the calculated fluxes, and compare simulations of friction velocity, sensible heat 

flux, and latent heat flux. 

The COARE-calculated variables are based on observations at a specific monitoring 

location. In contrast, the Eta model predictions represent averages over a grid square with 

dimensions of 40 km x 40 km. Also, since the Eta model is a three-dimensional, time-dependent, 

numerical weather prediction model, its predictions represent a solution to the equations of 

motion, using some assimilation of observations such as from buoys but based primarily on 

mass-conservation and other physical constraints. 

The Eta model has no horizontal resolution at scales less than the grid size (40 km). 

Consequently, if a monitoring site is being investigated near the Gulf of Mexico coastline, the 

Eta model constructs an average of the land-use conditions within that grid square. If the grid 

square consists of 75% land and 25% sea, the model will simulate that square as if it were mostly 

land, with resulting diurnal patterns of heat fluxes more typical of land than sea. 

5.7.1 Analysis of January 20-25, 2000 

Data from January 20-25, 2000, from buoy 42040 are discussed here to illustrate the 

analysis methods and the typical results. Buoy 42040 is located several tens of kilometers east of 

the Mississippi River Delta. 

This case study analysis was carried out in summer 2001 as a preliminary exercise, and 

results were reported in a conference paper by Hanna et al. (2001). Subsequent subsections 

discuss more recent case study analyses. 

The time series of observed hourly-averaged air and skin temperatures and wind speed 

are plotted in Figure 5-54. This was an active synoptic period, with large swings in wind speed 

and air temperature. Air temperatures were 5-20 ̊C cooler than skin temperatures for the first 

two days and for the last day and a half. Wind speeds were moderate to strong (about 5 to 

15 m/s) during these periods. However, from about 1800 CST on January 22 to about 1200 CST 

on January 25, the air warmed slowly to approach and even exceed the skin temperature for over 

12 hours. The winds dropped to near zero just before a frontal passage occurred at about 

0300 CST on January 24, after which time the air temperature dropped 5 ̊C in an hour and wind 

speed rapidly increased to 16 m/s. 
5-20

Sensible Heat Fluxes

Eta model simulations were compared with COARE-estimated sensible and latent heat 

fluxes. Eta model simulations produce forecasts up to 48 hours in the future in 6-hr increments. 

In addition, the model is run every 12 hours, once at 0000 UTC (00 Z) and once at 1200 UTC 

(12 Z), everyday. The 6- and 12-hr forecasts from the 00 Z and the 12 Z model runs were 

combined to yield a continuous record of every sixth hour simulated sensible and latent heat 

fluxes. A second continuous record was prepared using the 30- and 36 hr forecasts from the 

00 Z and 12 Z model runs. In addition, the Eta-simulated sensible and latent heat fluxes every 

six hours were interpolated to yield hourly values. The continuous records of simulated sensible 

and latent heat fluxes were then compared to the COARE-estimated sensible and latent heat 

fluxes.

Figure 5-55 shows the COARE-calculated and Eta-simulated sensible heat fluxes during 

this time period. The COARE model used the buoy-observed meteorological variables and 

produced very large (for the ocean) sensible heat fluxes with magnitudes of about 150 W/m2

between 2200 CST on January 20 and 0600 CST on January 21, when the skin-air temperature 

differences were very large (5° to 10°C) and the wind speeds were also large (about 10 to 

15 m/s). However, during the 12- to 15-hr period in the middle of the time series, when the air 

temperature exceeded the skin temperature (i.e., stable conditions), the COARE-calculated 

sensible heat fluxes were negative (i.e., towards the water surface) with magnitudes of about 

10 W/m2

. COARE will always calculate a negative sensible heat flux when the air temperature 

exceeds the skin temperature. Figure 5-54 shows that the Eta model simulations of sensible heat 

flux are only about 30% larger than the COARE-calculated values during the periods with large 

unstable air-skin temperature differences. However, during the middle period, the Eta model 

simulated positive (upward) sensible heat fluxes, in contrast to the negative (downward) COARE 

sensible heat fluxes, although they are small (about 0 to 20 W/m2

). This tendency is apparent for 

all sites and periods. Occasionally, sites show periods with observed air temperatures warmer 

than skin temperatures leading to COARE-calculated negative heat fluxes, while the Eta model 

usually simulates positive (but small) heat fluxes. During the late spring, the air temperature 

observed to be greater than the skin temperature about 20% to 40% of the time can lead to long 

periods of mismatches in the signs of the COARE-calculated and Eta simulated sensible heat 

fluxes. 

Latent Heat Fluxes 

Figure 5-56 shows the COARE-calculated and Eta-simulated latent heat fluxes from 

January 20-25 at buoy 42040. Large latent heat fluxes of about 500 W/m2

 were calculated by 

both COARE and Eta for the unstable periods with moderate winds near the beginning and end 

of the five days. This is the same magnitude as the incoming solar heat flux at the water surface 

on a summer day. These large sensible heat fluxes are due to the large difference between the 

skin and air temperatures and the moderate wind speeds. Note from Figure 5-54 that, even in 

January, the Gulf of Mexico skin temperature is still fairly warm (about 21 ̊C) implying that the 

saturation-specific humidity is large and, therefore, allows large latent heat fluxes to occur. 
5-21

During the 12- to 18-hr period on January 23 when the air temperature slightly exceeded 

the skin temperature and winds decreased, COARE-calculated latent heat fluxes decreased to 

values as low as 20 W/m2

. 

The Eta-model simulations of latent heat flux plotted in Figure 5-56 approximately track 

the COARE calculations, with differences of about 30% during the two periods with high fluxes. 

During the period with small fluxes, the Eta simulations are similar to the COARE calculations. 

There appears to be no relation between the age of the Eta simulation and the agreement with the 

COARE curve in the figure. 

5.7.2 Analysis of January 4-6, 2001 

This case study is based on data collected at the VRM platform from January 4-6, 2001. 

The VRM site is only a few km off the Louisiana coast. Just prior to January 4, a trough had 

passed through the Gulf of Mexico region and a weak ridge was building into the area. 

Figure 5-57 contains time series plots of hourly averaged wind speed, air temperature, 

skin temperature, and relative humidity for the three-day period. All but the skin temperature 

were observed at an elevation of about 25 m msl, or about 3 m above the surface of the oil 

platform. 

This case study was characterized by steadier conditions than those during the January 

2000 case study. Air temperature varied between 9o and 17oC and skin temperature varied 

between 7o and 13oC, with a steady increase through the three days. Air temperature was warmer 

than skin temperature (i.e., a stable Tv profile) by 1o to 5oC during most of the period, except 

between 1300 and 1800 CST on January 6, when the air temperature was about 1oC less than the 

skin temperature (i.e., an unstable Tv profile). Wind speed was light (between 0 and 7 m/s) with 

periods of very light winds (wind speeds less than 2 m/s) on January 4 and 6. Relative humidity 

ranged from 55% to 95%, with the higher values associated with decreases in air temperature, 

probably due to cloudy conditions. 

COARE Outputs of Friction Velocity and Sensible and Latent Heat Fluxes 

Figure 5-58 illustrates the COARE outputs of hourly-averaged friction velocity and 

sensible and latent heat fluxes. Friction velocity closely follows the shape of the wind speed 

time series observations, ranging from near zero during nearly calm periods to 0.18 m/s during 

periods with wind speeds of 6 to 7 m/s. In general, wind speed divided by friction velocity 

equals 30 to 40, which was a slightly larger value than at the buoys because the observing height 

was high (25 m) on the oil platforms. The sensible and latent heat fluxes were small (magnitudes 

of less than 20 W/m2

) because of the stable Tv profile, cool temperatures, and weak winds. 

The sensible heat flux was negative (i.e., downward towards the sea surface) or near zero 

most of the time because the air temperature was usually warmer than the skin temperature. An 

exception was midday on January 6, when skin temperature was greater than air temperature for 

a few hours and the sensible heat flux switched to positive values, still less than 5 W/m2

. 
5-22

The latent heat flux reached maximum values of about 20 W/m2

 from 0300 to 0400 CST 

on January 4 (with low relative humidity and high wind speeds) and from about 1500 to 

1800 CST on January 6 (with high relative humidity and an unstable Tv profile). Note that the 

sensible heat flux does not necessarily have the same sign as the latent heat flux. 

COARE Outputs of Wave Height and Period and Surface Roughness 

The wave characteristics and the surface roughness length estimated by COARE are 

plotted in Figure 5-59. The observed wind speed is also plotted. The estimated surface 

roughness length is bimodal, with a value of 0.00005 m (i.e., 0.05 mm) with wind speeds greater 

than 2 m/s. When wind speeds were greater than 2 m/s, the wave height ranged from 0.5 to 1 m 

and the wave period ranged from 2 to 5 seconds. However, when wind speeds were less than 

2 m/s and wave height was small, the wave period was parameterized to drop to 1 second, and 

the surface roughness length was estimated to increase by an order of magnitude from 0.0005 to 

0.001 m (0.5 to 1 mm). Estimates of surface roughness length when wind speeds were less than 

2 m/s appeared to be too large and did not agree with the Charnock relation for surface 

roughness length over water that states that surface roughness length is proportional to friction 

velocity squared (or wind speed squared). 

Comparison of COARE and Eta Outputs of Sensible and Latent Heat Fluxes 

The COARE estimates of sensible and latent heat fluxes were made using observations 

from the VRM oil platform. Eta forecasts of sensible and latent heat fluxes were based on 

fundamental solutions to the equations of motion, using some observations at buoys and on-shore 

rawinsonde sites to generate analyzed fields for inputs. Figure 5-60 compares these estimates 

for the January 4-6, 2001, period. 

Recall that over most of the period, sensible and latent heat fluxes were small and often 

negative because the air temperature was greater than the skin temperature during most of the 

three-day period. The COARE estimates were quite different from the Eta simulations, which 

had a marked diurnal variability that was not present in the COARE outputs. The Eta-predicted 

fluxes peaked at noon, with values of about 150 W/m2

 for latent heat flux and about 100 W/m2

for sensible heat flux. These magnitudes were an order of magnitude larger than the magnitudes 

from COARE. Even at midnight, the Eta-predicted latent heat flux was still 20 to 30 W/m2

. In 

general, the Eta-predicted latent heat flux never dropped below zero. However, the Eta-predicted 

sensible heat flux predictions dropped below zero during the nights of January 5 and 6, 

somewhat in agreement with the COARE estimates. 

Comparison of COARE and Eta Outputs of Hourly-averaged Friction Velocity 

The COARE and Eta estimates of hourly-averaged friction velocity are plotted in 

Figure 5-61. On average, the Eta-predicted hourly-averaged friction velocity values were about 

0.2 m/s whereas the COARE hourly-averaged friction velocity values were about 0.05 m/s, a 

difference of a factor of four. This difference was probably caused by differences in the 

parameterized stability. COARE accounts for the observation that air temperature greater than 

skin temperature assumes stable conditions most of the time, while Eta assumes unstable 

conditions most of the time and much larger sensible and latent heat fluxes. 
5-23

The COARE estimates of observing height divided by L are also shown in Figure 5-61. 

Positive (stable) values occurred most of the time. Observing height divided by L became 

slightly negative for a few hours on January 6 when both sensible and latent heat fluxes were 

negative (upward). Since the observing height was about 25 m, it can be inferred that L was as 

low as 0.2 m during the few periods (e.g., near noon on January 4 and near 0900 CST on 

January 6) with very light winds and air temperature greater than skin temperature. Because L is 

proportional to friction velocity cubed, L is a very strong function of wind speed. 

5.7.3 Analysis of July 30-August 1, 1999 

This case study is based on data collected at the VRM and SMI platforms from July 30 to 

August 1, 1999. The VRM site is only a few kilometers off the Louisiana coast, while the SMI 

site is about 100 km offshore. A strong upper-level synoptic ridge was present during this period 

with a surface high pressure system centered over the Gulf of Mexico and associated light winds. 

This is a typical mid-summer scenario.

Figures 5-62a and 5-62b are time series plots of hourly-averaged wind speed, air 

temperature, skin temperature, and relative humidity for the three-day period at VRM and SMI, 

respectively. All but the skin temperature were observed at an elevation of about 25 m msl, or 

about 3 m above the surface of the oil platform. 

This case study was characterized by much warmer conditions than the January case 

studies. A major difference was the skin temperature—in January it was consistently lower than 

the skin temperature during the summer. For the July 30-August 1 period, air temperature was 

nearly constant at VRM and SMI, varying between 28o and 31oC. Skin temperature was also 

nearly constant at VRM and SMI, varying between 30o and 33oC. Skin temperature was warmer 

than air temperature (i.e., an unstable Tv profile) by an average of about 1o to 2oC during most of 

the period. An exception occurred during the few hours around noon each day, when the skin 

and air temperatures were nearly equal (i.e., neutral Tv profile). Wind speed averages were 

slightly higher at VRM than at SMI (4 m/s versus 2.5 m/s, respectively). The wind speed 

dropped below 2 m/s about half the time at SMI. Relative humidity was fairly constant at about 

70% at both sites. 

COARE Outputs of Friction Velocity and Sensible and Latent Heat Fluxes 

Figures 5-63a and 5-563b illustrate the COARE parameterizations of hourly-averaged 

friction velocity and sensible and latent heat flux. Friction velocity averaged about a factor of 

two lower at SMI than at VRM (0.07 m/s versus 0.14 m/s, respectively). In general, wind speed 

divided by friction velocity equaled about 30, in rough agreement with what was found for the 

January 5-6, 2001, case study. The COARE-estimated latent heat fluxes were always larger than 

50 W/m2

 but reached larger maxima (220 W/m2 versus 160 W/m2) at VRM than at SMI because 

of the larger wind speeds at VRM. 

The sensible heat flux is also about twice as large at VRM as at SMI and is nearly always 

positive (i.e., upward from the sea surface) because the air temperature is usually a few degrees 

cooler than the sea temperature. An exception occurred at noon on all three days at SMI, when 

the skin temperature was approximately equal to or less than the air temperature for a few hours 
5-24

and sensible heat flux values became negative (downward), but these values were small (less 

than 5 W/m2

). The maximum upward sensible heat flux at VRM was about 30 W/m2 and at SMI 

about 20 W/m2

; both maximums occurred during the night, from 0000 to 0600 CST on July 31. 

The maximum latent heat fluxes are about seven times the maximum sensible heat fluxes, 

as is found at most over-water sites in mid-summer. 

COARE Outputs of Wave Height and Period and Surface Roughness 

The hourly-averaged wave characteristics and the surface roughness length estimated by 

COARE for VRM and SMI for this case study are plotted in Figures 5-64a and 5-64b. The 

observed wind speed is also plotted. Because of the high frequency of wind speeds less than 

2 m/s at SMI, there was a strong bimodal distribution of COARE-calculated surface roughness 

length at that site, with a value of about 0.00002 m (i.e., 0.02 mm) and wind speeds greater than 

2 m/s. When the wind speed was greater than 2 m/s, the wave height ranged up to 0.5 m and the 

wave period ranged from 2 to 4 seconds. However, when the wind speed was less than 2 m/s 

and the wave height was small, the wave period was parameterized to drop to 1 second and the 

surface roughness length was estimated to increase by an order of magnitude to about 0.0005 m 

(i.e., 0.5 mm). These surface roughness length estimates when wind speed was less than 2 m/s 

appear to be too large and do not agree with the Charnock relation for surface roughness length 

over water that states that surface roughness length is proportional to friction velocity squared (or 

wind speed squared). 

At VRM, where the wind speeds are generally higher than at SMI, the wind speed 

dropped below 2 m/s during the morning of August 1, and surface roughness length increased by 

an order of magnitude. 

Comparison of COARE and Eta Outputs of Sensible and Latent Heat Flux 

The COARE estimates of sensible and latent heat flux were made using observations 

from the VRM and SMI oil platforms. The Eta forecasts of sensible and latent heat flux were 

based on fundamental solutions to the equations of motion, using some observations at buoys 

and on-shore radiosonde sites to generate analyzed fields for inputs. Figures 5-65a and 5-65b

compare these estimates for the July 30 to August 1, 1999, period. 

The COARE parameterizations of sensible and latent heat flux agree fairly well, on 

average, with the Eta forecasts of these fluxes. This is the type of scenario (warm summer 

periods) for which COARE was derived and calibrated, and Eta does well with these periods of 

persistent summertime conditions. Eta appears to match the average COARE latent heat flux 

values at VRM and SMI fairly well, although the time variations are not well-simulated. For 

example, at VRM, Eta predicts a strong diurnal variation of latent heat flux, while the diurnal 

variation is not found at all in the COARE parameterizations. The diurnal behavior simulated by 

Eta may be partly explained by the fact that the Eta grid square containing the VRM site includes 

a fraction of land surfaces. 

The Eta sensible heat fluxes at SMI are in good agreement with the COARE values of 

0 to 20 W/m2

. At VRM, the Eta forecasts of sensible heat flux tend to have a strong diurnal 
5-25

variation, with a peak value of about 50 W/m2

 at noon each day, dropping to zero or below at 

night. The COARE parameterizations of sensible heat flux do not show this diurnal variability 

and the values are lowest values at midday when the Eta forecast values have are highest. 

Comparison of COARE and Eta outputs of hourly-averaged friction velocity 

The COARE and Eta estimates of hourly-averaged friction velocity are plotted in 

Figures 5-66a and 5-66b for VRM and SMI, respectively. On average, the Eta-predicted 

hourly-averaged friction velocity values are about a factor of two larger than the COARE values. 

The COARE estimates of the observing height divided by L are also shown in the figures. 

Negative (unstable) values occurred all the time, with the observing height divided by L equal to 

about –3 at VRM and –10 at SMI. Since the observing height was about 25 m, it can be inferred 

that L was about –7 m at VRM and about –2.5 m at SMI. The smaller magnitudes of L at SMI 

were caused by the smaller wind speeds.

5.7.4 Analysis of September 18-20, 2001 

This case study was based on data collected at the VRM and SMI platforms from 

September 18-20, 2001. This period was marked by weak onshore flow. On September 20, a 

weak cold front was oriented west-to-east along the Gulf Coast from Houston, Texas, to Mobile, 

Alabama. 

Figures 5-67a and 5-67b are time series plots of hourly-averaged wind speed, air 

temperature, skin temperature, and relative humidity for the three-day period for VRM and SMI, 

respectively. All but the skin temperature were observed at an elevation of about 25 m msl, or 

about 3 m above the surface of the oil platform. 

This case study was characterized by conditions similar to, but slightly cooler than, those 

in the July-August case study. The air temperatures in September were only a few degrees lower 

than those in July, and the skin temperature was usually less than the skin temperature in July. 

Air temperature varied from 24o to 33oC at VRM and from 26o to 30oC at SMI. Skin temperature 

was more constant over the three days at VRM and SMI, varying between 27o and 32oC. Skin 

temperature was warmer than air temperature (i.e., an unstable Tv profile) by an average of about 

1 to 2oC during the entire three-day period at SMI and about half the time at VRM. An 

exception occurred at VRM from 0500 to 1300 CST on September 19 and from 2100 CST on 

September 19 to 1200 CST on September 20, when air temperature exceeded skin temperature 

by as much as 5oC (i.e., a stable Tv profile). This phenomenon may have been related to the 

presence of a cold front along the coast, since VRM is much nearer the coast than SMI. Wind 

speed ranged from near zero to about 8 m/s at both VRM and SMI, with speeds of about 5 m/s 

for the first half of the period, dropping to 1 or 2 m/s for the last half of the period. The wind 

speed dropped below 2 m/s for a small fraction of the time at both sites. Relative humidity was 

fairly constant at about 80% at both sites. 
5-26

COARE Outputs of Hourly-averaged Friction Velocity and Sensible and Latent Heat Flux 

Figures 5-68a and 5-68b (for VRM and SMI, respectively) illustrate the COARE 

parameterizations of hourly-averaged friction velocity and sensible and latent heat flux. Hourlyaveraged friction velocity averaged about 0.15 m/s at SMI during the first half of the period, then 

averaged about 0.005 m/s during the last half of the period, due primarily to the reduction in 

wind speed in the last half of the period. In general, wind speed divided by friction velocity was 

about 30 to 40, in rough agreement with similar conditions in the January and July case studies. 

The COARE-estimated latent heat fluxes were always larger than 30 W/m2

 with a 

maximum of 230 W/m2

 at SMI, where air temperature was always less than the skin temperature. 

At VRM, the maximum latent heat flux was the same as at SMI, but the minimum was near zero 

or slightly less than zero for the several hours when the air temperature was greater than the skin 

temperature. 

The maximum sensible heat flux was about 40 W/m2

 at both VRM and SMI. The 

maximum occurred at a time when the wind speed and the difference between the skin and air 

temperatures were large (8 m/s and 5°C, respectively). The minimum sensible heat flux at SMI 

was nearly zero when winds were low and the air and skin temperatures were nearly equal. 

However, at VRM, the minimum sensible heat flux was negative (about –10 W/m2

) because skin 

temperatures were lower than air temperatures at that site. 

The maximum latent heat fluxes were about six times the maximum sensible heat fluxes, 

in agreement with results for the July case study and those found at most over-water sites in the 

summer. 

COARE Outputs of Wave Height and Period and surface Roughness 

The hourly-averaged wave characteristics and the surface roughness length estimated by 

COARE for VRM and SMI in September are plotted in Figures 5-69a and 5-69b. The observed 

wind speed is also plotted. The results are similar to those found for the other case studies in that 

there was a strong bimodal distribution of COARE-calculated surface roughness length at both 

sites. A surface roughness length value of about 0.00003 m (0.03 mm) was calculated when 

wind speeds exceeded 2 m/s. However, when wind speeds were less than 2 m/s, surface 

roughness length was estimated to increase by more than an order of magnitude from 0.0005 to 

0.001 m (0.5 to 1 mm). 

Comparison of COARE and Eta Outputs of Sensible and latent Heat Flux 

The COARE estimates of sensible and latent heat flux were made using observations 

collected from the VRM and SMI oil platforms. The Eta meteorological forecast model bases its 

forecasts of sensible and latent heat flux on fundamental solutions to the equations of motion, 

using some observations at buoys and on-shore radiosonde sites to generate analyzed fields for 

inputs. Figures 5-70a and 5-70b show a comparison of these estimates for the 

September 18-20, 2001, case study period. 
5-27

As with the July case study, the COARE parameterizations of sensible and latent heat 

flux agreed fairly well, on average, with the Eta forecasts of these fluxes. This was the type of 

scenario (warm summer periods) for which COARE was derived and calibrated. Eta appeared to 

match the average and the maximum COARE latent heat flux values at VRM and SMI, although 

the time variations were not well-simulated. For example, at VRM, Eta predicted a strong 

diurnal variation of latent heat flux, with peaks near noon and minima near midnight, while the 

diurnal variation was minimal in the COARE parameterizations. Part of the reason for the 

diurnal fluctuations forecasted by Eta may be that the grid cell in which VRM is located includes 

mostly land surfaces. Both COARE and Eta agree on the low latent heat flux values from 

0000 to 0600 CST on September 20, when the cold front, which was oriented along the Gulf 

Coast, was near the VRM site. 

At the SMI site, located 100 km south of the VRM site and the cold front, the COAREand Eta-simulated latent heat flux did not drop as low as at VRM. 

The Eta-simulated sensible heat fluxes at the far-offshore site, SMI, were in good 

agreement with the COARE values of 0 to 40 W/m2

. At the VRM site nearer the shore, the Eta 

forecasts of sensible heat flux tended to have a strong diurnal variation, with a peak value of 

40 to 110 W/m2

 at noon each day, dropping to below zero (about –10 W/m2) at night. The 

COARE parameterizations of sensible heat flux did not show this diurnal variability and were 

determined by the difference between the skin and air temperatures. For the few hours when the 

difference between the skin and air temperatures was greater than zero (i.e., stable), the COARE 

simulations of sensible heat flux ranged from –10 W/m2

 to zero. 

Comparison of COARE and Eta Outputs of Hourly-averaged Friction Velocity 

The COARE and Eta estimates of hourly-averaged friction velocity for the September 

case study are plotted in Figures 5-71a and 5-71b, for VRM and SMI, respectively. As for the 

July case study, on average, the Eta-predicted hourly-averaged friction velocity values were a 

factor of two larger than the COARE values. 

The COARE estimates of the observing height divided by L are also shown in the figures. 

Negative (unstable) values occurred all the time at SMI, with the observing height divided by L 

equal to –5 to –2 at the beginning of the period and –3 to –35 for the last half of the period. At 

VRM, where there were several stable periods (i.e., when the difference between the skin and air 

temperatures was greater than zero), observing height divided by L was both positive (stable) 

and negative (unstable), ranging from –10 to +65. 

5.7.5 Summary of Results of Four Case Studies 

 The case study analyses of COARE and Eta outputs focused on three monitoring sites: 

buoy 42040, the VRM platform, and the SMI platform. Buoy 42040 is a few tens of kilometers 

east of the Mississippi Delta, the VRM site is only a few kilometers off the Louisiana coast, and 

the SMI site is about 100 km offshore. 

Four representative multi-day case study periods were chosen for analysis: 

January 20-24, 2000; January 5-6, 2001; July 30-August 1, 1999; and September 18-20, 2001. 
5-28

The previous four subsections discussed the results of the analyses of the individual case studies, 

and this subsection provides summary conclusions. 

For each case study period, time series of observed hourly-averaged wind speed, air 

temperature, skin temperature, and relative humidity were plotted for the multi-day period for 

each monitoring site. These observations were used as inputs to the COARE program, which 

provided estimates of friction velocity, sensible heat flux, and latent heat flux. The COARE 

estimates were compared with predictions made by the Eta numerical weather prediction model. 

The four case studies cover a range of meteorological conditions. For example, the 

January 20-24, 2000, period was an active synoptic period, with frequent moderate winds, large 

fluctuations in air temperature, and large swings in sensible and latent heat flux. The 

January 5-6, 2001, period was cool but with the air temperature warmer than the skin 

temperature most of the time, leading to frequent stable conditions. The July 1999 and 

September 2001 periods were typical summertime periods when the skin temperature was 

usually greater than the air temperature (i.e., unstable conditions) and winds were light to 

moderate. 

COARE Outputs of Friction Velocity and Sensible and Latent Heat Flux 

A few general conclusions can be reached about the COARE outputs. In general, wind 

speed divided by friction velocity equals 30 to 40 for the COARE estimates for all the case 

studies, in rough agreement with the logarithmic wind profile formula u/u* = 2.5 ln (z/zo) where 

u is wind speed, u* is friction velocity, z is observing height, and zo is surface roughness length. 

This is valid for nearly neutral conditions and observing height divided by surface roughness 

length equal to about 1000 to 100,000. These ratios of surface roughness length are valid for the 

ranges of observing height (2 to 25 m) and surface roughness length (0.00002 to 0.001 m) 

encountered in the case studies. 

On average, during most periods with skin temperatures greater than air temperatures 

(i.e., an unstable Tv profile), the COARE-estimated latent heat fluxes were 5 to 10 times larger 

than the sensible heat fluxes, in agreement with the results found at most over-water sites. At 

these times, both the sensible and latent heat fluxes were roughly proportional to friction 

velocity. The “skin temperature greater than air temperature” scenario occurred a majority of the 

time in the three and a half years of Gulf of Mexico data, at most ocean sites at low to mid 

latitudes. 

Latent heat fluxes were estimated by COARE to equal about 100 to 200 W/m2

 when air 

temperatures were greater than skin temperatures during typical summertime periods. During 

the January 20-25, 2000, case study, there was a period of 20 or 30 hours, after a cold front 

passage, when a large difference between skin and air temperatures occurred with a large wind 

speed, which led to exceptionally large latent heat flux values of about 500 W/m2

. Latent heat 

flux rarely becomes negative during periods with skin temperatures less than air temperatures 

and high relative humidity. 

Sensible heat fluxes were usually positive upward with magnitudes of 50 W/m2

 or less 

when skin temperatures were less than air temperatures (i.e., most of the time). When skin 
5-29

temperature was less than air temperature, the sensible heat flux became negative, but had a 

magnitude of less than 10 W/m2

. 

The sensible heat flux was negative more often than the latent heat flux because the 

sensible heat flux is negative whenever the skin temperature is less than the air temperature. 

However, the latent heat flux becomes negative only when the skin temperature is less than the 

air temperature and the relative humidity of the air near the surface is very high. 

COARE Outputs of Wave Height and Period and Surface Roughness Length 

The hourly-averaged wave characteristics and the surface roughness length estimated by 

COARE were plotted and analyzed. In general, the Charnock relation, zo = au*2

 (where zo is 

surface roughness length, a is a constant, and u* is friction velocity), was valid for moderate to 

high wind speeds (greater than 2 m/s), when an average surface roughness length value of 

0.00002 m to 0.00005 m (0.02 to 0.05 mm) was estimated by COARE for these case studies. 

However, when wind speed was less than 2 m/s, surface roughness length was estimated by 

COARE to increase by more than an order of magnitude to 0.0005 to 0.001 m (0.5 to 1 mm). 

This strong bimodal distribution of COARE-calculated surface roughness length was found for 

all four case studies and is thought to be caused by the revised surface roughness length 

formulation, which allows surface roughness length to be prescribed as a function of wave height 

and period. For wind speeds less than 2 m/s, COARE parameterized a large decrease in wave 

period (from 4 to 5 seconds to 1 second), which translated into an increase in surface roughness 

length. 

 

Comparison of COARE and Eta Outputs of Sensible and Latent Heat Flux 

The COARE estimates of Hs and Hl were made using observations at buoy 42040 or the 

VRM and SMI oil platforms. The Eta model forecasts of sensible and latent heat flux were 

based on fundamental solutions to the equations of motion, using some observations at buoys 

and on-shore radiosonde sites to generate analyzed fields for inputs. 

As previously mentioned, for observing sites close to shore such as VRM, the 

encompassing Eta horizontal grid square may include a portion of the coast and the inland area. 

Consequently, Eta may model that grid square as if it is not 100% over water, affecting friction 

velocity and sensible and latent heat flux predictions. 

The COARE parameterizations of sensible and latent heat flux agreed fairly well, on 

average, with the Eta simulations of these fluxes. Agreement was best for warm summer periods 

for which COARE was derived and calibrated. Despite the fact that Eta appears to match the 

average and the maximum COARE sensible and latent heat flux values, the time variations were 

not well-simulated. For example, at VRM in September, Eta predicted a strong diurnal variation 

of the latent heat flux, with peaks near noon and minima near midnight, while the diurnal 

variation was minimal in the COARE parameterizations. Part of the reason for the diurnal 

fluctuations forecasted by Eta may be that the grid cell in which VRM is located includes a large 

fraction of land surfaces. 
5-30

The COARE-estimated sensible heat flux was determined primarily by the difference 

between the air temperature and the skin temperature. For the few hours when this temperature 

difference was greater than zero (i.e., stable), the COARE simulations of sensible heat flux 

ranged from -10 W/m2

 to zero. The Eta model sometimes matched these negative or near-zero 

values, but more often, the Eta model predicted a slight positive (upward) sensible heat flux 

during these periods when COARE sensible heat flux was negative. 

Comparison of COARE and Eta Outputs of Hourly-averaged Friction Velocity 

The COARE and Eta estimates of hourly-averaged friction velocity were compared for 

the four case studies. Eta forecasts for two starting times were evaluated but there was little 

difference between the two Eta forecasts and the COARE results. On average, the Eta-predicted 

hourly-averaged friction velocity values were about a factor of two larger than the COARE 

hourly-averaged friction velocity values. Since the momentum flux or surface stress is 

proportional to friction velocity squared, the Eta momentum fluxes were a factor of two to four 

larger than the COARE estimates. 

This difference is difficult to understand from a boundary layer perspective, since it has 

already been noted that the overall average and maximum sensible and latent heat flux values 

estimated by COARE and Eta agreed fairly well. Because both sensible and latent heat fluxes 

are proportional to hourly-averaged friction velocity, we would also expect the Eta-predicted 

sensible and latent heat flux values to be a factor of two larger than the COARE estimates. 
5-31

-10

0

102030405060708090

1 2 3 4 5 6 7 8 9 10 1

Month

Sensible Heat Flux (W/m2)

Figure 5-1a. COARE monthly average sensible heat fluxes by site for May 1998 through Oct
5-32

-10

0

102030405060708090

1 2 3 4 5 6 7 8 9 10 11 

Month

Sensible Heat Flux (W/m2) 

Figure 5-1b. COARE monthly average sensible heat fluxes by BAMP site for September 2000 through S
5-33

0

50

100150200250300

1 2 3 4 5 6 7 8 9 10 11 

Month

Latent Heat Flux (W/m2)

Figure 5-2a. COARE monthly average latent heat fluxes by site for May 1998 through October 
5-34

0

50

100150200250300

1 2 3 4 5 6 7 8 9 10 11 

Month

Latent Heat Flux (W/m2) 

Figure 5-2b. COARE monthly average latent heat fluxes by BAMP site for September 2000 through Se
5-35

Figure 5-3a. Observed monthly average wind speed by site for May 1998 through October 20

0123456789

1 2 3 4 5 6 7 8 9 10 11 

Month

Wind Speed (m/s)
5-36

0123456789

1011

1 2 3 4 5 6 7 8 9 10 11 

Month

Wind Speed (m/s) 

Figure 5-3b. Observed monthly average wind speed by BAMP site for September 2000 through Septe
5-37

Figure 5-4a. Monthly average skin temperature minus air temperature by site for May 1998 through O

-1

0123456

1 2 3 4 5 6 7 8 9 10 11 

Month

Temperature Difference (deg. C)
5-38

-4-2

02468

1 2 3 4 5 6 7 8 9 10 11 

Month

Temperature Difference (deg. C) 

 Figure 5-4b. COARE monthly average skin temperature minus air temperature by BAMP site for Septemb

September 2001. 
5-39

0

50

100150200250300350

1 2 3 4 5 6 7 8 9 10 11 

Month

Total Heat Flux (W/m2)

Figure 5-5a. COARE monthly average of total heat fluxes (sensible plus latent) by site for May 1998 throu
5-40

0

50

100150200250300350

1 2 3 4 5 6 7 8 9 10 11 

Month

Total Heat Flux (W/m2) 

 Figure 5-5b. COARE monthly average total heat fluxes (sensible plus latent) by BAMP site for Septemb

September 2001. 
5-41

0

50

100150200250300

1 2 3 4 5 6 7 8 9 10 11 

Month

Latent Heat Flux (W/m2)

Figure 5-6. Eta monthly average latent heat fluxes by site for May 1998 through October 2001, for the 6- t
5-42

Figure 5-7. Eta monthly average sensible heat fluxes by site for May 1998 through October 2001, for the 6- 

-15

5

25456585

105125

1 2 3 4 5 6 7 8 9 10 1

Month

Sensible Heat Flux (W/m2)
5-43

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 

Month

Friction Velocity (m/s)

Figure 5-8a. COARE monthly average friction velocity by site for May 1998 through October 
5-44

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 

Month

Friction Velocity (m/s) 

Figure 5-8b. COARE monthly average friction velocity by BAMP site for September 2000 through Sep
5-45

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 

Month

Friciton Velocity (m/s)

Figure 5-9. Eta monthly average friction velocity by site for May 1998 through October 2001, for the 6- t
5-46

-0.2

-0.15

-0.1

-0.05

0

0.05

1 2 3 4 5 6 7 8 9 10 11 

Month

Temperature Scaling Parameter (deg. C) 

Figure 5-10a. COARE calculated monthly average temperature scaling parameter by site for May 1998 thro
5-47

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

1 2 3 4 5 6 7 8 9 10 11 

Month

Temperature Scaling Parameter (deg. C) 

Figure 5-10b. COARE calculated monthly average temperature scaling parameter by BAMP site for Septem

September 2001. 
5-48

-0.0005

-0.00045

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

1 2 3 4 5 6 7 8 9 10 1

Month

Humidity Scaling Parameter (kg/kg) 

Figure 5-11a. COARE calculated monthly average humidity scaling parameter by site for May 1998 throu
5-49

-0.0005

-0.00045

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

1 2 3 4 5 6 7 8 9 10 11 

Month

Humidity Scaling Parameter (kg/kg) 

Figure 5-11b. COARE calculated monthly average humidity scaling parameter by BAMP site for Septemb

September 2001. 
5-50

05

1015202530

1 2 3 4 5 6 7 8 9 10 11 

Month

Temperature (deg. C)

Figure 5-12a. Observed monthly average air temperature by site for May 1998 through October 
5-51

05

1015202530

1 2 3 4 5 6 7 8 9 10 11 

Month

Temperature (deg. C) 

Figure 5-12b. Observed monthly average air temperature by BAMP site for September 2000 through Se
5-52

05

101520253035

1 2 3 4 5 6 7 8 9 10 11 

Month

Water Temperature (deg. C)

Figure 5-13a. Observed monthly average skin temperature by site for May 1998 through Octobe
5-53

05

101520253035

1 2 3 4 5 6 7 8 9 10 11 

Month

Water Temperature (deg. C) 

Figure 5-13b. Observed monthly average skin temperature by BAMP site for September 2000 through S
5-54

Figure 5-14. Eta average downwelling longwave radiation by synoptic class by site for May 1998 through 

for the 6- to 12-hr forecast. 

0

50

100150200250300350400450

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Downwelling Longwave Radiation (W/m2) 
5-55

Figure 5-15. Eta average shortwave radiation by synoptic class by site for May 1998 through Octo

for the 6-to 12-hr forecast.

0

50

100150200250300

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Shortwave Radiation (W/m2) 
5-56

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI V

Site

Humidity Scaling Parameter (kg/kg) 

Figure 5-16a. COARE average humidity scaling parameter by synoptic class by site for May 1998 throug
5-57

-0.0005

-0.00045

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

BIP DWP MBP SWP WDP 

Site

Humidity Scaling Parameter (kg/kg) 

Figure 5-16b. COARE average humidity scaling parameter by synoptic class by BAMP site for Septemb

September 2001. 
5-58

-0.25

-0.2

-0.15

-0.1

-0.05

0

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Temperature scaling parameter (degrees) 

Figure 5-17a. COARE average temperature scaling parameter by synoptic class by site for May 1998 throu
5-59

-2.50E-01-2.00E-01-1.50E-01-1.00E-01-5.00E-02

0.00E+00

BIP DWP MBP SWP WDP 

Site

Temperature scaling parameter (degrees) 

Figure 5-17b. COARE average temperature scaling parameter by synoptic class by BAMP site for Septem

September 2001.
5-60

0

0.00010.00020.00030.00040.00050.0006

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Roughness (m)

Figure 5-18a. COARE surface roughness by synoptic class by site for May 1998 through Octobe
5-61

0

0.00010.00020.00030.00040.00050.0006

BIP DWP MBP SWP WDP 

Site

Roughness (m)

Figure 5-18b. COARE surface roughness by synoptic class by BAMP site for September 2000 through S
5-62

0

102030405060708090

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Sensible Heat Flux (W/m2)

Figure 5-19a. COARE average sensible heat fluxes by synoptic class by site for May 1998 through O
5-63

0

102030405060708090

BIP DWP MBP SWP WDP 

Site

Sensible Heat Flux (W/m2)

Figure 5-19b. COARE average sensible heat fluxes by synoptic class by BAMP site for September 2000 throu
5-64

0

50

100150200250300

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Latent Heat Flux (W/m2)

Figure 5-20a. COARE average latent heat fluxes by synoptic class by site for May 1998 through Oct
5-65

0

50

100150200250300

BIP DWP MBP SWP WDP 

Site

Latent Heat Flux (W/m2)

Figure 5-20b. COARE average latent heat fluxes by synoptic class by BAMP site for September 2000 throug
5-66

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Friction Velocity (m/s)

Figure 5-21a. COARE average friction velocity by synoptic class by site for May 1998 through Oct
5-67

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

BIP DWP MBP SWP WDP 

Site

Friction Velocity (m/s)

Figure 5-21b. COARE average friction velocity by synoptic class by BAMP site for September 2000 throug
5-68

02468

1012

42001 42002 42007 42019 42020 42035 42040 BURL1 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Wind Speed (m/s)

Figure 5-22. Observed average wind speed by synoptic class by site for May 1998 through Octob
5-69

Figure 5-23. Eta average downwelling longwave radiation by general flow direction by site for May 1998 thr

for the 6-to 12-hr forecast. 

310320330340350360370380390400

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VR

Site

Downwelling Longwave Radiation (W/m2) 
5-70

Figure 5-24. Eta average shortwave radiation by general flow direction by site for May 1998 through O

for the 6-to 12-hr forecast. 

0

50

100150200250300350

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Shortwave Radiation (W/m2) 
5-71

-4.50E-04-4.00E-04-3.50E-04-3.00E-04-2.50E-04-2.00E-04-1.50E-04-1.00E-04-5.00E-05

0.00E+00

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI 

Site

Humidity Scaling Parameter (kg/kg) 

Figure 5-25a. COARE average humidity scaling parameter by general flow direction by site for May 1998 throu
5-72

-4.50E-04-4.00E-04-3.50E-04-3.00E-04-2.50E-04-2.00E-04-1.50E-04-1.00E-04-5.00E-05

0.00E+00

BIP DWP MBP SWP WDP 

Site

Humidity Scaling Parameter (kg/kg) 

Figure 5-25b. COARE average humidity scaling parameter by general flow direction by BAMP site for Sept

 September 2001. 
5-73

-1.80E-01-1.60E-01-1.40E-01-1.20E-01-1.00E-01-8.00E-02-6.00E-02-4.00E-02-2.00E-02

0.00E+00

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Temperature Scaling Parameter (deg. C) 

Figure 5-26a. COARE average temperature scaling parameter by general flow direction by site for May 1998 th
5-74

-1.80E-01-1.60E-01-1.40E-01-1.20E-01-1.00E-01-8.00E-02-6.00E-02-4.00E-02-2.00E-02

0.00E+00

BIP DWP MBP SWP WDP 

Site

Temperature Scaling Parameter (deg. C) 

Figure 5-26b. COARE average temperature scaling parameter by general flow direction by BAMP site for Sep

September 2001. 
5-75

0.00E+00

5.00E-051.00E-041.50E-042.00E-042.50E-043.00E-043.50E-04

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Roughness (m) 

Figure 5-27a. COARE average surface roughness by general flow direction by site for May 1998 through 
5-76

0.00E+00

5.00E-051.00E-041.50E-042.00E-042.50E-043.00E-043.50E-04

BIP DWP MBP SWP WDP 

Site

Roughness (m) 

Figure 5-27b. COARE average surface roughness by general flow direction by BAMP site for Septembe

 September 2001. 
5-77

0

10203040506070

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Sensible Heat Flux (w/m2) 

Figure 5-28a. COARE average sensible heat fluxes by general flow direction by site for May 1998 throug
5-78

0

10203040506070

BIP DWP MBP SWP WDP 

Site

Sensible Heat Flux (W/m2) 

Figure 5-28b. COARE average sensible heat fluxes by general flow direction by BAMP site for Septemb

September 2001. 
5-79

0

50

100150200250

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI V

Site

Latent Heat Flux (w/m2) 

Figure 5-29a. COARE average latent heat fluxes by general flow direction by site for May 1998 through 
5-80

0

50

100150200250

BIP DWP MBP SWP WDP 

Site

Latent Heat Flux (W/m2) 

Figure 5-29b. COARE average latent heat fluxes by general flow direction by BAMP site for September 

September 2001. 
5-81

0

0.05

0.1

0.15

0.2

0.25

0.3

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI VRM 

Site

Friction Velocity (m/s) 

Figure 5-30a. COARE average friction velocity by general flow direction by site for May 1998 through 
5-82

0

0.05

0.1

0.15

0.2

0.25

0.3

BIP DWP MBP SWP WDP 

Site

Friction Velocity (m/s) 

 Figure 5-30b. COARE average friction velocity by general flow direction by BAMP site for September 

September 2001. 
5-83

012345678

42001 42002 42007 42019 42020 42035 42040 BURL1 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Wind Speed (m/s) 

Figure 5-31. Observed average wind speed by general flow direction by site for May 1998 through O
5-84

-5

5

1525354555657585

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2

Time (LST)

Sensible Heat Flux (W/m2)

Figure 5-32. COARE hourly average sensible heat fluxes over buoy 42001 for May 1998 through Oc
5-85

-5

5

1525354555657585

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 

Time (LST)

Sensible Heat Flux (W/m2)

Figure 5-33. COARE hourly average sensible heat fluxes over SMI for May 1998 through Octob
5-86

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2

Time (LST)

Friction Velocity (m/s)

Figure 5-34. COARE hourly average friction velocity over SMI for May 1998 through October 
5-87

0

50

100150200250300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Time (LST)

Latent Heat Flux (W/m2)

Figure 5-35. COARE hourly average latent heat fluxes over VRM for May 1998 through Octobe
5-88

-5

1535557595

115

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2

Time (LST)

Sensible Heat Flux (W/m2)

Figure 5-36. COARE hourly average sensible heat fluxes over VRM for May 1998 through Octob
5-89

-1

0123456

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2

Time (LST)

Temperature Difference (deg. C)

Figure 5-37. Hourly average skin temperature minus air temperature over VRM for May 1998 through 
5-90

-5

5

1525354555657585

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2

Time (LST)

Sensible Heat Flux (W/m2)

Figure 5-38. COARE hourly average sensible heat fluxes over buoy 42040 for May 1998 through Oc
5-91

0

50

100150200250300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2

Time (LST)

Latent Heat Flux (W/m2)

Figure 5-39. COARE hourly average latent heat fluxes over buoy 42040 for May 1998 through Octo
5-92

-5

5

1525354555657585

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Time (LST)

Sensible Heat Flux (W/m2)

Figure 5-40. COARE hourly average sensible heat fluxes over GDIL1 for May 1998 through Octo
5-93

-1

0123456

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Temperature Difference (deg. C)

Figure 5-41. Hourly skin temperature minus air temperature over GDIL1 for May 1998 through Oct
5-94

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Friction Velocity (m/s)

Figure 5-42. COARE hourly friction velocity over GDIL1 for May 1998 through October 20
5-95

0

50

100150200250300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2

Time (LST)

Latent Heat Flux (W/m2)

Figure 5-43. COARE hourly average latent heat fluxes over GDIL1 for May 1998 through Octob
5-96

-10

0

102030405060

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Sensible Heat Flux (W/m2)

Figure 5-44. COARE hourly average sensible heat fluxes over BIP for September 2000 through Septe
5-97

0

50

100150200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Latent Heat Flux (W/m2)

Figure 5-45. COARE hourly average latent heat fluxes over BIP for September 2000 through Septem
5-98

0.050.070.090.110.130.150.170.190.210.230.25

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 

Time (LST)

Friction Velocity (m/s)

Figure 5-46. COARE hourly average friction velocity over BIP for September 2000 through Septem
5-99

-2

02468

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Temperature Difference (deg. C)

Figure 5-47. Hourly skin temperature minus air temperature over BIP for September 2000 through Sep
5-100

012345678

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Wind Speed (m/s)

Figure 5-48. Observed hourly average wind speed over BIP for September 2000 through Septemb
5-101

012345678

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Wind Speed (m/s)

Figure 5-49. Observed hourly average wind speed over DWP for September 2000 through Septem
5-102

-10

0

102030405060

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Sensible Heat Flux (W/m2)

Figure 5-50. COARE hourly average sensible heat fluxes over DWP for September 2000 through Sept
5-103

0

50

100150200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Latent Heat Flux (W/m2)

Figure 5-51. COARE hourly average latent heat fluxes over DWP for September 2000 through Septe
5-104

0.050.070.090.110.130.150.170.190.210.230.25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Time (LST)

Friction Velocity (m/s)

Figure 5-52. COARE hourly average friction velocity over DWP for September 2000 through Septem
5-105

-2

02468

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Hour (LST)

Temperature Difference (deg. C)

Figure 5-53. Hourly skin temperature minus air temperature over DWP for September 2000 through Se
5-106 0

5

1015202530

1/20/00 18:00 1/21/00 0:00 1/21/00 6:00 1/21/00 12:00 1/21/00 18:00 1/22/00 0:00 1/22/00 6:00 1/22/00 12:00 1/22/00 18:00 1/23/00 0:00 1/23/00 6:00 1/23/00 12:00 1/23/00 18:00 1/24/00 0:00 1/24/00 6:00 1/24/00 12:00 1/24/00 18:00 1/25/00 0:00 1/25/00 6:00 1/25/00 12:00

Time (CST)

Temperature 

[°C]

Air TemperatureWater TemperatureCoare Skin TemperatureWindspeed

Figure 5-54. Air and skin temperatures and wind speed at buoy 42040 for January 20 through 25
5-107

COARE Sensible Heat

Figure 5-55. COARE and Eta hourly sensible heat fluxes at buoy 42040 for January 20 through 25, 2000. Eta

heat fluxes were obtained from the 6- and 12-hr (30- and 36-hr) forecasts and interpolated to ho6- and 12-hr (30- and 36-hr) forecasts. 
5-108

Figure 5-56. COARE and Eta hourly latent heat fluxes at buoy 42040 for January 20 through 25, 2000. Eta

heat fluxes were obtained from the 6- and 12-hr (30- and 36-hr) forecasts and interpolated to 

between 6- and 12-hr (30- and 36-hr) forecasts. 
5-109

Figure 5-57. Hourly air and skin temperatures, wind speed, and relative humidity at VRM for January 4 t
5-110

Figure 5-58. COARE hourly average latent and sensible heat fluxes and friction velocity at VRM for January 
5-111

Figure 5-59. Estimated wave height and period, wind speed, and surface roughness length at VRM for Januar
5-112

Figure 5-60. COARE and Eta latent and sensible heat fluxes at VRM for January 4 through 6, 2001. Note: th

 after Eta in the key indicates the forecast period (i.e., 0612 is the-6- to 12-hr forecast). 
5-113

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

1/4/01

0:00

1/4/01

3:00

1/4/01

6:00

1/4/01

9:00

1/4/01

12:00

1/4/01

15:00

1/4/01

18:00

1/4/01

21:00

1/5/01

0:00

1/5/01

3:00

1/5/01

6:00

1/5/01

9:00

1/5/01

12:00

1/5/01

15:00

1/5/01

18:00

1/5/01

21:00

1/6/01

0:00

1/6/01

3:00

1/6/01

6:00

1/6/01

9:00

1/6/01

12:00

1/6/01

15:00

1/6/01

18:00

1/6/01

21:00

1/7/01

0:00

Time (LST)

Friction Velocity (m/s)

-02468

COARE Friction VelocityETA3036 Friction VelocityETA0612 Friction VelocityZ/L

Figure 5-61. COARE and Eta friction velocity and z/L at VRM for January 4 through January 6, 2001. No

number after Eta in the key indicates the forecast period (i.e., 0612 is the-6- to 12-hr forecast 30- to 36-hr forecast). 
5-114

05

10152025303540

7/30/99

0:00

7/30/99

3:00

7/30/99

6:00

7/30/99

9:00

7/30/99

12:00

7/30/99

15:00

7/30/99

18:00

7/30/99

21:00

7/31/99

0:00

7/31/99

3:00

7/31/99

6:00

7/31/99

9:00

7/31/99

12:00

7/31/99

15:00

7/31/99

18:00

7/31/99

21:00

8/1/99

0:00

8/1/99

3:00

8/1/99

6:00

8/1/99

9:00

8/1/99

12:00

8/1/99

15:00

8/1/99

18:00

8/1/99

21:00

8/2/99

0:00

Time (CST)

Other variables

Air Temperature (Degrees C) Wind Speed (m/sec)Skin temperature (Degrees C) RH (Fraction)

Figure 5-62a. Hourly air and skin temperatures, wind speed, and relative humidity at VRM for July 30 throu
5-115

05

10152025303540

7/30/99

0:00

7/30/99

3:00

7/30/99

6:00

7/30/99

9:00

7/30/99

12:00

7/30/99

15:00

7/30/99

18:00

7/30/99

21:00

7/31/99

0:00

7/31/99

3:00

7/31/99

6:00

7/31/99

9:00

7/31/99

12:00

7/31/99

15:00

7/31/99

18:00

7/31/99

21:00

8/1/99

0:00

8/1/99

3:00

8/1/99

6:00

8/1/99

9:00

8/1/99

12:00

8/1/99

15:00

8/1/99

18:00

8/1/99

21:00

8/2/99

0:00

Time (CST)

Other variables

00000000001

Air Temperature (Degrees C) Wind Speed (m/sec)Skin temperature (Degrees C) RH (Fraction)

Figure 5-62b. Hourly air and skin temperatures, wind speed, and relative humidity at SMI for July 30 throug
5-116

Figure 5-63a. COARE latent and sensible heat fluxes and friction velocity at VRM for July 30 through A
5-117

Figure 5-63b. COARE latent and sensible heat fluxes and friction velocity at SMI for July 30 through A
5-118

Figure 5-64a. Estimated wave height and period, and surface roughness length and wind speed at V

 July 30 through August 1, 1999. 
5-119

Figure 5-64b. Estimated wave height and period, and surface roughness length and wind speed at 

 July 30 through August 1, 1999. 
5-120

Figure 5-65a. COARE and Eta latent and sensible heat fluxes at VRM for July 30 through August 1, 1999. N

number after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr forecast). 
5-121

Figure 5-65b. COARE and Eta latent and sensible heat fluxes at SMI for July 30 through August 1, 1999. N

number after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr forecast)
5-122

 Figure 5-66a. COARE and Eta friction velocity and z/L at VRM for July 30 through August 1, 1999. No

number after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr foreca30- to 36-hr forecast).
5-123

Figure 5-66b. COARE and Eta friction velocity and z/L at SMI for July 30 through August 1, 1999. Note

number after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr foreca30- to 36-hr forecast). 
5-124

Figure 5-67a. Hourly air and skin temperatures, wind speed, and relative humidity at VRM for September 18 

05

10152025303540

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/2

Time (CST)

Other variables

Air Temperature (Degrees C) Wind Speed (m/sec)Skin temperature (Degrees C) RH (Fraction)

RH is estimated, w hich w ill influence the Latent Heat
5-125

Figure 5-67b. Hourly air and skin temperatures, wind speed, and relative humidity at SMI for September 18 

05

10152025303540

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/20/01

18

Time (CST)

Other variables

Air Temperature (Degrees C) Wind Speed (m/sec)Skin temperature (Degrees C) RH (Fraction)
5-126

0

50

100150200250

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/20/01

18:00

9/2

Time (CST)

Other variables

Latent Heat (w/m**2)

Sensible Heat (w/m**2)

Friction Velocity (m/sec)

Figure 5-68a. COARE latent and sensible heat fluxes and friction velocity at VRM for September 18 thr
5-127

Figure 5-68b. COARE latent and sensible heat fluxes and friction velocity at SMI for September 18 thro

0

50

100150200250

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/20/01

Time (CST)

Other variables

Latent Heat (w/m**2)Sensible Heat (w/m**2)Friction Velocity (m/sec)
5-128

Figure 5-69a. Estimated wave height and period, wind speed, and surface roughness length at VR

September 18 through 20, 2001. 

0123456789

10

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/20/01

1

Time (CST)

Other variables

Estimate Wave Height Estimate Wave Period Wind Speed (m/sec)Roughness (m)
5-129

Figure 5-69b. Estimated wave height and period, wind speed, and surface roughness length at S

September 18 through 20, 2001. 

0123456789

10

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/20/

Time (CST)

Other variables

Estimate Wave HeigEstimate Wave PerioWind Speed (m/sec)Roughness (m)
5-130

Figure 5-70a. COARE and Eta latent and sensible heat fluxes at VRM for September 18 through 20, 2001. N

 number after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr forecast). 

0

50

100150200250

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15

Time (CST)

Latent and Sensible Heat 

Latent Heat (w/m**Sensible Heat (w/mEta0612 Sensible Eta0612 Latent He
5-131

Figure 5-70b. COARE and Eta latent and sensible heat fluxes at SMI for September 18 through 20, 2001. N

 number after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr forecast)

0

50

100150200250

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12

0

Time (CST)

Latent and Sensible Heat 

Latent Heat (wSensible Heat Eta0612 SensEta0612 Laten
5-132

VRM

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/20/01

18:00

9/20/01

21

Time (CST)

Friction Velocity

Friction Velocity (m/sec)Eta3036 Friction Velocity (m/sec)Eta0612 Friction Velocity (m/sec)ZL

Figure 5-71a. COARE and Eta friction velocity and z/L at VRM for September 18 through 20, 2001. Note: th

after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr forecast and 3036 i30- to 36-hr forecast). 
5-133

Figure 5-71b. COARE and Eta friction velocity and z/L at SMI for September 18 through 20, 2001. Note: th

after Eta in the key indicates the forecast period (i.e., 0612 is the 6- to 12-hr forecast and 3036 30- to 36-hr forecast). 

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

9/18/01

0:00

9/18/01

3:00

9/18/01

6:00

9/18/01

9:00

9/18/01

12:00

9/18/01

15:00

9/18/01

18:00

9/18/01

21:00

9/19/01

0:00

9/19/01

3:00

9/19/01

6:00

9/19/01

9:00

9/19/01

12:00

9/19/01

15:00

9/19/01

18:00

9/19/01

21:00

9/20/01

0:00

9/20/01

3:00

9/20/01

6:00

9/20/01

9:00

9/20/01

12:00

9/20/01

15:00

9/20/01

18:0

Time (CST)

Friction Velocity

Friction Velocity (m/sec)Eta3036 Friction Velocity (m/sec)Eta0612 Friction Velocity (m/sec)ZL
6-1

6. METEOROLOGICAL AND AIR QUALITY MODELING 

A major component of the MMS Boundary Layer Study was the development of hourly 

three-dimensional gridded wind fields. The wind fields were developed using the CALMET 

diagnostic model driven by a combination of historic Eta model simulations and observations. 

The wind fields, along with other ABL parameters, were used to develop three-dimensional 

inputs to transport and dispersion models that were used to assess dispersion and transport 

characteristics under multiple meteorological patterns. These patterns include onshore and 

offshore flow regimes, pre- and post-cold-frontal boundary passages, strong surface and upperlevel high pressure systems, and upper-level flow transitioning from an area of low pressure to a 

weak area of high pressure. These meteorological patterns and their influence on transport and 

dispersion are captured in seven modeled case study periods: 

• July 30 – August 1, 1999 

• January 20-25, 2000 

• January 4-6, 2001 

• January 29, 2001 

• April 14-15, 2001 

• May 14-15, 2001 

• September 18-20, 2001 

The case studies were selected to cover a range of synoptic conditions, seasons, and wind 

directions. 

This section contains the results of a comparison between observations and model 

predictions of winds; background information about the CALMET diagnostic model; discussion 

of the methods used to derive the three-dimensional wind fields (i.e., data sources and model 

settings); and discussions of the model results, trajectories, and CALPUFF dispersion runs for 

the above case studies. Conclusions from this discussion are set out in Section 6.6. 

6.1 RADAR WIND PROFILER – EDAS COMPARISON 

The CALMET meteorological model can use both observations and regional-scale model 

predictions as input. The two data types can be weighted differently in the model, and the user 

must assign the weights. The weighting of observations and model predictions is of extreme 

importance in observationally sparse regions such as the Gulf of Mexico. To help determine the 

relative weighting that should be assigned to the regional scale model predictions and to the 

observations, horizontal wind observations collected by the six RWPs were compared with the 

wind predictions from the NCEP EDAS. 

6.1.1 Method 

The EDAS output consists of successive three-hour Eta model forecasts nudged by high 

frequency observing platforms, such as RWPs, hourly surface meteorological and buoy stations, 

aircraft observations, and winds derived from both satellite and radar measurements. However, 
6-2

the RWP data used in this study and the following comparisons were not part of the routine 

EDAS output. The output is interpolated to a 40 km, Lambert Conformal Grid covering the 

continental United States. RWPs used during MMS and BAMP (Figure 6-1) were LAP-3000, 

915-MHz boundary layer radars deployed on oil platforms. Two modes of data collection 

occurred at all RWP sites. The low mode represented 100-m resolution winds at heights from 

about 100 m above platform level (APL) to about 2000 m APL. The high mode represented 

200-m resolution winds at heights from about 200 m APL up to about 4000 m APL. These RWP 

data were subjectively quality-controlled by STI meteorologists. Any data that were deemed 

incorrect were invalidated and not used in the subsequent analyses. Typical problems that led to 

incorrect data were the presence of clutter due to sea waves and/or platform structures. 

Comparisons of EDAS-modeled and RWP-observed hourly wind speed and direction 

were made when EDAS wind heights were within 30 m of the RWP heights below 1000 m 

above ground level (agl), and within 50 m of the RWP heights above 1000 m agl. When wind 

speeds were less than 2 m/s, wind direction comparisons were not made. 

A difference exists between the averaging volumes represented by the EDAS model and 

those represented by the RWP observations; this difference will manifest itself by more scatter in 

the observations than in the predictions. The EDAS model data are created by bilinear 

interpolation of the 12-km Eta model output to a 40-km grid. Vertical interpolation is performed 

on the 12-km Eta model (60 levels) to the EDAS grid (39 levels). On the other hand, the RWP 

winds are a volume-averaged measurement that is dependent on vertical resolution and beam 

width. Because the profiler beams diverge with height, the volume is approximately 3.5 km 

wide at 4 km above ground. The RWP-derived wind components are a nearly instantaneous 

measurement, however when averaged over an hour, the winds can be representative of a radius 

of 3.5 km (zero wind) or greater depending on the wind speed through the profiler beams. This 

issue arises whenever observations are compared with grid model predictions (see Seaman, 

2000; Hanna and Yang, 2001). The grid-averaged predictions resolve only variations with scales 

greater than the grid dimensions. This should have little effect on the mean bias, as long as the 

instrument is well-sited and representative. However, the standard deviation of the RWPobserved wind will be larger than the standard deviation of the predicted wind, and this could 

lead to difficulties when the scatter is calculated between the observations and the predictions. 

The following statistics were computed: 

 Mean bias ∑( ) =

= −

n

i

Pi M i

n 1

1 (6-1)

where: 

n = number of observations 

Pi = observations by the RWP 

Mi = EDAS model “predictions” 

 Standard deviation ( ) ( )( )

2

1

1

∑=

= − − −

n

i

Pi M i Pi M i

n

(6-2)
6-3

 Mean absolute error ∑=

= −

n

i

Pi M i

n 1

1 (6-3)

The standard deviation defined in Equation 6-2 is a root-mean-square error, with the 

effect of the mean bias removed. However, the mean absolute error (MAE) defined in Equation 

6-3 includes the effects of the mean bias. Consequently, it is possible to have a large MAE even 

though the standard deviation is small, simply because there may be a large mean bias. 

Statistics were computed for those height bins containing at least 90% of the total number 

of RWP/EDAS possible data pairs. Sample sizes at each height and each RWP typically ranged 

from about 900 for the eastern sites associated with BAMP, to about 2000 for the western sites, 

which have been in operation for a longer period of time. 

6.1.2 Results 

Figure 6-2 illustrates the wind speed and direction mean bias, mean standard deviation, 

and MAE for the entire data collection period at all sites. In general, wind speeds were 

overestimated by the EDAS model by a slight amount f, with more mean bias at the lower 

heights and with gradual improvement above 1000 m. The coastal land site, FTM, had the 

lowest wind speed mean bias, ranging from –1 to 0 m/s. VRM, BIP, and WDP all had wind 

speed mean biases generally between –2 (near the surface) and –1 m/s (aloft). The far offshore 

sites (SMI and DWP) had the highest wind speed mean biases of –3 (near the surface) to –2 m/s 

(aloft) and –6 (near the surface) to –1 m/s (aloft), respectively. These wind speed mean biases 

suggest that the EDAS model tends to overestimate wind speeds in offshore areas, with the 

difference increasing as distance from shore increases. The standard deviations of wind speed 

difference were 2 to 4 m/s and indicate little variation with altitude, which is somewhat 

surprising as lower standard deviations are expected aloft because the upper-level flow patterns 

are known to vary less than flows near the surface (Seaman, 2000). 

Wind direction mean biases shown in Figure 6-2 were generally between –5° and 10° at 

all sites, with higher wind direction biases observed at heights below 1000 m at DWP (as high 

as 20°). DWP showed more wind direction mean bias near the surface, whereas the remaining 

sites tended to show a consistent mean bias with height. The mostly positive mean biases 

indicate that the EDAS model data had an overall counter-clockwise mean bias in wind 

direction. For example, with a 20° positive mean bias, if the observed mean wind direction were 

180°, then the EDAS-predicted mean wind direction would be 160°. The standard deviations of 

wind direction differences were generally about 25° to 35° and showed little variation with 

height. While the wind direction mean biases at offshore sites were similar to those at the nearshore sites, the standard deviations of the wind direction differences were generally about 40° at 

the offshore sites. These standard deviation values for wind speed and wind directions (2 to 

4 m/s and 20° to 50°) found for the six RWPs in the Gulf of Mexico domain agree well with 

standard deviations reported by Seaman (2000) and Hanna and Yang (2001) for other models 

and other geographic domains. 
6-4

In general, the MAE between the EDAS-predicted and the RWP-observed wind speeds at 

all sites was largest near the surface and increased with increasing distance from the shoreline 

(see Figure 6-2). The coastal site, FTM, had a MAE of 1 to 2 m/s. VRM, BIP, and WDP had 

MAEs of about 2 m/s, excluding the lowest height. SMI was observed to have an MAE of 2 to 

3 m/s, and DWP had an MAE of 2 to 6 m/s, with the largest MAEs near the surface in both 

cases. Because MAE is strongly influenced by the mean bias, the large 6 m/s MAE value at 

DWP near the surface is primarily due to the large mean bias of approximately the same 

magnitude. 

The wind direction MAE is generally constant with height. The wind direction MAE was 

found to be between 15° and 25° at the coastal and near-shore sites and 25° to 35° at the offshore 

sites. 

6.1.3 Conclusions 

Comparisons between RWP-observed wind data and EDAS-modeled wind data over the 

Gulf of Mexico show better agreement at near-shore sites and poorer agreement at offshore sites. 

In general, the EDAS model tended to overstate wind speeds, especially at levels below 1500 m. 

The EDAS model tended to have a positive wind direction mean bias (i.e., if the observed wind 

direction were 180°, the predicted wind direction might be 160°); however, this mean bias was 

usually 10° or less. In considering these comparisons, it should be noted that the EDAS data is 

created by a bilinear interpolation of a fine-scale grid onto a more coarse grid resolution, whereas 

the RWP observations are a volume-averaged measurement in which the measurement 

representativeness can vary with fluctuations in the wind speed.

The results suggest that RWP data might be weighted more heavily than the EDAS model 

data when creating high-resolution wind fields in an area where RWP observations are available. 

In addition, it is suggested that the Eta model may benefit from the use of offshore RWP data at 

the time of initialization. 

6.2 CALMET METEOROLOGICAL MODELING 

The CALMET meteorological model (Scire et al., 1999) is a software tool that combines 

objective and diagnostic analysis methods to create two- and three-dimensional meteorological 

fields. CALMET produces outputs of gridded meteorological fields of three-dimensional winds 

and air temperature; two-dimensional fields of surface friction velocity, convective velocity 

scale, mixing height, Monin-Obukhov length, Pasquill-Gifford-Turner stability class, and 

precipitation rate. CALMET also produces outputs of temperature, air density, short-wave solar 

radiation, and relative humidity defined at surface meteorological stations. CALMET includes a 

diagnostic wind field generator containing objective analysis and parameterized treatments of 

slope flows, kinematic terrain effects, terrain-blocking effects, a divergence minimization 

procedure, and a micro-meteorological model for overland and overwater boundary layers. 

CALMET attempts to resolve mesoscale and local-scale meteorological phenomena by blending 

observational data with synoptic-scale analyses. 
6-5

CALMET utilizes both geophysical and meteorological data inputs in order to derive the 

three-dimensional wind fields and other ABL parameters. The geophysical inputs to the 

CALMET model consisted of 0.9-km surface terrain height and 30-m land-use data. The 

meteorological inputs consisted of surface observations, buoy data, rawinsonde data, RWP wind 

measurements (i.e., wind and Tv profiles), and EDAS wind fields. Because CALMET cannot 

ingest observed mixing heights, RWP-derived mixing heights were not used in the modeling. 

Figure 6-3 illustrates the spatial coverage of the observed meteorological data inputs in the 

CALMET modeling domain used to derive three-dimensional wind fields for the MMS 

Boundary Layer Study. The CALMET wind fields were developed with a 5-km horizontal 

resolution across a modeling domain of 860 km x 560 km (NX=172 and NY=112), which 

includes portions of Texas, Louisiana, Mississippi, Alabama, and Florida (Figure 6-4). The 

vertical structure of the wind and temperature fields has 20 vertical layers with interfaces at: 0, 

20, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2250, 

2500, and 2750 m. This horizontal and vertical resolution was able to capture the timing, 

strength, and vertical structure of the important flow features, especially those important for the 

transport and diffusion of chemical species. 

An approach used in other projects utilized gridded mesoscale model output, such as 

EDAS, as the initial guess wind field instead of a single point value known as the “domain mean 

wind”, which is often used as a default. The use of EDAS has been demonstrated to improve 

model performance over large domains. Therefore, for this project we used Eta and EDAS 

model wind field data, as well as temperature, specific humidity, and cloud data for the threeyear period spanning the MMS Boundary Layer Study. The EDAS is constructed from 

successive 3-hr (eight analyses/day) Eta model forecasts. A bilinear interpolation of Eta model 

output is used to create the EDAS output on the AWIPS-212 grid. The AWIPS-212 grid is based 

upon a Lambert Conformal Conic Projection, which covers the contiguous United States, and 

consists of a horizontal resolution of 40 km (185 x 129) and twenty-six vertical levels (every 25 

mb up to 850 mb; and every 50 mb up to 50 mb) (Figure 6-5). A three-dimensional variational 

analysis (3DVAR) scheme is used in the model to assimilate high frequency observations, such 

as RWP measurements, aircraft winds, satellite-derived winds, land-surface meteorological 

measurements, and oceanic-surface data from ships and buoys. However, RWP measurements 

made during MMS and BAMP were not integrated into the EDAS. The EDAS wind data was 

used as the “domain mean winds” in the CALMET model runs. 

The wind-field model within CALMET is based on the Diagnostic Wind Model (DWM) 

(Douglas et al., 1990). The DWM has been modified within CALMET to allow the possibility 

of incorporation of three-dimensional meteorological fields from the Penn State/NCAR 

Mesoscale Models (MM4/MM5). Figure 6-6 shows the three optional steps (A, B, and C) for 

input of these gridded data within CALMET. The method in CALMET for using gridded data 

was adapted for incorporating the gridded EDAS analyses. At a minimum, CALMET requires 

00Z and 12Z NWS soundings to calculate a domain mean wind for use as the “first guess” field; 

however, the EDAS model output was incorporated into CALMET at Step A (Figure 6-6) in 

order to derive an initial guess field. This is particularly important, as it is difficult to represent a 

mean wind for larger analysis regions. Because the EDAS analysis is rather coarse (40-km grid 

spacing), the DWM slope flow algorithms (Allwine and Whitman, 1985) are used to estimate 

flows in and near complex terrain at a resolution of 1 to 4 km. The EDAS and slope flow 

estimates are then combined to produce the “Step 1” wind fields. This should improve the wind 
6-6

fields near the coastal areas. After the Step 1 wind field was derived, an objective analysis was 

performed on the extensive suite of observations discussed earlier. Before the final wind field 

(Step 2) is created, an objective combination of the Step 1 wind field and the observations was 

carried out. During stable conditions, a stable layer can persist for days at the surface with little 

exchange of mass with the layers above. This condition has been difficult to represent with the 

DWM. Two modifications have been made to the model to address this issue and can be applied 

if the situation warrants: 

• The O’Brien procedure (O’Brien, 1970) within the DWM has been modified to adjust the 

wind fields to minimize vertical velocities at the top of the stable layer instead of at the 

top of the modeling domain. This prevents the unrealistic exchange of mass between the 

stable layer and layers aloft that is a common problem in DWM analyses. 

• The terrain-blocking adjustment scheme in DWM (Allwine and Whitman, 1985) has been 

moved from the Step 1 analysis to the final analysis step, which allows terrain-blocking 

effects to be considered after the introduction of the objective analysis. This re-ordering 

of the scheme prevents extrapolation of observational data into regions of complex terrain 

when it is physically unlikely. However, this is likely to be of little importance in the 

Gulf of Mexico modeling domain. 

A mass-consistent wind field model in a terrain-following coordinate system which takes 

into account the density stratification was developed by Drake and Huang (1980); this wind field 

model was adopted in a mesoscale air quality modeling for complex terrain by Allwine and 

Whitman (1985). 

6.2.1 High Frequency RWP and RASS Measurements and Data Manipulation for Input 

to CALMET 

Upper-Air Files 

In the current release of CALMET, high frequency observations, such as RWP and RASS 

measurements, can be used as inputs but often require considerable data manipulation. This is 

especially true with regard to the upper-air file input to CALMET. The highest CALMET layer 

interface height at 2750 m was always much greater than the highest RASS Tv range gate height 

and occasionally greater than the height of the highest RWP wind range gate. In order for a 

successful CALMET model run, there needs to be an observation of wind speed, wind direction, 

and temperature above the highest CALMET layer interface (2750 m). Therefore, EDAS model 

output, matched according to the closest grid point to a particular station and the height at which 

a particular measurement was void, was used to fill in RWP and RASS data gaps in horizontal 

space and in the vertical to allow for successful CALMET runs. 

As discussed above, at a minimum, CALMET requires in horizontal and vertical space 

that the upper-air file for each upper-air station contain a vertical profile of winds and 

temperature collected every twelve hours. Occasionally, NWS soundings and RWP/RASS 

measurements were missing for periods exceeding twelve hours. In this situation, EDAS model 

output was used to fill in the missing time periods and provide the vertical wind and temperature 

profiles needed by CALMET to derive three-dimensional wind fields and other ABL parameters. 
6-7

However, when RWP wind observations and EDAS wind simulations are compared 

(Section 6.1), significant biases and scatter occur that could lead to discontinuities in the 

observed RWP wind profiles which have been “filled in” with EDAS predictions. If the time 

periods of the missing upper-air measurements were less than twelve hours, a linear interpolation 

scheme was used within CALMET. 

CALMET also requires a measurement of pressure, winds, and temperature below the 

lowest CALMET vertical layer (10 m) each hour. Because RWP/RASS observing platforms are 

not capable of obtaining measurements at heights less than 50 to 100 m, collocated surface 

temperature and wind measurements are required. Since CALMET upper-air files rely on 

measurements from two different observing systems (RWP/RASS and a collocated surface 

instrument), the probability of missing data from one of the systems is increased. Therefore, 

time gaps less than twelve hours in surface meteorological measurements were subjected to a 

sliding ±6-hr window in order to obtain the next closest measurement in time. The sliding ±6-hr 

window is an attempt to obtain a reasonable and representative surface measurement that 

completes the vertical profiles in CALMET’s upper-air files. For time gaps greater than twelve 

hours, the first gate (lowest elevation) of the RWP/RASS measurements was used for the surface 

observation, instead of the sliding ±6-hr window applied to the surface observation, along with a 

standard atmospheric pressure value. 

Because of CALMET’s limited flexibility in handling missing data in upper-air files, this 

complex method of accounting for missing data was undertaken. For future modeling, an 

alternative procedure within CALMET should be developed to handle missing upper-air 

measurements. Data from an upper-air station that has only one 12-hr time gap may still be 

usable in a CALMET model run. 

Surface Meteorological and Over-Water Files 

Compared to the scheme used by CALMET to process upper-air files, the scheme used 

by CALMET to manage time gaps greater than twelve hours in high frequency surface 

meteorological and in over-water measurements is much more efficient. A spatial interpolation 

using the non-missing observations is performed to account for missing surface data. 

Some important CALMET model settings used to derive the three-dimensional wind 

fields and other ABL parameters are listed below: 

• Sea-surface temperature was inut for buoy, C-MAN, and platform sites only. No 

satellite-derived sea temperature data were used. 

• Extrapolation of surface winds into the upper levels was not allowed because surface 

observations can be influenced by local terrain and other siting issues and we did not 

want to extrapolate the surface winds aloft where they would then be used to represent 

more regional-scale flows. 

• The maximum radius of influence over land in the surface layer was 20 km. 

• The maximum radius of influence over land in the aloft layers was 150 km. 

• The maximum radius of influence over water was 50 km 
6-8

The three threshold levels used to characterize the radius of influence of the observations were 

based on initial experiments designed to minimize the radius of influence, yet retain the ability to 

interpolate to every grid cell in the CALMET modeling domain. Maintaining the smaller-scale 

flows in the surface analysis fields was the goal. Utilizing too large a radius of influence can 

result in the elimination of mesoscale features. 

• Equal weighting of the “initial guess” field (EDAS) and observations in the surface layer 

occurs at 40 km from the observation. 

• Equal weighting of the “initial guess” field (EDAS) and observations in the aloft layers 

occurs at 150 km from the observation. 

These two settings were based on experiments. For the surface, allowing observations to 

dominate the analysis out to about two times the radius of influence enables a blending of 

objective analysis and EDAS fields. 

• One smoothing pass below 400 m and two smoothing passes elsewhere were utilized. 

This limited smoothing was performed to reduce any artifacts in the analysis fields due to 

variations in density and distribution of observations, while not to eliminate important 

mesoscale features, particularly in the boundary layer where the greatest variations are 

expected. 

6.3 CALPUFF DISPERSION MODELING 

CALPUFF is a multi-layer, multi-species, non-steady-state puff dispersion model that can 

simulate the effects of time- and space-varying meteorological conditions on pollutant transport, 

transformation, and removal. CALPUFF contains algorithms for near-source effects such as 

building downwash, transitional plume rise, partial plume penetration, subgrid scale terrain 

interactions as well as longer-range effects such as pollutant removal (wet scavenging and dry 

deposition), chemical transformation, vertical wind shear, over-water transport, and coastal 

interaction effects. It can accommodate arbitrarily varying point source and gridded area source 

emissions. Most of the algorithms contain options to treat the physical processes at different 

levels of detail depending on the model application. 

The CALPUFF dispersion model utilizes geophysical gridded data as well as the threedimensional diagnostic gridded wind fields and other ABL parameters (Section 6.1) that are 

output from the CALMET model. CALPUFF was applied with an arbitrary hypothetical 

emission rate from three platform sites in the Gulf of Mexico (SMI, DWP, BIP); the locations of 

the three platforms are shown in Figure 6-7. The goal of the CALPUFF simulations was to 

characterize, in a preliminary manner, the potential impact of offshore emission sources on 

coastal areas along the Gulf of Mexico. The CALPUFF simulations were intended to predict 

relative rather than absolute concentrations. The resulting patterns and extent of transport, and 

the diffusion of the plume, were compared for the three release locations, and for the days within 

case study periods, and for days under different synoptic regimes. 

The following source characteristics were assumed: 

• The stack heights above the platforms were set to 10 m. 
6-9

• The stack diameter was set to 10 m for each platform. 

• The exit velocity was assumed to equal 0.005 m/s. 

• The exit temperature was based on the ambient temperature measured at each platform 

site. 

• A continuous emission rate of 2000 g/sec was used at all platform locations. 

The results from the dispersion model are discussed in Section 6.5. 

6.4 TRANSPORT ANALYSIS 

The transport analysis was carried out by computing forward trajectories calculated over 

a duration of 24 hours and originating at heights of 10 m, 75 m, and 350 m from the SMI, DWP, 

and BIP platforms (see Figure 6-7 for the locations of the platforms). The goal of the transport 

analysis was to characterize the influence of the large-scale and local-scale meteorology on 

transport from the potential emission sources and analyze the potential impact of this transport 

on coastal regions. The forward trajectories were computed using the derived wind fields output 

from the CALMET meteorological model as input into an STI in-house trajectory model 

(TRAJMOD), and also using EDAS model output as input into the HYbrid Single-Particle 

Lagrangian Integrated Trajectory (HYSPLIT) model. The results from the transport analysis are 

discussed in Section 6.5. 

6.5 CASE STUDIES 

To assess the impact of offshore emissions on onshore areas along the Gulf Coast, threedimensional gridded wind fields and other ABL parameters (i.e., mixing heights) were calculated 

using the CALMET diagnostic meteorological model for seven case studies. The case studies 

were chosen to represent the variety of weather patterns that influence regional meteorological 

conditions, which have a direct impact on the transport and dispersion characteristics of 

pollutants in the western and central Gulf of Mexico. The boundary layer characteristics (i.e., 

heat flux, friction velocity, etc.) were also analyzed for these particular case studies and the 

results are presented in Section 5. 

The three-dimensional wind fields created by CALMET are a combination of 

observations and gridded EDAS output. Trajectories were calculated using the gridded wind 

fields generated by CALMET and were compared to trajectories calculated by the HYSPLIT 

model, which utilized EDAS output. It should be noted that the CALMET modeling domain was 

limited so the entire 24-hr forward trajectory may not have been completely calculated. 

Dispersion runs were calculated using the CALPUFF air quality model, which utilized the threedimensional diagnostic gridded fields output by CALMET. The dispersion plots that follow 

show the accumulation of material from the start of each case study to the time indicated on the 

plot. Accurate mixing heights are a critical parameter in transport and dispersion modeling. One 

important note regarding the scheme that the CALMET model utilizes to derive over-water 

mixing heights is that mixing height growth is entirely driven by mechanical mixing, negating 

any growth due to convective processes (buoyancy). This resulted in the underestimation of 
6-10

daytime mixing heights by CALMET when compared to mixing heights derived from RWP 

measurements. Therefore, the stand-alone dispersion results presented in each of the following 

case studies may be inaccurate; however, a comparison of the relative dispersion patterns and 

characteristics between episode types is still useful. 

6.5.1 July 30–August 1, 1999: Summer Period with Strong Upper-Level Ridge and 

Surface High Causing Weak Winds 

Overview: This case study period was chosen because it is typical of summer light wind 

conditions. The region was dominated by a large upper-level ridge of high pressure and a 

surface area of high pressure throughout July 30–August 1, 1999. Winds across the region 

lacked a significant onshore component because a surface area of high pressure was centered 

directly south of Louisiana. As a result, the hypothetical tracer emissions from the platforms did 

not have a major influence along the Gulf coast. The only exception was a brief period on July 

31, when tracers emitted from the SMI platform would have been transported toward the 

Mississippi River Delta. 

Large-Scale Aloft (500 mb): A large upper-level area of high pressure was in place across the 

Gulf of Mexico throughout the entire case study period. 

Large-Scale Surface: A large surface area of high pressure was located in the central Gulf of 

Mexico throughout the case study period. General flow across the Gulf of Mexico consisted of 

light southerly/southwesterly flow across the western regions of the Gulf and light westnorthwesterly flow along the Gulf Coast of Louisiana, Mississippi, and Alabama on July 30. As 

time progressed, the center of the area of high pressure moved closer to the modeling domain 

and winds became lighter and more variable. 

Modeled 24-hr Forward Trajectories: Trajectories calculated from both the CALMET wind 

fields (using TRAJMOD) and EDAS wind fields (using HYSPLIT) during the period, 0000 CST 

on July 30 through 0800 CST on August 1, 1999, were predominantly from a westerly direction. 

This flow direction observed near the platforms was caused by the anticyclonic circulation 

around an area of high pressure centered in the central Gulf of Mexico (Figures 6-8 through 

6-13). As time progressed, the trajectories began to shift more out of the northwest. 

Consequently, the trajectories and the associated tracer plumes had little if any interaction with 

areas along the Gulf Coast. The CALMET and EDAS trajectories were quite similar. 

Modeled Dispersion: On July 30, the westerly flow influencing the DWP and BIP platforms 

caused the hypothetical emissions to be transported eastward over open water where they had no 

impact on onshore areas (Figure 6-14). The simulated plume from the SMI platform contained 

more of a southerly component, which allowed a very minimal amount of the hypothetical 

emissions to impact areas along the immediate Louisiana coastline. As the center of the area of 

high pressure moved northward on July 31, the associated winds across the Gulf lightened 

considerably, which in turn produced less dilution of the plumes and also produced lower mixing 

heights derived by CALMET. Consequently, the hypothetical emissions slowly accumulated 

near the platforms. Winds near SMI on July 31 contained a slight onshore component, which 

caused hypothetical emissions to impact areas of the Mississippi River Delta in Louisiana 
6-11

(Figure 6-15). BIP and DWP experienced west-northwesterly flow on July 31, which kept 

hypothetical emissions from having an immediate impact along the Gulf Coast (Figure 6-15). 

On August 1, light and variable winds and low mixing heights across the Gulf of Mexico 

allowed the tracer to accumulate around all platform sites (Figure 6-16). However, with no 

onshore wind component the enhanced hypothetical emissions had no impact along the Gulf 

Coast. The CALPUFF dispersion results should be compared only in a relative sense, since the 

same emissions were released from all platforms at all times. It was concluded earlier that, 

because the CALMET-estimated mixing heights do not account for convection and are much too 

low over water, actual concentrations would be about a factor of three or four lower if correct 

mixing heights were used (i.e., the current estimated mixing heights are 100 m to 200 m, whereas 

the actual mixing heights are known to be 500 m to 600 m). 

A comparison of the dispersion contours in this case study with the contours from the 

January 20-24 case study, when winds were much higher, provides insight as to how transport 

and dispersion are influenced by the different meteorological conditions. The maximum relative 

concentrations are higher by a factor of four or five in the light-wind summer period. 

6.5.2 January 20-25, 2000: Winter Case Study with Shift in Wind Direction 

Overview: This case study period was characterized by post-frontal strong offshore flow on 

January 20 and 21, followed by strong onshore flow on January 22 and 23, and strong offshore 

flow again on January 24 and 25 after a frontal passage late on January 23. The two periods with 

strong offshore winds were marked by cold air temperatures and very large skin-air temperature 

differences, resulting in very large sensible and latent heat fluxes from the water surface. In 

contrast, the onshore flow was marked by more stable conditions. The strong winds resulted in 

persistent narrow calculated plumes with relatively low concentrations for the hypothetical tracer 

releases from the three platforms. 

Large-Scale Aloft (500 mb): Northwesterly flow aloft across the Gulf region on January 20 

and 21 was the result of a large upper-level area of low pressure centered in Ontario, Canada, 

whose influence extended south through the eastern half of the United States. An upper-level 

ridge extended throughout the Mountain West. On January 22, zonal flow was evident over the 

United States, as the result of the upper-level ridge over the Mountain West breaking down and 

the upper-level trough pushing off the eastern seaboard. However, on January 22, a shortwave 

trough was analyzed over the eastern Gulf of Mexico, while a shortwave ridge strengthened in 

the western Gulf of Mexico. By January 23 an upper-level trough began to strengthen across the 

eastern two-thirds of the United States. The trough remained in place over the Gulf of Mexico 

on January 24 before beginning to exit on January 25. 

Large-Scale Surface: On January 20, strong offshore, northerly flow was associated with a 

strong pressure gradient located between an area of high pressure moving through the Plains, 

centered in Kansas, and a low pressure area located over the eastern seaboard. As the area of 

high pressure moved toward the east, the flow over the Gulf of Mexico rotated from northerly-tonortheasterly-to-easterly on January 21. On that day, the Gulf region was located on the 

southern edge of the surface high, now centered in Tennessee. Strong southerly flow developed 

on January 22, and was associated with cyclonic circulation around an approaching surface low 
6-12

moving across the Central Plains. Southwesterly flow continued across the Gulf of Mexico on 

January 23 as the surface low pressure area became centered in Alabama, with an associated 

stationary front analyzed along the Gulf Coast. However, a surface high was building into the 

region from the Central Plains, behind the departing area of low pressure and its stationary 

frontal boundary. The anticyclonic flow around the approaching high pressure area drove strong 

northerly flow across the Gulf of Mexico from January 24-25. 

Modeled 24-hr Forward Trajectories: As noted, the period, 0000 CST on January 20 through 

0000 CST on January 25, 2000, consisted of offshore transport, followed by onshore transport, 

and ending with a period of strong offshore transport, which is depicted by trajectories calculated 

from both the CALMET wind fields (using TRAJMOD) and EDAS wind fields (using 

HYSPLIT). TRAJMOD-derived trajectories (including the RWP observations) and HYSPLITderived trajectories (utilizing EDAS wind fields and no Gulf of Mexico RWP observations) were 

calculated at 10 m, 75 m, and 350 m originating from the SMI, DWP, and BIP platforms and are 

shown in Figures 6-17 through 6-22 for the period from 0000 CST on January 19 through 

1600 CST on January 22. The trajectories between January 20 and early on January 21 of the 

analysis period are shown originating at the platform sites and moving out into the Gulf of 

Mexico due to the northerly wind component. Figures 6-17 through 6-22 also show onshore 

transport beginning later on January 21 and continuing through the afternoon hours on January 

23, with the trajectories from the latter part of the period shown in Figures 6-23 through 6-28. 

The onshore flow occurred at all heights, as a result of cyclonic circulation around the surface 

area of low pressure moving across the Central Plains. Because of the surface area of high 

pressure that built into the region on January 24 and 25, trajectories regained a strong, offshore 

northerly component at all heights (see Figures 6-23 through 6-28). Generally the same general 

time variations were seen at all heights (10 m, 75 m, and 350 m). However, as expected, winds 

and transport distances increased with height. Both the TRAJMOD- and HYSPLIT-calculated 

trajectories agree for the most part throughout the case study period. The HYSPLIT trajectories 

seem to indicate faster speeds, as found earlier when RWP winds (used to create CALMET wind 

fields for TRAJMOD) were compared with EDAS winds (used in HYSPLIT). Note, however, 

that because the TRAJMOD trajectories often truncated due to the limited CALMET modeling 

domain and the HYSPLIT trajectories had no such boundary limit, the lengths of the trajectories 

should not be compared for those cases. 

Modeled Dispersion: The strong northerly flow on January 20 (Figure 6-29) transported the 

hypothetical tracer emissions from the platforms over open waters of the Gulf of Mexico, 

causing no onshore impact. The strong winds contributed to the increased dilution of the 

hypothetical tracer, resulting in relatively low hypothetical concentrations. The estimated mixing 

heights were slightly higher on this day due to the higher wind speed (Figure 6-30). However, if 

the model had properly accounted for the influence of convection on the mixing height, the 

mixing heights would have been larger and more realistic, since the large water-air temperature 

differences led to extremely large heat fluxes. On January 21, the strong east-northeasterly flow 

(Figure 6-31) caused the hypothetical plume released from BIP to pass over Breton Island, while 

hypothetical emissions from SMI and DWP caused no onshore impact because they were 

transported out over open water (Figure 6-31). Figure 6-32 shows that the estimated mixing 

heights remained relatively low at about 200 m or less over water, which is likely to be a large 

underestimate. On January 22 (Figure 6-33) strong southerly flow from all platform locations 

allowed the hypothetical emissions to impact onshore locations to a certain degree, although 
6-13

relative concentrations were low because of the dilution effects of the strong winds. The mixing 

heights on January 22 are shown in Figure 6-34, which illustrates patterns similar to the other 

days. Southwesterly flow ahead of the frontal passage on January 23 is evident in Figure 6-35; 

onshore locations in Louisiana were directly influenced by tracers emitted at the SMI platform 

and onshore locations in Alabama were directly influenced by tracers emitted from BIP. The 

hypothetical concentrations on January 23 were higher than on January 22 due to lighter winds 

and lower mixing heights (Figure 6-36), which decreased dilution and mixing of pollutants. 

Strong northerly flow behind the cold front late on January 23 resulted in the transport of 

hypothetical emissions released at the platforms on January 24 (Figure 6-37) and January 25 

(Figure 6-38) away from the shore, with relatively low concentrations due to the strong dilution. 

The strong winds increased CALMET’s estimated mixing heights to about 400 m or 500 m in the 

area surrounding the RWP sites, as shown in Figures 6-39 and 6-40; but at distances beyond 

about 50 km from the RWP sites, the mixing heights dropped down to the usual unrealistically 

low values of 100 m or 200 m over the water. The observed mixing heights are likely to be 

much greater at these times, due to the extremely strong convective heat fluxes over water. 

6.5.3 January 4-6, 2001: Winter Period Post Upper-level Trough Transitioning into 

Weak Upper-level Ridge 

Overview: A strong surface pressure gradient existed across the Gulf of Mexico on January 4, 

which drove moderate northwesterly flow and kept hypothetical emissions from impacting 

onshore areas. Transitioning from January 4 to January 5, the pressure gradient gradually 

weakened and allowed a brief period of west-southwesterly surface flow, which caused 

hypothetical emissions calculated by CALPUFF to impact areas along the immediate coastline. 

Later on January 5 and into January 6, winds were moderate from a west-northwest direction and 

hypothetical emissions were simulated to remain offshore. 

Large-Scale Aloft (500 mb): An upper-level trough had passed through the region and was 

located along the eastern seaboard on the January 4. By January 5 an upper-level ridge building 

in the west and the eastward movement of the upper-level area of low pressure began to produce 

nearly zonal flow across the Gulf of Mexico in the upper levels for January 5 and 6. 

Large-Scale Surface: Moderate northwesterly flow across the Gulf of Mexico occurred on 

January 4 due to the strong pressure gradients between a high pressure system to the west and a 

low pressure system on the east coast. Late on January 4 and early on January 5, the pressure 

gradient began to weaken. A surface anticyclone developed just to the north of the Bay of 

Campeche, west of the Yucatan Peninsula, and began to influence flow across the Gulf. 

Westerly winds, with a brief period of west-southwesterly winds across the modeling domain on 

January 5, were the result of the anticyclonic circulation around the area of high pressure to the 

south. By January 6, the winds shifted more to the northwest and weakened. During the entire 

case study period, the winds were much stronger over the Gulf of Mexico than over the adjacent 

land areas. 

Modeled 24-hr Forward Trajectories: Trajectories calculated from both the CALMET wind 

fields (using TRAJMOD) and EDAS wind fields (using HYSPLIT) during the period, 0000 CST 

on January 4 through 0000 CST on January 6, 2001, generally were westerly and contained an 
6-14

offshore component. Initially on January 4 the trajectories indicate northwesterly flow, which 

transitioned midday to westerly on January 4 into January 5, before returning to northwesterly on 

January 6 (Figures 6-41 through 6-46). The trajectories were consistent with the large-scale 

meteorology discussed above. Both the TRAJMOD- and HYSPLIT-calculated trajectories were 

similar throughout the period. However, comparisons of the more distant portions of the 

TRAJMOD trajectories with HYSPLIT trajectories are not possible because the TRAJMOD 

trajectories truncate when they reach the boundary of the CALMET modeling domain. 

Modeled Dispersion: As seen in Figure 6-47, the northwesterly flow that persisted throughout 

January 4 caused the hypothetical emissions being released from the designated offshore source 

platforms to be transported southward, away from the Gulf Coast toward the southern part of the 

Gulf of Mexico. As the general flow rotated from northwesterly to west-southwesterly in the 

early morning of January 5 (Figure 6-48), the southern tip of the Mississippi River Delta was 

influenced by some of the hypothetical emissions from the SMI platform and the Alabama 

coastline was influenced by hypothetical emissions from BIP. As westerly flow strengthened 

throughout January 5 (Figure 6-49), most of the hypothetical emissions were transported 

eastward, causing little influence on the Gulf Coast. As seen in Figure 6-50, the light westnorthwesterly flow on January 6, transported hypothetical emissions from the platforms away 

from the Gulf Coast and into the southern part of the Gulf of Mexico. 

6.5.4 January 29, 2001: Winter Case with Strong Southerly Winds 

Overview: January 29, 2001, was characterized by strong southerly winds ahead of an 

approaching frontal boundary. Despite the fact that the simulated tracer plumes were transported 

directly toward coastal areas, relative concentrations were not predicted by CALPUFF to be 

large because of the strong dilution. 

Large-Scale Aloft (500 mb): Prior to January 29, the Gulf of Mexico was under the influence 

of a large upper-level area of high pressure. A strengthening upper-level area of low pressure 

moving out of the West toward the Central Plains aided in breaking down the upper-level ridge 

over the Gulf of Mexico. By January 30, the upper-level ridge influencing the Gulf region was 

eventually replaced by an upper-level trough. 

Large-Scale Surface: On January 28, a large area of high pressure covered the entire eastern 

third of the United States. A developing surface area of low pressure moved into the Central 

Plains on January 29, with an associated frontal boundary extending into the northwestern 

section of the Gulf of Mexico. Because the study region was located between the surface area of 

high pressure centered along the eastern seaboard and the approaching surface low, a strong 

pressure gradient existed that produced strong southerly flow across the entire Gulf of Mexico on 

January 29. 

Modeled 24-hr Forward Trajectories: As seen in Figures 6-51 through 6-56, the period, 

0000 CST on January 27 through 0000 CST on January 30, 2001, generally was characterized by 

strong onshore trajectories from the south at 10 m, 75 m, and 350 m across the Gulf of Mexico at 

all three platform sites. Some of the 24-hr HYSPLIT trajectories passed completely across the 

United States and entered Canada, reflecting an average wind speed of 30 m/s. Toward the end 
6-15

of the case study period, the influence of the approaching frontal passage on the trajectories was 

beginning to be observed, as the trajectories began to take on more of a westerly component. 

The strong, onshore trajectories were consistent with the large-scale synoptic patterns discussed 

above. The trajectories calculated from both the CALMET winds fields (using TRAJMOD) and 

EDAS wind fields (using HYSPLIT) were similar in transport direction and agreed in transport 

distance over the first few hours, but comparisons were not possible for times after the 

TRAJMOD-calculated trajectories truncated at the arbitrary boundaries. 

Modeled Dispersion: Figure 6-57 shows CALPUFF-estimated plume contours for hypothetical 

tracer releases from the SMI, DWP, and BIP platforms. The plumes generally were transported 

by the strong southerly winds toward the coast, although concentrations were relatively low 

because of the large dilution by the strong wind. The CALMET wind interpolation procedure 

can be seen in the area around DWP because the DWP RWP was recording more westsouthwesterly winds in the midst of generally southerly winds. CALMET causes the observed 

west-southwesterly wind direction to strongly influence grids out to about 50 km from the 

platform. Outside 50 km to 100 km, the winds do not deviate much from the southerly direction. 

6.5.5 April 14-15, 2001: Onshore Wind Case Study 

Overview: The April 15, 2001, case study was selected because the wind was onshore during 

the period. The moderate surface winds caused the hypothetical tracers emitted from the 

offshore platforms to be transported directly toward shore with relatively small lateral spreading. 

As a result, the impact on onshore areas was confined to small areas. 

Large-Scale Aloft (500 mb): The Gulf region was under a broad, weak upper-level ridge of 

high pressure on April 14, which gave way to zonal flow across the Gulf Coast on April 15. 

Large-Scale Surface: A nearly-stationary frontal boundary extended from northern Texas to 

southern Georgia, with a weak area of low pressure developing in Texas on April 14 and 15. An 

area of high pressure was also centered off of the western coast of Florida. Moderate 

southerly/southwesterly winds on the April 14 and 15 were associated with the pressure 

gradients between this area of high pressure and the lower pressure to the west. 

Modeled 24-hr Forward Trajectories: The period, 0000 CST on April 13 through 0000 CST 

on April 15, 2001, was dominated by southerly winds and consequently onshore transport from 

all platforms in the Gulf of Mexico as depicted by trajectories calculated from both the 

CALMET wind fields (using TRAJMOD) and EDAS wind fields (using HYSPLIT). At later 

times, the onshore transport weakened and changed to nearly calm and then northerly and 

easterly transport. As noted above, the onshore transport was caused by the anticyclonic 

circulation of air around the high pressure centered off the western coast of Florida. Southerly 

transport from each platform is seen at the 10-m level during the onshore transport period 

(Figures 6-58 and 6-59). At 75 m, the onshore transport period indicated consistent southerly 

transport from the SMI platform, but a more southwesterly component from the BIP and DWP 

platforms (Figure 6-60 and 6-61). At 350 m, the onshore transport period was dominated by 

southwesterly flow at all the sites (Figure 6-62 and 6-63). There was fair agreement (i.e., 

usually the directions agreed within about 20 or 30 degrees) between the TRAJMOD- and 
6-16

HYSPLIT-derived trajectories at the 10-m, 75-m, and 350-m levels. However, the HYSPLIT 

trajectories suggest faster speeds than the TRAJMOD trajectories, consistent with the findings in 

Section 6.1 that the EDAS model wind speeds (used for HYSPLIT) are a few m/s higher than the 

RWP wind speeds (used by CALMET and TRAJMOD), with the difference increasing as 

distance from shore increases. 

Modeled CALPUFF Dispersion: The moderate southerly/southwesterly onshore flow on 

April 14 caused the hypothetical emissions released from the SMI and BIP platforms to impact 

onshore coastal areas (Figure 6-64). Emissions from DWP do not impact the coastline in the 

domain shown on the figure. The estimated concentrations were higher in the DWP plume than 

in the SMI or BIP plumes (Figure 6-64), probably due to lower mixing heights simulated by 

CALMET at DWP (Figure 6-65). On April 15, the continued south/southwesterly flow near the 

platforms caused the hypothetical emissions released from SMI and BIP to impact onshore 

coastal areas, while emissions from DWP remained well offshore (Figure 6-66). The 

concentrations in the simulated plumes from SMI and DWP were higher than in the plume from 

BIP, probably due to lower wind speeds and lower mixing heights (Figure 6-67). The mixing 

heights, zi, shown over water in Figures 6-65 and 6-67 are only 100 m or 200 m, which are much 

lower than the observed values of 500 m or 600 m. The discrepancy is due to the fact that 

CALPUFF uses only the mixing height formula for neutral conditions, where zi is proportional to 

wind speed, and unrealistically ignores the contributions of convection over the water. 

6.5.6 May 14-15, 2001: Spring Case Study with Light Winds and Regional High Ozone 

Overview: This case study period was chosen because it featured high observed concentrations 

of ozone across the coastal region. As is typical of high ozone scenarios, the period was 

characterized by a surface high pressure area and light and variable winds. The hypothetical 

tracers released from the platforms as a test of CALPUFF tended to be transported very slowly 

and remain within 50 km to 100 km of the platforms during a 24-hr period. As a result the 

concentrations were relatively high but remained offshore for the most part. The estimated 

plume from BIP showed some coastal impact on both days, while the SMI plume impacted the 

areas across the Mississippi River Delta on May 15. 

Large-Scale Aloft (500 mb): The large-scale synoptic pattern for May 14-15 was dominated by 

an upper-level ridge of high pressure. On May 14 the ridge was in place across the Central 

Plains with the ridge axis extending into Texas. By May 15 the upper-level ridge of high 

pressure began to weaken and move into the midwestern United States with the ridge axis 

extending into Louisiana. 

Large-Scale Surface: The light northeasterly/east-northeasterly surface winds across the Gulf 

of Mexico on May 14 were associated with a large area of high pressure that encompassed the 

entire east coast with the center located over eastern Kentucky and Tennessee. By May 15, the 

region was still under the influence of the large, weak area of high pressure, which was now 

centered over the southeastern United States. Wind speeds were weak at the beginning of the 

period and weakened even more by May 15. However, a small anticyclonic circulation centered 

south of the Louisiana/Texas border caused weak westerly flow for most of May 15. 
6-17

Modeled 24-hr Forward Trajectories: As seen in Figures 6-68 through 6-73, the trajectories 

calculated from both the CALMET wind fields (using TRAJMOD) and EDAS wind fields (using 

HYSPLIT) for the analysis period, May 14 at 0000 CST through 1600 CST on May 15, 2001, 

indicated light and variable flow as a result of the large area of high pressure in place across the 

Gulf of Mexico. During the period, flow was first from the northeast quadrant, then became 

variable, and finally was from the west quadrant; the flow was weak at all times. However, very 

weak winds were present during the middle of the period. As a result of the weak winds, the 

calculated 24-hr trajectories remained in the Louisiana coastal area. The TRAJMOD- and 

HYSPLIT-derived trajectories are in fair agreement, although, as seen in all the case studies and 

described in Section 6.1, the speeds of the HYSPLIT trajectories are as much as a factor of two 

larger than those calculated by TRAJMOD using the CALMET wind fields because CALMET 

assimilates the RWP observations. On average, the RWP speeds are less than the EDAS speeds 

(used in HYSPLIT), with the difference increasing as distance from the shore increases. 

CALPUFF Modeled Dispersion: Light and variable winds (Figure 6-74), combined with low 

mixing depths (Figure 6-75) contributed to the accumulation of hypothetical emissions near each 

source platform on May 14 (Figure 6-74). A period of light winds from the northeast near BIP 

caused hypothetical emissions to impact coastal regions of the Mississippi River Delta 

(Figure 6-74). In fact, the dense part of the plume is very close to New Orleans. On May 15, the 

flow remained very light with a slight onshore component due to the development of the small 

anticyclonic circulation south of the Louisiana/Texas border. The combination of light winds 

(Figure 6-76) and low mixing heights (Figure 6-77) again on May 15, along with minimal 

dispersion of hypothetical emissions from the previous day, caused plumes containing high 

concentrations of the hypothetical tracer to cover large areas and eventually impact coastal areas 

of Louisiana and Alabama (Figure 6-76). In particular, the estimated path of the plume from BIP 

could result in impact of relatively high concentrations on the Alabama coastal area. These 

results suggest that, during light and variable wind conditions, plumes from the three platforms 

would have high concentrations but would usually remain offshore. However, in a few 

instances, it is possible that a persistent on-shore light wind for a few hours could cause 

relatively high impact on a coastline or on an offshore island, although the underestimate of 

mixing heights in CALMET produces higher relative pollutant concentrations than it should. 

6.5.7 September 18-20, 2001: Nearly Stationary Front Along the Gulf Coast 

Overview: Moderate south-southeasterly flow occurred in the Gulf of Mexico along the 

Louisiana coast region on September 18, associated with a surface high located along the eastern 

seaboard, and an approaching surface low. Consequently, hypothetical emissions released at 

offshore locations impacted onshore areas on September 18. Later on September 19 and 20, a 

stationary front developed over the coast and winds became light and variable, but with generally 

an east to northeast drift. Consequently, the hypothetical tracer emissions were transported to the 

northeast toward shore on September 19, but remained mostly offshore on September 20. 

Concentrations were relatively high in the plumes on September 19 and 20 because of the light 

winds. High concentrations were also due to the unrealistically low overwater mixing heights 

estimated by CALMET, as discussed in previous case studies. 
6-18

Large-Scale Aloft (500 mb): The aloft pattern for this case study period was characterized by a 

weak upper-level trough that moved out of the Rockies, across the Central Plains, and toward the 

eastern seaboard. At the same time, an upper-level area of high pressure developed over 

Mexico/western Gulf of Mexico and gradually began to influence the region throughout the case 

study period. 

Large-Scale Surface: The entire east coast was under the influence of a large area of high 

pressure, while a surface area of low pressure began to develop over the Central Plains. Southsoutheasterly flow across the region on September 18 was associated with the pressure gradient 

between the surface high that was centered in Georgia and the surface low pressure over the 

Central Plains. The area of low pressure began to move northeastward away from the Gulf 

region on September 19, and the associated frontal boundary pushed closer to the region. By 

September 20, the frontal boundary nearly stagnated along the Louisiana and Mississippi 

coastline and an area of high pressure moved in behind the frontal boundary. This caused weak 

and variable surface flow as the front boundary slowly passed to the south. 

Modeled 24-hr Forward Trajectories: As seen in Figures 6-78 through 6-83, the trajectories 

calculated from both the CALMET wind fields (using TRAJMOD) and the EDAS wind fields 

(using HYSPLIT) for the analysis period, 0000 CST on September 18 through 1600 CST on 

September 20, 2001, were consistent with the large-scale meteorological patterns influencing the 

Gulf of Mexico as discussed above. The trajectories at all sites and heights on September 18 

indicate onshore transport (due to the moderate southeast winds) originating at the platforms and 

moving toward the Gulf Coast. As the frontal boundary approached the region on September 19 

and the pressure gradients and winds weakened, the trajectories still had a slight onshore 

component as the winds became southwesterly (Figures 6-78 through 6-83). As the nearly 

stationary front slowly moved to the south, weak northerly winds occurred on September 20. 

The general flow directions and transport speeds for the TRAJMOD- and HYSPLIT-derived 

trajectories were quite similar, although the TRAJMOD-derived trajectory speeds were slightly 

less than the HYSPLIT-derived trajectory speeds for offshore locations, as discussed in Section 

6.1. 

CALPUFF Modeled Dispersion: The moderate south-southeasterly flow that was present on 

September 18 allowed the hypothetical emissions released from all three platforms (BIP, DWP, 

SMI) to impact onshore areas (Figure 6-84). On that day, the hypothetical tracer emissions from 

SMI and DWP affected coastal areas of Louisiana, while those emitted from BIP affected 

Mississippi. The light southerly and southwesterly flow ahead of the approaching weak frontal 

boundary on September 19 also caused hypothetical emissions from offshore platforms to impact 

onshore coastal areas (Figure 6-85). The emissions from BIP and DWP reached the Mississippi 

coastline on September 19, while lighter winds near SMI contributed to a broader plume with 

higher concentrations which influenced parts of Louisiana (Figure 6-85). As the flow on 

September 20 adopted more of a westerly component before giving way to flow with more of a 

northerly component later in the day as a result of the passage of the weak front boundary, the 

hypothetical emissions were transported offshore for the most part, with little influence on 

onshore areas (Figure 6-86). Again, light wind speeds allowed the accumulation of emissions 

near the platforms, which resulted in broad plumes being calculated by CALPUFF out over the 

open waters of the Gulf of Mexico. 
6-19

6.6 CONCLUSIONS 

This section summarizes the results discussed in Section 6. Sections 6.1 to 6.3 

summarized the comparisons of RWP and EDAS winds and the procedures for running 

CALMET and CALPUFF. Subsequent sections summarized the results of the seven case 

studies: 

1. The EDAS-simulated wind fields and the observed RWP winds from six sites were 

compared. EDAS is based on a combination of Eta model forecast winds and diagnostic 

interpolations of observed winds but does not include RWP data. The comparison is 

complicated because the EDAS simulations represent averages over a grid volume of size 

about 40 km by 40 km by 100 m whereas the RWP observations represent an average 

over a much smaller grid volume with a radius about 5 m; consequently, more turbulent 

variations are expected in the observations than in the EDAS simulations. The mean 

wind speed (WS) bias was near zero close to the shore but increased with offshore 

distance, such that the EDAS mean WS exceeded the RWP mean wind speed by 1 to 

2 m/s at 50 km offshore and by 2 to 6 m/s at 100 to 200 km offshore. Mean wind 

direction (WD) bias was relatively small, with about a 10° to 20° difference (e.g., if the 

RWP WD was 180°, then the EDAS WD would be 160°). Standard deviations of the 

differences (with mean bias removed) were 1 to 2 m/s for WS and 20 to 40° for WD, in 

agreement with findings for other domains and models (Hanna and Yang, 2001). 

2. The CALMET diagnostic wind model was applied to the Gulf of Mexico domain using 

RWP and other observations. Methods were devised for interpolating between missing 

observations, especially for the vertical profiles of winds and temperature, since 

CALMET has stringent requirements for data continuity. Furthermore, recommendations 

were made for assumptions concerning length scales related to spatial interpolations. For 

example, based on the evaluations of EDAS simulations and RWP observations (see 

Item 1), a distance scale of 150 km from the observing location was chosen for the point 

where RWP and EDAS simulations would have equal weight. 

3. The procedure for applying the CALPUFF transport and dispersion model was described 

in Section 6.3. Since actual source emission data were not available and no tracer studies 

had been done, the CALPUFF runs were made using arbitrary assumptions for 

hypothetical tracers from the three oil platforms, BIP, SMI, and SWP. The major model 

outputs for analysis were contour plots of 24 hr average concentration. 

4. Twenty-four hour trajectories of hypothetical emissions released from the three oil 

platforms were calculated for several times at heights of 10 m, 75 m, and 350 m, using 

(1) CALMET wind fields and an in-house STI trajectory model (TRAJMOD), and 

(2) EDAS wind fields and the HYSPLIT trajectory model. However, the trajectory 

comparisons were hampered by the truncation of the CALMET trajectories at the domain 

boundary. 

5. Seven multi-day case studies were analyzed using EDAS, HYSPLIT, CALMET, and 

CALPUFF. These seven periods covered the range of representative synoptic conditions 

and seasons, such as strong-wind January days and light-wind July days. Some general 

conclusions may be drawn: 
6-20

• The CALMET trajectories and the EDAS-HYSPLIT trajectories agree within 20° to 

30° most of the time, although the speeds of the EDAS trajectories are larger by as 

much as a factor of two (see the evaluations of mean biases under Item 1 above). 

However, because the CALMET trajectories often truncate at the edges of the 

CALMET domain, the comparisons with HYSPLIT trajectories are limited. 

• The CALPUFF-simulated plumes from the three oil platforms sometimes impact the 

shoreline or the offshore islands, depending on wind direction. The concentrations are 

higher during light winds, when dilution is less. It is fortunate that the most persistent 

winds, associated with onshore impact near the same location for several hours, are 

nearly always marked by high winds and consequently lower concentrations. When 

winds are light and variable, the local centerline concentration may be higher, but the 

plume does not remain long over a specific point. 

• The CALMET-CALPUFF estimates of overwater mixing depth were low, 100 to 

200 m, in contrast to observed mixing depths of about 600 m. This factor of a three to 

six difference causes overpredictions in relative pollutant concentrations because the 

plume is constricted to the mixing layer. The underpredictions of mixing depth appear 

to be due to the neglect of convective mixing processes offshore, where CALMET 

currently assumes that the mixing depth is due solely to mechanical mixing and is, 

therefore, proportional to wind speed. 
6-21

Figure 6-1. Gulf of Mexico study region with site locations for the six RWPs. 
6-22

 

 Figure 6-2. Comparison of RWP wind speeds and directions with EDAS simulations: (a) wind 

speed and direction mean bias, (b) mean standard deviation (STD), and (c) mean 

absolute error (MAE) for all RWP sites shown in Figure 6.1. 

(a) 

(c) 

(b) 
6-23

Figure 6-3. Locations of meteorological stations used to provide inputs to the CALMET 

diagnostic meteorological model to derive three-dimensional wind fields and 

other ABL parameters. 
6-24

Figure 6-4. CALMET modeling domain for the Gulf of Mexico coastal region from mid-Texas 

to western Florida; 860 X 560 km (NX=172 and NY=112); 5-km horizontal grid 

resolution. 

Figure 6-5. EDAS modeling domain using a horizontal resolution of 40 km 

(NX=185 X NY=129) 
6-25

Figure 6-6. Standard options for incorporating gridded model output into a CALMET analysis 

(from Scire et al., 1999). 
6-26

Figure 6-7. Locations of oil platform (red stars) where the arbitrary hypothetical tracers were 

assumed to be emitted for the air quality modeling exercise. The other symbols 

represent CALPUFF meteorological measuring stations. 
6-27

Figure 6-8. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for July 29 at 0000 CST through August 1, 1999, at 0800 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-9. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

July 29 at 0000 CST through August 1, 1999, at 0800 CST. RWP observations 

are not used in EDAS. 
6-28

Figure 6-10. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for July 29 at 0000 CST through August 1, 1999, at 0800 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

 Figure 6-11. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

July 29 at 0000 CST through August 1, 1999, at 0800 CST. RWP 

observations are not used in EDAS. 
6-29

Figure 6-12. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for July 29 at 0000 CST through August 1, 1999, at 0800 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-13. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

July 29 at 0000 CST through August 1, 1999, at 0800 CST. RWP observations 

are not used in EDAS. 
6-30

Figure 6-14. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on July 30, 1999, at 2200 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-15. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on July 31, 1999, at 1600 CST. The same amount of 

tracer is assumed to be released from each source. 
6-31

Figure 6-16. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on August 1 at 1700 CST. The same amount of tracer is 

assumed to be released from each source. 

Figure 6-17. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for January 19 at 0000 CST through January 22, 2000, at 1600 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-32

 Figure 6-18. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 19 at 0000 CST through January 22, 2000, at 1600 CST. RWP 

observations are not used in EDAS. 

Figure 6-19. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for January 19 at 0000 CST through January 22, 2000 at 1600 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-33

 Figure 6-20. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 19 at 0000 CST through January 22, 2000 at 1600 CST. RWP 

observations are not used in EDAS. 

 Figure 6-21. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for January 19 at 0000 CST through January 22, 2000, at 1600 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-34

Figure 6-22. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 19 at 0000 CST through January 22, 2000, at 1600 CST. RWP 

observations are not used in EDAS. 

Figure 6-23. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for January 22 at 0000 CST through January 25, 2000, at 0800 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-35

Figure 6-24. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 22 at 0000 CST through January 25, 2000, at 0800 CST. RWP 

observations are not used in EDAS. 

Figure 6-25. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for January 22 at 0000 CST through January 25, 2000, at 0800 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-36

Figure 6-26. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 22 at 0000 CST through January 25, 2000, at 0800 CST. RWP 

observations are not used in EDAS. 

 Figure 6-27. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for January 22 at 0000 CST through January 25, 2000, at 0800 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-37

Figure 6-28. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 22 at 0000 CST through January 25, 2000, at 0800 CST. RWP 

observations are not used in EDAS. 

Figure 6-29. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 20, 2000, at 1600 CST. The same amount of 

tracer is assumed to be released from each source. 
6-38

Figure 6-30. CALMET-derived mixing heights for January 20, 2000, at 1400 CST. 

 Figure 6-31. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 21, 2000, at 1600 CST. The same amount of 

tracer is assumed to be released from each source. 
6-39

Figure 6-32. CALMET-derived mixing heights for January 21, 2000, at 1400 CST. 

Figure 6-33. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 22, 2000, at 1900 CST. The same amount of 

tracer is assumed to be released from each source. 
6-40

Figure 6-34. CALMET-derived mixing heights for January 22, 2000, at 1400 CST. 

 Figure 6-35. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 23, 2000, at 1200 CST. The same amount of 

tracer is assumed to be released from each source. 
6-41

Figure 6-36. CALMET-derived mixing heights for January 23, 2000, at 1400 CST. 

Figure 6-37. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 24, 2000, at 1200 CST. The same amount of 

tracer is assumed to be released from each source. 
6-42

Figure 6-38. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 25, 2000, at 1400 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-39. CALMET-derived mixing heights for January 24, 2000, at 1400 CST. 
6-43

Figure 6-40. CALMET-derived mixing heights for January 25, 2000, at 1400 CST. 

Figure 6-41. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for January 3, at 0000 CST through January 6, 2001, at 0000 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-44

Figure 6-42. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 3 at 0000 CST through January 6, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 

Figure 6-43. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for January 3 at 0000 CST through January 6, 2001, at 0000 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-45

Figure 6-44. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 3 at 0000 CST through January 6, 2001, at 0000 at 0800 CST. RWP 

observations are not used in EDAS. 

 Figure 6-45. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for January 3 at 0000 CST through January 6, 2001, at 0000 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-46

Figure 6-46. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 3 at 0000 CST through January 6, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 

Figure 6-47. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 4, 2001, at 0800 CST. The same amount of 

tracer is assumed to be released from each source. 
6-47

Figure 6-48. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 5, 2001, at 0300 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-49. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 5, 2001, at 1700 CST. The same amount of 

tracer is assumed to be released from each source. 
6-48

Figure 6-50. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 6, 2001, at 1000 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-51. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for January 27 at 0000 CST through January 30, 2001, at 0000 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-49

 Figure 6-52. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

January 27 at 0000 CST through January 30, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 

Figure 6-53. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for January 27 at 0000 CST through January 30, 2001, at 0000 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-50

 Figure 6-54. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

January 27 at 0000 CST through January 30, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 

 Figure 6-55. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for January 27 at 0000 CST through January 30, 2001, at 0000 CST. The 

RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though 

the total time period has not elapsed. 
6-51

Figure 6-56. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

January 27 at 0000 CST through January 30, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 

Figure 6-57. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on January 29, 2001, at 1200 CST. The same amount of 

tracer is assumed to be released from each source. 
6-52

Figure 6-58. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for April 13 at 0000 CST through April 16, 2001, at 0000 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-59. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

April 13 at 0000 CST through April 16, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 
6-53

Figure 6-60. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for April 13 at 0000 CST through April 16, 2001, at 0000 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-61. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

April 13 at 0000 CST through April 16, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 
6-54

 Figure 6-62. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for April 13 at 0000 CST through April 16, 2001, at 0000 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-63. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

April 13 at 0000 CST through April 16, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 
6-55

Figure 6-64. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on April 14, 2001, at 1900 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-65. CALMET-derived mixing heights for April 14, 2001, at 1400 CST. 
6-56

Figure 6-66. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on April 15, 2001, at 1100 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-67. CALMET-derived mixing heights for April 15, 2001, at 1400 CST. 
6-57

Figure 6-68. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for May 13 at 0000 CST through May 16, 2001, at 0000 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-69. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

May 13 at 0000 CST through May 16, 2001, at 0000 CST. RWP observations 

are not used in EDAS. 
6-58

Figure 6-70. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for May 13 at 0000 CST through May 16, 2001, at 0000 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-71. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields for 

May 13 at 0000 CST through May 16, 2001, at 0000 CST. RWP observations 

are not used in EDAS. 
6-59

Figure 6-72. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for May 13 at 0000 CST through May 16, 2001, at 0000 CST. The RWP 

observations are used in CALMET. Note that the trajectories terminate when 

they reach the arbitrary boundary of the CALMET domain, even though the total 

time period has not elapsed. 

Figure 6-73. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

May 13 at 0000 CST through May 16, 2001, at 0000 CST. RWP observations 

are not used in EDAS. 
6-60

Figure 6-74. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on May 14, 2001, at 0600 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-75. CALMET-derived mixing heights for May 14, 2001, at 1400 CST. 
6-61

Figure 6-76. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on May 15, 2001, at 2200 CST. The same amount of 

tracer is assumed to be released from each source. 

Figure 6-77. CALMET-derived mixing heights for May 15, 2001, at 1400 CST. 
6-62

Figure 6-78. CALMET 24-hr forward trajectory at 10 m based on CALMET diagnostic wind 

fields for September 17 at 0000 CST through September 21, 2001, at 0000 CST. 

The RWP observations are used in CALMET. Note that the trajectories 

terminate when they reach the arbitrary boundary of the CALMET domain, even 

though the total time period has not elapsed. 

Figure 6-79. HYSPLIT 24-hr forward trajectory at 10 m based on EDAS wind fields for 

September 17 at 0000 CST through September 21, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 
6-63

Figure 6-80. CALMET 24-hr forward trajectory at 75 m based on CALMET diagnostic wind 

fields for September 17 at 0000 CST through September 21, 2001, at 0000 CST. 

The RWP observations are used in CALMET. Note that the trajectories 

terminate when they reach the arbitrary boundary of the CALMET domain, even 

though the total time period has not elapsed. 

 Figure 6-81. HYSPLIT 24-hr forward trajectory at 75 m based on EDAS wind fields 

for September 17 at 0000 CST through September 21, 2001, at 0000 CST. 

The RWP observations are not used in EDAS. 
6-64

Figure 6-82. CALMET 24-hr forward trajectory at 350 m based on CALMET diagnostic wind 

fields for September 17 at 0000 CST through September 21, 2001, at 0000 CST. 

The RWP observations are used in CALMET. Note that the trajectories terminate 

when they reach the arbitrary boundary of the CALMET domain, even though the 

total time period has not elapsed. 

Figure 6-83. HYSPLIT 24-hr forward trajectory at 350 m based on EDAS wind fields for 

September 17 at 0000 CST through September 21, 2001, at 0000 CST. RWP 

observations are not used in EDAS. 
6-65

Figure 6-84. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on September 18, 2001, at 2200 CST. The same amount 

of tracer is assumed to be released from each source. 

Figure 6-85. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on September 19, 2001, at 1900 CST. The same amount 

of tracer is assumed to be released from each source. 
6-66

Figure 6-86. CALPUFF dispersion simulations for hypothetical tracers originating from SMI, 

DWP, and BIP ending on September 20, 2001, at 1300 CST. The same amount 

of tracer is assumed to be released from each source. 
7-1

7. SUMMARY OF MAJOR FINDINGS AND RECOMMENDATIONS 

The project objectives were described in Section 1: (1) creating a quality-controlled data 

inventory and tools to view the data; (2) understanding the annual, seasonal, and diurnal 

variations in the ABL’s structure; (3) understanding the processes governing variations in the 

ABL’s structure; (4) creating three-dimensional gridded wind fields; and (5) characterizing the 

variation of transport and dispersion under different weather conditions. Sections 2 through 6 

provided detailed analyses of the ABL data from the Gulf of Mexico to satisfy these objectives. 

This section summarizes the major findings and provides a set of recommendations for further 

research with the data that have been collected. The recommendations also include some 

suggestions for future routine meteorological measurements. 

7.1 SUMMARY OF FINDINGS 

Major project findings are discussed in the following subsections. Each subsection 

references the report section in which the specific information is available and, when 

appropriate, a deliverable that accompanies this report. 

7.1.1 Data and Data Viewer (Section 2) 

All data collected as part of this study, as well as other relevant data, have been placed in 

a common Microsoft SQL Server database. In addition, the data are contained in quarterly 

Microsoft Access databases. These data sets were delivered to MMS. The data are generally 

available for the period May 1998 through September 2001. The data have been validated and 

are ready for immediate use by data analysts and modelers. The data include 

• Hourly RWP and RASS Tv data collected at five platforms and one coastal site. Note 

that data from four RWP sites (WDP, DWP, BIP, and FTM) are available only from 

September 2000 through September 2001. 

• Rawinsonde data collected from Lake Charles and Slidell, Louisiana, at 0000 UTC and 

1200 UTC, for each day during the study. 

• Hourly surface meteorological data collected at the RWP sites and from buoy and 

C-MAN sites. The routine data collected at most sites include wind speed and direction, 

temperature, relative humidity, station pressure, and skin temperature. The buoy sites 

also collected wave height and wave period data. 

• Hourly surface meteorological data collected at land-based surface sites throughout the 

Gulf of Mexico region. These data were input into a Microsoft SQL Server database; 

however, they were not quality-controlled. 

• Hourly boundary layer parameters such as heat fluxes and scaling parameters derived for 

all over-water sites using the COARE model. 

• Eta forecast model geopotential height, friction velocity, latent heat flux, sensible heat 

flux, low, middle, and high cloud cover, and EDAS model wind speed and wind direction 

at grid points nearest each over-water site location. 
7-2

• Daily aloft synoptic weather classifications and surface flow classifications. 

• Averages of RWP wind and RASS Tv data. Averages were created for the entire 

1998-2001 study period by year, season, month, and aloft classification. 

In addition to the data contained in the database, CALMET wind fields derived for seven 

selected case studies are also available in their native binary format. 

To effectively display this diverse set of data for use in data analysis, the Environmental 

Data Analysis Tool (EDAT) was developed and delivered to MMS. EDAT is designed to work 

with environmental data sets such as RWP, RASS, rawinsonde, air quality, surface 

meteorological, and modeling data sets. EDAT reads from a Microsoft Access database or a 

Microsoft SQL Server database. EDAT can produce four types of plots including time series, 

time-height cross-sections, vertical profiles, and spatial plots, and can display images. 

7.1.2 Atmospheric Boundary Layer Characteristics (Sections 3-5) 

To understand the characteristics of the meteorology in the Gulf of Mexico, several types 

of data were studied that capture a variety of phenomena that occur over time and space. The 

data analyzed include aloft synoptic weather, surface flow speed and direction, vertical profiles 

of wind and temperature, near-surface stability, mixing heights, and boundary layer parameters 

such as heat fluxes, friction velocity, surface roughness, and Monin-Obukhov length. Both 

statistical and case study analyses of these data were performed, and the major findings from 

these analyses are presented below. 

ABL Characteristics Related to Aloft Synoptic Weather (Section 3)

For the purposes of this project, “aloft” is defined as anything above the surface layer. It 

is obvious that synoptic-scale, upper-air weather patterns have a strong impact on local and 

regional weather conditions, especially in the ABL. To understand the relationship between 

synoptic-scale weather and local ABL conditions, upper-level patterns over the Gulf of Mexico 

were classified for each day during the study (May 1998 through September 2001). The 

classification patterns are ridge, weak ridge, flat, zonal, trough, weak trough, post-trough, cut-off 

low, and tropical storm. 

The ridge of high pressure was the dominant aloft upper-air pattern, occurring 

approximately one-third of the time. This is important because the ridge pattern is often 

associated with ABL characteristics (e.g., light winds with low mixing depths) that lead to high 

pollutant concentrations. The trough was the second most predominant aloft or upper-air feature 

and was observed about one-fourth of the time. This is important because the ABL 

characteristics under trough scenarios typically lead to periods with relatively low air pollution 

concentration episodes, because of stronger winds and strong vertical mixing. Weak troughs 

occurred less frequently, observed on about one of every six days. The other patterns were found 

to occur far less frequently; tropical storms were rare. A summary of the influence of the aloft 

patterns on local boundary layer parameters follows; the local parameters are derived from 

observations using the COARE algorithm. 
7-3

The Longwave Radiation is a component of the surface energy balance. It has little variation by 

synoptic class or by site, ranging from 290 to 420 W/m2

. The magnitude is less for post-trough 

synoptic conditions since such periods are generally cool and clear. The magnitude of longwave 

radiation is largest for tropical storms, which are marked by warm temperatures, high humidity, 

and a maximum amount of natural aerosols (i.e., fog, clouds, and rain). 

The Shortwave (Solar) Radiation is another component of the surface energy balance and 

reaches a maximum during ridge conditions, which are usually clear and sunny, and a minimum 

during weak troughs or tropical storms, which are more likely characterized by clouds and rain. 

The Humidity Scaling Parameter is a key parameter in Monin-Obukhov similarity theory and is 

proportional to the latent heat flux divided by the friction velocity. The latent heat flux tends to 

be maximized during periods with a low dew point in the air and/or periods when the skin 

temperature is much higher than the air temperature, for example, after a cold front passes or in 

the middle of a large high pressure system The humidity scaling parameter is, therefore, also 

expected to be largest during low humidity periods or hot high pressure periods. As expected, 

the humidity scaling factor is larger during post-trough and ridge periods. It is smallest during 

tropical storms, when the air is likely to be saturated and the same temperature as the water. 

The Temperature Scaling Parameter is also a key parameter in Monin-Obukhov similarity theory 

and is proportional to the sensible heat flux divided by the friction velocity. The sensible heat 

flux is largest during periods when the air is much cooler than the water, such as after a cold 

front passes. As expected, the temperature scaling factor is much larger during post-trough 

periods with cold air advection. It is smallest during tropical storms, when the air is likely to be 

the same temperature as the water. 

The Sensible Heat Flux is another component of the surface energy balance and is calculated 

using observations of wind speed and the skin-air temperature difference. It increases as the 

wind speed and/or skin-air temperature difference increases. Sensible heat flux is maximized 

for post-trough synoptic conditions, which are likely to be marked by above average wind speeds 

and by low air temperature relative to water temperature. There is a factor of ten variability 

across the nine synoptic classes. There are some differences among the sites but they are not 

consistent and need further investigation. 

The Latent Heat Flux is also a component of the surface energy balance and, over water at the 

latitude of the Gulf of Mexico, is about an order of magnitude greater than the sensible heat flux. 

Over water, the variability in the latent heat flux is less than that in the sensible heat flux, 

perhaps because the latent heat flux (calculated from observations of wind speed, air-skin 

temperature difference, and relative humidity) tends to be nearly always positive, since the air at 

the water surface is always saturated with water vapor. In contrast, the sensible heat flux can 

sometimes be negative, when air temperature is greater than skin temperature. The latent heat 

flux is largest during post-trough synoptic condition, due to the higher wind speeds and the 

relatively low dew points that follow a cold front. 

The Friction Velocity is calculated using the log wind profile relation, given the observed wind 

speed near the surface. The wind speed averages 6 m/s, ranging from 4 m/s for ridge and flat 

classes to 11.5 m/s for the tropical storm class. Since friction velocity is proportional to wind 
7-4

speed, the friction velocity values are largest during high-wind periods during tropical storms. 

Aside from the anomaly during tropical storms, there is little variability in friction velocity from 

site to site or by synoptic class. The friction velocity averages 0.2 m/s. 

ABL Characteristics Related to Surface Flow (Section 3)

Surface wind speed and direction data collected at the C-MAN, buoy, and platform 

surface monitors were analyzed to characterize the surface flow patterns in the Gulf of Mexico. 

The analysis involved creating wind rose plots for all sites to characterize surface flows and 

classifying the flow at selected sites on each day of the study period as a function of four wind 

direction classes relative to the local orientation of the shoreline: onshore, offshore, parallel 

west, or parallel east. The daily surface wind speed and direction flow classifications are 

included in the database. The buoy and platform sites are separated by large distances, stretching 

from buoy 42019, located about 200 km southwest of Houston, to buoy 42040 near southern 

Alabama, to as far as 100 km offshore. These distances alone will cause variability in the nature 

of the onshore and offshore flow characteristics. 

An onshore flow that was light to moderate in speed was observed most of the time for 

the entire study period at the four sites used for analyzing the daily flow characteristics. Onshore 

flow occurred about twice as often as offshore flow. In 1999, less onshore flow was observed at 

buoy 42019 and VRM compared to 1998 and 2000. This pattern was not observed at buoy 

42035 or SMI. This difference is important because it can impact the ABL characteristics listed 

below. The dominance of onshore flow was evident for all of the upper-air patterns. Annual and 

seasonal results were similar. Stronger winds were observed under the trough pattern as opposed 

to the ridge pattern.. In general, stronger winds were observed more often at the offshore sites. 

A summary of the influence of the surface flow patterns on local boundary layer parameters 

follows, using the same surface energy balance and similarity parameters discussed in the 

previous subsection: 

The Downwelling Longwave Radiation shows little variation by flow direction or by station, 

ranging from 340 to 390 W/m2

. The magnitude is slightly less for offshore flow directions since 

such periods are generally associated with post-frontal northerly wind directions that are cool 

and clear. 

The Shortwave Radiation does not vary much with site or with flow direction, since the 

minimum and maximum values in the figures are 170 and 290 W/m2

, respectively. The behavior 

at each of the 14 monitoring sites is consistent, with higher values (averaging about 240 W/m2

) 

for onshore and parallel west flow directions, and lower values (averaging about 190 W/m2

) for 

offshore and parallel east flow directions. The difference may be caused by differences in cloud 

cover. 

The Humidity Scaling Parameter shows little (less than factor of two) variability across the 

14 sites and the four flow directions. No obvious trends are apparent. 

The Temperature Scaling Parameter is largest during offshore flow periods because the sensible 

heat flux tends to be maximized during periods when the air temperature is cooler than the water 

temperature, such as for northerly offshore wind flow patterns. It is smallest during onshore 
7-5

flow periods at the buoy sites, when the air is likely to be at the same temperature as the water. 

At the oil platform and C-MAN sites, the temperature scaling parameter is smallest during either 

onshore or parallel west flow directions. 

The Sensible Heat Flux increases as the wind speed and the skin-air temperature difference 

increase. Sensible heat flux is maximized for northerly offshore flow directions, which are more 

likely to be marked by above average wind speeds and by low air temperatures. The sensible 

heat flux is lowest for onshore flow directions, when the boundary layer air temperatures are in 

balance with the water surface. The average difference in sensible heat flux for offshore and 

onshore flow directions across the nine stations is about a factor of ten. There are some 

differences between the sites but they are not consistent and the reasons for the differences are 

not obvious. 

The Latent Heat Flux shows some differences at most sites between offshore and onshore wind 

directions. The latent heat flux is largest during offshore (northerly) flows, which tend to be 

associated with post-trough synoptic conditions, when higher wind speeds and relatively low 

dew points follow a cold front. With any offshore flow, the dew point in the air is likely to be 

less than that usually found over water. Minimum latent heat fluxes occur with onshore flows, 

which tend to be boundary layer flows when nearly saturated air is in balance with the water 

surface. 

Friction Velocity is proportional to wind speed; thus, it is highest when winds are offshore since 

offshore winds have larger speeds than onshore or parallel winds. These high winds are often 

associated with post-cold-front conditions from the north quadrant. Minimum friction velocity 

occurs during parallel west wind directions. 

Aloft Winds and Temperature (Section 4 and Appendix D)

The aloft winds and temperature data consist of quality-controlled RWP and RASS data 

from six sites. As part of the analysis, these data were averaged over several intervals to 

determine their characteristics and patterns. For example, averaging was performed by month, 

season, year, upper-air class, and entire operational period. In addition, surface wind and Tv data 

were averaged and analyzed along with the aloft data to give a more complete picture of the 

lower levels of the ABL. The winds were vector-averaged, which inherently produces lighter 

wind speeds than the scalar averages that are more typically reported . 

Wind data were averaged by hour and height to create an average diurnal profile for a 

given interval. Tv data were grouped by height and into day (0600 to 1800 CST) or night 

(1800 to 0600 CST) categories before averaging to yield a daytime and nighttime Tv profile for 

each averaging period. Averages were only calculated if at least 50% of the possible 

measurements contributing to that average were valid. 

Average wind profiles from the platform height of 25 m to the top of the RWP range 

(about 3500 m) are characterized by the following conclusions: 

• Southwest through easterly flows were dominant throughout all seasons and years; the 

most frequent flow direction was southeasterly. 
7-6

• In the fall, easterly flows occurred at lower levels and southwesterly flows occurred aloft, 

with the transition height near 1000 m. 

• In the winter, easterly surface flows occurred and were decoupled from south to 

southwesterly flows that were observed aloft. 

• In the spring, southerly winds were observed up to 1000 m and southwesterly winds 

above 1000 m. 

• In the summer, winds ranged from easterly to southwesterly below 2000 m. The most 

diurnal variability occurred at VRM. 

• With a ridge pattern, winds were south to southeasterly below 1100 m, and southwest to 

easterly aloft. 

• With a trough pattern, winds were mostly southwesterly aloft, with southeasterly to 

northeasterly flow in the low levels. Stronger troughs had a more defined shear layer. 

The following conclusions were reached for the RASS data. The average Tv, observed by 

RASS were analyzed for elevations ranging from 131 m (above the level of the instrument on the 

oil platform) to about 700 m. The RASS data were combined with Tv observations collected by 

thermometers on short towers on the oil platforms at heights of about 25 msl to obtain 

“complete” vertical profiles that show the following: 

• A discontinuity often occurs in the temperature gradient at the lower two or three RASS 

levels (e.g., 131 m) due to a known cold bias in the measurement system. 

• The average profiles, which extend to about 700 m, do not show an elevated inversion or 

mixing height, despite the fact that a mixing depth of 500 to 700 m is expected and often 

observed in the reflectivity (Cn

2

) data. 

• The differences in temperature between the surface and RASS measurements showed 

variability inconsistent with scientific expectations. Because the surface and 131-m 

temperatures are measured by two types of instruments, biases may occur that influence 

the diagnosis of stable or unstable temperature gradients. 

Near-Surface Stability (Final Presentation in Appendix D)

Near-surface stability was calculated by skin temperature minus surface air temperature. 

Average diurnal profiles of near-surface stability were averaged by month and show the 

following characteristics: 

• Most sites are unstable most of the time (80%) and are, therefore, stable about 20% of the 

time. 

• January and February are the most stable months, which may be due to nonrepresentative stability created during the day by platform heating by the sun. 
7-7

RWP- and RASS-Estimated Mixing Heights (Section 5)

RWP/RASS-estimated Cn

2

 and Tv data are often used to estimate mixing heights at 

overland sites. Mixing heights are important in air quality issues because the mixing height 

defines the maximum vertical extent to which surface- (or platform-) based emissions can mix. 

A goal of the project was to use automatic mixing height detection algorithms to produce hourly 

mixing heights at the RWP sites. The automatic system is needed when there are thousands of 

soundings that must be analyzed, as was the case with this study. However, frequent sea clutter 

in the lowest 600 m contaminated the reflectivity data. Furthermore, the aloft inversion that caps 

the ABL was rarely observed in the RASS data, since the RASS could not “see” high enough. It 

was not possible to automatically calculate the mixing heights for nearly all of the hours of this 

study. Instead, mixing heights were manually estimated (by a meteorologist), but only for case 

study periods. For the seven case studies, manually estimated mixing heights ranged from 400 m 

to 1000 m and were usually around 600 m above ground level. 

Boundary Layer Parameterization by COARE (Section 5)

To characterize the ABL surface fluxes and scaling parameters, the COARE algorithm 

was used to estimate hourly surface fluxes of momentum (also called the surface stress), sensible 

heat, and latent heat from observations of wind speed, air temperature, and water vapor mixing 

ratio at some standard reference height near the water surface and the skin temperature at the 

water surface. The COARE algorithm was originally derived from the TOGA-COARE research 

project. 

When COARE was applied to the first portions of the data, a problem sometimes 

occurred with the evaporative cooling calculation due to unrealistically high amounts of solar 

energy estimated to reach the ocean surface. To solve this problem, the first coefficient in the 

equation for the net absorption by the ocean (Equation 7-1) was changed from 0.137 to 0.060, 

based on tests performed by Dr. Christopher Fairall, a COARE developer. This change provided 

a more realistic representation of the actual absorption, which caused the evaporative cooling 

calculations to better agree with observations.

 Net = SW*(.137+11*CST -6.6e-5/ (CST*(1-exp(-CST/8.0e-4)))) (7-1)

where: 

Net = Net absorption by the ocean (watts per square meter) 

SW = Incoming short wave radiation (watts per square meter) 

CST = Cool skin thickness (meters) 

During early daylight hours, under light wind conditions when the air temperature was 

warmer than skin temperature (i.e., a stable near-surface layer), COARE calculated unrealistic 

rapid increases in skin temperature (up to 500oC). A lack of heat removal due to very small 

accumulated stress (surface momentum flux) and a very thin (almost zero) warm layer thickness 

caused this condition. To correct this problem, a minimum stress of 0.002 N/m2

 was imposed for 

this calculation. This value was chosen after analysis of measured stresses during TOGACOARE (personal communication with Dr. Christopher Fairall, July 2002). 
7-8

In addition to the change in the basic calculations, the COARE program was changed to 

incorporate Eta model analyzed fields and/or predictions. The capability of flagging COARE 

output based on the validity of the incoming data was also incorporated. 

Statistical and case study analyses were carried out with the COARE input and output 

data, and the following results are summarized: 

Fluxes and Scaling Parameters. The fluxes and scaling parameters calculated by the COARE 

algorithm in the Gulf of Mexico are physically consistent with expectations and are similar in 

magnitude to the observations and COARE calculations for TOGA, which took place in the 

warm western Pacific Ocean near the equator. Calculated monthly average sensible heat fluxes 

in the Gulf of Mexico ranged from 5 to 30 W/m2

, typical of other over-water areas. Similarly, 

calculated monthly average latent heat fluxes ranged from 50 to 150 W/m2

, also typical of other 

over-water areas. Both the latent and sensible heat fluxes were highest in the late fall and early 

winter and lowest in the late spring and summer, although the yearly cycle in latent heat values is 

less pronounced than the seasonal cycle. Sensible heat flux is maximized for post-trough 

synoptic conditions, which are likely to be marked by above average wind speeds and by low air 

temperature. The latent heat flux is consistently large during the post-trough synoptic condition, 

due to the higher wind speeds and the low dew points that follow a cold front. It can also be 

large during tropical storms because of the high temperatures and strong winds. 

The study of the estimates of annual variations of latent and sensible heat fluxes reveal smaller 

fluxes in the summer. These results are consistent with lighter winds and smaller skin-air 

temperature differences in the summer compared to other times of year. Calculated monthly 

average sensible heat fluxes were about one-fifth the calculated monthly average latent heat 

fluxes, and the differences between the two were generally greater in the summer and smaller in 

the late fall and winter. 

The calculated fluxes are generally in good agreement with the monthly average Eta model 

latent and sensible heat fluxes. However, the Eta model fluxes did not show as much variation 

between sites as the calculated fluxes. In addition, the Eta model fluxes were about 20% greater 

than the calculated fluxes in the fall and early winter, but were very similar during the spring and 

summer. 

Friction Velocity. The COARE-calculated monthly average friction velocity for the buoys, the 

C-MAN sites, and the SMI platform shows agreement among these sites well within a factor of 

two and often within 20%. This agreement is important because the monthly average friction 

velocity is the key scaling velocity for estimating transport speeds and dispersion rates. 

However the VRM, BIP, DWP, MBP, SWP, and WDP platforms (part of BAMP) suggest mean 

friction velocities that are 30% to 40% less than the other sites. Possible explanations are that 

the wave height and frequency are estimated from empirical relations given observations of wind 

speed at the platforms, whereas they are directly measured at the buoys. Also, the platform wind 

observations are corrected from a height of >20 m to 10 m and are, on average, less (at the 

10-m height) than at the other non-BAMP sites. All data show that the calculated monthly 

average friction velocity was slightly lower from May through August and peaked in late fall and 

early winter. The monthly average Eta model friction velocity showed the same yearly pattern as 

the calculated friction velocity. However, the Eta model friction velocity was 10% to 20% 
7-9

higher than the calculated friction velocity in the fall and early winter. This is most likely the 

reason why the Eta model fluxes were slightly high during the same period. 

Temperature and Humidity Scaling Parameter. The COARE-calculated monthly average 

temperature scaling parameter and humidity scaling parameter generally showed a factor of two 

or better agreement among sites. The monthly average temperature scaling parameter and the 

humidity scaling parameter tended to be smaller in April and May, when the difference between 

the skin and air temperatures was at its minimum, and tended to be larger in November through 

January, when the difference between the skin and air temperatures was at its maximum.

Skin and Air Temperature Differences. The differences between the skin and air temperatures 

were, on average, +1 to +3°C at most sites all year. The differences were fewer in late spring 

and greater in late fall and early winter. This persistent positive temperature difference has been 

noted by Dr. Christopher Fairall at most other sites located on warm-water oceans. 

Surface Wind Speed. Scalar monthly average wind speeds showed good agreement among sites. 

The lowest speeds occurred in July and August and the highest in December and January. For 

some years, there was a transition from lower wind speeds in August to higher wind speeds in 

September and October. Weather maps indicate that the high wind speeds in September and 

October on some years were probably a result of tropical storms. 

7.1.3 Wind Fields, Transport, and Dispersion (Section 6) 

Wind fields were developed using the CALMET diagnostic model driven by a 

combination of historic Eta model simulations and observations. The wind fields, along with 

other ABL parameters, were used to develop three-dimensional inputs to the CALPUFF 

transport and dispersion model. Trajectories from the CALMET wind fields and the EDAS wind 

fields were compared. CALPUFF was used to assess dispersion and transport characteristics 

under several types of meteorological patterns. These patterns include onshore and offshore flow 

regimes, pre- and post-cold-frontal boundary passages, strong surface and upper-level high 

pressure systems, and upper-level flow transitioning from an area of low pressure to a weak area 

of high pressure. The conclusions from this study are summarized: 

1. The EDAS-simulated wind fields and the observed RWP winds from six sites were 

compared. EDAS is based on a combination of Eta model forecast winds and diagnostic 

interpolations of observed winds but does not include the RWP data. The comparison is 

complicated because the EDAS simulations represent averages over a grid volume size of 

40 km by 40 km by 100 m whereas the RWP observations represent an average over a 

much smaller grid volume with a radius of 1 km to 2 km; consequently, more turbulent 

variations are expected in the observations than in the EDAS simulations. The mean 

wind speed (WS) bias was near zero close to the shore but increased with offshore 

distance, so that the EDAS mean wind speed exceeded the RWP mean wind speed by 

1 to 2 m/s at 50 km offshore and by 2 to 6 m/s at 100 to 200 km offshore. Mean wind 

direction (WD) bias was small, about a 10° to 20° difference (e.g., if the RWP WD was 

180°, then the EDAS WD would be 160°). Standard deviations of the differences (with 

mean bias removed) were 1 to 2 m/s for WS and 20° to 40° for WD, in agreement with 

findings for other domains and models (Hanna and Yang, 2001). 
7-10

2. The CALMET diagnostic wind model was applied to the Gulf of Mexico domain using 

RWP and other observations. Methods had to be devised for interpolating between 

missing observations, especially for the vertical profiles of winds and temperature, since 

CALMET has stringent requirements for data continuity. Furthermore, recommendations 

were made for assumptions concerning length scales related to spatial interpolations. For 

example, based on the evaluations of EDAS simulations and RWP observations (see 

Item 1), a distance scale of 150 km from the observing location was chosen for the point 

where RWP and EDAS simulations would have equal weight. 

3. The procedure for applying the CALPUFF transport and dispersion model was described. 

Since actual source emission data were not available and no tracer studies were 

performed, the CALPUFF runs were made using arbitrary assumptions for hypothetical 

tracers from the three oil platforms, BIP, SMI, and SWP. The major model outputs for 

analysis were contour plots of 24-hr average concentrations. 

4. Twenty-four-hour trajectories were calculated for releases of hypothetical emissions from 

the three oil platform at several times and at heights of 10 m, 75 m, and 350 m using 

(1) the CALMET wind fields and an in-house STI trajectory model (TRAJMOD) and 

(2) the EDAS wind fields and the HYSPLIT trajectory model. However, the trajectory 

comparisons were hampered by the truncation of the CALMET trajectories at the domain 

boundary. 

5. Seven multi-day case studies were analyzed using EDAS, HYSPLIT, CALMET, and 

CALPUFF. These seven periods covered the range of representative synoptic conditions 

and seasons, such as strong-wind January days and light-wind July days. Some general 

conclusions follow: 

• The CALMET trajectories and the EDAS-HYSPLIT trajectories agree within 20° to 

30° most of the time, although the speeds of the EDAS trajectories are larger by as 

much as a factor of two (see the evaluations of mean biases under Item 1). However, 

since the CALMET trajectories are often truncated at the edges of the CALMET 

domain, the comparisons with HYSPLIT trajectories are limited. 

• The CALPUFF-simulated plumes from the three oil platforms sometimes impact the 

shoreline or offshore islands, depending on wind direction. The concentrations are 

higher during light winds, when dilution is less. It is fortunate that the most persistent 

winds, associated with onshore impact near the same location for several hours, are 

nearly always marked by high winds and consequently lower concentrations. When 

winds are light and variable, the local centerline concentration may be higher, but the 

plume does not remain for long over a specific point. 

• The CALMET-CALPUFF estimates of over-water mixing depth were low, about 

100 to 200 m, in contrast to observed mixing depths of about 600 m. This factor of 

three to six difference causes model overpredictions in concentrations, since the plume 

is constricted to the mixing layer. The underpredictions of mixing depth appear to be 

due to the neglect of convective mixing processes offshore, where CALMET currently 

assumes that the mixing depth is due solely to mechanical mixing and is therefore 

proportional to wind speed. 
7-11

7.2 RECOMMENDATIONS 

Based on the conclusions listed in Section 7.1, several recommendations can be made for 

future studies with the existing data set to enhance the research already completed. A few 

recommendations require the collection of additional data. The recommendations are arranged 

into five categories: Collaboration, Publication, Analysis, Modeling, and Measurements. 

Collaboration – Follow-on work involving collaboration with outside organizations: 

• Work with NCEP to better understand over-water wind differences between the Eta 

model and observed RWP winds. Analysis has shown that Eta model winds are biased 

compared to RWP winds. 

• Compare Eta 12-km gridded predictions to observed data; compare to the comparisons 

made with EDAS 40-km predictions/observations. The results will help guide how finerresolution Eta model data should be used in high-resolution modeling efforts. 

• Work with NOAA ETL to design a scheme to remove sea-clutter from profiler data so 

that mixing heights can be automatically estimated for data from the ABL study and 

future studies using existing mixing-height algorithms. 

• Work with Dr. Christopher Fairall at NOAA to improve COARE predictions at high 

surface roughness. Roughness increases under very low wind speeds, which influences 

estimations of the ABL parameters. 

• Conduct a joint meeting on COARE to further improve the model for use in the Gulf of 

Mexico. Participants might include MMS representatives, Dr. Christopher Fairall of 

NOAA, STI, Earth Tech, and Hanna Consultants. 

• Make better use of ABL measurements and analyses in other MMS-sponsored projects by 

reviewing plans and progress and recommending ways to incorporate ABL data and 

analysis and modeling results. 

Publication – Plan a special issue (of, for example, Journal of Applied Meteorology, Journal of 

Geophysical Research, or Boundary Layer Meteorology) on ABL issues in the Gulf and prepare 

specific papers on the following: 

• Eta/RWP wind comparisons. 

• Three-year climatology of surface ABL parameters calculated using COARE in a shallow 

water ocean and modifications made to COARE (jointly with NOAA?). 

• Modeled and estimated mixing heights in the Gulf of Mexico. 

• Results from related MMS-sponsored projects. 

Analysis

• Compare satellite-derived sea-surface temperatures to radiometer temperatures and buoy 

temperatures measured during this study. Accurate spatial sea-surface temperatures are 

important for accurate modeling. 
7-12

• Compare estimates of sea-surface temperatures to the radiometer temperatures when 

clouds obscure the satellite’s view of the Gulf (currently estimated using hole-filling 

techniques). 

• Identify several additional periods of super-stable conditions in the existing data set (i.e., 

a period of southerly flow after a cold outbreak has cooled the water in the shallow 

portion of the Gulf) and perform a ABL case study similar to other case studies. 

• Determine the best method for estimating wave height and frequency as a function of 

water depth from wind speed alone. When wave data is not available at the platforms, 

inaccurate estimations of wave characteristics can result in inaccurate estimations of 

surface roughness, which influence ABL parameterizations. Evaluate the roughness 

estimations from wind speed alone; compare to observed wave data. 

• Integrate onshore and offshore air quality data into the meteorological data set and 

analyses performed during this project. This will expand the applicability of the results 

and provide further evaluation of the methods used. 

• Revise the North-East Gulf of Mexico Meteorological Statistical Expert System to use 

improved model output and now-available data; this will result in a more accurate tool for 

visualization of meteorological data and of estimates of transport and dispersion from 

specific locations offshore. 

• Use buoyancy flux to estimate mixing heights when winds are less than 6 m/sec and 

compare to RWP-derived mixing heights. 

Modeling

• Update the CALMET model to better estimate mixing heights; perform additional 

comparisons of observation-based estimations of mixing heights to model mixing 

heights. Currently, CALMET does a poor job estimating mixing heights in the Gulf of 

Mexico, primarily because it ignores convective mixing over water. 

• Run CALMET using the pseudo-shoreline of 3-m water depth to represent marshland. 

Compare results to prior modeling. 

• Update the CALPUFF dispersion runs using new CALMET output created with an 

improved mixing-height scheme. Compare the results from the new runs to those created 

as part of the current project. 

• Compare CALMET diagnostic model runs to MM5 prognostic model runs and 

observational data and create best estimates of gridded mixing heights and winds. 

• Modify the way diagnostic and prognostic models treat the diffuse shoreline of the Gulf 

of Mexico; operate the models and compare results with observations. 

• Quantify the differences between the CALMET and HYSPLIT trajectories and the 

differences between the CALPUFF-calculated concentrations. The current conclusions 

use subjective statements such as “the trajectories were similar” or “the plume impacts 

were different”. In other trajectory comparisons, two trajectories were compared by 

calculating the difference in the two positions after certain travel times. The differences 

can then be expressed as function of time for that trajectory and a root mean square error 
7-13

(rmse) calculated for a group of trajectories. The difference can be categorized by its 

components (e.g., radial distance and angular distance). The studies by Kahl and Samson 

(1986) usually found an rmse difference of 100 to 200 km after one day. Much of this 

difference is ascribed to stochastic variations. It would be of interest to determine if the 

rmse’s that could be calculated with model output from the current study were similar to 

those found by others and if they differed with synoptic condition or wind speed. 

• Compare CALPUFF concentration predictions quantitatively because the same amount of 

tracer was released in each case. For example the following outputs could be compared: 

− Maximum concentration at the point the shoreline is hit. 

− Maximum (centerline) concentration at specific downwind times (e.g., 3 hrs, 6 hrs, 

etc.) and distances (50 km, 100 km, etc.) 

− Penetration distance (downwind distance) for a given concentration. 

− Width of plume for a given concentration contour at a given travel time or distance. 

• Develop an alternative procedure within CALMET to handle missing upper-air 

measurements. 

Measurements – Conduct continuous measurements to (1) support routine source-based 

modeling for lessees and special-research MMS objectives; (2) provide long-term information on 

spatial and temporal ABL characteristics; and (3) support routine comparisons with Eta model 

predictions for routine estimates of ABL characteristics, for real-time modeling, and for special 

research studies involving ABL gradients on- and off-shore, etc. 

• Collocate a radiometer and underwater temperature sensor to better determine the 

relationship and accuracy of the COARE-estimated warm-layer and cool-skin effect. 

This effect is used to estimate skin temperature at buoys, an important parameter for the 

estimation of ABL parameters and for model initial conditions. Work with NOAA to 

adjust COARE as needed. 

• On a platform, operate temperature, relative humidity, and wind sensors at two heights 

within the surface layer, as well as a solar radiometer. Use this data to verify COARE 

estimations of ABL parameters that used surface ABL data at only one level. 

• Continue routine operations of surface and upper-air meteorological measurements at the 

Lumcon site near the Mississippi River Delta. 

• Routinely operate a measurement system on an offshore platform that measures a range 

of meteorological parameters at several depths of the surface layer and boundary layer. 

Such a system could include a mini-Sodar, an RWP/RASS system, and a surface 

meteorological monitoring system on a platform to obtain wind and temperature 

measurements. The addition of the mini-Sodar would fill the measurement void that 

exists from 30 m to 200 m; this hole is often the location of plumes. 

• Improve the RWP and RASS sounders so that they are not so susceptible to interference 

from waves and nearby objects (e.g., oil platforms). 
8. REFERENCES 

Allwine K.J. and Whiteman D. (1985) MELSAR: a mesoscale air quality model for complex 

terrain: volume 1 – overview, technical description and user's guide. Report prepared by 

Pacific Northwest Laboratory, Richland, WA. 

Arya S. P. (1999) Air Pollution Meteorology and Dispersion. Oxford University Press, New 

York, NY, 98-100. 

Blackadar A.K. (1997) Turbulence and diffusion in the atmosphere. Springer, New York, NY, 

73-76 and Appendix C. 

Bradley E.F. and Weller R.A. (1995) Third Workshop of the TOGA COARE Air-Sea Interaction 

(Flux) Working Group. Honolulu, HI, August 2-4, 1995. UCAR/TCIPO, UCAR 

Communications, Boulder, CO. 

Bradley E.F, Moncrieff M.W., and Weller R.A. (1997) Joint workshop of the TOGA COARE 

Flux and Oceans Working Groups, and the GEWEX GCSS Working Group 4. Boulder, 

CO, May 14-16, 1997. UCAR/TCIPO, UCAR Communications, Boulder, CO. 

Bradley E.F. and Weller R.A. (1997) Fourth Workshop of the TOGA COARE Air-Sea 

Interaction (Flux) Working Group. Woods Hole, October 9-11, 1996. UCAR/TCIPO. 

UCAR Communications, Boulder, CO. 

Brooks I.M. and Rogers D.P. (1999) Observations of the turbulence structure of a welldeveloped internal boundary layer over the Persian Gulf. 13th Symposium on Boundary 

Layers and Turbulence, American Meteorology Society, Boston, MA, pp. 367-370. 

Businger J.A. (1982) The fluxes of specific enthalpy, sensible heat, and latent heat near the 

earth’s surface. J. Atmos. Sci. 39, 1889-1892. 

Caldwell D.R. and Elliott W.H. (1971) Surface stresses produced by rainfall, J. Phys. Oceanog.

1, 145-148. 

Carson D.J. (1973) The development of a dry inversion-capped convectively unstable boundary 

layer. Quart. J. Roy. Meteorol. Soc., 99, 450-467. 

Charnock H. (1955) A note on empirical wind-wave formulae. Quart. J. Roy. Meteorol. Soc., 84, 

443-447. 

Curry J.A., Clayson C.A., Rossow W.B., Reeder R., Zhang Y.-C., Webster P.J., Liu G. and Sheu 

R.-S. (1999) High-resolution satellite-derived dataset of the surface fluxes of heat, 

freshwater, and momentum for the TOGA-COARE IOP. Bull. Am. Meteorol. Soc. 80, 

2059-2080. 

Doneland M. (1990) Air-Sea Interactions. Ocean Engin. Sci. (B. LeMehaute and D.M. Hanes, 

eds.), John Wiley, 239-291. 

Douglas S.G., Kessler R.C., and Carr E.L. (1990) User's guide for the urban airshed model. 

Volume III: user's manual for the diagnostic wind model. Office of Air Quality Planning 

and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, 

EPA-450/4-90-007C. 

8-1
Drake R.L. and Huang C.H. (1980) Mass-consistent, interpolated wind fields for complex 

terrain. Presented at the Symposium on Intermediate Range Atmospheric Transport 

Processes and Technical Assessment, Gatlinburg, TN, October 1-3. 

Edwards K.A. and Rogers D.P. (1999) Scaled mean profiles of the MBL during coastal waves 

96. 13th Symposium on Boundary Layers and Turbulence, American Meteorology 

Society, Boston, MA, pp. 413-416. 

Fairall C.W., Bradley E.F., Rogers D.P., Edson J.B., and Young G.S. (1996a) Bulk 

parameterization of air-sea fluxes for TOGA-COARE. J. Geophys. Res., 101, 3747-

3764. 

Fairall C.W., Bradley E.F., Godfrey J.S., Wick G.A., Edson J.B., and Young G.S. (1996b) The 

cool skin and the warm layer in bulk flux calculations. J. Geophys. Res. 101, 1295-1308. 

Garratt J.R. and Ryan F.B. (1989) The structure of the stable internal boundary layer in offshore 

flow over the sea. Bound. Lay. Meteorol., 47, 17-40. 

Garratt, J.R. (1992) The Atmospheric Boundary Layer. Cambridge University Press, UK. 

Godfrey J.S. and Beljaars (1991) On the turbulent fluxes of buoyancy, heat and moisture at the 

air-sea interface at low wind speeds. J. Geophys. Res. 96, 22043-22048. 

Gosnell R., Fairall C.W., and Webster P.J. (1995) The sensible heat flux of rainfall in the tropical 

ocean. J. Geophys. Res. 100, 18437-18442. 

Hanna S.R. (1969) The thickness of the planetary boundary layer. Atmos. Environ. 3, 519-536. 

Hanna S.R., Briggs G.A. and Hosker R.P. (1982) Handbook on Atmospheric Diffusion. 

DOE/TIC-11223 (DE82-002045). NTIS/USDOC, Springfield, VA. 

Hanna S.R., Paine R.J. and Schulman L.L. (1984) Overwater dispersion in coastal regions. 

Bound. Lay. Meteorol. 30, 389-411. 

Hanna, S.R., Schulman L.L., Paine R.J., Pleim J.E., and Baer M. (1985) Development and 

evaluation of the Offshore and Coastal Diffusion Model. J. Air Poll. Control Assoc. 35, 

1039-1047. 

Hanna S.R. (1987) An empirical formula for the height of the coastal internal boundary layer. 

Bound. Lay. Meteorol. 40, 205-207. 

Hanna S.R. and Paine R.J. (1989) Hybrid Plume Dispersion Model (HPDM) development and 

evaluation. J. Appl. Meteorol. 28, 206-224. 

Hanna S.R. and Chang J.C. (1992a) Boundary layer parameterizations for applied dispersion 

modeling over urban areas. Bound. Lay. Meteorol. 58, 229-259. 

Hanna S.R. and Chang J.C. (1992b) Representativeness of wind measurements on a mesoscale 

grid with station separations of 312 m to 10000 m. Bound. Lay. Meteorol. 60, 309-324. 

Hanna S.R. and Chang J.C. (1995) Relations between meteorology and ozone in the Lake 

Michigan region. J. Appl. Meteorol. 34, 670-678. 

Hanna S.R. and Britter R.E. (2001) Wind flow and vapor cloud dispersion at industrial and urban 

sites. AIChE, New York, NY. 

8-2
Hanna S.R., Roberts P.T., and MacDonald C.P. (2001) Estimation of boundary layer fluxes and 

profiles over the Gulf of Mexico using new observations and using the COARE program. 

Paper 1-7 in American Meteorological Society Conference on Air-Sea Interaction, 8 

pages. 

Hanna S.R. and Yang R. (2001) Evaluations of mesoscale model predicitions of near-surface 

winds, temperature gradients, and mixing depths. J. Appl. Meteorol. 42, 453-466. 

Hare J.E., Persson P.O.G., Fairall C.W., and Edson J.B. (1999) Behavior of Charnock’s 

relationship for high wind conditions. 13th Symposium on Boundary Layers and 

Turbulence, American Meteorology Society, Boston, MA, pp. 252-255. 

Hsu S.A. (1988) Coastal Meteorology. Academic Press, San Diego, CA, 260 pages. 

Hsu S.A. (1989) The relationship between the Monin-Obukhov stability parameter and the Bulk 

Richardson Number at sea. J. Geophys. Res. 94, 8053-8054. 

Hsu S.A. (1997) Estimating overwater convective boundary layer height from routine 

meteorological measurements for diffusion applications at sea. J. Appl. Meteorol. 36, 

1245-1248. 

Kazanski A.B. and Monin A.S. (1961) On the dynamical interaction between the atmosphere and 

the earth’s surface. Bull. Acad. Sci. USSR, Series Geophysics, Number 5, 786-788. 

Kahl J.D. and Samson P.J. (1986) Uncertainty in trajectory calculations due to low resolution 

meteorological data, J. Clim. Appl. Meteorol. 25, 1816-1831. 

Lambert D., Durand P., Thoumieux F., Benech B., and Druilhet A. (1999) The marine 

atmospheric boundary layer during SEMAPHORE. II: Turbulence profiles in the mixed 

layer. Q. J. R. Meteorol. Soc. 125, 513-528. 

Ledvina D.V., Young G.S., Miller R.A., and Fairall C.W. (1993) The effect of averaging on bulk

estimates of heat and momentum fluxes for the tropical western Pacific Ocean. J. 

Geophys. Res. 98, 20211-20217. 

Lindsey C.G., Ray S.E., Dye T.S., Arthur M., Roberts P.T., and Stuart C. (1997a) Data collected 

by 915-MHZ radar profilers and surface meteorological stations during the 1996 Paso 

Del Norte ozone study. Data volume prepared for the U.S. Environmental Protection 

Agency, Research Triangle Park, NC by Sonoma Technology, Inc., Santa Rosa, CA, STI996293-1729-DV, EPA Work Assignment III-101, Contract No. 68-D3-0030, July. 

Lindsey C.G., Ray S.E., Schoell B.M., Dye T.S., and Arthur M. (1997b) Meteorological data 

collected at the Walnut Grove Tower facility during IMS95. Letter report prepared for 

the California Air Resources Board, Sacramento, CA, by Sonoma Technology, Inc., 

Petaluma, CA, May. 

Liu W.T, Katsaros K.B., and Businger J.A. (1979) Bulk parameterization of the air-sea exchange 

of heat and water vapor including the molecular constraints at the interface. J. Atmos. Sci.

36, 1722-1735. 

8-3
MacDonald C.P., Roberts P.T., Knoderer C.A., Miller D.S., Lilly M.R., and Hanna S.R. (2003) 

Boundary layer study in the western and central Gulf of Mexico. Presented at the Final 

Meeting of the Technical Review Group, Minerals Management Group, New Orleans, 

LA, October (STI-998555-2265). 

Mahrt L., Vickers D., Edson J., Sun J., Hojstrup J., Hare J., and Wilczac J. (1998) Heat flux in 

the coastal zone. Bound. Lay. Meteorol. 86, 421-446. 

Mahrt L., Vickers D., Sun J., Crawford T.L., Vogel C., and Dumas E. (1999) Coastal zone 

boundary layers. 13th Symposium on Boundary Layers and Turbulence, American 

Meteorology Society, Boston, MA, pp. 403-406. 

Nieuwstadt F.T.M. (1981) The steady-state height and resistance laws of the nocturnal boundary 

layer: Theory compared with CABAUW observations. Boundary-Layer Meteorol. 20, 3-

17. 

O'Brien J.J. (1970) Alternative solutions to the classical vertical velocity problem. J. Appl. 

Meteorol. 9, 197-203. 

Oost W.A., Komen G.J., Jacobs C.M.J., and van Wort C. (2001) New evidence for a relation 

between wind stress and wave age from measurements during ASGAMAGE. Tech. 

Report 2001-5, Royal Dutch Meteorological Institute (KNMI), De Bilt, The Netherlands. 

Price J.F., Weller R.A., and Pinkel R. (1986) Diurnal cycling: Observations and models of the 

upper ocean response to diurnal heating, cooling, and wind mixing. J. Geophys. Res. 91, 

8411-8427. 

Saunders P.M. (1967) The temperature at the ocean-air interface. J. Atmos. Sci. 24, 269-273. 

Scire S.S., Robe F.R., Fernau M.F., and Yamartino R.J. (1999) A user’s guide for the CALMET 

Meteorological model (Version 5.0). EarthTech, Inc., Concord, MA, September. 

Seaman N.L. (2000) Meteorological modeling for air quality assessments. Atmos. Environ. 34, 

2231-2259. 

Smedman A.-S., Bergstrom H., and Grisogono B. (1997) Evolution of the stable boundary layer 

over a cold sea. J. Geophys. Res. 102, 1091-1099. 

Smith S.D. (1988) Coefficients for sea surface wind stress, heat flux, and wind profiles as a 

function of wind speed and temperature. J. Geophys. Res. 93, 15467-15472. 

Stull R.B. (1988) An Introduction to Boundary Layer Meteorology. Kluwer Academic 

Publishers, Boston, MA. 

Sun J., Mahrt L., Vickers D., Wong J., Crawford T.L., Vogel C., Dumas E., Mourad P., and 

Vandemark D. (1999) Air-sea interaction in the coastal shoaling zone. 13th Symposium on 

Boundary Layers and Turbulence, American Meteorology Society, Boston, MA, pp. 343-

346. 

Taylor P. K. and Yelland M. J. (2001) The dependence of sea surface roughness on the height 

and steepness of the waves. J. Phys. Oceanography, 31, 572-590. 

Ternstrom M. and Smedman A.-S. (1992) The vertical turbulent structure of the coastal marine 

atmospheric boundary layer. J. Geophys. Res. 98, 4809-4826. 

8-4
Vaisala Meteorological Systems, Inc. and Sonoma Technology, Inc. (2002) Profilers and data 

collection for the MMS boundary layer study in the western and central Gulf of Mexico: 

 final performance report. Prepared for the U.S. Department of the Interior, Minerals 

Management Service, Gulf of Mexico OCS Region, New Orleans, LA, OCS Study MMS 

2002-028. 

Verkaik J.W. (1999) Estimation of form drag using satellite data. 13th Symposium on Boundary 

Layers and Turbulence, American Meteorology Society, Boston, MA, pp. 286-287 

Vickers D. and Mahrt L. (1999) Monin-Obukhov similarity in the coastal zone. 13th Symposium 

on Boundary Layers and Turbulence, American Meteorology Society, Boston, MA, pp. 

407-410. 

Vogel C.A., Crawford T.L., Sun J., and Mahrt L. (1999) Spatial variation of the atmospheric 

surface drag coefficient within a coastal shoaling zone. 13th Symposium on Boundary 

Layers and Turbulence, American Meteorology Society, Boston, MA, pp. 347-348. 

Webb E.K., Pearman G.I., and Leuning R. (1980) Correction of flux measurements for density 

effects due to heat and water vapour transfer. Q.J.R. Meteorol. Soc. 106, 85-100. 

Webster P.J. and Lukas R. (1992) TOGA-COARE: The coupled ocean-atmosphere response 

experiment. Bull. Am. Meteorol. Soc. 73, 1377-1416. 

Yelland M. and Taylor P. K. (1996) Wind stress measurements from the open ocean. J. Phys. 

Oceanogr. 26, 541-558. 

Zeng X., Zhao M., and Dickenson R.E. (1997) Intercomparison of bulk aerodynamic algorithms

for the computation of sea surface fluxes using the TOGA-COARE and TAO data. J. 

Climat. 11, 2628-2644. 

8-5
A-1 

APPENDIX A 

EDAT DATABASE FORMAT 

Appendix A contains information on the format and structure of the MMS EDAT 

database. 
A-3 

EDAT DESIGN DOCUMENT 

1. EDAT DATABASE TABLES...............................................................................................4 

1.1 Table Class....................................................................................................................4 

1.2 Table Data.....................................................................................................................4 

1.3 Table Parameter............................................................................................................4 

1.4 Table QCCode ..............................................................................................................5

1.5 Table QCLevel..............................................................................................................5 

1.6 Table Site......................................................................................................................5 

2. EDAT DATABASE RELATIONS DIAGRAMS .................................................................6 
A-4 

1. EDAT DATABASE TABLES 

1.1 Table Class 

Surface, Model, Profiler, RASS are current classes. 

Name Type Description Constraints 

uClassID tinyint Surrogate PK Unique auto increment integer 

sName varchar(50) Class name Unique 

1.2 Table Data 

Contains observed or modeled data. 

Name Type Description Constraints 

uDataID integer Surrogate PK Unique auto increment integer 

uSiteID smallint FK to Site Table’s PK Referential Integrity 

uClassID tinyint FK to Class Table’s PK Referential Integrity 

uParameterID smallint FK to Parameter Table’s PK Referential Integrity 

dUTC smalldatetime Greenwich Mean Time (GMT) for which data was 

collected. 

rValue float 

rHeight float 

uQCLevelID tinyint FK to QCLevel Table’s PK Referential Integrity 

uQCCodeID tinyint FK to QCCode Table’s PK Referential Integrity 

 

1.3 Table Parameter 

Contains all of the information about each air quality parameter stored and used in the database. Many of 

the fields are printed in the header sections of each data group in the exported OBS files. 

Name Type Description Constraints 

uParameterID smallint Surrogate PK Unique auto increment integer 

sCode varchar(50) Parameter short code May be NULL 

sName varchar(100) 

sUnit varchar(50) 

uAIRSParameterID integer Natural AIRS parameter number 

sAIRSUnitID varchar(50) AIRS Units 
A-5 

1.4 Table QCCode 

Name Type Description Constraints 

uQCCodeID tinyint Natural PK Unique 

sName varchar(50) Unique 

1.5 Table QCLevel 

Name Type Description Constraints 

uQCLevelID tinyint Natural PK Unique 

sName varchar(50) Unique 

1.6 Table Site 

Contains information about each of the air quality monitoring sites. 

Name Type Description Constraints 

uSiteID smallint Surrogate PK Unique auto increment integer 

sCode varchar(50) 

sName varchar(50) Site name 

rElevation real Elevation of monitoring site purposes only 

rLatitudeDecimalDeg float Latitude of site in decimal degrees 0 to 360 

rLongitudeDecimalDeg float Longitude of site in decimal degrees -180 to 180 

iUTCOffset tinyint Time zone offset of monitoring site from GMT 

sStateCode char(2) State Abbreviation 

sAIRSCde char(9) Candidate Key 

bOverWater bit 

rHeightSeaTemp real 

rHeightAirTemp real 

rHeightAnemometer real 

rUtmX real 

rUtmY real 

iUTMGridZone smallint 
A-6 

2. EDAT DATABASE RELATIONS DIAGRAMS 

Figure 1 – EDAT Database Diagram 
B-1 

APPENDIX B 

COARE DOCUMENTATION FROM NOAA’S FTP SITE 

Appendix B contains information about the COARE program from NOAA’s ftp site at 

ftp://ftp.etl.noaa.gov/et7/anonymous/cfairall/bulkalg/ 
B-3 

COARE BULK AIR-SEA FLUX ALGORITHM 

January 1, 2000 

C. Fairall (NOAA/ERL) 

E.F. Bradley (CSIRO Land and Water) 

History

In 1993, Chris Fairall, Frank Bradley and David Rogers began development of a bulk air-sea flux 

algorithm for use by the COARE community. Based on the model of Liu, Katsaros and Businger 

(1979, LKB), it took account of the light wind, strongly convective conditions over tropical 

oceans. Version 1.0 was released in November 1993, and included modifications to the basic 

LKB code for wind roughness length (Smith, 1988), Monin-Obukhov profile functions for strong 

convection, and low-wind "gustiness" (Godfrey and Beljaars, 1991). Version 2.0 (August 1994) 

included code to model the cool skin physics (Saunders, 1967), and also daytime near-surface 

warming based on a simplified version of the Price, Weller and Pinkel (1986) ocean mixing 

model (Fairall et al., 1996a). These optional features enable conversion from bulk to true skin 

temperature for calculating the fluxes. Calculation of fluxes of momentum (Caldwell and Elliott, 

1971) and sensible heat (Gosnell, Fairall and Webster, 1995) due to rainfall are incorporated in 

the code, as is the so-called Webb correction to latent heat flux which arises from the 

requirement that the net dry mass flux be zero (Webb et al., 1980). The formalism of the 

algorithm is fully described in Fairall et al. (1996b). 

The next major modifications to the algorithm were made at the COARE Air-Sea Interaction 

(Flux) Group Workshop in Honolulu, 2-4 August 1995 (Bradley and Weller, 1995). Transfer 

coefficients were adjusted by six percent to give better average agreement with covariance latent 

heat fluxes from several COARE ships. This produced version 2.5b, which has been used 

successfully on various ocean-atmosphere field campaigns by members of the Flux Group, at 

various locations and from a variety of platforms. At the Woods Hole workshop, 9-11 October 

1996 (Bradley and Weller, 1997) it was agreed that no further development would be attempted 

to the community version of the COARE Bulk Flux Algorithm, and that a version 2.5b bulk 

algorithm "package" would be made available, consisting of the Fortran source code and a test 

data set. This was released at a meeting of the Flux Group at NCAR, 14-16 May 1997 

(Bradley, Moncrieff and Weller, 1997), and was made available from the following archive sites: 

1. The Florida State University COAPS (Center for Ocean Atmospheric Prediction Studies) 

http://www.coaps.fsu.edu/COARE/flux_algor/ 

OR 

ftp://coaremet.fsu.edu/pub/coare/flux_algor/ 

2. Scripps Institution of Oceanography Physical Oceanography Research Division 

http://penarth.ucsd.edu/coare/ 

OR 

ftp://penarth.ucsd.edu/coare/ 

3. NCAR (National Center for Atmospheric Research) Data Support Section 
B-4 

http://www.scd.ucar.edu/dss/datasets/ds606.1.html 

In December of 1999, Bradley and Fairall made available version 2.6a in both Fortran and 

matlab forms. The new version of the model has several changes that are summarized as 

follows: 

1. The empirical constants in the convective portion of the profile functions have been changed 

for improved matching to direct profile observations (Grachev et al., 1999). These are referred 

to as psiu_26 and psit_26; the original forms are referred to as psiu_25 and psit_25. 

2. The Kansas stable profile functions have been replaced by those from Beljaars and Holtslag 

(1991) which is a better fit to new profile data taken over the Arctic ice cap in the SHEBA 

project. 

3. A fixed value of the Charnock parameter ("=0.011) has been replaced by a formulation with a 

simple wind-speed dependence above 12 m/s based on data from Yelland and Taylor (1996) and 

Hare et al. (1999). 

4. The Liu et al. (1979) scalar roughness relationship [ fx(Rr) ] has been replaced with a much 

simpler one that fits both the COARE, several additional ETL flux data sets, and HEXMAX 

data base (DeCosmo et al., 1996). 

5. The stability iteration loop has been reduced from 20 to 3 using bulk Richardson number 

parameterization for an improved first guess (Grachev and Fairall, 1997). 

6. The latent heat flux has been reformulated in terms of mixing ratio, q, instead of water vapor 

density, Q, to eliminate the need for a Webb et al. (1980) correction. This change is not apparent 

in the input variables, which used mean mixing ratio (as does version 2.6). However, the 

original transfer coefficients were fit to the measurements of fluxes in the form <w’Q’>/Da rather 

than the correlation of vertical velocity with mixing ratio, because <w’Q’> was the actual 

measured quantity. In the new version of the model, we have fit the transfer coefficients to 

<w’Q’>/Da + Webb = <w’q’> because the mixing ratio is the quantity that is fundamentally 

conserved during mixing. 

In January of 2000, Bradley and Fairall made available version 2.6a in both Fortran and matlab 

forms. That version of the model was described in the coare26a_readme file. A new edition that 

incorporates surface gravity wave information, version 26bw, has been produced in June 2001. 

We recommend using 2.6bw; there will be no further 2.6 versions. If you are not interested in 

the wave aspects, just set the wave switch to 0 and put in dummy numbers for the wave 

properties. 

 

Version 2.6bw has three small changes relative to 2.6a in addition to the wave effects: 

(1). The zoq parameterization has been changed to 

 zoq=min(1.15e-4,5.5e-5/rr^.6); 

This slightly reduces the moisture and heat transfer coefficients at low winds. 

(2) The xlamx parameter limit has been changed from 30 to 6 in the ‘warm skin’ regime to 

eliminate unreasonable values in very light winds. 

(3) The date is input in Y2K format (YYYY instead of YY). 
B-5 

It .has simple additions for waves as follows: 

The data inputs have been expanded to allow three additional parameters: a switch coded 0,1, or 

2 to designate the wave model used, wave period and significant wave height. 

wave=0: No wave model, just use the specified Charnock parameter in the version 2.6a code. 

wave=1: Use the Oost et al. (2001) wave age parameterization. In this case you must specify 

wave period 

wave=2: Use the Taylor and Yelland (2000) wave slope/height model. In this case you must 

specify wave period and significant wave height. 

 

Description of the bulk algorithm "package"

The "package" consists of a input data, bulk algorithm program, and output data files: 

Input data 

test2_5b.dat (Test data set, with headers) 

test2_6b.txt (Test data set, without headers, Y2K) 

Programs 

cor2_6bw.for (Fortran source code) and .m (matlab source code). This is the new version 2.6b 

setup to use the Fairall near-surface temperature sensor for Ts bulk. 

Output files (sea surface T source X=f or h) 

tst2_6bX.out Fortran output file from test data using Charnock formula 

oea2_6bw.out Output file using the Oost et al. formula and fully developed sea 

tay2_6bw.out Output file using the Taylor and Yelland formula and fully developed sea 

Bulk algorithm program

A full description of the code and the test data set appears at the head of the Fortran file. We 

provide some notes here: 

1. The input "read" statement is set up for the test data file test2_5b.dat . This consists of four 

days of Moana Wave COARE data, 26-29 Nov 1992, prepared from Chris Fairall's hourly data 

file wavhr2_5.asc dated 31/10/96. A full description of the Moana Wave operations, instruments 

and data set is given at 

http://www.ncdc.noaa.gov/coare/catalog/data/air_sea_fluxes/moana_flux.html 

2. Only those observations required by the flux algorithm were extracted from Chris' lines of 

data, excepting that his independently calculated bulk fluxes are included for comparison. 
B-6 

3. Some parameters are not input, but must be redefined in the code if necessary (e.g., the height 

of sensors (hum, htm), the bulk temperature sensor depth (ts_depth), needed for calculation of 

the warm layer effect, and pressure and mixed layer height (pp and zi) if available). 

4. Because Chris' Tsea was measured at only 0.05m depth, we have added Ts at 6m depth from 

Mike Gregg's Advanced Microstructure Profiler (AMP, but called MSP in the file) to 

demonstrate the warm layer code. The Profiler was operated from the Moana Wave during 

leg 1, and the data was kindly provided in suitable form for the test file by Hemantha Wijesekera 

(Oceanography Dept., Oregon State University). 

5. The warm layer and/or cool skin code may be bypassed by setting jwarm and/or jcool to zero 

in the code. Note that if jcool or jwarm are set to zero, then values for dt_cool and dt_warm are 

still computed and passed back by the code, but are not used in calculations of the flux. 

6. To demonstrate the warm layer and cool skin, we output the respective delta-temperatures and 

the warm layer thickness. Note that dt_warm is the warming across the entire warm layer--only if 

tk_pwp is less than the sensor depth (ts_depth = 6m in the test case) will 

T0=ts-dt_cool*jcool+dt_warm*jwarm. Otherwise, a linear profile is assumed, and the 

appropriate fraction of warming above the bulk sensor calculated. Chris' Tsea at 0.05m depth 

will generally include most of the warm layer but not the cool skin effect. 

7. The Webb correction to latent heat flux is now included because we have adjusted the transfer 

coefficient to include it. Instead of the correction to the latent heat flux, the new version of the 

code returns the mean vertical velocity appropriate for applying the Webb correction to any 

measurements of scalar concentration flux. The sensible heat flux due to rainfall is NOT added 

internally in the code. This is output separately, and may be accounted for at the user's discretion. 

We provide some notes on just the wave aspects here. 

1. The Oost et al. (2001) formula has been written in the form: 

zo=50/2/pi*lwave*(usr/cwave)^4.5+0.11*visa/usr

2. The Taylor and Yelland (2000) formula is 

zo=1200*hwave*(hwave/lwave)^4.5+0.11*visa/usr

Note, lwave (wave length) and cwave (phase speed) are computed in the code from twave using 

standard deep water wave formulae. If you have shallow water, you will have to put in the depth 

and use the appropriate formulae. 

Test input file 

 

1 Date: YYYYMMDDHHmmss, YYYY=year, MM=month, DD=day, HH=hour, 

mm=minute,ss=sec 

2 U: true wind speed at 15-m height m/s 

3 Tsea: sea surface temp (at about 0.05m depth) deg.C 
B-7 

4 Tair: Vaisala air temperature (about 15 m) deg.C 

5 qair: Vaisala air specific humidity (about 15 m) g/kg 

6 Hsb: Fairall's original BASIC code bulk sensible heat flux W/m2 

7 Hlb: Fairall's original BASIC code bulk latent heat flux W/m2 

8 Taub: Fairall's original BASIC code bulk surface stress N/m2 

9 Rs: solar irradiance W/m2 

10 Rl: downwelling longwave irradiance W/m2 

11 Rain: precipitation mm/hr 

12 Lat: Latitude 

13 Lon: Longitude 

14 MSP: MSP temperature at 6m depth deg.C 

Because the test input file does not contain wave information, we have added formulae in the 

master program to estimate typical wave parameters for a fully developed sea: 

b=.729; 

Twave=b*u; 

hwave=0.018*u.^2.*(1+.015*u); 

The programs are presently setup with wave=0, so no wave data is used. 

Test output file 

1 index: data line number 

2 xtime: YYYYMMDDHHmmss, date and time as read in 

3 hsb: Fairall's bulk sensible heat flux as read in W/m2 

4 hlb: Fairall's bulk latent heat flux as read in W/m2 

5 taub: Fairall's bulk surface stress as read in N/m2 

6 ts: Bulk water temperature: MSP at 6m depth (h version) or Fairall at 0.05 m depth (f 

version) as read in deg.C 

7 HF: calculated sensible heat flux W/m2 

8 EF: calculated latent heat flux W/m2 

9 TAU: calculated surface stress N/m2 

10 T0: calculated sea skin temperature deg.C 

11 Webb mean vertical velocity (2.6) m/s 

12 RainF: sensible heat flux due to precipitation W/m2 

13 rain: precipitation mm/hr as read in 

14 dt_cool: cool skin effect deg.C 

15 dt_warm: total warming across warm layer thickness deg.C 

16 tk_pwp: warm layer thickness m 

MATLAB Programs

cor2_5bf .m and cor2_5bh .m

 Read the data, do the warm layer calculations, draw some graphs, write the new files 
B-8 

 Calls the flux and cool skin subroutine cor25.m 

 This routine operates of the data vector 

 x=[u us ts t qs q Rs Rl rain zi P zu zt zq lat jcool]

 and returns a long data vector of 21 quantities described at the end of the routine.

 Other subroutines used: psiu_25.m, psit_25.m, qsee.m, grv.m 

cor2_6af .m and cor2_6ah .m

 Read the data, do the warm layer calculations, draw some graphs, write the new files 

 Calls the flux and cool skin subroutine cor26.m 

 This routine operates of the data vector 

 x=[u us ts t qs q Rs Rl rain zi P zu zt zq lat jcool]

 and returns a long data vector of 21 quantities described at the end of the routine.

 Other subroutines used: psiu_26.m, psit_26.m, qsee.m, grv.m 

Note: if you are not interested in the warm layer, then fluxes can be computed by calling 

cor25(x) or cor26a(x) as a simple function. 

cor2_6bfw.m. This is the new version 2.6b setup to use the Fairall near-surface temperature 

sensor for Ts bulk. 

 Read the data, do the warm layer calculations, draw some graphs, write the new files 

 Calls the flux and cool skin subroutine cor26w.m 

 This routine operates of the data vector 

 x=[u us ts t qs q Rs Rl rain zi P zu zt zq lat jcool wave twave hwave]

 and returns a long data vector of 21 quantities described at the end of the routine. Other 

subroutines used: psiu_26.m, psit_26.m, qsee.m, grv.m 

cor2_6bhw.m.This is the new version 2.6b setup to use the MSP temperature at a depth of 6 m 

for Ts bulk. This implies greater dependence on the warm layer code for flux calculations. 

Note: if you are not interested in the warm layer, then fluxes can be computed by calling 

y=cor26bw(x) as a simple function. 

Output files (sea surface T source X=f or h) 

tst2_6bXw_out.txt Matlab output file from test data in ascii format 

tst2_6bXw_out.mat Matlab output file from test data as matlab mat file 

References

Beljaars, A. C. M., and A. A. M. Holtslag, 1991: Flux parameterization over land surfaces for 

atmospheric models. J. Appl. Meteor., 30, 327-341. 

Bradley, E.F., and R.A. Weller, 1995: Third Workshop of the TOGA COARE Air-Sea 

Interaction (Flux) Working Group. Honolulu, 2-4 Aug 1995. UCAR/TCIPO. UCAR 

Communications, PO Box 3000, Boulder CO 80307-3000 USA. 
B-9 

Bradley, E.F., and R.A. Weller, 1997: Fourth Workshop of the TOGA COARE Air-Sea 

Interaction (Flux) Working Group. Woods Hole, 9-11 Oct 1996. UCAR/TCIPO. UCAR 

Communications, PO Box 3000, Boulder CO 80307-3000 USA. 

Bradley, E.F, M.W. Moncrieff and R.A. Weller, 1997: Joint workshop of the TOGA COARE 

Flux and Oceans Working Groups, and the GEWEX GCSS Working Group 4. Boulder, 

Colorado, 14-16 May 1997. NCAR/MMM, PO Box 3000, Boulder CO 80307-3000 

USA. 

Caldwell, D.R. and W.H. Elliott, 1971: Surface stresses produced by rainfall. J. Phys. Oceanog. 

1, 145-148. 

DeCosmo, J., K. B. Katsaros, S. D. Smith, R. J. Anderson, W. A. Oost, K. Bumke, and H. 

Chadwick, 1996: Air-sea exchange of water vapor and sensible heat: The Humidity 

Exchange Over the Sea (HEXOS) results. J. Geophys. Res., 101, 12001-12016. 

Fairall, C.W., E.F. Bradley, J.S. Godfrey, G.A. Wick, J.B. Edson, and G.S. Young, 1996a: The 

cool skin and the warm layer in bulk flux calculations. J. Geophys. Res. 101, 1295-1308. 

Fairall, C.W., E.F. Bradley, D.P. Rogers, J.B. Edson, G.S. Young, 1996b: Bulk parameterization 

of air-sea fluxes for TOGA COARE. J. Geophys. Res. 101, 3747-3764. 

Godfrey, J.S., and Beljaars, 1991: On the turbulent fluxes of buoyancy, heat, and moisture at the 

air-sea interface at low wind speeds. J. Geophys. Res. 96, 22043-22048. 

Gosnell, R., C.W. Fairall, and P.J. Webster, 1995: The sensible heat flux of rainfall in the 

tropical ocean. J. Geophys. Res. 100, 18437-18442. 

Grachev, A.A., and C.W. Fairall, 1997: Dependence of the Monin-Obukhov stability parameter 

on the bulk Richardson number for unstable conditions over the ocean. J. Appl. 

Meteorol., 36, 406-414. 

Grachev, A. A., C. W. Fairall, and E. F. Bradley, 1999: Convective profile constants revisited. 

Bound.-Layer Meteorol., to appear. 

Hare, J. E., P. O. G. Persson, C. W. Fairall, and J. B. Edson, 1999: Behavior of Charnock’s 

relationship for high wind conditions. Proc. 13th Symposium of Boundary Layers and 

Turbulence. AMS. Dallas, TX, Jan. 15-20, paper 5B.8. 

Liu, W.T, K.B. Katsaros and J.A. Businger, 1979: Bulk parameterization of the air-sea exchange 

of heat and water vapor including the molecular constraints at the interface, J. Atmos. 

Sci. 36, 1722-1735. 

Price, J.F., R.A. Weller and R. Pinkel, 1986: Diurnal cycling: Observations and models of the 

upper ocean response to diurnal heating, cooling, and wind mixing, J. Geophys. Res. 91, 

8411-8427. 
B-10 

Oost, W. A., G. J. Komen, C. M. J. Jacobs, and C. van Wort, 2001: New evidence for a relation 

between wind stress and wave age from measurements during ASGAMAGE. Tech. Report 

2001-5, Royal Dutch Meteorological Institute (KNMI), De Bilt, The Netherlands, pp30. 

Saunders, P.M., 1967: The temperature at the ocean-air interface. J. Atmos. Sci. 24, 269-273. 

Smith, 1988: Coefficients for sea surface wind stress, heat flux, and wind profiles as a function 

of wind speed and temperature. J. Geophys. Res. 93, 15467-15472. 

Taylor, P. K., and M. J. Yelland, 2000: The dependence of sea surface roughness on the height 

and steepness of the waves. J. Phys. Oceanography, 31, 572-590. 

Webb, E.K., G.I. Pearman and R. Leuning, 1980: Correction of flux measurements for density 

effects due to heat and water vapour transfer, Q.J.R. Meteorol. Soc. 106, 85-100. 

 

Yelland, M. and P. K. Taylor, 1996: Wind stress measurements from the open ocean. J. Phys. 

Oceanogr., 26, 541-558. 

For more information, please contact: 

Chris Fairall 

NOAA/ERL/WPL 

325 Broadway 

Boulder, CO 80303 USA 

e-mail: cwf@etl.noaa.gov 

Phone: (303)497-3253 

Fax: (303)497-6101 

OR 

E. Frank Bradley 

CSIRO Land and Water 

GPO Box 1666 

Canberra, ACT 2601 AUSTRALIA 

e-mail: frank.bradley@cbr.clw.csiro.au 

Phone: (61) 2 6246 5575 

Fax: (61) 2 6246 5560 
C-1 

APPENDIX C 

COARE FORTRAN CODE 

 Appendix C contains Fortran code of COARE 26bw.for that was modified for use in the 

MMS ABL project. This version of the COARE program was used to make estimates of 

fundamental boundary layer scaling parameters such as the surface roughness length, zo, the 

friction velocity, u*, the scaling temperature, T*, the scaling water vapor mixing ratio, q*, and 

the Monin-Obukhov length, L from routine surface meteorological observations in the Gulf of 

Mexico. 
C-3 

c $debug 

c....................................................................... 

c PROGRAM: bulk_v2.6 

c 

c 16/5/01 in San Diego. This is cor2_6aw.for with wave state options 

c Made from cor2_6af.for i.e. uses Chris' SST sensor. zoq modification 

c 

c COARE bulk flux version 2.6a was made from 2.5b by Frank Bradley 3/12/99 

c Replace 20 iterations with Grachev and Fairall first guess z/L routine 

c J. App. Meteor. 36, 406-414, 1997 

c 

c Add Chris' mods as used in Jasmine of rr-zoq,charnock,cool skin 

c 

c Untangle some complexity which had crept into 2.5b 

c Use separate phiu,phit functions with Grachev et al (2000) constants 

c Stable functions according to Beljaars and Holtslag 

c J. Appl. Meteor. 30, 327-341, 1991 

c Return Webb Wbar because Webb flux correction already included in QE 

c 

c THIS version cor2_6af.for uses Chris' seasnake for Ts 

c Another version cor2_6ah.for uses Hemantha's 6m depth MSP data for Ts 

c Set up to read COARE test data set, see Bradley, Moncrieff and Weller, 

c Proceedings of the COARE Flux Group workshop, May 14-16 1997, 

c NCAR/MMM, PO Box 3000, Boulder, CO 80307-3000, USA 

c COARE test data file is test2_5b.dat 

c This routine outputs tst2_6af.out 

c 

c Output compared with Chris Fairall's Matlab version - OK 

c...................................................... 

c input data - converted for subroutine call because of conflict with COMMON: 

c xtime (COARE convention yymnddhhmmss.ssss GMT) 

c zu (wind measurement height) m 

c zt (T&rh measurement height) m 

c zus (wind standard height) m - changes to different ref. height. 

c zts (T&rh standard height) m 

c ts_depth (depth of sst instrument) - positive m - for cool skin/warm layer correction 

c u (wind speed relative to the sea surface) m/s 

c ts (sea surface temp.) deg. C 

c t (air temperature) deg. C 

c q (specific humidity) g/kg or qq (RH as decimal) - code works internally in kg/kg!! 

c rs (shortwave radiation) W/m2 

c rl (downwelling longwave) W/m2 

c rain (average rainrate in timestep) mm/hour 

c p (pressure) mb; use 1008mb if data unavailable 

c zi (boundary-layer depth; use 600m if data unavailable) m 

c jcool (=1 for cool skin calculation; =0 if SST measured by IR radiometer) 
C-4 

c jwarm (=1 for warm layer calculation; =0 if SST measured by IR radiometer) 

c xlat (latitude) degrees [latitude north +ve, latitude south -ve] 

c xlon (longitude) degrees [Longitude east +ve, longitude west -ve] 

c.................................................................... 

c output: 

c QH W/m**2 (Sensible heat flux) - turbulent part only 

c QE W/m**2 (Latent heat flux) - turbulent part only 

c QR W/m**2 (Rainfall heat flux) 

c TAU N /m**2 (wind stress) - turbulent part only 

c Ustar m/s (velocity scaling parameter - friction velocity) 

c Qstar kg/kg (humidity scaling parameter) 

c Tstar C (temperature scaling parameter) 

c CDN - neutral drag coefficient 

c CHN - neutral transfer coefficient for heat 

c CEN - neutral transfer coefficient for moisture 

c RR - Roughness Reynolds number 

c RT - Roughness Reynolds number for temperature 

c RQ - Roughness Reynolds number for moisture 

c ZL - height/L where L is the Obukhov length 

c Z0 - roughness length 

c zot - roughness length for temperature 

c zoq - roughness length for humidity 

c dt_wrm - total warm layer temperature difference C 

c tk_pwp - thickness of warm layer 

c dter - cool skin temperature difference C 

c T0 - skin temperature C (T0 = sst - dter + dt_wrm*ts_depth/tk_pwp) 

c wg - gustiness factor m/s 

c Taur - momentum flux due to rain N/m**2 

c Wbar - Webb mean vertical velocity m/s 

c 

 program fluxes 

 real*8 ws_h,Ta_h,qq_h 

 real*8 zu,zt,zus,zts,u,ts,t,q,p,zi,rain,xlat,xlon,tt 

 real*8 QH,QE,TAU,Ustar,Qstar,Tstar 

 real*8 rl,rs,QR,T0,ts_depth,wg 

 real*8 CDN,CEN,CHN,RR,RT,RQ,ZL 

 real*8 Zo,zot,zoq,dt_wrm,dter,S 

 real*8 Wbar,Tau_r,glat 

 real*8 time_old,qcol_ac,tau_ac,tau_old,rf_old,hf_old,ef_old 

 real*8 intime,sol_time,tk_pwp,fxp,Tsin 

 real*8 hwave,twave 

 integer hh,yy,dd,ss 

 

 real*8 HEeta0612,HEeta1824 

 real*8 HEeta3036,HEeta4248 

 
C-5 

 real*8 HSeta0612,HSeta1824 

 real*8 HSeta3036,HSeta4248 

 

 real*8 Fricveta0612,Fricveta1824 

 real*8 Fricveta3036,Fricveta4248 

 

 real*8 Lowcloud,Midcloud,Highcloud 

 

 Integer Heflag0612 

 Integer Heflag1824,Heflag3036 

 Integer Heflag4248 

 

 Integer HSflag0612,HSflag1824 

 Integer HSflag3036,HSflag4248 

 Integer Fricvflag0612,Fricvflag1824 

 Integer Fricvflag3036, Fricvflag4248 

 

 Integer Lowflag,Midflag,Highflag 

 Integer shortflag,longflag 

 

 integer Uflag,tsflag,tflag,qflag 

 integer rsflag,rlflag, rainflag, xlatflag 

 integer xlonflag, pflag, ziflag,outflag,hwaveflag,twaveflag 

 

 character*17 chtime 

 character*12 xtime 

 character*5 site 

 

 

 

 COMMON /old/time_old,qcol_ac,tau_ac,tau_old,rf_old,hf_old, 

 & ef_old,jamset,jump,fxp,tk_pwp,index 

c 

c initialize variables 

 qcol_ac=0. 

 tau_ac=0. 

 time_old=0. 

 jamset=0. 

 tau_old=0. 

 hf_old=0. 

 ef_old=0. 

 rf_old=0. 

 jamset=0 

 jump=0 

c 

c 
C-6 

 open (unit=15,file='config.dat') !info on tdepth,jwarm,jcool 

 open(unit=3,file='indata.dat') ! original coare2.5b input data 

 open(unit=9,file='coare.out') ! output file from this program 

c open(unit=10,file='exch2_6c.out') ! CDN,CHN and CEN from this program 

c 

 write(9,500) 

c ADD variables (MMS) 

500 format('SITE xtime xlat xlon 

 1 t tflag q qflag u uflag ts tsflag tsin tsflag 

 1 rs shortflag rl longflag p pflag Zi Ziflag 

 & outflag QH QE TAU T0 rain rainflag dter dt_wrm tk_pwp 

 & ZL RR ZO ustar tstar qstar 

 1 Fricveta0612 Fricvflag0612 Fricveta1824 Fricvflag1824 

 1 Fricveta3036 Fricvflag3036 Fricveta4248 Fricvflag4248 

 1 Heeta0612 Heflag0612 Heeta1824 Heflag1824 

 1 Heeta3036 Heflag3036 Heeta4248 Heflag4248 

 1 HSeta0612 HSflag0612 HSeta1824 HSflag1824 

 1 HSeta3036 HSflag3036 HSeta4248 HSflag4248 

 1 lowcloud lowflag midcloud midflag highcloud highflag') 

c 

c Sensor heights zu and zt and ts_depth to be read in from indata (MMS) 

c 

c zu=15. !height of wind measurement 

c zt=15. !height of air temp. and RH 

 zus=10. !10m standard levels 

 zts=10. 

c ts_depth=0.05 !Chris Fairall's floating sensor 

c ts_depth=0.45 !from IMET buoy 

c ts_depth=6.0 !Hemantha's 6m data 

c 

c default values for pressure and mixed layer height 

c read in from input file instead 

c p=1008. 

c zi=600. 

c 

c initial guesses to the warm layer parameters, these values simulate what is expected 

c in early morning: fxp=0.5 implies a shallow heating layer to start the integration; 

c tk_pwp=19.0 implies the thickness is a maximum from the day before and is not meant to 

c match this timestep's fxp. 

 fxp=0.5 

 tk_pwp=19.0 

 

c if SST sensed by IR radiometer, set jwarm and jcool to zero 

c read in config (MMS) 

c jwarm=1 (MMS readin) 
C-7 

c jcool=1 (MMS readin) 

c jwave=1 ! (MMS readin) 0=Charnock,1=Oost et al,2=Taylor and Yelland. Also choose 

output file name 

 READ (15,505)ADUM ! READ IN CONFIG HEADER 

 READ (15,431)ZU,ZT,TS_DEPTH,JCOOL,JWARM,jwave !READ IN 

JCOOL,JWARM,TS_DEPTH 

 print *, ZU,ZT,TS_DEPTH,JCOOL,JWARM,jwave 

431 FORMAT (F4.1,1X,F4.1,1X,F4.2,1X,I1,1X,I1,1x,i1) 

c loop through data 

c 

 index=0 

 READ(3,505)ADUM ! skip header line of test data 

c READ(4,505)ADUM ! skip header line of test output data 

505 FORMAT(A1) 

 do ijk=1,1000000 !start of loop 

 index=index+1 !count data records (hours) 

c 

c Read in data where Ts is either skin or underwater. If underwater Jcool and Jwarm = 1 

 

700 READ (3,705,end=910) site,xtime,u,uflag,ts,tsflag, 

 1 t,tflag, q,qflag,rs,shortflag, 

 1 rl,longflag, 

 1 rain,rainflag,xlat,xlon, 

 1 p,pflag,zi, ziflag, 

 1 Fricveta0612, Fricvflag0612, 

 1 Fricveta1824, Fricvflag1824, 

 1 Fricveta3036, Fricvflag3036, 

 1 Fricveta4248, Fricvflag4248, 

 1 Heeta0612, Heflag0612, 

 1 Heeta1824, Heflag1824, 

 1 Heeta3036, Heflag3036, 

 1 Heeta4248, Heflag4248, 

 1 HSeta0612, HSflag0612, 

 1 HSeta1824, HSflag1824, 

 1 HSeta3036, HSflag3036, 

 1 HSeta4248, HSflag4248, 

 1 lowcloud, lowflag, 

 1 midcloud, midflag, 

 1 highcloud, highflag, 

 1 hwave, hwaveflag, 

 1 twave, twaveflag 

 

 

 
C-8 

705 FORMAT(a5,1x,a12,3x,3(F9.1,3x,i1,3x),F11.3,3x,i1,3x, 

 1 3(F9.1,3x,i1,3x),2(F8.2,4x),f9.1,3x,i1,3x,f9.0,3x,i1,3x 

 1 4(f10.5,3x,i1,3x),8(f9.2,3x,i1,3x),3(f6.2,3x,i1,3x), 

 1 2(f7.1,3x,i1,3x)) !wave formats 

 

 

c Set ts orig so can see warm and cool effect 

 tsin=ts 

c 

c set u=.1 and hwave to .1 and twave to 7 when 0 to avoid crash 

 

 if (u .eq. 0.) then 

 u=0.1 

 endif 

 

 if (hwave .eq. 0.) then 

 hwave=0.1 

 endif 

 

 if (twave .eq. 0.) then 

 twave=1 

 endif 

 

c IF pressure is missing and read in as -999. set pp=1008. (MMS) 

 

 if (p .lt. 0.) then 

 p=1008. 

 endif 

 

c IF mixing height is missing and read in as -999. set zi=600. (MMS) 

 

 if (zi .lt. 0.) then 

 zi=600. 

 endif 

c 

c 

 glat=xlat 

 

c check warm layer, cool skin switches 

c 

 if(Jwarm.gt.0) then 

 if(index.eq.1) then 

 Jwarm=2 

 else 

 Jwarm=1 
C-9 

 endif 

 endif 

c 

c convert time to decimal hours (e.g. yymnddhhmmss -> hh.hhhh) 

c 

 

 read(xtime,12) yy,mn,dd,hh,mm,ss 

12 format(6i2) 

 

 intime=(float(hh)+float(mm)/60.+float(ss)/3600.) !eg 18.4833 

c 

c and convert to local solar time in seconds xlon/15 is UTC offset = 6.12 

c ex. intime=00 leaves 6.12*3600 = 22032 for lon=90.10 

c seconds past midnight 

 sol_time=mod(xlon/15+intime+24.,24.)*3600. !eg 17580 

c 

c Set dummy values when -999 so program continues to run (MMS) 

c set flags 

c set outflag =8, leave uflag =9 etc 

 outflag=0 

 if (u .lt. 0.) then 

 u=3. 

 outflag=8 

 endif 

 

 if (t .lt. 0.) then 

 t=30. 

 outflag=8 

 endif 

 

 if (ts .lt. 0.) then 

 ts=31. 

 outflag=8 

 endif 

 

 if (q .lt. 0.) then 

 q=.80 

 outflag=8 

 endif 

c c default values for wave height and period for equilibrium sea 

 if (hwave.eq.-999.) then 

 hwave=0.018*u*u*(1+.015*u) 

 hwave=max(hwave,.1) !Set minimum hwave to .1 CPM 7/4/2002 
C-10 

 hwaveflag=2 

 endif 

 

 if (twave.eq.-999.) then 

 twave=0.729*u 

 twave=max(twave,1) !Set minimum twave to 1 CPM 7/4/200 

 twaveflag=2 

 endif 

 

c set dummy's for missing rs and rl only if warm effect ie jwarm=1 

 if (jwarm .gt. 0 .and. rs .eq. -999.) then 

 temptime=sol_time*3600 

 if (sol_time .lt. 21600. .or. sol_time .gt. 64800)then 

 rs = 0. 

 rl=400. 

 else 

 rs =sin((3.14/2)*(sol_time/3600-6)/6)*1380 

 rl=400. 

 endif 

 if (outflag .ne. 8) then !set outflag to 7 if jwarm is on, all obs available, but rs estimated 

 outflag =7 

 endif 

 

 

 endif 

 

c Set flag=3 for COARE calculated parmeters if from interpolated data i.e input flag=3 

c But if rs estimated and data interp flag=6 

c 

 

 if (tflag .eq. 3 .or. qflag .eq. 3 .or. uflag .eq. 3 

 1 .or. tsflag .eq. 3) then 

 

 if (outflag .eq. 7) then ! But if rs estimated and data interp flag=6 

 outflag=6 

 endif 

 

 if (outflag .eq. 8 .or. outflag .eq. 6) then ! Don't want to reset to 3 if rs is dummy and 

jwarm is on ! 

 goto 2333 

 else 

 outflag=3 

 endif 

2333 continue 

 endif 
C-11 

 

 

c 

c call bulk flux routine 

c 

 call bulk_flux(sol_time,xlat,zu,zt,zus,zts,Jwave,hwave,twave, 

 & u,ts,t,q,ws_h,Ta_h,qq_h,rs,rl,rain,p,zi,Jcool,Jwarm, 

 & QH,QE,QR,TAU,Ustar,Tstar,Qstar, 

 & CDN,CHN,CEN,RR,RT,RQ,ZL,Zo,zot,zoq,S, 

 & dt_wrm,dter,T0,ts_depth,wg,TAU_r,Wbar) 

c output results 

c 

 write(9,200)SITE,xtime,xlat,xlon, 

 1 t,tflag,q,qflag,u,uflag,ts,tsflag,tsin,tsflag, 

 1 rs,shortflag,rl,longflag, p,pflag ,Zi,Ziflag, 

 & outflag,QH,QE,TAU,T0,rain,rainflag,dter,dt_wrm,tk_pwp, 

 & ZL,RR,ZO,ustar,tstar,qstar, 

 1 Fricveta0612, Fricvflag0612, 

 1 Fricveta1824, Fricvflag1824, 

 1 Fricveta3036, Fricvflag3036, 

 1 Fricveta4248, Fricvflag4248, 

 1 Heeta0612, Heflag0612, 

 1 Heeta1824, Heflag1824, 

 1 Heeta3036, Heflag3036, 

 1 Heeta4248, Heflag4248, 

 1 HSeta0612, HSflag0612, 

 1 HSeta1824, HSflag1824, 

 1 HSeta3036, HSflag3036, 

 1 HSeta4248, HSflag4248, 

 1 lowcloud, lowflag, 

 1 midcloud, midflag, 

 1 highcloud, highflag, 

 1 hwave, hwaveflag, 

 1 twave, twaveflag 

 

200 format(A5,a16,2(f8.2),9(f9.2,1x,i1,1x),i1,1x 

 1 2(f11.1),f11.4,f11.2,f9.2,1x,i1,1x,4(f11.2),5(f14.7), 

 1 3x,4(f10.5,3x,i1,3x),8(f9.2,3x,i1,3x),3(f6.2,3x,i1,3x), 

 1 2(f6.1,3x,i1,3x)) !wave formats 

c 

c the following write is useful to monitor various other outputs of interest 

c write(10,202)index,u,cdn,chn,cen !to check with Chris' figures 

c202 format(i4,2x,f7.2,3(1pe10.2)) !take care p affects everything following 

 

 write(*,*) index 

c 
C-12 

 enddo !return to beginning of loop 

910 continue 

c 

c end of loop 

c 

 stop 

 end 

c 

c***************************************************************** 

 subroutine bulk_flux(sol_time,glat,zux,ztx,zusx,ztsx,Jwave,hwavex, 

 & twavex,ux,tsx,tx,qx,U_hs,T_hs,Q_hs,rs,rl,rainx,px,zix,Jcool, 

 & Jwarm,HF,EF,RF,TAU,Ustar,Tstar,Qstar, 

 & CD,CH,CE,RRx,RTx,RQx,ZLx,ZOx,zotx,zoqx,S, 

 & dt_wrmx,dterx,T0,ts_depthx,wgx,TAU_r,Wbar) 

c 

 real*8 zux,ztx,zusx,ztsx,U_hs,T_hs,Q_hs,ts_depthx 

 real*8 ZU,ZT,ZQ,ZUs,ZTs,ZQs,glat 

 real*8 ux,tsx,tx,qx,rainx,px,zix,wgx 

 real*8 U,TS,QS,T,Q,rl,rs,rain,p,zi,QA,S,DU_Wg,Wg,Wbar 

 real*8 HF,EF,TAU,RF,Ustar,Qstar,Tstar,TAU_r,ef_webb 

 real*8 CD,CE,CH,USR,TSR,QSR 

 real*8 Zox,zotx,zoqx,RRx,RTx,RQx,Zlx 

 real*8 ZO,zot,zoq,RR,RT,RQ,RI,zL 

 real*8 T0,ee,rns,rnl 

c various constants 

 real*8 al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK,visa 

 real*8 visw,von,fdg 

c rain heat variables 

 real*8 alfac,dqs_dt,dwat,dtmp 

c warm layer variables 

 real*8 sol_time,newtime,time_old,ctd1,ctd2,rich 

 real*8 qcol_ac,tau_ac,tau_old,rf_old,hf_old,ef_old 

 real*8 fxp,tk_pwp,dsea,dt_wrmx,dterx,qjoule,qr_out,dtime 

 real*8 dt_wrm,dter,dqer,tkt 

 real*8 hwave,twave,hwavex,twavex 

c 

 COMMON /old/time_old,qcol_ac,tau_ac,tau_old,rf_old,hf_old, 

 & ef_old,jamset,jump,fxp,tk_pwp,index 

 COMMON/PIN/U,T,Q,TS,QS,rns,rnl,ZU,ZT,ZQ,zi,P,ID 

 COMMON/POUT/USR,TSR,QSR,ZO,zot,zoq,ZL,RR,RT,RQ,RI, 

 & dter,dqer,tkt,DU_Wg,Wg 

 COMMON/const/al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK, 

 & visa,visw,von,fdg 

 COMMON/wave/hwave,twave ! pass to ASL 

c 

 Data dt_wrm /0.d0/ !set undefined variable to zero 
C-13 

 Data RTdefault /0.d0/ 

 Data RQdefault /0.d0/ 

 RT=RTdefault 

 RQ=RQdefault 

c 

c convert back variables that appear in COMMON 

c 

 ZU=zux !height of wind measurement 

 ZT=ztx !height of temperature measurement 

 ZQ=ztx !height of water vapor measurement 

 ZUs=zusx !standard height of wind measurement 

 ZTs=ztsx !standard height of temperature measurement 

 ZQs=ztsx !standard height of water vapor measurement 

 U=ux !wind speed m/s 

 TS=tsx !surface temp. Celsius 

 T=tx !air temp. Celsius 

 q=qx 

 P=px !pressure mb 

 zi=zix !atmospheric boundary layer depth 

 hwave=hwavex 

 twave=twavex 

c 

 toK=273.16 

 Rnl= 0.97*(5.67e-8*(TS+toK)**4-rl) !Net longwave (up = +) 

 Rns=0.945*rs !Net shortwave (into water) 

 rain=rainx !rainfall 

 ts_depth=ts_depthx !depth of sst measurement 

 call gravity(glat,grav) 

c grav=9.72 ! gravity equatorial value (ref. IGPP-SIO) 

c 

c Warm Layer 

c 

 if(Jwarm.ne.0) then 

 newtime=sol_time !run time in secs JUMP=1 first go or missing chunk of data 

 if(Jwarm.eq.2) then !jwarm=2 for first run need to set dt_wrm to 0.0 

 jump=1 

 goto 16 !set time_old and pass thru' ASL 

 elseif(newtime.gt.21600.and.jump.eq.1) then 

 goto 16 !6 am too late to start 

 elseif(newtime.lt.time_old) then !reset all var. at midnight 

 jump=0 !test threshold q morning only 

 jamset=0 

 fxp=0.5 

 tk_pwp=19.0 

 tau_ac=0.0 

 qcol_ac=0.0 
C-14 

 dt_wrm=0.0 

 goto 16 

 else 

 rich=.65 !critical Rich. No. 

 ctd1=sqrt(2*rich*cpw/(al*grav*rhow)) !u*^2 integrated so 

 ctd2=sqrt(2*al*grav/(rich*rhow))/(cpw**1.5) !has /rhow in both 

 dtime=newtime-time_old !delta time 

 qr_out=rnl+hf_old+ef_old+rf !flux out from previous pass 

 q_pwp=fxp*rns-qr_out !effective net warming 

 if(q_pwp.lt.50.and.jamset.eq.0) go to 16 !integration threshold 

 jamset=1 

 tau_ac=tau_ac+(max(tau_old,.001)*dtime) !tau from previous pass CPM ADD 

minimum stress .002 to prevent dt_wrm blowup 

c 

 if(qcol_ac+q_pwp*dtime.gt.0) then 

 do 10 iter1=1,5 !iterate for warm layer thickness 

 fxp=1.-(0.28*0.014*(1-dexp(-tk_pwp/0.014)) ! 

 & +0.27*0.357*(1-dexp(-tk_pwp/0.357)) ! 

 & +.45*12.82*(1-dexp(-tk_pwp/12.82)))/tk_pwp !solar absorb. prof 

 qjoule=(fxp*rns-qr_out)*dtime 

 if((qcol_ac+qjoule.gt.0.0)) 

 & tk_pwp=min(19,ctd1*tau_ac/sqrt(qcol_ac+qjoule)) 

 10 continue 

 else 

 fxp=.76 

 tk_pwp=19 

 qjoule=(fxp*rns-qr_out)*dtime 

 endif 

c 

 qcol_ac=qcol_ac+qjoule !integrate heat input 

 if(qcol_ac.gt.0) then 

 dt_wrm=ctd2*(qcol_ac)**1.5/tau_ac !pwp model warming 

 else 

 dt_wrm=0. 

 endif 

 endif 

 if(tk_pwp.lt.ts_depth) then !sensor deeper than pwp layer 

 dsea=dt_wrm !all warming must be added to ts 

 else !warming deeper than sensor 

 dsea=dt_wrm*ts_depth/tk_pwp !assume linear temperature profile 

 endif 

 ts=ts+dsea !add warming above sensor for new ts 

 16 time_old=newtime 

 endif 

c 

c end of warm layer 
C-15 

c 

 15 call humidity(T,P,QA) !Teten's formula returns sat. air in mb 

 if(q.lt.2.) then !checks whether humidity in g/Kg or RH 

 R=q 

 ee=QA*R !convert from RH using vapour pressure 

 Q=.62197*(ee/(P-0.378*ee)) !Spec. humidity kg/kg 

 else 

 Q=q/1000. !g/kg to kg/kg 

 endif 

 QA=.62197*(QA/(P-0.378*QA)) !convert from mb to spec. humidity kg/kg 

 call humidity(TS,P,QS) !sea QS returned in mb 

 QS=QS*0.98 !reduced for salinity Kraus 1972 p. 46 

 QS=.62197*(QS/(P-0.378*QS)) !convert from mb to spec. humidity kg/kg 

 Rnl= 0.97*(5.67e-8*(TS+toK)**4-rl) !Recompute net longwave (up = +) 

c 

c calculate atmospheric surface layer 

c 

 call ASL(Jcool,Jwave,IER,index) ! pass Jwave option 

 if(IER.ge.0) then 

c 

c compute surface stress (TAU), sensible heat flux (HF), 

c latent heat flux (EF) & other parameters 

c 

 S=sqrt(u*u + wg*wg) !velocity incl. gustiness param. 

 TAU=rhoa*USR*usr*u/S !kinematic units 

 HF=-cpa*rhoa*USR*TSR 

 EF=-xlv*rhoa*USR*QSR 

 tau_old=tau 

 ef_old=ef 

 hf_old=hf 

c compute heat flux due to rainfall 

 dwat=2.11e-5*((T+toK)/toK)**1.94 !water vapour diffusivity 

 dtmp=(1.+3.309e-3*T-1.44e-6*T*T)*0.02411/(rhoa*cpa) !heat diffusivity 

 dqs_dt=QA*xlv/(rgas*(T+toK)**2) !Clausius-Clapeyron 

 alfac= 1/(1+0.622*(dqs_dt*xlv*dwat)/(cpa*dtmp)) !wet bulb factor 

 RF= rain*alfac*cpw*((TS-T-dter*jcool)+(QS-Q-dqer)*xlv/cpa)/3600. 

c compute momentum flux due to rainfall 

 TAU_r=0.85*rain/3600*u 

c Webb correction to latent heat flux already in EF via zoq/rr function so return Wbar 

 Wbar=-1.61*usr*qsr/(1+1.61*q)-usr*tsr/(T+toK) 

c compute transfer coefficients 

c CD=(USR/S)**2 

c CH=USR*TSR/(S*(T-TS+.0098*zt+dter*jcool)) !revise 2e to 2f to include '+dter' 

c CE=USR*QSR/(S*(Q-QS+dqer)) 

c compute neutral transfer coefficients and met variables at standard height 

 CD=(0.4/dlog(zus/zo))**2 
C-16 

 CH=0.4*0.4/(dlog(zus/zo)*dlog(zts/zot)) 

 CE=0.4*0.4/(dlog(zus/zo)*dlog(zqs/zoq)) 

 T0=ts-dter*jcool 

 ihumid=0 

c Bypass attempt to accommodate q as RH. Don't have time to fix it. Bradley 

c if(q .lt. 2) ihumid=1 

 call h_adjust(ZUs,ZTs,ZQs,U_hs,T_hs,Q_hs,ihumid) 

c ws_h=U_hs 

c Ta_h=T_hs 

c qq_h=Q_hs 

c Convert a few things back to pass through parameter list 

 dterx=dter !cool skin parameters 

 tktx=tkt 

 dt_wrmx=dt_wrm !warm layer parameter 

 Ustar=USR 

 Tstar=TSR 

 Qstar=QSR 

 RRx=RR 

 RTx=RT 

 RQx=RQ 

 ZLx=ZL 

 Zox=Zo 

 zotx=zot 

 zoqx=zoq 

 wgx=wg 

 else !input parameters out of range 

 EF=-999. 

 HF=-999. 

 TAU=-999. 

 TAUr=-999. 

 EF_webb=-999. 

 Ustar=-999. 

 Tstar=-999. 

 Qstar=-999. 

 RRx=-999. 

 RTx=-999. 

 RQx=-999. 

 ZLx=-999. 

 ZOx=-999. 

 ws_h=-999. 

 Ta_h=-999. 

 qq_h=-999. 

 wg=-999. 

 endif 

 return !return to main program 

 end 
C-17 

c 

c ------------------------------------------------------------------ 

 subroutine ASL(Jcool,Jwave,IER,index) 

c 

c TO EVALUATE SURFACE FLUXES, SURFACE ROUGHNESS AND STABILITY OF 

c THE ATMOSPHERIC SURFACE LAYER FROM BULK PARAMETERS BASED ON 

c LIU ET AL. (79) JAS 36 1722-1735 

c 

 real*8 U,T,Q,TS,QS,rns,rnl,ZU,ZT,ZQ,zi,P,DU_Wg,Wg 

 real*8 USR,TSR,QSR,Zo,zot,zoq,ZL,RR,RT,RQ,RI,zetu,L10,L,zet 

c constants 

 real*8 al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK,visa 

 real*8 visw,von,fdg,charn,psiu,psit 

c cool skin quantities 

 real*8 wetc,bigc,be,cpv,dq,dt,dter,dqer,tkt,Bf,tcw 

 real*8 hsb,hlb,alq,qcol,qout,dels,xlamx,pr,du,ta 

c Grachev and Fairall variables 

 real*8 u10,zo10,cd10,ch10,ct10,zot10,cd,ct,cc,ribcu,ribu 

 real*8 hwave,twave,cwave,lwave,twopi 

c 

 COMMON/PIN/U,T,Q,TS,QS,rns,rnl,ZU,ZT,ZQ,zi,P,ID 

 COMMON/POUT/USR,TSR,QSR,ZO,zot,zoq,ZL,RR,RT,RQ,RI, 

 & dter,dqer,tkt,DU_Wg,Wg 

 COMMON/const/al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK, 

 & visa,visw,von,fdg 

 COMMON/wave/hwave,twave 

c Factors 

 Beta=1.2 !Given as 1.25 in Fairall et al.(1996) 

 Von=0.4 ! von Karman's "constant" 

c fdg=1.00 ! Fairall's LKB rr to von karman adjustment 

 fdg=1.00 !based on results from Flux workshop August 1995 

 toK=273.16 ! Celsius to Kelvin 

 twopi=3.14159*2. 

 

c Air constants and coefficients 

 Rgas=287.1 !J/kg/K gas const. dry air 

 xlv=(2.501-0.00237*TS)*1e+6 !J/kg latent heat of vaporization at TS 

 Cpa=1004.67 !J/kg/K specific heat of dry air (Businger 1982) 

 Cpv=Cpa*(1+0.84*Q) !Moist air - currently not used (Businger 1982) 

 rhoa=P*100./(Rgas*(T+toK)*(1.+.61*Q)) !kg/m3 Moist air density ( " ) 

 visa=1.326e-5*(1+6.542e-3*T+8.301e-6*T*T-4.84e-9*T*T*T) !m2/s 

 !Kinematic viscosity of dry air - Andreas (1989) CRREL Rep. 89-11 

c 

c Cool skin constants 

 al=2.1e-5*(ts+3.2)**0.79 !water thermal expansion coefft. 

 be=0.026 !salinity expansion coefft. 
C-18 

 cpw=4000. !J/kg/K specific heat water 

 rhow=1022. !kg/m3 density water 

 visw=1.e-6 !m2/s kinematic viscosity water 

 tcw=0.6 !W/m/K Thermal conductivity water 

 bigc=16.*grav*cpw*(rhow*visw)**3/(tcw*tcw*rhoa*rhoa) 

 wetc=0.622*xlv*QS/(rgas*(TS+toK)**2) !correction for dq;slope of sat. vap. 

c 

c Wave parameters 

 cwave=grav*twave/twopi 

 lwave=cwave*twave 

c 

c Initial guesses 

c 

 IER=0 

 Dter=0.3*jcool !cool skin Dt 

 Dqer=0. !cool skin Dq 

 Zo=0.0001 

 Wg=0.5 !Gustiness factor initial guess 

 tkt= 0.001 ! Cool skin thickness first guess 

 DU=U !assumes U is measured rel. to current 

 DU_Wg=(DU**2.+Wg**2.)**.5 !include gustiness in wind spd. difference 

 !equivalent to S in definition of fluxes 

 DT=Ts-T-0.0098*zt !potential temperature diff. Changed sign 

 DQ=Qs-Q ! from Coar2_5b 

c 

c **************** neutral coefficients ****************** 

c 

 u10=DU_Wg*dlog(10/Zo)/dlog(zu/Zo) 

 usr=0.035*u10 

 zo10=0.011*usr*usr/grav+0.11*visa/usr 

 Cd10=(von/dlog(10/zo10))**2 

 Ch10=0.00115 

 Ct10=Ch10/sqrt(Cd10) 

 zot10=10/dexp(von/Ct10) 

 Cd=(von/dlog(zu/zo10))**2 

c 

c ************* Grachev and Fairall (JAM, 1997) ********** 

c 

 Ct=von/dlog(zt/zot10) ! Temperature transfer coefficient 

 CC=von*Ct/Cd ! z/L vs Rib linear coefficient 

 Ribcu=-zu/(zi*0.004*Beta**3) ! Saturation or plateau Rib 

 TA=T+toK 

 Ribu=-grav*zu*((DT-dter)+0.61*TA*DQ)/(TA*DU_Wg**2) 

 if (Ribu.lt.0.) then 

 zetu=CC*Ribu/(1+Ribu/Ribcu) ! Unstable G and F 

 else 
C-19 

 zetu=CC*Ribu*(1+27/9*Ribu/CC) ! Stable, Chris forgets origin 

 endif 

 L10=zu/zetu ! MO length 

 thing=psiu(zetu) 

 if (zetu.gt.50) then 

 nits=1 

 else 

 nits=3 ! number of iterations 

 endif 

c 

c ****** First guess stability dependent scaling params. ****** 

c 

 usr= DU_Wg*von/(dlog(zu/zo10)-psiu(zu/L10)) 

 tsr=-(DT-dter)*von*fdg/(dlog(zt/zot10)-psit(zt/L10)) 

 qsr=-(DQ-wetc*dter)*von*fdg/(dlog(zq/zot10)-psit(zq/L10)) 

c 

 charn=0.011 !then modify Charnock for high wind speeds Chris' data 

 if(DU_Wg.gt.10) charn=0.011+(0.018-0.011)*(DU_Wg-10)/(18-10) 

 if(DU_Wg.gt.18) charn=0.018 

c 

c ******************* bulk loop ************************ 

c 

 do 10 iter=1,nits 

 zet= von*grav*zu/ta*(tsr+0.61*ta*qsr)/(usr*usr) 

 ZL=zet 

 if(Jwave.eq.0) then 

 zo=charn*USR*USR/grav + 0.11*visa/usr !after Smith 1988 

 else if(Jwave.eq.1) then 

 zo=(50./twopi)*lwave*(usr/cwave)**4.5+0.11*visa/usr !Oost et al. 

 else if(Jwave.eq.2) then 

 zo=1200.*hwave*(hwave/lwave)**4.5+0.11*visa/usr !Taylor and Yelland 

 endif 

 rr=zo*usr/visa 

c 

c *** zoq and zot fitted to results from several Chris cruises ************ 

c 

 zoq=min(1.15e-4,5.5e-5/rr**0.6) !was 0.63, changed 15/05/01 

 zot=zoq 

c 

 L=zu/zet 

 psu=psiu(zu/L) 

 pst=psit(zt/L) 

 usr=DU_Wg*von/(dlog(zu/zo)-psiu(zu/L)) 

 tsr=-(DT-dter*jcool)*von*fdg/(dlog(zt/zot)-psit(zt/L)) 

 qsr=-(DQ-wetc*dter*jcool)*von*fdg/(dlog(zq/zoq)-psit(zq/L)) 

 Bf=-grav/ta*usr*(tsr+0.61*ta*qsr) 
C-20 

 if (Bf.gt.0) then 

 Wg=Beta*(Bf*zi)**.333 

 else 

 Wg=0.2 

 endif 

c 

c ********** break into coare2.5b code again ************* 

c 

 DU_Wg=sqrt(DU**2.+Wg**2.) !include gustiness in wind spd. 

 hsb=-rhoa*cpa*usr*tsr 

 hlb=-rhoa*xlv*usr*qsr 

 qout=rnl+hsb+hlb 

 dels=rns*(.06+11*tkt-6.6e-5/tkt*(1-dexp(-tkt/8.0e-4))) ! Eq.16 changed .137 to .060 

CPM from CF 7/3/02 

 qcol=qout-dels 

 alq=Al*qcol+be*hlb*cpw/xlv !Eq. 7 Buoy flux water 

 if(alq.gt.0.) then !originally (qcol.gt.0) 

 xlamx=6/(1+(bigc*alq/usr**4)**.75)**.333 !Eq 13 Saunders coeff. 

 else 

 pr=bigc*abs(alq)/usr**4 !new from Chris 

 if(pr.lt.1) then 

 xlamx=6/(1-pr**.75)**.333 !Eq 13 Saunders coeff. 

 else 

 xlamx=6. !was 30 - caused excessive warm skins 

 endif 

 endif 

 tkt=xlamx*visw/(sqrt(rhoa/rhow)*usr) ! Eq.11 Sublayer thickness 

 dter=qcol*tkt/tcw ! Eq.12 Cool skin 

 dqer=wetc*dter 

 10 continue ! end Chris iterations 

c 

 idum=index ! avoids warning on compilation 

 return !to main subroutine, bulk_flux 

 end 

c 

c------------------------------------------------------------------ 

 subroutine humidity(T,P,Qsat) 

c 

c Tetens' formula for saturation vp Buck(1981) JAM 20, 1527-1532 

c 

 real*8 T,P,Qsat 

c 

 Qsat = (1.0007+3.46e-6*P)*6.1121*dexp(17.502*T/(240.97+T)) 

 return 

 end 

c 
C-21 

c------------------------------------------------------------------ 

 function psiu(zL) 

c 

c psiu and psit evaluate stability function for wind speed and scalars 

c matching Kansas and free convection forms with weighting f 

c convective form follows Fairall et al (1996) with profile constants 

c from Grachev et al (2000) BLM 

c stable form from Beljaars and Holtslag (1991) 

c 

 real*8 zL,x,y,psik,psic,f,psiu,c 

 if(zL.lt.0) then 

 x=(1-15.*zL)**.25 !Kansas unstable 

 psik=2.*dlog((1.+x)/2.)+dlog((1.+x*x)/2.)-2.*atan(x)+2.*atan(1.) 

 y=(1.-10.15*zL)**.3333 !Convective 

 psic=1.5*dlog((1.+y+y*y)/3.)-sqrt(3.)*atan((1.+2.*y)/sqrt(3.)) 

 & +4.*atan(1.)/sqrt(3.) 

 f=zL*zL/(1.+zL*zL) 

 psiu=(1.-f)*psik+f*psic 

 else 

 c=min(50.,0.35*zL) !Stable 

 psiu=-((1.+1.*zL)**1.+.6667*(zL-14.28)/dexp(c)+8.525) 

 endif 

 return 

 end 

c-------------------------------------------------------------- 

 function psit(zL) 

 real*8 zL,x,y,psik,psic,f,psit,c 

 if(zL.lt.0) then 

 x=(1-15.*zL)**.5 !Kansas unstable 

 psik=2.*dlog((1.+x)/2.) 

 y=(1.-34.15*zL)**.3333 !Convective 

 psic=1.5*dlog((1.+y+y*y)/3.)-sqrt(3.)*atan((1.+2.*y)/sqrt(3.)) 

 & +4.*atan(1.)/sqrt(3.) 

 f=zL*zL/(1.+zL*zL) 

 psit=(1.-f)*psik+f*psic 

 else 

 c=min(50.,0.35*zL) !Stable 

 psit=-((1.+2.*zL/3.)**1.5+.6667*(zL-14.28)/dexp(c)+8.525) 

 endif 

 return 

 end 

 

c------------------------------------------------------------- 

 subroutine ZETA(T,Q,USR,TSR,QSR,Z,ZL) 

C 
C-22 

C TO EVALUATE OBUKHOVS STABILITY PARAMETER Z/L FROM AVERAGE 

C TEMP T IN DEG C, AVERAGE HUMIDITY Q IN GM/GM, HEIGHT IN M, 

C AND FRICTIONAL VEL,TEMP.,HUM. IN MKS UNITS 

C SEE LIU ET AL. (1979) 

C 

 real*8 T,Q,OB,TVSR,TV,TA,sgn 

 real*8 USR,TSR,QSR,Z,ZL 

 real*8 al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK,visa 

 real*8 visw,von,fdg 

 COMMON/const/al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK, 

 & visa,visw,von,fdg 

 TA=T+toK 

 TV=TA*(1.+0.61*Q) 

 TVSR=TSR*(1.+0.61*Q)+0.61*TA*QSR 

 sgn=sign(1.,tvsr) !added this to avoid program 

 if(abs(tvsr) .lt. 1.e-3) then !failure when TVSR is very small 

 tvsr=sgn*tvsr 

 endif 

 OB=TV*USR*USR/(grav*VON*TVSR) 

 ZL=Z/OB 

c if(ZL .gt. 1000) ZL=1000. 

 goto 99 

 10 ZL=0. 

 99 return 

 end 

 

c------------------------------------------------------------------------- 

 subroutine H_ADJUST(ZUs,ZTs,ZQs,U_hs,T_hs,Q_hs,IHUMID) 

c 

c This subroutine adjusts the U,T,Q variables to the specified 

c standard height (ZUs,ZTs,ZQs) using the loglayer profiles. 

c The DELTA correction (adjustment) is relative to the surface 

c measurement. Cronin 4/13/94 

c Modified to use new profile relations psiu,psit Bradley 26/10/99 

c 

 real*8 ZUs,ZTs,ZQs,U_hs,T_hs,Q_hs,ZUsL,ZTsL,ZQsL 

 real*8 U,T,Q,TS,QS,rns,rnl,ZU,ZT,ZQ,zi,P,PUZs,PTZs,PQZs 

 real*8 U_wg_hs,Rho_hs,Rho_avg,QA,Rho,P_hs,ee 

 real*8 USR,TSR,QSR,ZO,zot,zoq,ZL,RR,RT,RQ,RI,dter,dqer,tkt 

 real*8 al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK,visa 

 real*8 visw,von,fdg,DU_Wg,Wg,S,D,psit,psiu 

c 

 COMMON/PIN/U,T,Q,TS,QS,rns,rnl,ZU,ZT,ZQ,zi,P,ID 

 COMMON/POUT/USR,TSR,QSR,ZO,zot,zoq,ZL,RR,RT,RQ,RI, 

 & dter,dqer,tkt,DU_Wg,Wg 

 COMMON/const/al,beta,cpa,cpw,grav,xlv,rhoa,rhow,rgas,toK, 
C-23 

 & visa,visw,von,fdg 

c 

 call ZETA(T,Q,USR,TSR,QSR,ZUs,ZUsL) 

 call ZETA(T,Q,USR,TSR,QSR,ZTs,ZTsL) 

 call ZETA(T,Q,USR,TSR,QSR,ZQs,ZQsL) 

 PUZs= PSIu(ZUsL) 

 PTZs= PSIt(ZTsL) 

 PQZs= PSIt(ZQsL) 

 

 S = (dlog(ZTs/zot)-PTZs)/(von*fdg) 

 D = (dlog(ZQs/zoq)-PQZs)/(von*fdg) 

 T_hs =TSR*S +TS - dter -.0098*ZTs 

 Q_hs =(QSR*D + QS - dqer)*1000 

 U_wg_hs = USR*(dlog(ZUs/ZO) - PUZs)/0.4 

 if(U_wg_hs.ge.Wg) then 

 U_hs = SQRT(U_wg_hs**2 - Wg**2) 

 else 

 U_hs = U_wg_hs 

 endif 

c 

 if(IHUMID.eq.1) then ! then need to convert sp hum into rh 

 Q_hs = Q_hs/1000 ! sh kg/kg 

 RHO=1./(287.*(T+273.16)*(1.+.61*Q))*P*100. 

 P_hs = P - (RHO*grav*(ZTs - ZT))/100 !Approx hydrost.Pressure mb 

 RHO_hs=1./(287.*(T_hs+273.16)*(1.+.61*Q_hs))*P_hs*100 

 RHO_avg = (RHO + RHO_hs)/2 

 P_hs = P -(RHO_avg*grav*(ZTs - ZT))/100 !hydrostatic Pressure 

 call humidity(T_hs,P_hs,QA) !Teten's formula for Pvap,sat 

 ee=Q_hs*P_hs/(.62197 + .378*Q_hs) !to get vapor pressure 

 Q_hs = ee/QA !to get relative humidity 

 endif 

 return 

 end 

c------------------------------------------------------------------------ 

 Subroutine gravity(lat,g) 

c calculates g as a funccton of latitude using the 1980 IUGG formula 

c 

c Bulletin Geodesique, Vol 62, No 3, 1988 (Geodesist's Handbook) 

c p 356, 1980 Gravity Formula (IUGG, H. Moritz) 

c units are in m/sec^2 and have a relative precision of 1 part 

c in 10^10 (0.1 microGal) 

c code by M. Zumberge. 

c 

c check values are: 

c 

c g = 9.780326772 at latitude 0.0 
C-24 

c g = 9.806199203 at latitude 45.0 

c g = 9.832186368 at latitude 90.0 

c 

 real*8 gamma, c1, c2, c3, c4, phi, lat, g 

 gamma = 9.7803267715 

 c1 = 0.0052790414 

 c2 = 0.0000232718 

 c3 = 0.0000001262 

 c4 = 0.0000000007 

 phi = lat * 3.14159265358979 / 180.0 

 g = gamma * (1.0 

 $ + c1 * ((sin(phi))**2) 

 $ + c2 * ((sin(phi))**4) 

 $ + c3 * ((sin(phi))**6) 

 $ + c4 * ((sin(phi))**8)) 

c 

 return 

 end 

 

 

 
D-1 

APPENDIX D 

BOUNDARY LAYER STUDY IN THE 

WESTERN AND CENTRAL GULF OF MEXICO 

FINAL MEETING 

PRESENTED TO: 

MINERALS MANAGEMENT SERVICE 

TECHNICAL REVIEW GROUP 

OCTOBER 15-16, 2003 
D-3

By:

Clinton P. MacDonald, Paul T. Roberts

Charley A. Knoderer, Dianne S. Miller, Mark R. Lilly

Sonoma Technology, Inc.

Petaluma, CA

Steven R. Hanna

Hanna Consultants

Kennebunkport, ME

October 15-16, 2003

Presented to:

Minerals Management Service

Technical Review Group

998555-2265

Boundary Layer Study in the Western and 

Central Gulf of Mexico Final Meeting

• Focus on atmospheric boundary layer (ABL) in the 

western and central Gulf of Mexico, 1998-2002

• Produce quality-controlled data inventory and tools to 

view data

• Evaluate annual, seasonal, and diurnal variations in 

the ABL’s structure

• Describe the processes governing the variations in 

the ABL’s structure

• Provide three-dimensional gridded wind fields for 

study period

• Evaluate transport and mixing characteristics

Project Objectives
D-4

• Estimate impact of Outer Continental Shelf 

(OCS) 

oil and gas activities

• Provide quality-controlled data set for use in 

other MMS research studies

• Provide access to, and statistical summaries 

of, quality controlled data set

• Synthesize ABL characteristics and pollutant 

transport and dispersion

MMS Uses of Study Results (1 of 2)

• Provide a conceptual model summary, with 

examples, of processes that influence ABL 

characteristics and variability

• Provide a conceptual model summary, with 

examples, of processes that influence 

pollutant transport and dispersion

MMS Uses of Study Results (2 of 2)
D-5

• Data Collection and Inventory

• Data Base 

• Data Analysis Tool (EDAT)

• Analysis of the ABL structure

– Observed data

– COARE

• Modeling, Transport, and Dispersion Analysis

Main Tasks

• Data and sources

• Data validation

• Database

• Graphical user interface

– Environmental Data Analysis Tool (EDAT)

915-MHz radar wind profiler, RASS, and surface 

meteorological station at the South Marsh Island site

Data

So much data: 68,000,000+ records!
D-6

May 1998 through October 2001 

• Upper Air

• Surface

• Derived

• Eta Model

• Statistical

• Meteorological Classes

• CALMET

Data – Types

Vermillion Platform

Data – Site Map
D-7

Data – Upper Air (1 of 2)

Profiler/RASS (6 sites)

• Hourly virtual temperature profiles

– 100 m to 1500 m agl

– 60-m resolution

– Reality 160 m to 800 m agl

• Hourly wind profiles

– 100 m to 2000 m agl at 60-m resolution

– 100 m to 4000 m agl at 120-m 

resolution

– Reality 300 m to 2000+ m agl

• Cn

2

– Changes of the index of refraction

– Two-minute

• Vertical velocity

Data – Upper Air (2 of 2)

Rawinsonde

• National Climatic Data Center

• Lake Charles, Louisiana 

• Slidell, Louisiana

• 0000 and 1200 UTC
D-8

Data – Surface

Dauphin Island

• Buoy (7) and C-MAN (5)

– National Buoy Data Center 

• Collocated with profilers (6)

– ABL field program

– BAMP field program

• Surface land sites (40)

– National Climatic Data Center

Data – Surface Over Water (1 of 3)

Site Site ID 

Air 

Temperature 

Near-Sea 

Surface 

Temperature Skin Temperature

Relative 

Humidity Wind Pressure 

Wave Height 

and Period 

Mid Gulf 180 nm South of 

Southwest Pass LA 

42001 9 9 9 9 9 9

West Gulf 240 nm SouthSoutheast of Sabine TX 42002 9 9 9 9 9 9

Biloxi 22 nm SouthSoutheast of Biloxi MS 42007 9 9 9 9 9 9

Freeport TX. 60 nm South 

of Freeport TX 

42019 9 9 9 9 9

Corpus Christi TX 50 nm 

Southeast of Corpus 

Christi 

42020 9 9 9 9 9 9

Galveston 22 nm East of 

Galveston TX 

42035 9 9 9 9 9 9

Mobile South 64 nm 

South of Dauphin Island 

AL 

42040 9 9 9 9 9 9

Southwest Pass LA BURL11 9 9 9 9

Dauphin Island AL DPIA11 9 9 9 9

Grand Isle LA GDIL11 9 9 9 9 9

Port Aransas TX PTAT21 9 9 9 9 9

South Marsh Gulf of 

Mexico 

SMI 9 9 9 9 9

Sabine TX SRST21 9 9 9 9

Vermillion Gulf of Mexico VRM 9 9 9 9 9

Breton Island Platform BIP 9 9 9 9 9

Deep Water Platform DWP 9 9 9 9 9

Shallow Water Platform SWP 9 9 9 9 9

Mid Buoy Platform MBP 9 9 9 9 9

West Delta Platform WDP 9 9 9 9 9
D-9

Data – Surface Over Water (2 of 3)

S#

S#

Port Aransas, TX

200 0 200 400 600 800 Meters

N

Port Aransas TX Site, adjusted location in yellow

Jan. 7, 1995 Digital Orthophotoquad

Data – Surface Over Water (3 of 3)

Locations and Measurement Heights

Site Name Site 

Latitude 

(degrees N)

Longitude 

(degrees W) 

Elevation 

(m msl) 

Air Temperature 

Height Above 

Site (m) 

Anemometer 

Height Above 

Site (m) 

Sea 

Temperature 

Height (m) 

Mid Gulf 180 nm South of 

Southwest Pass LA 

42001 25.93 89.65 0.0 10.0 10.0 -1.0 

West Gulf 240 nm SouthSoutheast of Sabine TX 42002 25.89 93.57 0.0 10.0 10.0 -1.0 

Biloxi 22 nm South-Southeast of 

Biloxi MS 

42007 30.10 88.78 0.0 4.0 5.0 -0.6 

Freeport TX. 60 nm South of 

Freeport TX 

42019 27.92 95.35 0.0 4.0 5.0 -0.6 

Corpus Christi TX 50 nm 

Southeast of Corpus Christi 

42020 26.92 96.70 0.0 4.0 5.0 -0.6 

Galveston 22 nm East of 

Galveston TX 

42035 29.25 94.41 0.0 4.0 5.0 -0.6 

Mobile South 64 nm South of 

Dauphin Island AL 

42040 29.18 88.30 0.0 4.0 5.0 -0.6 

Southwest Pass LA BURL1 28.90 89.43 0.0 11.9 30.5 -0.5 

Dauphin Island AL DPIA1 30.25 88.07 0.0 9.1 17.4 -0.5 

Grand Isle LA GDIL1 29.27 89.96 1.8 15.2 15.8 -0.5 

Port Arkansas TX PTAT2 27.83 97.05 0.0 9.1 14.9 -0.5 

Sabine TX SRST2 29.67 94.05 0.9 11.9 12.5 -0.5 

Breton Island Platform BIP 29.77 88.71 20.0 2.0 3.0 0.0 

Deep Water Platform DWP 28.15 89.10 41.0 2.0 3.0 0.0 

Shallow Water Platform SWP 29.98 88.60 20.0 2.0 2.0 0.0 

Mid Buoy Platform MBP 29.62 88.57 20.0 2.0 3.0 0.0 

West Delta Platform WDP 28.83 89.78 20.0 2.0 3.0 0.0 

Vermillion Gulf of Mexico VRM 29.47 92.55 21.0 2.0 3.0 0.0 

South Marsh Gulf of Mexico SMI 28.15 91.91 25.0 2.0 3.0 0.0 
D-10

Data – Derived

• COARE algorithm: originally derived from the 

Tropical Ocean-Global Atmosphere Coupled-Ocean 

Atmosphere Response Experiment (TOGA COARE) 

research project

• Calculates fundamental boundary layer scaling 

parameters over water using routine surface 

observation

– Heat fluxes

– Surface roughness length

– Friction velocity

– Scaling temperature

– Scaling water vapor mixing ratio

– Monin-Obukhov length, etc.

Data – Model Predictions

• Six-hourly Eta and three-hourly Eta Data 

Assimilation System (EDAS) predictions

– Eta forecasts have many more parameters such as 

friction velocity, heat fluxes, etc.

– EDAS has nudged data from observations.

• University Corporation for Atmospheric Research 

(UCAR)

• 00 and 12 UTC model runs out to 48 hours

• Resolutions 40-km x 40-km with 38 vertical levels 

• Data at grid points nearest to site stored in 

database 

• Other data in GRIB format 
D-11

Data – Statistical

Monthly, yearly, and seasonal average wind 

and temperature profiles

00 12 06 18 23

Time CST

Fall average winds at VRM from 0000 to 2300 CST, September 24 to December 22

Data – Meteorological Classifications

Tropical storm

Cut-off low

Trough

Weak trough

Weak post-trough

Post-trough

Zonal

Flat

Weak ridge

Ridge

Classifications • Daily upper-air synoptic 

classifications — Based 

on 12 UTC 500-mb charts

• Daily surface-flow speed 

and direction 

classifications for each site

• Wind roses

• 1998-2001

• Western/central Gulf of 

Mexico Parallel west bbbb

Parallel east Strong (10 +)

Offshore Moderate (5 to 10)

Onshore Light (0 to 5)

Flow Direction Flow Speed (m/sec)
D-12

Meteorological Classifications

Upper Air (1 of 4)

Example of an upper-air ridge pattern for the Gulf of Mexico region on March 22, 2000, at 

1200 UTC (0600 CST). Solid lines indicate height contours (decameters). 

Example of an upper-air cut-off low pattern for the Gulf of Mexico region on March 30, 1999, at 

0000 UTC (March 29, 1999, at 1800 CST). Solid lines indicate height contours (decameters). 

Meteorological Classifications

Upper Air (2 of 4)
D-13

Example of an upper-air trough pattern for the Gulf of Mexico region on January 5, 1999, at 

0000 UTC (January 4, 1999, at 1800 CST). Solid lines indicate height contours (decameters).

Meteorological Classifications

Upper Air (3 of 4)

Meteorological Classifications

Upper Air (4 of 4)

0

5

10

15

20

25

30

35

Cut-off Low

Flat

Post Trof

Ridge

Trof

Tropical Storm

Weak Ridge

Weak Trof

Zonal

Percentages
D-14

Data – CALMET Modeling

• Seven case studies

– September 18–20, 2001

– January 20–25, 2000

– January 4–6, 2001

– July 30–August 1, 1999

– May 14–15, 2001

– April 15, 2001

– January 29, 2001

• Range of meteorological and transport conditions

• Data stored as binary CALMET files

Data – CALMET Modeling

• Vertical resolution included 

20 interfaces (21 levels in 

meters)

(0, 20, 50, 100, 200, 300, 400, 

500, 600, 700, 800, 900, 1000, 

1200, 1400, 1600, 1800, 2000, 

2250, 2500, 2750 m)

• Horizontal resolution of 5 km

• Modeling domain, 860 km x 

560 km
D-15

Data Validation (1 of 2)

• Objectives

– Evaluate the internal, spatial, temporal, and 

physical consistency of the data

– Produce a working Microsoft SQL database with 

values that are validated and of known quality

– Save quarterly subsets of Microsoft SQL 

database in MS Access databases

– Determine the suitability of the data for analysis 

and modeling

Data Validation (2 of 2)

• Platform data previously validated by STI as 

part of the data collection process

– Issue with data recovery rates at higher 

altitude

– Issue with sea clutter at lower altitude

• Buoy, C-MAN, and COARE output data 

visually and range-checked

• Secondary QC performed during analysis and 

CALMET modeling, resulting in changes to 

the COARE software and data reprocessing
D-16

Profiler Data Issues – Sea Clutter (1 of 2)

BIP profiler data on September 18, 2001

BIP profiler data on September 29, 2000

Profiler Data Issues – Sea Clutter (1 of 2)
D-17

Data Validation – Flags

• Valid = 0

• Invalid data = 8. Observations judged inaccurate or in 

error

• Missing data = 9. Observations not collected (the data 

were assigned a value of -999.0)

• Coare output flags

– Out flag = 0: Radiation predictions from Eta model cloud data 

and all observations needed by COARE are available.

– Out flag = 3: Observations were interpolated in time, and 

radiation data exist from Eta model cloud data.

– Out flag = 6: Observations were interpolated in time; radiation 

was estimated by time of year, day, and latitude.

– Out flag = 7: Observations exist; radiation was estimated by 

time of year, day, and latitude.

Data Validation – Problems (1 of 4)

Warm Layer Error at SMI

0

20

40

60

80

100

120

140

160

180

200

10516000000 10516050000 10516100000 10516150000 10516200000 10516250000

Time UTC (ymmddhhmmss)

Warm Layer (Degrees C)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Wind Speed (m/s)

Sunrise

May 16, 2001

Warm layer error at SMI
D-18

Data Validation – Problems (2 of 4)

• Problem: unrealistic sea surface warming

– Daylight hours 

– Light wind conditions 

– Stable vertical temperature gradient

• Cause: lack of heat removal due to the very small 

accumulated stress (surface momentum flux) and the 

very thin (almost zero) warm layer thickness

• Solution: a minimum stress of 0.002 N/m2 imposed for 

this calculation only (Christopher Fairall, Steve Hanna, 

and STI)

Data Validation – Problems (3 of 4)

• Problem

– The representation in COARE follows from laboratory 

measurements with artificial light sources

– Unrealistic evaporative cooling calculation due to 

unrealistic amounts of solar energy reaching the ocean 

surface

• Solution: for the net absorption equation, coefficient 

changed from 0.137 to 0.060 (based on calculational

tests by Christopher Fairall)

Net = SW*(0.060+11*CST -6.6e-5/ CST*(1-exp(-CST/8.0e-4)))

where

Net = Net absorption by the ocean

SW = Incoming short wave radiation

CST = Cool skin thickness
D-19

Data Validation – Problems (4 of 4)

• Problem: when wave period is very short 

(< 4 seconds) and waves are greater than 

1 m, surface roughness becomes large.

• Solution: further investigation is needed.

Database

• 68,000,000+ records stored in a MS SQL 

database 

• Quarterly MS Access databases

• Scalable data structure, handles most 

environmental data types
D-20

Database – Structure

1. Surface

2. Eta Model

3. Profiler

4. RASS

5. Rawinsonde

6. Derived

EDAT 

• Environmental Data Analysis Tool

• Displays data from MS SQL or MS Access database 

including the profiler/RASS, rawindsonde, surface 

meteorological, modeling, and COARE data sets

– time series

– time-height cross-sections

– vertical profiles

– spatial plots

• Exports to EPA’s WRLPlot

wind rose program

• Allows users to save data subsets
D-21

EDAT – Time Series

• Time-series plots can 

display any type of 

data. For example, 

this display enables 

the user to analyze 

hourly or diurnal 

changes in a single 

variable.

EDAT – Time-Height Cross Sections

• Time-height crosssections are ideal for 

displaying radar wind 

profiler data. For 

example, this display 

enables the user to 

identify regions of 

vertical and 

horizontal wind shear 

from the profiler data.
D-22

EDAT – Vertical Profiles

• Vertical profiles are 

ideal for displaying 

RASS data. 

EDAT – Spatial

• Spatial plot maps can 

display any type of data in 

the database on a userselected base map
D-23

EDAT – Wind Rose Data

• On the Spatial Plot Map selection menu, there is a 

checkbox option to save wind rose data. When the box 

is checked, EDAT will extract all surface wind speed 

and direction data and format them to work with the 

wind rose program, WRPLOT View, a program 

available at no charge on the Intranet at 

http:\\www.lakes-environmental.com. 

EDAT – Display Options 

Color Selection

• The user may define some 

of the color settings on the 

graphs. The foreground 

and background colors 

may be changed, and the 

colors based on QC code 

may be changed.
D-24

EDAT – Display Options

Time Zone

• The user may define the time zone in which 

the data should be displayed. All the data in 

the database are in UTC, but for analysis 

purposes, local time may be more useful. 

All time zones within the continental United 

States are available.

• Lines and points

– When a time series or vertical profile plot is created, the 

data are displayed as points, with a line connecting them 

as a default.

– The points are the only 

way to visually discern 

(by color) the QC code. 

The line colors are 

determined by the series 

number; for example, a time series plot may have two 

series displayed. The first series is a blue line, and the 

second series is a green line. For vertical profile plots, 

each hour of data is displayed as a different color line.

EDAT – Display Options

Lines and Points
D-25

• The toolbar and status bar may be turned 

on or off.

– The toolbar displays the time and height 

scrollbars and the buttons to open a new 

file, print the current graph, and save the 

current graph.

– The status bar displays the details of the 

data point selected: site, data class, 

parameter, height, date-time, value, and QC 

code.

EDAT – Display Options

Toolbar and Status Bar

Profiler, RASS, and Surface Data

Summary

• Statistical averages

– Surface wind roses

– Profiler wind time-height cross-sections

– RASS virtual temperature profiles

• EDAS profiler comparison

– Case examples

– Statistical

• Estimated mixing heights

– Issues

– Comparison with CALMET
D-26

Meteorological Classifications

Tropical storm

Cut-off low

Trough

Weak trough

Weak post-trough

Post-trough

Zonal

Flat

Weak ridge

Ridge

Classifications

• Daily upper-air synoptic 

classifications — Based 

on 12 UTC 500-mb 

charts

• Daily surface flow speed 

and direction 

classifications for each 

site

• Wind roses

Parallel west b

Parallel east Strong (10 +)

Offshore Moderate (5 to 10)

Onshore Light (0 to 5)

Flow Direction Flow Speed (m/sec)

Meteorological Classifications – UA (1 of 9)

Example of an upper-air ridge pattern for the Gulf of Mexico region for March 22, 2000, at 1200 UTC 

(0600 CST). Solid lines indicate height contours (decameters). 
D-27

Example of an upper-air cut-off low pattern for the Gulf of Mexico region for March 30, 1999, at 0000 UTC 

(March 29, 1999, at 1800 CST). Solid lines indicate height contours (decameters). 

Meteorological Classifications – UA (2 of 9)

Example of an upper-air trough pattern for the Gulf of Mexico region for January 05, 1999, at 0000 UTC 

(January 4, 1999 at 1800 CST). Solid lines indicate height contours (decameters).

Meteorological Classifications – UA (3 of 9)
D-28

Overall frequency distribution of grouped upper-air patterns observed for the entire study period

0

5

10

15

20

25

30

35

40

45

Grouped Ridge Pattern Grouped Trough Pattern Grouped Other

Percentages

Meteorological Classifications – UA (4 of 9)

0

5

10

15

20

25

30

35

Cut-off Low

Flat

Post Trof

Ridge

Trof

Tropical Storm

Weak Ridge

Weak Trof

Zonal

Percentages

Frequency distribution of upper-air patterns observed for the entire study period

Meteorological Classifications – UA (5 of 9)
D-29

Frequency distribution of grouped upper-air patterns observed for each MMS year, June 

through May, during the study period

0

5

10

15

20

25

30

35

40

45

50

Grouped Ridge

Pattern

Grouped Trough

Pattern

Grouped Other

Percentages

1998

1999

2000

2001

Meteorological Classifications – UA (6 of 9)

Frequency distribution of grouped upper-air patterns observed for each season for all 

years during the MMS study period

Fall All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped Trof Grouped Other

Percentage

Winter All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped Trof Grouped Other

Percentage

Spring All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped Trof Grouped Other

Percentage

Summer All Years

0

10

20

30

40

50

60

Grouped Ridge Grouped Trof Grouped Other

Percentage

Meteorological Classifications – UA (7 of 9)
D-30

Frequency distribution upper-air pattern observed for each season for all years 

during the MMS study period

Fall All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

Trof Weak

Trof

Cut-off

Low

Post

Trof

Flat ZonalTropical

Storm

Percentage

Winter All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

Trof Weak

Trof

Cut-off

Low

Post

Trof

Flat ZonalTropical

Storm

Percentage

Spring All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

Trof Weak

Trof

Cut-off

Low

Post

Trof

Flat ZonalTropical

Storm

Percentage

Summer All Years

0

5

10

15

20

25

30

35

40

45

50

Ridge Weak

Ridge

Trof Weak

Trof

Cut-off

Low

Post

Trof

Flat ZonalTropical

Storm

Percentage

Meteorological Classifications – UA (8 of 9)

Frequency distribution of grouped upper-air patterns observed for each month for all years 

during the MMS study period

0

10

20

30

40

50

60

70

80

90

01 02 03 04 05 06 07 08 09 10 11 12

Month

Total Number of Days

Grouped Ridge Pattern Grouped Trof Pattern Grouped Other

Meteorological Classifications – UA (9 of 9)
D-31

• Buoy 42035 and the VRM platform site 

represent near-shore characteristics.

• Buoy 42019 and the SMI platform site 

represent offshore characteristics. 

Meteorological Classifications – Surface (1 of 4)

Yearly Surface Flow Direction (42035)

0

10

20

30

40

50

60

70

80

90

1998 1999 2000 2001

Percentage

offshore

onshore

parallel east

parallel west

Yearly Surface Flow Direction (SMI)

0

10

20

30

40

50

60

70

80

1998 1999 2000 2001

Percentage

offshore

onshore 

parallel east

parallel west

Yearly Surface Speed (42035)

0

10

20

30

40

50

60

70

80

90

1998 1999 2000 2001

Percentage

light

moderate

strong

Yearly Surface Speed (SMI)

0

10

20

30

40

50

60

70

80

90

1998 1999 2000 2001

Percentage

light

moderate

strong

Yearly frequency distributions of surface direction and speed (top graphs show direction, 

bottom graphs show speed) for the near-shore site, buoy 42035, and the offshore site, SMI. 

These two sites are about 200 km apart.

Meteorological Classifications – Surface (2 of 4)
D-32

Seasonal Surface Direction (42019)

0

10

20

30

40

50

60

70

80

90

Fall Spring Summer Winter

Percentage

offshore

onshore

parallel east

parallel west

Seasonal Surface Direction (42035)

0

10

20

30

40

50

60

70

80

90

Fall Spring Summer Winter

Percentage

offshore

onshore

parallel east

parallel west

Seasonal Surface Direction (SMI)

0

10

20

30

40

50

60

70

80

90

Fall Spring Summer Winter

Percentage

offshore

onshore

parallel east

parallel west

Seasonal Surface Direction (VRM)

0

10

20

30

40

50

60

70

80

90

Fall Spring Summer Winter

Percentage

offshore

onshore

parallel east

parallel west

Meteorological Classifications – Surface (3 of 4)

Frequency distribution of seasonal surface directions for near-shore and offshore sites

Percentage Flow Speeds for Upper-Air 

Ridge

0

20

40

60

80

100

42019 SMI 42035 VRM

Light Flow Speed

Moderate Flow

Speed

Strong Flow

Speed

Percentage Flow Directions for Upper-Air 

Ridge

0

20

40

60

80

100

42019 SMI 42035 VRM

Onshore Flow

Direction

Offshore Flow

Direction

Parallel to Shore

Flow Direction

Percentage Flow Speeds for Upper-Air 

Trough

0

20

40

60

80

100

42019 SMI 42035 VRM

Light Flow Speed

Moderate Flow

Speed

Strong Flow Speed

Percentage Flow Directions for Upper-Air 

Trough

0

20

40

60

80

100

42019 SMI 42035 VRM

Onshore Flow

Direction

Offshore Flow

Direction

Parallel to Shore

Flow Direction

Percentage Flow Speeds for Other UpperAir Patterns

0

20

40

60

80

100

42019 SMI 42035 VRM

Light Flow Speed

Moderate Flow

Speed

Strong Flow Speed

Percentage Flow Directions for Other 

Upper-Air Patterns

0

20

40

60

80

100

42019 SMI 42035 VRM

Onshore Flow

Direction

Offshore Flow

Direction

Parallel to Shore

Flow Direction

Frequency distribution for 

MMS study period of surface 

flow typing for upper-air ridge, 

upper-air trough, and other 

upper-air patterns

Meteorological Classifications – Surface (4 of 4)
D-33

Wind Rose (1 of 3)

Group A map

VRM

SRST2

42035

PTAT2

42019

42020

42002 42001

Louisiana Texas

MS

Group B map

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Mississippi

Alabama

Florida

Data suggested two site groups.

Wind Rose (2 of 3)

WIND ROSE PLOT

Station #00002 - , 

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

UNIT

m/s

DISPLAY

Wind Speed

CALM WINDS

4.52%

MODELER

DATE

5/28/2002

COMPANY NAME

COMMENTS

WRPLOT View 3.5 by Lakes Environmental Software - www.lakes-environmental.com

PLOT YEAR-DATE-TIME

2000 

Jan 1 - Dec 31

Midnight - 11 PM

AVG. WIND SPEED

5.87 m/s

ORIENTATION

Direction

(blowing from)

PROJECT/PLOT NO.

The VRM wind rose is representative of the wind rose plots at group A sites.
D-34

Wind Rose (3 of 3)

WIND ROSE PLOT

Station #00017 - , 

NORTH

SOUTH

WEST EAST

2%

4%

6%

8%

10%

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

UNIT

m/s

DISPLAY

Wind Speed

CALM WINDS

2.67%

MODELER

DATE

5/28/2002

COMPANY NAME

COMMENTS

WRPLOT View 3.5 by Lakes Environmental Software - www.lakes-environmental.com

PLOT YEAR-DATE-TIME

2000 

Jan 1 - Dec 31

Midnight - 11 PM

AVG. WIND SPEED

5.71 m/s

ORIENTATION

Direction

(blowing from)

PROJECT/PLOT NO.

Buoy 42040 is representative of the wind rose plots at Group B sites.

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTH

SOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

Group A – Overall

VRM SRST2

PTAT2

42019

42020

42002

Louisiana Texas

AL

42001

42035

NORTH

SOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80
D-35

NORTH

SOUTH

WEST EAST

2%

4%

6%

8%

10%

Group B – Overall

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Alabama

Mississippi

Florida

NORTH

SOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTH

SOUTH

WEST EAST

2%

4%

6%

8%

10%

NORTH

SOUTH

WEST EAST

3%

6%

9%

12%

15%

NORTH

SOUTH

WEST EAST

2%

4%

6%

8%

10%

NORTH

SOUTH

WEST EAST

3%

6%

9%

12%

15%

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

Group A – Fall

VRM SRST2

PTAT2

42019

42020

42002

Louisiana Texas

MS

42001

42035

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%
D-36

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

NORTH

SOUTH

WEST EAST

4%

8%

12%

16%

20%

Group B – Fall

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Mississippi

Alabama

Florida

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

Group A – Spring

VRM SRST2

PTAT2

42019

42020

42002

Louisiana Texas

MS

42001

42035

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%
D-37

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

NORTH

SOUTH

WEST EAST

7%

14%

21%

28%

35%

Group B – Spring

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Mississippi

Alabama

Florida

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

Group A – Summer

VRM SRST2

PTAT2

42019

42020

42002

Louisiana Texas

MS

42001

42035

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%
D-38

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

Group B – Summer

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Mississippi

Alabama

Florida

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80 NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

6%

12%

18%

24%

30%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25% NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

Group A – Winter

VRM SRST2

PTAT2

42019

42020

42002

Louisiana Texas

MS

42001

42035

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%
D-39

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

NORTH

SOUTH

WEST EAST

5%

10%

15%

20%

25%

Group B – Winter

GDIL1

DPIA1 42007

42040

BURL1

SMI

Louisiana

Mississippi

Alabama

Florida

Wind Speed (m/s)

> 11.06

8.49 - 11.06

5.40 - 8.49

3.34 - 5.40

1.80 - 3.34

0.51 - 1.80

Wind Rose – Overall

• Dominant southeasterly flow, with a secondary flow 

from the northeast 

• Almost non-existent westerly flow within the region

• Group A

– Strong southeasterly flow 

– Very little southwest through northeast wind flow 

– Southeasterly flow likely a reflection of the predominant 

weather feature, the Bermuda High, as well as the sea 

breeze. The northeasterly flow is likely a result of 

continental high pressure systems.

• Group B 

– Dominated by southeasterly flow

– More evenly distributed throughout other directions 

than Group A
D-40

Wind Rose – Seasons

• Fall 

– Group B sites: predominantly north-northeast 

flow and very little southwesterly flow 

– Group A sites: predominantly southeasterly 

flow with secondary flows from the northnortheast

• Winter 

– Similar to fall, except stronger southeast flow 

at the Group B sites 

Wind Rose – Seasons

• Spring 

– Very different at both site groups compared to fall and 

winter 

– Predominant southeasterly flow with very little northerly 

flow at the Group A sites 

– Group B sites dominated by a broad peak from the eastsoutheast to the southwest

• Summer

– Group A sites: similar to spring with a dominant 

southeast peak

– Near-shore sites: more frequent southerly peak, likely 

due to the land/sea breeze circulation

– Group B sites: evenly distributed peak from east through 

south to west, with the exception of SMI, which only had 

a southwest peak
D-41

Profiler and RASS Statistics

• Characteristics of boundary layer winds and 

temperature profiles at VRM and SMI

• How these characteristics change by year, 

season, month, and upper-air classification 

and between sites

Profiler and RASS Statistics – Method

• Winds were vectorially averaged.

• Virtual temperature data were grouped into 

“day” (0600 to 1800 CST) and “night”

(1800 to 0600 CST). 

• Averages were only calculated if at least 

50% of the possible measurements 

contributing to that average were valid.

• Note: SMI and VRM provided three years of 

data, whereas BAMP sites provided one year 

of data.
D-42

VRM and SMI Overall

00 12 06 18 23

Time CST

00 12 06 18 23

Time CST

Overall average winds at 

SMI (top) and VRM (bottom) 

from 0000 to 2300 CST, 

June 1, 1998, to May 31, 2001

BIP Overall Mean Winds

Overall average winds at BIP from 0000 to 2300 CST, September 2000 to September 2001
D-43

DWP Overall Mean Winds

Overall average winds at DWP from 0000 to 2300 CST, September 2000 to September 2001

FTM Overall Mean Winds

Overall average winds at FTM from 0000 to 2300 CST, September 2000 to September 2001
D-44

WDP Overall Mean Winds

Overall average winds at WDP from 0000 to 2300 CST, September 2000 to September 2001

Profiler Winds – Fall

00 12 06 18 23

Time CST

00 12 06 18 23

Time CST

Fall average winds at 

SMI (top) and VRM (bottom)
D-45

WDP Mean Winds – Fall

BIP Mean Winds – Fall
D-46

DWP Mean Winds – Fall

FTM Mean Winds – Fall
D-47

Profiler Winds – Winter

00 12 06 18 23

Time CST

00 12 06 18 23

Time CST

Winter average winds at 

SMI (top) and VRM (bottom)

BIP Mean Winds – Winter
D-48

DWP Mean Winds – Winter

FTM Mean Winds – Winter
D-49

WDP Mean Winds – Winter

Profiler Winds – Spring

00 12 06 18 23

Time CST

00 12 06 18 23

Time CST

Spring average winds at 

SMI (top) and VRM (bottom) 
D-50

BIP Mean Winds – Spring

DWP Mean Winds – Spring
D-51

FTM Mean Winds – Spring

WDP Mean Winds – Spring
D-52

Profiler Winds – Summer

00 12 06 18 23

Time CST

00 12 06 18 23

Time CST

Summer average winds at 

SMI (top) and VRM (bottom) 

BIP Mean Winds – Summer
D-53

DWP Mean Winds – Summer

FTM Mean Winds – Summer
D-54

WDP Mean Winds – Summer

Profiler Winds – Summary (1 of 2)

• Overall

– Southwest through easterly flow throughout all 

seasons, years, and sites; southeasterly flow the most 

frequent direction

– At WDP winds were more easterly in the lowest 500 m 

compared to southerly at the other sites.

• Ridge (not shown here)

– South to southeasterly below 1100 m and southwest to 

easterly aloft

• Trough (not shown here) 

– Mostly southwesterly flow aloft

– Southeast to northeasterly flow in the low levels, with 

strong troughs having a more defined shear layer 
D-55

Profiler Winds Summary (2 of 2)

• Fall

– Easterly flow at lower levels 

– Southwesterly flow aloft 

• Winter

– Easterly surface flow very decoupled from south to 

southwesterly flow aloft

– Northerly flow at the surface at near-shore sites

• Spring

– Coupled surface and aloft flow with southerly flow up to 

1000 m 

– Southwesterly flow above 1000 m

• Summer

– Easterly to southwesterly flow below 2000 m 

– Most diurnal variability at VRM compared to all 

seasons and sites

VRM and SMI Overall

Tv, oC

Tv, oC

Average overall daytime 

and nighttime temperature 

profiles at SMI (top) and 

VRM (bottom). 
D-56

BIP Overall

DWP Overall
D-57

FTM Overall

WDP Overall
D-58

SMI and VRM – Fall

Tv, oC

Tv, oC

Fall overall daytime and 

nighttime temperature 

profiles at SMI (top) and 

VRM (bottom).

BIP – Fall
D-59

DWP – Fall

FTM – Fall
D-60

WDP – Fall

SMI and VRM – Winter

Tv, oC

Tv, oC

Winter overall daytime 

and nighttime temperature 

profiles at SMI (top) and 

VRM (bottom), June 1, 

1998, to May 31, 2001. 

Hour 12 is the daytime 

profile and hour 00 is the 

nighttime profile.
D-61

BIP – Winter

DWP – Winter
D-62

FTM – Winter

WDP – Winter
D-63

SMI and VRM – Spring

Tv, oC

Tv, oC

Spring overall daytime 

and nighttime temperature 

profiles at SMI (top) and 

VRM (bottom), June 1, 

1998, to May 31, 2001. 

Hour 12 is the daytime 

profile and hour 00 is the 

nighttime profile.

BIP – Spring
D-64

DWP – Spring

FTM – Spring
D-65

WDP – Spring

SMI and VRM – Summer

Tv, oC

Tv, oC

Summer overall daytime 

and nighttime temperature 

profiles at SMI (top) and 

VRM (bottom), June 1, 

1998, to May 31, 2001.
D-66

BIP – Summer

DWP – Summer
D-67

FTM – Summer

WDP – Summer
D-68

RASS Virtual Temperature – Summary ( 1 of 2)

• There is often a discontinuity in temperature gradient 

at the lower two or three RASS levels (e.g., 131 m), 

due to a known cold bias. 

• The surface temperature and the 131-m temperature 

are measured by two types of instruments, which 

may influence the diagnosis of stable or unstable 

temperature gradients. 

• The average profiles, which extend to about 700 m, 

do not show an elevated inversion or mixing height, 

despite the fact that a mixing depth of 500 to 700 m is 

expected and often observed in the Cn

2 data.

• Overall 

– VRM is more stable than other sites.

– BIP has strong stable inversion in lowest layer, other 

sites do not. 

• Fall

– FTM has surface inversion at night, others do not.

• Winter

– All sites have an inversion during the day and night 

except VRM and BIP. Inversion may be a result of 

platform radiational cooling.

• Spring and Summer

– All sites are about adiabatic.

RASS Virtual Temperature – Summary ( 2 of 2)
D-69

Near-Surface Stability

• Skin temperature (Ts) minus surface temperature 

(Tsurface).

• Diurnal profiles by month

• Stable defined as when Ts minus Tsurface is less 

than zero.

Annual Average

Ts at the buoys is estimated from the underwater 

temperature in COARE.

Percentages of Stable and Unstable Tskin - Tair

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

4200142002

4200742019

42020

42035

42040

GDIL1

PTAT2

SMI

VRM

Stable Count Unstable Count
D-70

VRM – Monthly Average Diurnal Profiles

SMI – Monthly Average Diurnal Profiles
D-71

BIP – Monthly Average Diurnal Profiles

DWP – Monthly Average Diurnal Profiles
D-72

WDP – Monthly Average Diurnal Profiles

SWP – Monthly Average Diurnal Profiles
D-73

MBP – Monthly Average Diurnal Profiles

Stability Summary

• Most sites are about 20% stable and 80% 

unstable.

• January and February are the most stable 

months.

• Possible non-representative daytime stability 

created by platform heating.
D-74

Estimated Mixing Heights

• Goal – Automatically produce hourly mixing heights 

using observed data

– RASS virtual temperature and surface temperature

– Profiler reflectivity and vertical velocity

• Findings

– Sea clutter in lowest 600 m contaminated reflectivity 

data 

– Aloft inversion capping boundary layer was rarely 

observed in RASS data

• Conclusion – Automatic processing difficult over 

warm water

• Solution – Case study mixing heights

Mixing Depth – RWP (1 of 2)

• Reflectivity

– Measures variations in the refractive index of the 

atmosphere

– Turbulence produces variations in atmospheric 

temperature, humidity, and pressure, which in turn 

cause variations in the refractive index.

– Reflectivity largest at inversion capping convective 

or marine boundary

– CBL height-finding algorithms (Angevine et al., 

1994; Dye et al., 1995; Bianco and Wilczak, 2002)
D-75

Mixing Depth – RWP (2 of 2)

• Vertical Velocity

– The radial velocity measured by the RWP vertical 

beam is a direct measure of vertical velocity

– Convective thermals within the CBL act to vertically 

redistribute heat, moisture, and momentum

– Identification of the vertical extent of convective 

thermals helps obtain an estimate of mixing depth

• Spectral Width

– The range of radial velocities measured within the 

scatter volume is illustrated by spectral width

– Locating the gradient in the spectral width (variability in 

the scales of turbulence) can be used as a reasonable 

estimate of mixing depth

RWP Mixing Heights – Moments

SNR

Vertical Velocity

Spectral Width
D-76

RWP Mixing Heights – Wind Profiles

Change in WS and WD

Profiler Data Issues – Sea Clutter

BIP profiler data on September 18, 2001
D-77

RWP Mixing Heights – Sea Clutter

Different WS and WD

SMI

July 30 to August 1, 1999

VRM

September 18, 2001

Mixing Height – Case Examples
D-78

SMI – July 30, 1999

SMI – July 31, 1999
D-79

SMI – August 1, 1999

VRM – September 18, 2001
D-80

CALMET Mixing Heights

CALMET uses two different schemes to model 

the boundary layer

1. Overland – determined from observed temperature 

soundings and the computed hourly surface heat 

fluxes using a modified Carson (1973) method 

based on Maul (1980).

2. Overwater

– “Calculated using the neutral barotropic scaling 

relationship” (Blackadar and Tennekes, 1968).

– This relationship takes into account only 

mechanical mixing and not convective mixing 

(neglects the surface heat flux).

CALMET Mixing Heights – Example
D-81

CALMET Mixing Heights

To create a mixing height of 800 m, the current 

CALMET overwater mixing height scheme, 

requires a surface wind speed of ~24.5 knots 

(12.5 m/s).

Mixing Height Comparison

Goal:

– Distinguish whether any difference exists 

between mixing height estimates derived from 

RWP moments data and mixing heights 

modeled by CALMET for case study periods.

Method:

– Subjective and limited statistical comparison 

was carried out on case study periods when 

the mixing heights could be determined from 

the RWP moments data.
D-82

Mixing Height Comparison

July 31 – August 1, 2001

Mixing Height Comparison

January 20-25, 2000
D-83

Mixing Height Comparison

January 4-7, 2001

Mixing Height Comparison

September 15-21, 2001
D-84

Mixing Height Comparison

All Case Studies

Mixing Summary (1 of 2)

• Mixing heights were created for selected 

episodes when data permitted

– September 18-20, 2001

– January 20-25, 2000

– January 4-6, 2001

– July 30 – August 1, 1999

– May 14-15, 2001

– April 15, 2001

– January 29, 2001

• Estimated mixing heights can be used to 

verify mixing heights generated by MM5
D-85

Mixing Summary (2 of 2)

Because CALMET underestimates mixing heights 

compared to estimates derived from RWP 

measurements, the following recommendation 

should be considered:

When surface wind speeds are below a specified 

threshold at overwater sites, a convective scheme 

should be used to calculate mixing heights at 

these sites. This will enable more realistic 

modeling of mixing over the ocean

Wind Field Comparisons (1 of 2)

• Goal: Determine if Eta Data Assimilation 

System (EDAS) winds properly represent 

observations. 

• Method: Compare three-hourly historic 

EDAS winds (horizontal grid resolution of 

40 km) to observations.

• Poster presented at the International 

Symposium on Tropospheric Profiling Needs 

and Technologies.
D-86

Wind Field Comparisons (2 of 2)

• EDAS

– Horizontal grid of 40 km x 40 km

– Vertical resolution of 25 constant pressure 

surfaces from 1000 mb to 25 mb at intervals of 

50 mb (in the lowest 2 km, the interval is 25 mb)

• Profilers

– VRM and SMI plus four BAMP profilers

RWP/EDAS Comparison – Method

• Statistical and limited subjective comparisons 

were made

• The closest EDAS model grid point were 

compared to the location of the RWP sites

• Wind direction (WD) comparisons were not made 

when wind speeds (WS) were less than 2 m/s

• Comparisons of WS and WD were carried out 

when the heights of EDAS winds were within

– 30-m of a RWP measurement below 1000-m

– 50-m of a RWP measurement above 1000-m

• Point-to-point time matching was used
D-87

RWP/EDAS Comparison – Statistics

• Statistics were computed on height bins that, 

when sorted by number of samples, 

comprised 90% of the total number of 

samples

• Statistics were calculated for the total period, 

by synoptic class, and by flow pattern

RWP/EDAS Comparison – Sample 

Selection Example for SMI
D-88

RWP/EDAS Comparison – Statistics

∑( ) =

−

n

i

Pi Mi

n 1

1 Bias =

[ ] ( )( ) 2

1

1

∑=

− − −

n

i

Pi Mi Pi Mi n Standard Deviation =

∑=

−

n

i

Pi Mi n 1

1 Mean Absolute Error (MAE) =

Where:

n = number of observations

P = ith observation by the RWP

Mi = ith EDAS model “observation”

RWP Winds and Eta Model Winds at SMI, January 21, 2000
D-89

RWP Winds and Eta Model Winds at SMI, January 21, 2000

RWP Winds and Eta Model Winds at SMI, July 31, 1999
D-90

RWP Winds and Eta Model Winds at SMI, September 18, 2001

RWP Winds and Eta Model Winds at VRM, September 18, 2001
D-91

RWP/EDAS Comparison - Results

• Wind speed – entire period

– Overestimated by EDAS model 

output

– Greater negative bias and larger 

MAE were observed in the lower 

levels; however, bias and MAE 

improved with height

– Sites further offshore illustrated 

greater bias (negative) and had 

larger MAE than sites closer to the 

shoreline

• When sorted by synoptic class 

and flow direction, the statistics 

were similar 

RWP/EDAS Comparison - Results

• Wind direction – entire period

– Generally, bias were between 

0o and 10o

– The overall positive bias 

illustrates that the EDAS model 

output had a counter-clockwise 

bias

– MAE was 15o – 25o at sites 

closer to shore, while sites 

further offshore exhibited a 

25o – 35o

• When sorted by synoptic 

class and flow direction the 

statistics were similar
D-92

RWP/EDAS Comparison - Conclusions

• Results suggest that RWP measurements 

should be given considerable weight when 

creating high-resolution wind fields

• Meteorological and air quality models may 

undergo considerable improvement from the use 

of RWP measurements

• More case study comparisons would provide 

more guidance on when EDAS and RWP data 

agree and disagree.

Modeling Overview

• Overall Goals

• CALMET

– Background

– Data (data manipulation, 

missing data)

– Model Settings

– Example

• CALPUFF

– Background

– Data inputs

– Source characteristics

– Example

• Trajectory Calculation

• Final Thoughts
D-93

Overall Goals

Goals:

• Assess dispersion and transport characteristics 

under multiple meteorological patterns and 

determine the effect of large-scale meteorology on 

transport and dispersion

• Investigate potential impact of offshore oil platform 

emissions on onshore areas

CALMET – Background

• What is CALMET?

– CALMET is a meteorological model, which 

includes a diagnostic wind field generator 

containing objective analysis and parameterized 

treatments of slope flows, kinematic terrain 

effects, terrain-blocking effects, a divergence 

minimization procedure, and a micrometeorological model for overland and overwater

boundary layers

• Why use CALMET?

– To resolve mesoscale and local-scale 

meteorological phenomena by blending 

observational data with synoptic-scale analyses
D-94

Observational Meteorological 

Data Sources (1 of 2)

• 2 NWS rawinsonde sites – Sidell, Lake Charles

• 2 RWP with surface meteorological measurements – Vermillion, 

South Marsh Island (5/98 – 8/00)

• 6 RWP with surface meteorological measurements – Vermillion, 

South Marsh Island, Breton Island, Fort Morgan, Deep Water Platform, 

West Delta Platform (9/00 – 9/01)

• 2 Platforms with surface meteorological measurements – Mid Buoy 

Platform, Shallow Water Platform

• 7 NDBC buoys

• 5 NDBC C-Man stations

• 45 stations reporting METAR observations

Observational Meteorological 

Data Sources (2 of 2)
D-95

Geophysical Data Sources

• 0.9-km resolution terrain data

• 30-m resolution land use data 

Eta Data Assimilation System (EDAS)

• EDAS output is constructed from successive 3-hr (eight analyses/day) 

ETA model forecasts (Black, 1994)

• Bilinear interpolation of ETA model output is used to create the EDAS 

output on the AWIPS-212 grid

• AWIPS-212 grid

– Lambert Conformal Projection

– 40-km horizontal resolution (185 X 129)

– 26 vertical levels (every 25 mb up to 850 mb, every 50 mb up to 50 mb)

• Three-dimensional variational analysis (3DVAR) scheme to assimilate 

surface and upper-air observations (Rogers et al., 1997):

– Pibals

– GOES satellite data

– radar wind profilers

– aircraft soundings

– NEXRAD derived winds
D-96

EDAS Domain

CALMET Diagnostic Wind Model

Standard options for 

incorporating gridded 

model output into a 

CALMET analysis (Scire

et al., 1999)
D-97

CALMET Initialization

• Typical “Initial Guess” Field

– At a minimum, CALMET requires 00Z and 12Z NWS 

soundings to calculate a domain mean wind for use as the 

“first guess” field.

• MMS “Initial Guess” Field

– Instead, the EDAS three-dimensional wind fields on the 

AWIPS-212 grid were used as the “initial guess” field and 

interpolated to a 5-km CALMET grid. 

CALMET Grid Resolution

• 20 vertical layers with 

interfaces at 0, 20, 50, 

100, 200, 300, 400, 500, 

600, 700, 800, 900, 1000, 

1200, 1400, 1600, 1800, 

2000, 2250, 2500, 

and 2750 m

• Horizontal resolution of 

5 km

• Modeling domain NX = 172 & NY = 112 (860 x 560 km)
D-98

EDAS and CALMET Domain

CALMET Data Manipulation

• Upper-air files

– Convert Tv Æ T

where q is the EDAS specific humidity; Tv is 

measured by RASS

• Surface files

– Closest observation to the top of the hour used

– Cloud cover and derived ceiling height from 6-hr 

and 12-hr ETA forecasts

( )⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ = q

T

T v

1 .61*
D-99

Missing Data

• Upper-air files

– RWP/RASS data 

• Filled in top of vertical WS, WD, and Tv profiles with EDAS 

as needed 

• Time gaps > 12 hrs filled with EDAS

• Time gaps < 12 hrs CALMET linear interpolation

– NWS rawinsonde data

• Time gaps > 12 hrs filled with EDAS

– Surface data

• Time gap < 12 hrs filled by moving +/- 6-hr window (no 

interpolation)

• Time gap > 12 hrs first gate of RWP/RASS used at surface

• Surface meteorology and over-water files

– Surface meteorology and buoy data

• Time gaps > 12 hrs CALMET spatial interpolation 

Model Settings

• No extrapolation of surface winds to upper levels

• Maximum radius of influence over land in the surface layer – 20 km

• Maximum radius of influence over land aloft – 150 km

• Maximum radius of influence over water – 50 km

• Equal weighting of the “initial guess” field and observations in the 

surface layer occurs at 40 km from the observation

• Equal weighting of the “initial guess” field and observations in aloft 

layers occurs at 150 km from the observation

• One smoothing pass below 400 m and two smoothing passes 

elsewhere
D-100

Example - CALMET

CALPUFF – Background

• What is CALPUFF?

– CALPUFF is a multi-layer, multi-species, non-steady-state 

puff dispersion model that can simulate the effects of timeand space-varying meteorological conditions on pollutant 

transport, transformation, and removal.

Note: An arbitrary emission rate was utilized, and the goal is not to predict 

absolute concentrations, but to predict relative concentrations.

• What were the inputs?

– Geophysical and meteorological data from CALMET

– Emissions inputs
D-101

Data Inputs

• Geophysical data – gridded fields 

of

– surface roughness lengths

– Land use categories

– Terrain elevations

– Leaf area indices

• Meteorological Data

– Gridded fields of

• u, v, w wind components (3-D)

• Air temperature (3-D) 

• Surface friction velocity

• Convective velocity scale

• Mixing height

• Monin-Obukhov length

• PGT stability class

• Precipitation rate

– Hourly values of the following 

parameters at surface met 

stations

• Air density

• Air temperature

• Short-wave solar radiation

• Relative humidity

• Precipitation type

Emissions Inputs

Inert tracers were emitted from three offshore platforms in the Gulf of 

Mexico to assess potential onshore impact:

• South Marsh Island (SMI)

• Breton Island Platform (BIP)

• Deep Water Platform (DWP) 

*

* SMI DWP*

* BIP
D-102

Source Characteristics

• Stack heights and stack diameters set to 

10 m agl

• Exit velocity of .005 m/s

• Exit temperature based on the temperature measured 

on each platform

• Continuous emission rates of 2000 g/sec used for all 

three platforms

Example - CALPUFF
D-103

Trajectory Calculation

• HYSPLIT (EDAS)

• TRAJMOD (CALMET)

Final Thoughts

• High frequency data requires considerable data 

manipulation of upper-air files

• EDAS may impose synoptic features on the local scale, 

particularly when local observations 

are missing

• Mixing heights are buoyancy driven
D-104

References

Black T. (1994) The new NMC mesoscale Eta model: description and forecast 

examples. Wea. Forecasting. 9, 265-278. 

Rogers E., Baldwin M., Black T., Brill K., Chen F., DiMego G., Gerrity J., 

Manikin G., Mesinger F., Mitchell K., Parrish D., and Zhao Q. (1997) 

Changes to the NCEP operational “Early” Eta Analysis/Forecast System. 

Technical Procedures Bulletin, Series No. 447, National Weather Service, 

Office of Meteorology, December. Available on the Internet at 

<http://www.nws.noaa.gov/om/tpb/447.htm>

Scire J.S., Robe F.R., Fernau M.E., and Yamartino R.J. (1999) Auser’s guide 

for the CALMET meteorological model (version 5.0). Prepared by Earth 

Tech, Inc., Concord, MA, September.

CALMET/CALPUFF Modeling

Case Studies

• September 18–20, 2001

• *January 20-25, 2000 – Winter Case Study 

with Shift in Wind Direction 

• January 4-6, 2001

• July 30 – August 1, 1999

• *May 14-15, 2001 – Spring Case Study 

with Regional High Ozone

• *April 15, 2001 – Onshore Flow Case Study

• January 29, 2001

*Cased in red are

discussed today
D-105

Onshore Wind Case Study

April 15, 2001

Onshore Wind Case Study

April 14, 2001: 12Z – 500-mb Heights

The region was under a 

broad, weak upperlevel ridge of high 

pressure at 500-mb

H
D-106

Onshore Wind Case Study

April 14, 2001: 12Z – Sea-level Pressure

• Stationary frontal 

boundary oriented 

east-west across the 

Gulf Coast

• South/southwesterly 

winds at the surface

L H

Onshore Wind Case Study

April 15, 2001: 12Z – 500 mb Heights

Zonal flow at 500 mb

across the Gulf region L

L
D-107

Onshore Wind Case Study

April 15, 2001: 12Z – Sea-level Pressure

• Southerly winds at 

the surface across 

the central and 

western part of the 

domain

• Southwesterly 

surface winds across 

the eastern part of 

the domain 

L

L

H

H

Forward Trajectories (10 m) from SMI, 

BIP, and DWP on April 13-16, 2001

Onshore transport from each of the platforms at 10 m from 4/13/01 at 

0000 CST – 4/15/01 at 0000 CST. Fair agreement between CALMET 

and EDAS wind fields.

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (4/13/01 0000 – 4/16/01 0000 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(4/13/01 0000 – 4/16/01 0000 CST)
D-108

Forward Trajectories (75 m) from SMI, 

BIP, and DWP on April 13-16, 2001

• Onshore, southerly transport from SMI and onshore transport out of 

the southwest from BIP and DWP at 75 m

• Onshore transport changed to near-calm or north or east transport 

toward the end of the case study period

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (4/13/01 0000 – 4/16/01 0000 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(4/13/01 0000 – 4/16/01 0000 CST)

Forward Trajectories (350 m) from SMI, 

BIP, and DWP on April 13-16, 2001

• Onshore transport out of the southwest at 350 m from each of the

platforms from 4/13/01 at 0000 CST – 4/15/01 at 0000 CST

• Onshore transport changed to near-calm or north or east transport 

toward the end of the case study period

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (4/13/01 0000 – 4/16/01 0000 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(4/13/01 0000 – 4/16/01 0000 CST)
D-109

CALMET Derived Mixing Heights

April 14, 2001

Dispersion Patterns from SMI, BIP, and 

DWP – April 14, 2001

Start time 1900 CST

Same source emission 

rate assumed at each 

platform

– Hypothetical emissions from 

SMI and BIP impact 

onshore coastal areas

– Emissions from DWP do not 

impact the coastline even 

though the concentrations 

are higher than at SMI and 

BIP, probably due to lower 

mixing heights at DWP
D-110

CALMET Derived Mixing Heights

April 15, 2001

Dispersion Patterns from SMI, BIP, and 

DWP – April 15, 2001

Start time 1100 CST

Same source emission 

rate assumed at each 

platform

– Hypothetical emissions from 

SMI and BIP impact onshore 

coastal areas

– Emissions from DWP do 

not impact coastal areas

– Concentrations from SMI 

and DWP are higher, 

probably due to lower wind 

speeds and lower mixing 

heights 
D-111

Winter Case Study with Shift in Wind 

Direction

January 20-25, 2000

Winter Case Study with Shift in Wind Direction

January 20, 2000: 12Z – 500-mb Heights

L • Strong upper-level area 

of low pressure at 500 mb

was centered in Ontario 

and extended south 

through the eastern half 

of the U.S.

• 500-mb ridge in place 

across the Mountain West
D-112

Winter Case Study with Shift in Wind Direction 

January 20, 2000: 12Z – Sea-level Pressure

Surface high-pressure area 

centered over the Central 

Plains and low-pressure 

area located over the 

eastern seaboard drove 

strong, offshore, northerly 

flow across the modeling 

domain

H L

L

Winter Case Study with Shift in Wind Direction 

January 21, 2000: 12Z – 500-mb Heights

L

• Strong upper-level area 

of low pressure at 

500 mb continued to 

dominate the eastern 

half of the United States

• Upper-level ridge at 

500 mb began to 

weaken across the 

western United States
D-113

Winter Case Study with Shift in Wind Direction 

January 21, 2000: 12Z – Sea-level Pressure

• Surface area of high 

pressure moved eastward 

and became centered in 

Tennessee

• Northerly winds on 

January 20 rotated to 

northeasterly, and 

easterly on January 21, 

as the high pressure 

center moved across the 

northern edge of the 

modeling domain 

L

H

Winter Case Study with Shift in Wind Direction 

January 22, 2000: 12Z – 500-mb Heights

L

H

• Upper-level ridge at 

500 mb broke down across 

the western United States

• Upper-level area of low 

pressure at 500 mb was 

centered over New England

• Generally zonal flow 

occurred across the United 

States

• A shortwave ridge was 

analyzed in the western Gulf 

of Mexico and a shortwave 

trough was analyzed in the 

eastern Gulf of Mexico 
D-114

Winter Case Study with Shift in Wind Direction 

January 22, 2000: 12Z – Sea-level Pressure

Strong onshore, southerly 

flow at the surface was 

associated with a departing 

surface high along the 

eastern seaboard and an 

approaching low pressure 

system centered over 

Nebraska

L

L

L

H

Winter Case Study with Shift in Wind Direction 

January 23, 2000: 12Z – 500-mb Heights

• Strengthening upperlevel area of low 

pressure at 500 mb

again dominated the 

eastern two-thirds of the 

United States

• Upper-level ridge at 

500 mb built across the 

West

L
D-115

Winter Case Study with Shift in Wind Direction 

January 23, 2000: 12Z – Sea-level Pressure

L

H

L

H

L

Onshore, southwesterly 

flow at the surface 

continued as the low 

pressure area moved 

into Alabama on the 

January 23 with an 

associated stationary 

boundary along the Gulf 

Coast

Winter Case Study with Shift in Wind Direction

January 24, 2000: 12Z – 500-mb Heights

Upper-level area of low 

pressure at 500 mb

continued to strengthen 

across the eastern 

United States and the 

modeling domain

L

H

L
D-116

Winter Case Study with Shift in Wind Direciton

January 24, 2000: 12Z – Sea-level Pressure

H

L

L

Offshore, northerly flow 

across the modeling 

domain was associated 

with an approaching 

surface high centered over 

the Great Plains and a 

departing area of low 

pressure centered over 

Florida 

Winter Case Study with Shift in Wind Direction

January 25, 2000: 12Z – 500-mb Heights

• Upper-level area of low 

pressure at 500 mb

dominated the entire 

eastern half of the 

United States, 

including the modeling 

domain

• Upper-level ridge 

strengthened across 

the West

L

L

L
D-117

Winter Case Study with Shift in Wind Direction

January 25, 2000: 12Z – Sea-level Pressure

L

H

Offshore, northerly flow 

across the modeling 

domain was again 

associated with the 

surface high centered over 

the Great Plains and the 

surface area of low 

pressure centered off the 

Mid-Atlantic coast

Forward Trajectories (10 m) from SMI, BIP, 

and DWP on January 19-22, 2000

Trajectories at 10 m begin with SW flow on 1/19, changing to strong offshore 

transport on 1/20 and early on 1/21 before turning onshore late on 1/21/01 through 

1/22/01. Note the clockwise progression of the trajectories on 1/20 through 1/22. 

CALMET and EDAS winds agree for the most part.

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (1/19/00 0000 – 1/22/00 1600 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(1/19/00 0000 – 1/22/00 1600 CST)
D-118

Forward Trajectories (75 m) from SMI, BIP, 

and DWP on January 19-22, 2000

The trajectories at 75 m are similar to those at 10 m (see previous 

slide)

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (1/19/00 0000 – 1/22/00 1600 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(1/19/00 0000 – 1/22/00 1600 CST)

Forward Trajectories (350 m) from SMI, BIP, 

and DWP on January 19-22, 2000

As expected, trajectories at 350 m indicate stronger winds and 

longer transport distances. The general behavior with time is 

similar to that for 10 m and 75 m (see previous two slides)

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (1/19/00 0000 – 1/22/00 1600 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(1/19/00 0000 – 1/22/00 1600 CST)
D-119

Forward Trajectories (10 m) from SMI, BIP, 

and DWP on January 23-25, 2000

Trajectories at 10 m begin with onshore flow on 1/22, changing to 

offshore flow from midday on 1/23 through 1/25. The trajectories 

agree fairly well for the CALMET and EDAS wind fields.

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (1/22/00 0000 – 1/25/00 0800 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(1/22/00 0000 – 1/25/00 0800 CST)

Forward Trajectories (75 m) from SMI, BIP, 

and DWP on January 23-25, 2000

The trajectories at 75 m are similar to those at 10 m (see 

previous slide)

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (1/22/00 0000 – 1/25/00 0800 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(1/22/00 0000 – 1/25/00 0800 CST)
D-120

Forward Trajectories (350-m) from SMI, BIP, 

and DWP on January 23-25, 2000

The trajectories at 350 m are similar to those at 10 m and 75 m 

(see previous two slides). There are stronger winds and longer 

transport distances at 350 m as expected.

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (1/22/00 0000 – 1/25/00 0800 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(1/22/00 0000 – 1/25/00 0800 CST)

CALMET Derived Mixing Heights

January 20, 2000
D-121

Dispersion Patterns from SMI, BIP, and 

DWP – January 20, 2000

• Same source emission 

rate assumed at each 

platform

– Strong, offshore 

northerly winds 

transported the 

hypothetical tracers 

out into the Gulf of 

Mexico, causing no 

onshore impact

– The strong winds 

contributed to decreasing 

the concentration 

Start time 1600 CST

CALMET Derived Mixing Heights

January 21, 2000
D-122

Dispersion Patterns from SMI, BIP, and 

DWP – January 21, 2000

• Same source emission 

rate assumed at each 

platform

– East winds caused 

BIP plume to pass 

over Breton Island

– Minimal onshore 

impact

Start time 1600 CST

CALMET Derived Mixing Heights

January 22, 2000
D-123

Dispersion Patterns from SMI, BIP, and 

DWP – January 22, 2000

• Same source emission 

rate assumed at each 

platform

– Southerly flow was 

observed at all three 

sites, causing the 

plumes to impact 

onshore areas

Start time 1900 CST

CALMET Derived Mixing Heights

January 23, 2000
D-124

Dispersion Patterns from SMI, BIP, and 

DWP – January 23, 2000

Start time 1200 CST

Same source emission rate 

assumed at each platform

– Southerly flow allows 

hypothetical tracers 

emitted at SMI and BIP 

to impact onshore areas 

along the Gulf Coast

– Concentrations are higher 

than on Jan 22 due to 

lighter winds and reduced 

CALMET assumed mixing 

heights on Jan 23

CALMET Derived Mixing Heights

January 24, 2000
D-125

Dispersion Patterns from SMI, BIP, and 

DWP – January 24, 2000

Same source emission rate 

assumed at each platform

• Strong, offshore northerly 

winds behind the front 

transported the 

hypothetical tracers out 

into the Gulf of Mexico, 

causing no onshore impact 

• The strong winds caused 

increased dilution and 

increased mixing depth 

• Similar situation as on 

January 20

Start time 1200 CST

CALMET Derived Mixing Heights

January 25, 2000
D-126

Dispersion Patterns from SMI, BIP, and 

DWP – January 25, 2000

Same source emission 

rate assumed at each 

platform

• Similar to January 24

• Strong, offshore 

northerly winds 

transported the plumes 

out into the Gulf of 

Mexico, causing no 

onshore impact Start time 1400 CST

Spring Case Study with Regional High Ozone

May 14-15, 2001
D-127

Spring Case Study with Regional High Ozone

May 14, 2001: 12Z – 500-mb Heights

L

L

Ridge of high pressure 

extended from Texas, north 

through the Central Plains, 

and into Canada

Spring Case Study with Regional High Ozone

May 14, 2001 12Z – Sea-level Pressure

H

L

Light east-northeasterly 

surface winds across the 

Gulf of Mexico region are 

associated with the large 

area of high pressure that 

was centered over the 

central Appalachian Mts.
D-128

Spring Case Study with Regional High Ozone

May 15, 2001 12Z – 500-mb Heights

Upper-level area of high 

pressure in the Midwest 

weakened L

Spring Case Study with Regional High Ozone

May 15, 2001 12Z – Sea-level Pressure

L

H

H

• Large, weakening area 

of high pressure centered 

over the southeastern 

United States

• High pressure area 

includes the Gulf of 

Mexico region
D-129

Spring Case Study with Regional High Ozone

May 15, 2001 18Z – EDAS Surface Winds

H

• Generally light winds in 

center of high pressure

• Weak, anticyclonic

circulation centered 

south of the 

Louisiana/Texas border 

in the Gulf of Mexico 

driving

– southwesterly flow 

across the western 

sections of the modeling 

domain

– light and variable flow off 

the coasts of Louisiana 

through Florida 

Forward Trajectories (10 m) from SMI, 

BIP, and DWP on May 13-16, 2001

• Lower wind speeds calculated by CALMET than by EDAS at 10 m

• Light and variable winds across the Gulf of Mexico associated with 

the area of high pressure

• Few trajectories at 10 m impact onshore locations

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (5/13/01 0000 – 5/16/01 0000 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(5/13/01 0000 – 5/16/01 0000 CST)
D-130

Forward Trajectories (75 m) from SMI, 

BIP, and DWP on May 13-16, 2001

• Conclusions similar to those for 75 m (see previous slide)

• Wind speed and transport distances are slightly larger at 75 m than at 10 m, as expected

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (5/13/01 0000 – 5/16/01 0000 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(5/13/01 0000 – 5/16/01 0000 CST)

Forward Trajectories (350 m) from SMI, 

BIP, and DWP on May 13-16, 2001

• Conclusions at 350 m similar to those for 10 m and 75 m (see previous two slides)

• Little onshore impact of trajectories originating at 350 m

• Exception being transport late in the case study period originating from SMI at 350 m 

begins to impact onshore areas across the Mississippi River Delta in response to the 

southwest winds generated by the anticyclonic circulation developing in the western 

sections of the modeling domain

CALMET 24-hr forward trajectories based on CALMET

diagnostic wind fields (5/13/01 0000 – 5/16/01 0000 CST)

HYSPLIT 24-hr forward trajectories based on EDAS wind fields 

(5/13/01 0000 – 5/16/01 0000 CST)
D-131

CALMET Derived Mixing Heights

May 14, 2001

Dispersion Patterns from SMI, BIP, and 

DWP – May 14, 2001

• Same source emission 

rate assumed at each 

platform

– Light and variable winds, 

combined with low mixing 

depths contributed to the 

accumulation of tracers 

near each source

– A period of light winds out 

of the northeast caused 

hypothetical tracers from 

BIP to impact coastal 

regions of the Mississippi 

River Delta Start time 0600 CST
D-132

CALMET Derived Mixing Heights

May 15, 2001

Dispersion Patterns from SMI, BIP, and 

DWP – May 15, 2001

• Same source emission 

rate assumed at each 

platform

– Winds remained light 

with an onshore 

component at SMI and 

BIP

– Mixing depth remained 

low (200 m or less)

– Relatively high 

concentrations of tracer 

are seen, covering a 

much larger area than 

found for the January or 

April case studies

Start time 2200 CST
D-133

Meteorological Characterization of the ABL –

COARE

• Background

• Data requirements and availability

• Estimation of fluxes and other ABL 

parameters

• Average monthly variables

• Diurnal variation by month

• Case studies

COARE Background (1 of 4)

• Derived from the Tropical Ocean-Global Atmosphere CoupledOcean Atmosphere Response Experiment (TOGA COARE) 

project

• Allows surface fluxes and other scaling parameters over the 

ocean to be accurately parameterized using routine observations 

in the surface boundary layer (Fairall et al., 1996)

– Heat fluxes

– Surface roughness length

– Friction velocity

– Scaling temperature

– Scaling water vapor mixing ratio

– Monin-Obukhov length, etc.

• Originally designed for deep tropical ocean

• Outgrowth of the Liu-Katsaros-Businger method (Liu et al., 1979)
D-134

COARE Background (2 of 4)

• COARE originated in 1993.

• Three newer versions were used in the 

current Gulf of Mexico ABL study.

• Version 2.5b, released in May 1997, included 

updated transfer coefficients and was used 

until January 2000 when Version 2.6b was 

released.

• The major difference between Versions 2.5b 

and 2.6b was a change in the Charnook

“constant” to a parameter based on wind 

speed data.

COARE Background (3 of 4)

• Version 2.6b was used for this Gulf of Mexico 

study until June 2000. 

• Version 2.6bw was released in June 2000, 

and all COARE outputs presented are from 

this latest version. 

• Version 2.6bw incorporates surface gravity 

wave information, based on wave height and 

period data. 
D-135

COARE Background (4 of 4)

• We modified COARE to 

– Use Eta model predictions to estimate short and 

long wave radiation for warm layer and cool skin 

temperature calculation

– Read configuration for easy data processing

– Interpolate missing data

– Calculate wave height and period when not 

observed

– Impose a minimum stress of .002 N/m2 for warm 

layer calculation only

– Better parameterize net absorption by the ocean

– Incorporate data quality descriptors flags

Data Requirements and Availability

• Data used by COARE

• Data availability

• Data issues and assumptions
D-136

Data Used by COARE 

• Surface layer wind speed

• Surface layer air temperature

• Skin temperature (Ts) or near-surface underwater 

sea temperature

• Surface layer relative humidity or mixing ratio at 

two levels

• Mixing height

• Site time and position

• Long- and short-wave radiation (not required)

• Precipitation (not required)

Data Availability – 1998 through 2001

Offshore buoys (7), C-MAN stations (5), platforms (7)

Site Name Site

Latitude

(degrees N)

Longitude

(degrees W)

Elevation

(m msl)

Air Temperature

Height Above

Site (m)

Anemometer

Height Above

Site (m)

Sea

Temperature

Height (m)

Mid Gulf 180 nm South of

Southwest Pass LA

42001 25.93 89.65 0.0 10.0 10.0 -1.0

West Gulf 240 nm SouthSoutheast of Sabine TX42002 25.89 93.57 0.0 10.0 10.0 -1.0

Biloxi 22 nm South-Southeast of

Biloxi MS

42007 30.10 88.78 0.0 4.0 5.0 -0.6

Freeport TX. 60 nm South of

Freeport TX

42019 27.92 95.35 0.0 4.0 5.0 -0.6

Corpus Christi TX 50 nm

Southeast of Corpus Christi

42020 26.92 96.70 0.0 4.0 5.0 -0.6

Galveston 22 nm East of

Galveston TX

42035 29.25 94.41 0.0 4.0 5.0 -0.6

Mobile South 64 nm South of

Dauphin Island AL

42040 29.18 88.30 0.0 4.0 5.0 -0.6

Southwest Pass LA BURL1 28.90 89.43 0.0 11.9 30.5 -0.5

Dauphin Island AL DPIA1 30.25 88.07 0.0 9.1 17.4 -0.5

Grand Isle LA GDIL1 29.27 89.96 1.8 15.2 15.8 -0.5

Port Arkansas TX PTAT2 27.83 97.05 0.0 9.1 14.9 -0.5

Sabine TX SRST2 29.67 94.05 0.9 11.9 12.5 -0.5

Breton Island Platform BIP 29.77 88.71 20.0 2.0 3.0 0.0

Deep Water Platform DWP 28.15 89.10 41.0 2.0 3.0 0.0

Shallow Water Platform SWP 29.98 88.60 20.0 2.0 3.0 0.0

Mid Buoy Platform MBP 29.62 88.57 20.0 2.0 3.0 0.0

West Delta Platform WDP 28.83 89.78 20.0 2.0 3.0 0.0

Vermillion Gulf of Mexico VRM 29.47 92.55 21.0 2.0 3.0 0.0

South Marsh Gulf of Mexico SMI 28.15 91.91 25.0 2.0 3.0 0.0
D-137

• Issue – Platform wind and temperature monitors are 

placed about 25 m msl.

Assumption – The measurements are within the 

surface layer.

• Issue – VRM, some buoys, and C-MAN stations are not 

deep-water sites.

Assumption – The sea-state at VRM and buoy sites 

behaves like the sea-state at deep-water sites, and the 

wave data should give a better estimate of roughness.

• Issue – Mixing height data are not available for all days 

and sites.

Assumption – Analysis shows that mixing heights are 

typically 600 m msl.

Data Issues and Assumptions (1 of 3)

• Issue – Buoy sites do not provide Ts or radiation data 

from which to estimate Ts using the cool-skin or warm 

layer correction.

Solution – Use Eta cloud predictions to estimate 

short- and long-wave radiation. 

• Issue – Platform sites do not provide wave data.

Solution – Estimate wave data from wind speed.

• Issue – Roughness is overestimated at very low wind 

speeds.

Solution – Informed Christopher Fairall of problem;

he is investigating cause. 

Data Issues and Assumptions (2 of 3)
D-138

Estimation of Fluxes and Other ABL Parameters 

• BAMP sites now included

• Average monthly variables by total study period, 

synoptic class, and surface flow

• Diurnal variation by month

• Hs, He, Total, u*,T*,q*, u, T, Ts, RH, Zo, wave height 

and period, Eta data, radiation

• Case studies

– July 30 through August 1, 1999

– January 20 through 25, 2000

– January 4 through 6, 2001

– September 18 through 20, 2001

COARE monthly average sensible heat fluxes (1 of 2)

COARE monthly average sensible heat fluxes by site for May 1998 through October 2001 

-10

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 8 9 10 11 12

Month

Sensible Heat Flux (W/m2)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI

SRST2

VRM
D-139

COARE monthly average sensible heat fluxes (2 of 2)

COARE monthly average sensible heat fluxes by BAMP site for 

September 2000 through September 2001

-10

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 8 9 10 11 12

Month

Sensible Heat Flux (W/m2)

BIP 

DWP 

MBP

SWP

WDP 

COARE monthly average latent heat fluxes (1 of 2)

COARE monthly average latent heat fluxes by site for May 1998 through October 2001

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12

Month

Latent Heat Flux (W/m2)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI

SRST2

VRM
D-140

COARE monthly average latent heat fluxes (2 of 2)

COARE monthly average latent heat fluxes by BAMP site for September 2000 through September 2001

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12

Month

Latent Heat Flux (W/m2)

BIP 

DWP 

MBP

SWP

WDP 

Observed monthly average wind speed (1 of 2)

Observed monthly average wind speed by site for May 1998 through October 2001

0

1

2

3

4

5

6

7

8

9

1 2 3 4 5 6 7 8 9 10 11 12

Month

Wind Speed (m/s)

42001

42002

42007

42019

42020

42035

42040

BURL1

DPIA1

GDIL1

PTAT2

SMI

SRST2

VRM
D-141

Observed monthly average wind speed (2 of 2)

Observed monthly average wind speed by BAMP site for 

September 2000 through September 2001

0

1

2

3

4

5

6

7

8

9

10

11

1 2 3 4 5 6 7 8 9 10 11 12

Month

Wind Speed (m/s)

BIP 

DWP 

MBP

SWP

WDP 

Monthly average skin temperature minus 

air temperature (1 of 2)

Monthly average skin temperature minus air temperature by site 

for May 1998 through October 2001

-1

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11 12

Month

Temperature Difference (deg. C)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI 

VRM 
D-142

Monthly average skin temperature minus 

air temperature (2 of 2)

COARE monthly average skin temperature minus air temperature by BAMP site 

for September 2000 through September 2001

-4

-2

0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12

Month

Temperature Difference (deg. C)

BIP

DWP

MBP

SWP

WDP

COARE monthly average of total heat fluxes (1 of 2)

COARE monthly average of total heat fluxes (sensible plus latent) by site

for May 1998 through October 2001

0

50

100

150

200

250

300

350

1 2 3 4 5 6 7 8 9 10 11 12

Month

Total Heat Flux (W/m2)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI

SRST2

VRM
D-143

COARE monthly average total heat fluxes (2 of 2)

COARE monthly average total heat fluxes (sensible plus latent) by BAMP site

for September 2000 through September 2001

0

50

100

150

200

250

300

350

1 2 3 4 5 6 7 8 9 10 11 12

Month

Total Heat Flux (W/m2)

BIP

DWP

MBP

SWP

WDP

Eta monthly average latent heat fluxes

Eta monthly average latent heat fluxes by site

for May 1998 through October 2001 for the 6- to 12-hr forecast

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12

Month

Latent Heat Flux (W/m2)

42001

42002

42007

42019

42020

42035

42040

BURL1

DPIA1

GDIL1

PTAT2

SMI

SRST2

VRM
D-144

Eta monthly average sensible heat fluxes 

Eta monthly average sensible heat fluxes by site

for May 1998 through October 2001 for the 6- to 12-hr forecast

-15

5

25

45

65

85

105

125

1 2 3 4 5 6 7 8 9 10 11 12

Month

Sensible Heat Flux (W/m2)

42001

42002

42007

42019

42020

42035

42040

BURL1

DPIA1

GDIL1

PTAT2

SMI

SRST2

VRM

COARE monthly average friction velocity (1 of 2)

COARE monthly average friction velocity by site for May 1998 through October 2001

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 12

Month

Friction Velocity (m/s)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI

SRST2

VRM
D-145

COARE monthly average friction velocity (2 of 2)

COARE monthly average friction velocity by BAMP site 

for September 2000 through September 2001

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 12

Month

Friction Velocity (m/s)

BIP 

DWP 

MBP

SWP

WDP 

Eta monthly average friction velocity by site

Eta monthly average friction velocity by site

for May 1998 through October 2001 for the 6- to 12-hr forecast

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 12

Month

Friciton Velocity (m/s)

42001

42002

42007

42019

42020

42035

42040

BURL1

DPIA1

GDIL1

PTAT2

SMI

SRST2

VRM
D-146

COARE calculated monthly average temperature 

scaling parameter (1 of 2)

COARE calculated monthly average temperature scaling parameter

by site for May 1998 through October 2001

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

1 2 3 4 5 6 7 8 9 10 11 12

Month

Temperature Scaling Parameter (deg. C)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI

SRST2

VRM

COARE calculated monthly average temperature 

scaling parameter (2 of 2)

COARE calculated monthly average temperature scaling parameter

by BAMP site for September 2000 through September 2001

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

1 2 3 4 5 6 7 8 9 10 11 12

Month

Temperature Scaling Parameter (deg. C)

BIP 

DWP 

MBP

SWP

WDP 
D-147

COARE calculated monthly average humidity 

scaling parameter (1 of 2)

COARE calculated monthly average humidity scaling parameter

by site for May 1998 through October 2001

-0.0005

-0.00045

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

1 2 3 4 5 6 7 8 9 10 11 12

Month

Humidity Scaling Parameter (kg/kg)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI

SRST2

VRM

COARE calculated monthly average humidity 

scaling parameter (2 of 2)

COARE calculated monthly average humidity scaling parameter

by BAMP site for September 2000 through September 2001

-0.0005

-0.00045

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

1 2 3 4 5 6 7 8 9 10 11 12

Month

Humidity Scaling Parameter (kg/kg)

BIP 

DWP 

MBP

SWP

WDP 
D-148

Observed monthly average air temperature (1 of 2)

Observed monthly average air temperature by site for May 1998 through October 2001

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12

Month

Temperature (deg. C)

42001

42002

42007

42019

42020

42035

42040

BURL1

DPIA1

GDIL1

PTAT2

SMI

SRST2

VRM

Observed monthly average air temperature (2 of 2)

Observed monthly average air temperature by BAMP site

for September 2000 through September 2001

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12

Month

Temperature (deg. C)

BIP 

DWP 

MBP

SWP

WDP 
D-149

Observed or estimated (at buoys) monthly average 

skin temperature (1 of 2)

Observed monthly average skin temperature by site for May 1998 through October 2001

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8 9 10 11 12

Month

Water Temperature (deg. C)

42001

42002

42007

42019

42020

42035

42040

GDIL1

PTAT2

SMI

SRST2

VRM

Observed monthly estimated (at buoys) average 

skin temperature (2 of 2)

Observed monthly average skin temperature by BAMP site 

for September 2000 through September 2001

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8 9 10 11 12

Month

Water Temperature (deg. C)

BIP 

DWP 

MBP

SWP

WDP 
D-150

Summary of Monthly Averages (1 of 7)

• Sensible and latent heat fluxes are typical of 

other non-Gulf, over-water sites.

• Average sensible heat fluxes in the Gulf of 

Mexico are about 5 to 30 w/m2, typical of other 

over-water sites. 

• Average latent heat fluxes are about 50 to 

150 w/m2, also typical of other over-water sites. 

• Latent and sensible heat fluxes are higher in the 

late fall and winter and are lowest in the summer, 

which is consistent with the light winds and 

smaller skin temperature-to-air temperature 

differences in the summer.

Summary of Monthly Averages (2 of 7)

• The monthly average calculated total heat flux is in fair 

agreement (within a factor of 2 most of the time) among 

the sites in the Gulf of Mexico

• The largest relative variations (ranging from 20 to 

170 w/m2) occurred in February when the total heat flux 

was relatively small due to the cool water temperatures 

and the small difference between the skin and air 

temperatures. 

• The smallest relative variations (ranging from 110 to 

235 w/m2) occurred in September when the total heat 

flux was relatively large due to the warm water 

temperatures and large difference between the skin and 

air temperature.
D-151

• Eta model latent and sensible heat fluxes are 

generally in good agreement with the 

calculated fluxes.

• However, the model fluxes do not show as 

great a variation among sites as do the 

calculated fluxes.

• The model fluxes are about 20% greater than 

the calculated fluxes in the fall and early 

winter but are very similar during the spring 

and summer.

Summary of Monthly Averages (3 of 7)

Summary of Monthly Averages (4 of 7)

• u* is within a factor of two and often within 20% 

among sites. 

• However, the platform sites (except SMI) show mean 

friction velocities that are about 30% or 40% less 

than the other sites. 

• Possible explanations are that the wave height and 

frequency are estimated from wind speed at the 

platforms, whereas, they are measured at the buoys. 

Also, the platform wind observations are corrected 

from 20+ meters to 10 meters and are, on average, 

less than the other non-BAMP sites.
D-152

Summary of Monthly Averages (5 of 7)

• u* is slightly lower from May through August and 

peaks in late fall and early winter. 

• Eta friction velocity shows the same yearly pattern as 

the calculated friction velocity. 

• However, the Eta model friction velocity is about 

10% to 20% higher than the calculated friction 

velocity in the fall and early winter. This is most likely 

why the Eta model fluxes are high during the same 

period.

Summary of Monthly Averages (6 of 7)

• The difference between skin temperature minus the 

air temperature is about +1 to +3°C at most sites all 

year and reaches a maximum of about +8°C at BIP in 

November.

• The difference is less in late spring and is greater in 

late fall and early winter. 

• This persistent positive temperature difference has 

been noted by Dr. Christopher Fairall at most other 

sites located on warm water oceans. 
D-153

Summary of Monthly Averages (7 of 7)

• Wind speed shows good agreement among sites.

• The lowest speeds occur in July and August and the 

highest in December and January. 

• For some years, there is a transition between lower 

wind speeds in August to higher winds speeds in 

September.

• Weather maps indicate that high wind speeds in 

October are a result of strong continental winds and 

tropical storms.

• RH is in good agreement at all sites and is about

80% year-round.

Eta average downwelling longwave radiation by 

synoptic pattern

Eta average downwelling longwave radiation by synoptic class by site

for May 1998 through October 2001 for the 6- to 12-hr forecast

0

50

100

150

200

250

300

350

400

450

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Downwelling Longwave Radiation (W/m2)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-154

Eta average shortwave radiation by synoptic pattern 

by synoptic pattern

Eta average shortwave radiation by synoptic class by site

for May 1998 through October 2001 for the 6- to 12-hr forecast

0

50

100

150

200

250

300

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Shortwave Radiation (W/m2)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm

COARE average humidity scaling parameter by 

synoptic pattern (1 of 2)

COARE average humidity scaling parameter by synoptic class by site

for May 1998 through October 2001

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Humidity Scaling Parameter (kg/kg)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-155

COARE average humidity scaling parameter by 

synoptic pattern (2 of 2)

COARE average humidity scaling parameter by synoptic class by BAMP site

for September 2000 through September 2001

-0.0005

-0.00045

-0.0004

-0.00035

-0.0003

-0.00025

-0.0002

-0.00015

-0.0001

-0.00005

0

BIP DWP MBP SWP WDP 

Site

Humidity Scaling Parameter (kg/kg)

Ridge

Weak Ridge

Flat

Zonal

Post-trof

Weak Trof

Trof

Cut-off Low

Tropical Storm

COARE average temperature scaling parameter by 

synoptic pattern (1 of 2)

COARE average temperature scaling parameter by synoptic class by site

for May 1998 through October 2001

-0.25

-0.2

-0.15

-0.1

-0.05

0

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Temperature scaling parameter (degrees)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-156

COARE average temperature scaling parameter by 

synoptic pattern (2 of 2)

COARE average temperature scaling parameter by synoptic class by BAMP site

for September 2000 through September 2001

-2.50E-01

-2.00E-01

-1.50E-01

-1.00E-01

-5.00E-02

0.00E+00

BIP DWP MBP SWP WDP 

Site

Temperature scaling parameter (degrees)

Ridge

Weak Ridge

Flat

Zonal

Post-trof

Weak Trof

Trof

Cut-off Low

Tropical Storm

COARE surface roughness by synoptic pattern by 

synoptic pattern (1 of 2)

COARE surface roughness by synoptic class by site 

for May 1998 through October 2001

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Roughness (m)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-157

COARE surface roughness by synoptic pattern by 

synoptic pattern (2 of 2)

COARE surface roughness by synoptic class by BAMP site 

for September 2000 through September 2001

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

BIP DWP MBP SWP WDP 

Site

Roughness (m)

Ridge

Weak Ridge

Flat

Zonal

Post-trof

Weak Trof

Trof

Cut-off Low

Tropical Storm

COARE average sensible heat fluxes by 

synoptic pattern (1 of 2)

COARE average sensible heat fluxes by synoptic class by site 

for May 1998 through October 2001

0

10

20

30

40

50

60

70

80

90

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Sensible Heat Flux (W/m2)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-158

COARE average sensible heat fluxes by 

synoptic pattern (2 of 2)

COARE average sensible heat fluxes by synoptic class by BAMP site

for September 2000 through September 2001

0

10

20

30

40

50

60

70

80

90

BIP DWP MBP SWP WDP 

Site

Sensible Heat Flux (W/m2)

Ridge

Weak Ridge

Flat

Zonal

Post-trof

Weak Trof

Trof

Cut-off Low

Tropical Storm

COARE average latent heat fluxes by 

synoptic pattern (1 of 2)

COARE average latent heat fluxes by synoptic class by site 

for May 1998 through October 2001

0

50

100

150

200

250

300

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Latent Heat Flux (W/m2)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-159

COARE average latent heat fluxes by 

synoptic pattern (2 of 2)

COARE average latent heat fluxes by synoptic class by BAMP site

for September 2000 through September 2001

0

50

100

150

200

250

300

BIP DWP MBP SWP WDP 

Site

Latent Heat Flux (W/m2)

Ridge

Weak Ridge

Flat

Zonal

Post-trof

Weak Trof

Trof

Cut-off Low

Tropical Storm

COARE average friction velocity by synoptic pattern (1 of 2)

COARE average friction velocity by synoptic class by site 

for May 1998 through October 2001

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Friction Velocity (m/s)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-160

COARE average friction velocity by synoptic pattern (2 of 2)

COARE average friction velocity by synoptic class by BAMP site

for September 2000 through September 2001

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

BIP DWP MBP SWP WDP 

Site

Friction Velocity (m/s)

Ridge

Weak Ridge

Flat

Zonal

Post-trof

Weak Trof

Trof

Cut-off Low

Tropical Storm

Observed average wind speed by synoptic pattern

Observed average wind speed by synoptic class by site 

for May 1998 through October 2001

0

2

4

6

8

10

12

42001 42002 42007 42019 42020 42035 42040 BURL1 DPIA1 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Wind Speed (m/s)

Ridge

Weak Ridge

Flat

Zonal

Post-Trough

Trough

Weak Trough

Cutoff Low

Tropical Storm
D-161

Synoptic Average Summary – Sensible Heat

• There is a large factor of 10 variability across 

the nine synoptic classes. There are some 

differences among the sites.

• Sensible heat flux is maximized for posttrough (i.e., post-frontal) synoptic conditions, 

which are likely to be marked by aboveaverage wind speeds and by low air 

temperature. 

• The latent heat flux is about one order of 

magnitude greater than the sensible heat flux.

• There is also less variability in the latent heat 

flux.

• Latent heat flux is largest during the “posttrough” synoptic condition due to higher wind 

speeds and relatively low dew points that 

follow a cold front.

Synoptic Average Summary – Latent Heat Flux
D-162

• Aside from the anomaly during tropical 

storms, there is relatively little variability in 

u* in synoptic class.

• The BAMP sites and VRM friction velocity is 

about 20% less than the other sites.

• Wind speed averages about 6 m/s for nonBAMP sites and 4 m/sec for BAMP sites and 

varies in a similar manner to u*.

Synoptic Average Summary –

Wind Speed and Friction Velocity

Synoptic Average Summary –

Temperature Scaling Parameter

• The temperature scaling parameter varies 

widely, from near zero to about –0.22°.

• The temperature scaling factor is much larger 

during “post-trough” periods.

• It is smallest during tropical storms when the 

air and water are likely to be at the same 

temperature. 
D-163

Synoptic Average Summary –

Roughness

• Roughness is typically about .0001 to .0015 m.

• Roughness is much less variable among the synoptic 

patterns for the platform sites compared to the buoy 

sites.

• Possible explanations are that the wave height and 

frequency are estimated from wind speed at the 

platforms, whereas, they are measured at the buoys. 

Also, the platform wind observations are corrected 

from 20+ meters to 10 meters and are, on average, 

less than the other non-BAMP sites.

Eta average downwelling longwave radiation 

by flow direction

Eta average downwelling longwave radiation by general flow direction by site

for May 1998 through October 2001 for the 6-to 12-hr forecast

310

320

330

340

350

360

370

380

390

400

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Downwelling Longwave Radiation (W/m2)

Onshore

Offshore

Parallel East

Parallel West
D-164

Eta average shortwave radiation by flow direction

Eta average shortwave radiation by general flow direction by site

for May 1998 through October 2001 for the 6-to 12-hr forecast

0

50

100

150

200

250

300

350

42001 42002 42007 42019 42020 42035 42040 DPIA1 GDIL1 PTAT2 SMI VRM 

Site

Shortwave Radiation (W/m2)

Onshore

Offshore

Parallel East

Parallel West

COARE average humidity scaling parameter 

by flow direction (1 of 2)

COARE average humidity scaling parameter by general flow direction by site

for May 1998 through October 2001

-3.50E-04

-3.00E-04

-2.50E-04

-2.00E-04

-1.50E-04

-1.00E-04

-5.00E-05

0.00E+00

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Humidity Scaling Parameter (kg/kg)

Onshore

Offshore

Parallel East

Parallel West
D-165

COARE average humidity scaling parameter 

by flow direction (2 of 2)

COARE average humidity scaling parameter by general flow direction by BAMP site

for September 2000 through September 2001

-4.50E-04

-4.00E-04

-3.50E-04

-3.00E-04

-2.50E-04

-2.00E-04

-1.50E-04

-1.00E-04

-5.00E-05

0.00E+00

BIP DWP MBP SWP WDP 

Site

Humidity Scaling Parameter (kg/kg)

Onshore

Offshore

Parallel East

Parallel West

COARE average temperature scaling parameter 

by flow direction (1 of 2)

COARE average temperature scaling parameter by general flow direction by site

for May 1998 through October 2001

-1.80E-01

-1.60E-01

-1.40E-01

-1.20E-01

-1.00E-01

-8.00E-02

-6.00E-02

-4.00E-02

-2.00E-02

0.00E+00

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Temperature Scaling Parameter (deg. C)

Onshore

Offshore

Parallel East

Parallel West
D-166

COARE average temperature scaling parameter 

by flow direction (2 of 2)

COARE average temperature scaling parameter by general flow direction by BAMP site

for September 2000 through September 2001

-1.80E-01

-1.60E-01

-1.40E-01

-1.20E-01

-1.00E-01

-8.00E-02

-6.00E-02

-4.00E-02

-2.00E-02

0.00E+00

BIP DWP MBP SWP WDP 

Site

Temperature Scaling Parameter (deg. C)

Onshore

Offshore

Parallel East

Parallel West

COARE average surface roughness 

by flow direction (1 of 2)

COARE average surface roughness by general flow direction by site 

for May 1998 through October 2001

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Roughness (m)

Onshore

Offshore

Parallel East

Parallel West
D-167

COARE average surface roughness 

by flow direction (2 of 2)

COARE average surface roughness by general flow direction by BAMP site

for September 2000 through September 2001

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

BIP DWP MBP SWP WDP 

Site

Roughness (m)

Onshore

Offshore

Parallel East

Parallel West

COARE average sensible heat fluxes 

by flow direction (1 of 2)

COARE average sensible heat fluxes by general flow direction by site 

for May 1998 through October 2001

0

10

20

30

40

50

60

70

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Sensible Heat Flux (w/m2)

Onshore

Offshore

Parallel East

Parallel West
D-168

COARE average sensible heat fluxes 

by flow direction (2 of 2)

COARE average sensible heat fluxes by general flow direction by BAMP site

for September 2000 through September 2001

0

10

20

30

40

50

60

70

BIP DWP MBP SWP WDP 

Site

Sensible Heat Flux (W/m2)

Onshore

Offshore

Parallel East

Parallel West

COARE average latent heat fluxes by flow direction (1 of 2)

COARE average latent heat fluxes by general flow direction by site 

for May 1998 through October 2001

0

50

100

150

200

250

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Latent Heat Flux (w/m2)

Onshore

Offshore

Parallel East

Parallel West
D-169

COARE average latent heat fluxes by flow direction (2 of 2)

COARE average latent heat fluxes by general flow direction by BAMP site

for September 2000 through September 2001

0

50

100

150

200

250

BIP DWP MBP SWP WDP 

Site

Latent Heat Flux (W/m2)

Onshore

Offshore

Parallel East

Parallel West

COARE average friction velocity by flow direction (1 of 2)

COARE average friction velocity by general flow direction by site 

for May 1998 through October 2001

0

0.05

0.1

0.15

0.2

0.25

0.3

42001 42002 42007 42019 42020 42035 42040 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Friction Velocity (m/s)

Onshore

Offshore

Parallel East

Parallel West
D-170

COARE average friction velocity by flow direction (2 of 2)

COARE average friction velocity by general flow direction by BAMP site

for September 2000 through September 2001

0

0.05

0.1

0.15

0.2

0.25

0.3

BIP DWP MBP SWP WDP 

Site

Friction Velocity (m/s)

Onshore

Offshore

Parallel East

Parallel West

Observed average wind speed by flow direction

Observed average wind speed by general flow direction by site 

for May 1998 through October 2001

0

1

2

3

4

5

6

7

8

42001 42002 42007 42019 42020 42035 42040 BURL1 DPIA1 GDIL1 PTAT2 SMI SRST2 VRM 

Site

Wind Speed (m/s)

Onshore

Offshore

Parallel East

Parallel West
D-171

General Flow Summary – Sensible Heat Flux

• At the non-BAMP sites, sensible heat flux is 

maximized for northerly flow conditions, which 

are more likely to be marked by above-average 

wind speeds and relatively low air temperatures.

• At BAMP sites, sensible heat flux is maximized 

for northerly and westerly flow conditions. 

• The difference in sensible heat flux between 

offshore and onshore flow directions across the 

nine synoptic classes is about a factor of 10.

General Flow Summary – Latent Heat Flux

• The latent heat flux is largest during northerly 

flow conditions, which tend to be associated with 

“post-trough” synoptic conditions, higher wind 

speeds, and relatively low dew points. 

• The latent heat is less variable for the BAMP 

sites compared to the non-BAMP sites.

• The minimum latent heat fluxes occur during 

onshore flow conditions, which tend to happen 

when boundary layer flows are in balance with 

the water surface and maximum dew points.
D-172

General Flow Summary –

Friction Velocity and Wind Speed

• High u* values are associated with high-wind 

periods, which tend to occur during offshore 

flow.

• U* is less variable for the BAMP sites 

compared to the non-BAMP sites.

General Flow Summary –

Temperature Scaling Parameter

• The temperature scaling parameter tends to be 

maximized during periods when the air is cooler than 

the water, such as during northerly offshore wind 

flow patterns. 

• It is smallest during onshore flow periods at the buoy 

sites when the air and water are likely to be at the 

same temperature. 

• At the oil platform (VRM and SMI) and C-MAN sites, 

the temperature scaling parameter is smallest during 

either onshore or parallel west flow directions.

• At DWP and WDP the temperature scaling 

parameter is not smallest during parallel west flow 

direction.
D-173

Diurnal Statistics

• Buoy 42001 (a deep-water buoy), the VRM, 

SMI, BIP, and DWP platforms, buoy 42040 (a 

near-shore site), and C-MAN site GDIL were 

selected for analysis.

• Diurnal variations of latent and sensible heat 

flux, friction velocity, wind speed, and sea-toair temperature difference were analyzed by 

month.

• Selected examples are shown in the following 

slides.

Diurnal – COARE hourly average sensible 

heat fluxes

COARE hourly average sensible heat fluxes over 42001 

for May 1998 through October 2001

-5

5

15

25

35

45

55

65

75

85

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Sensible Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-174

Diurnal – COARE hourly average sensible 

heat fluxes

COARE hourly average sensible heat fluxes over SMI 

for May 1998 through October 2001

-5

5

15

25

35

45

55

65

75

85

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Sensible Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly average friction velocity

COARE hourly average friction velocity over SMI for May 1998 through October 2001

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Friction Velocity (m/s)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-175

Diurnal – COARE hourly average latent heat fluxes

COARE hourly average latent heat fluxes over VRM for May 1998 through October 2001

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Latent Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly average sensible 

heat fluxes

COARE hourly average sensible heat fluxes over VRM 

for May 1998 through October 2001

-5

15

35

55

75

95

115

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Sensible Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-176

Diurnal – Hourly average skin temperature 

minus air temperature

Hourly average skin temperature minus air temperature over VRM 

for May 1998 through October 2001

-1

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Temperature Difference (deg. C)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly average sensible 

heat fluxes

COARE hourly average sensible heat fluxes over buoy 42040 

for May 1998 through October 2001

-5

5

15

25

35

45

55

65

75

85

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Sensible Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-177

Diurnal – COARE hourly average latent heat fluxes

COARE hourly average latent heat fluxes over buoy 42040 

for May 1998 through October 2001

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Latent Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly average sensible 

heat fluxes

COARE hourly average sensible heat fluxes over GDIL1 for May 1998 through October 2001

-5

5

15

25

35

45

55

65

75

85

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Sensible Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-178

Diurnal – Hourly skin temperature 

minus air temperature

Hourly skin temperature minus air temperature over GDIL1 

for May 1998 through October 2001

-1

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Temperature Difference (deg. C)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly friction velocity

COARE hourly friction velocity over GDIL1 for May 1998 through October 2001

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Friction Velocity (m/s)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-179

Diurnal – COARE hourly average latent heat fluxes

COARE hourly average latent heat fluxes over GDIL1 for May 1998 through October 2001

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Latent Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly average sensible 

heat fluxes

COARE hourly average sensible heat fluxes over BIP 

for September 2000 through September 2001

-10

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Sensible Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-180

Diurnal – COARE hourly average latent heat fluxes

COARE hourly average latent heat fluxes over BIP 

for September 2000 through September 2001

0

50

100

150

200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Latent Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly average friction velocity

COARE hourly average friction velocity over BIP 

for September 2000 through September 2001

0.05

0.07

0.09

0.11

0.13

0.15

0.17

0.19

0.21

0.23

0.25

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Time (LST)

Friction Velocity (m/s)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-181

Diurnal – Hourly skin temperature 

minus air temperature

Hourly skin temperature minus air temperature over BIP 

for September 2000 through September 2001

-2

0

2

4

6

8

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Temperature Difference (deg. C)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – Observed hourly average wind speed

Observed hourly average wind speed over BIP 

for September 2000 through September 2001

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Wind Speed (m/s)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-182

Diurnal – COARE hourly average sensible 

heat fluxes

COARE hourly average sensible heat fluxes over DWP 

for September 2000 through September 2001

-10

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Sensible Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – COARE hourly average latent heat fluxes

COARE hourly average latent heat fluxes over DWP 

for September 2000 through September 2001

0

50

100

150

200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Latent Heat Flux (W/m2)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-183

Diurnal – COARE hourly average friction velocity

COARE hourly average friction velocity over DWP 

for September 2000 through September 2001

0.05

0.07

0.09

0.11

0.13

0.15

0.17

0.19

0.21

0.23

0.25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Friction Velocity (m/s)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal – Hourly skin temperature 

minus air temperature

Hourly skin temperature minus air temperature over DWP 

for September 2000 through September 2001

-2

0

2

4

6

8

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour (LST)

Temperature Difference (deg. C)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec
D-184

Diurnal – Observed hourly average wind speed

Observed hourly average wind speed over DWP

for September 2000 through September 2001

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (LST)

Wind Speed (m/s)

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Diurnal Summary – Buoy 42001

The latent and sensible heat fluxes, friction 

velocity, and skin temperature-minus-air 

temperature difference show almost no diurnal 

variation, which makes physical sense at an 

over-water site
D-185

Diurnal Summary – SMI

• The latent and sensible heat fluxes show very little diurnal 

variation but slightly more than buoy 42001.

• In December, the greatest diurnal variation in sensible 

heat flux, about 20%, is observed. The variation is 

associated with a smaller friction velocity in the afternoon 

and not due to variations in the vertical temperature 

gradients.

• In May, sensible heat fluxes are near zero during most of 

the daylight hours and are associated with vertical 

temperature gradients near zero.

Diurnal Summary – VRM

• From June through September, latent heat fluxes peak in 

both the morning and afternoon.

• During other months, latent heat fluxes show very little 

diurnal variation. 

• In the winter months, sensible heat fluxes have strong 

diurnal cycles, peaking at sunrise. The morning peaks in 

the sensible heat flux are due to peaks in the skin 

temperature-minus-air temperature difference.

• Sensible heat flux in December is much higher than in 

other months. The high sensible heat flux in December is 

a result of a higher-than-average skin temperature-minusair temperature difference and higher-than-average 

friction velocity.
D-186

Diurnal Summary – Buoy 42040

• The sensible heat flux is similar to that at SMI. 

• There is a maximum diurnal variation of about 20% in 

December and January. 

• The maximum sensible heat flux occurs in December 

due to a combination of higher-than-average friction 

velocity and skin temperature-minus-air temperature 

difference. 

• The latent heat flux shows little diurnal variation and 

is also greatest in December.

Diurnal Summary – C-MAN GDIL1

• The sensible heat flux indicates that GDIL1 is not 

strongly influenced by land since sensible heat 

flux is lowest in mid-afternoon. 

• Sensible heat flux is never negative at night.

• However, the sensible heat flux curve shows a 

diurnal cycle.

• The diurnal cycle closely follows the diurnal cycle 

in skin temperature-minus-air temperature 

difference and not frictional velocity.

• The latent heat flux is somewhat flat but peaks in 

the afternoon during the summer months 
D-187

Diurnal Summary – BIP

• Sensible heat flux has minimal diurnal variation and 

is largest (about 20 to 30 w/m2) in late fall and early 

winter, when the water temperature is warm relative 

to the air temperature.

• During the other months, the sensible heat flux is 

small (less than 10 w/m2). 

• Latent heat flux also has minimal diurnal variation 

and is largest (about 150 to 200 w/m2) in July –

October, when the water temperature is the greatest. 

• In February, when water temperatures are cool, the 

latent heat flux drops to about 30 w/m2.

Diurnal Summary – BIP

• The COARE-calculated friction velocity shows minimal 

diurnal variation and varies by as much as a factor of 2 

from month to month. However, the month-to-month 

variation appears random and no physical causes can be 

identified. 

• The difference between skin (water surface) and air 

temperature shows about a 1° or 2°C diurnal variation. 

• As mentioned for other sites, the temperature difference is 

larger (2°C or greater) in the fall and is smaller (between 

–1° and +1°C in the late winter). 

• The wind speeds show little diurnal variation and are 

about 30% less in July–September when they are about 

4 m/s versus 5 m/s for most of the other months.
D-188

Diurnal Summary – DWP

• The DWP wind speeds show little diurnal variation 

and are about 30% less in July–October (behavior 

similar to BIP wind speeds) when they are about 

3 m/s versus 4 to 5 m/s for most of the other months. 

• Sensible heat flux has very little diurnal variation and 

is largest (about 15 to 25 w/m2) in late fall and early 

winter when the water temperature is warm relative to 

the air temperature (behavior similar to that found in 

BIP data). 

• During the other months, the sensible heat flux is 

small (less than 10 w/m2, with the minimal average of 

about 4 w/m2 in May). 

Diurnal Summary – DWP

• The latent heat flux has insignificant diurnal variation 

and is largest (about 120 w/m2) in the fall when the 

water temperature is the greatest. 

• In February, when water temperatures are cool, the 

latent heat flux drops to about 70 w/m2. 

• The COARE-calculated friction velocity shows some 

diurnal variations but the variations are not consistent 

from month to month. The average friction velocity 

varies by as much as a factor of 2 from month to 

month. However, the month-to-month variation 

appears random and no physical causes can be 

identified. 
D-189

Diurnal Summary – DWP

• The difference between skin (water surface) and air 

temperature shows about a 1° or 2°C diurnal 

variation.

• As mentioned for other sites, the temperature 

difference is larger (4°C or greater) in the late fall and 

is smaller (between –1° and 1°C in the spring (e.g., 

negative or stable temperature differences occur in 

May in the afternoon). A negative temperature 

difference will lead to a negative sensible heat flux.

Case Studies

• Four periods

• Buoy 42040, VRM, and SMI

• Large-scale meteorology

• Surface meteorological observations

• Profiler and RASS data

• COARE output

• Comparisons to Eta

• Mixing height
D-190

Abbreviations

• Sensible Heat - Hs

• Latent Heat - He

• Friction Velocity - u*

• Temperature Scaling Parameter - T*

• Humidity Scaling Parameter - q*

• Wind Speed - u 

• Air Temperature - T

• Virtual Temperature - Tv

• Skin Temperature - Ts

• Relative Humidity - RH

• Monin-Obukhov Length – z/L

• Surface Roughness - Zo

Case Studies – General Meteorology

• July 30 through August 1, 1999

– Strong upper-level ridge, surface high pressure, and light 

winds

• January 20 through 25, 2000

– Post frontal offshore flow on January 20 and 21

– Onshore flow on January 22 and 23

– Strong offshore flow on January 24 and 25 behind another 

cold front

• January 4 through 6, 2001

– Post upper-level trough (January 4 and 5) fading into weak 

ridge

– Air temperature much warmer than skin temperature

• September 18 through 20, 2001

– Weak onshore flow 

– A weak cold front orientated west to east along the Gulf 

Coast from Houston to Mobile on September 20
D-191

Buoy 42040

Air and Water Temperatures and Wind Speed

Air and water temperatures and wind speed at buoy 42040, January 20 through 25, 2000

0

5

10

15

20

25

30

1/20/00 18:00

1/21/00 0:001/21/00 6:00

1/21/00 12:00

1/21/00 18:00

1/22/00 0:001/22/00 6:00

1/22/00 12:00

1/22/00 18:00

1/23/00 0:00

1/23/00 6:00

1/23/00 12:001/23/00 18:00

1/24/00 0:00

1/24/00 6:00

1/24/00 12:001/24/00 18:00

1/25/00 0:00

1/25/00 6:00

1/25/00 12:00

Time (CST)

Temperature 

[°C]

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Wind Speed [m/s]

Air Temperature

Water Temperature

Coare Skin Temperature

Windspeed

Buoy 42040

COARE and Eta Hourly Sensible Heat Fluxes

COARE and Eta hourly sensible heat fluxes at buoy 42040, January 20 through 25, 2000 
D-192

Buoy 42040

COARE and Eta Hourly Latent Heat Fluxes

COARE and Eta hourly latent heat fluxes at buoy 42040, January 20 through 25, 2000

Mixing Heights and Tv at SMI, January 21, 2000

0900 UTC 1300 UTC 1700 UTC 2100 UTC
D-193

Winds at SMI, January 21, 2000

January 21, 2000, Summary

• The mixing heights were estimated to be about 750 m 

from midnight through 0400 to 1300 UTC. An increase 

was observed from 1300 to 1600 UTC, at which time the 

mixing heights peaked at about 1150 m. The mixing 

heights were estimated to have remained at about 

1100 m through 2400 UTC. 

• The virtual temperature (Tv) data during this period of time 

showed a weak inversion at about 150 m. The lowest 

30 m show a superadiabatic layer because the air 

temperature was much cooler than the skin temperature 

on this day.

• Winds within the lowest 1400 m switched from moderate 

easterly to light-to-moderate southwesterly at about 

1800 CST. 
D-194

VRM

Hourly Air and Skin Temperatures, Wind Speed, 

and Relative Humidity

Hourly air and skin temperatures, wind speed and relative humidity at VRM, January 4 through 6, 2001

VRM

COARE Hourly Average Latent and Sensible Heat Fluxes 

and Friction Velocity

COARE hourly average latent and sensible heat fluxes and friction velocity at VRM, January 4 through 6, 2001 
D-195

VRM

Estimated Wave Height and Period, 

Wind Speed, and Surface Roughness Length

Estimated wave height and period, wind speed, and surface roughness length 

at VRM, January 4 through 6, 2001 

VRM

COARE and Eta Latent and Sensible Heat Fluxes

COARE and Eta latent and sensible heat fluxes at VRM, January 4 through 6, 2001 

Note: the four-digit number after Eta in the key indicates 

the forecast period (i.e., 0612 is the 6- to 12-hr forecast). 
D-196

VRM

COARE and Eta Friction Velocity and z/L

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

1/4/01 0:00

1/4/01 3:00

1/4/01 6:00

1/4/01 9:00

1/4/01 12:00

1/4/01 15:00

1/4/01 18:00

1/4/01 21:00

1/5/01 0:00

1/5/01 3:00

1/5/01 6:00

1/5/01 9:00

1/5/01 12:00

1/5/01 15:00

1/5/01 18:00

1/5/01 21:00

1/6/01 0:00

1/6/01 3:00

1/6/01 6:00

1/6/01 9:00

1/6/01 12:00

1/6/01 15:00

1/6/01 18:00

1/6/01 21:00

1/7/01 0:00

Time (LST)

Friction Velocity (m/s)

-20

0

20

40

60

80

100

120

140

160

Z/L

COARE Friction Velocity

ETA3036 Friction Velocity

ETA0612 Friction Velocity

Z/L

COARE and Eta friction velocity and z/L at VRM, January 4 through January 6, 2001 

Note: the four-digit number after Eta in the key indicates the forecast period 

(i.e., 0612 is the 6- to 12-hr forecast and 3036 is the 30- to 36-hr forecast). 

January 4, 2001, Summary

No data available
D-197

VRM

COARE Latent and Sensible Heat Fluxes and Friction Velocity

COARE latent and sensible heat fluxes and friction velocity at VRM, July 30 through August 1, 1999 

SMI

COARE Latent and Sensible Heat and Friction Velocity

COARE latent and sensible heat fluxes and friction velocity at SMI, July 30 through August 1, 1999
D-198

VRM

Estimated Wave Height and Period, Wind Speed, 

and Surface Roughness Length

Estimated wave height and period, wind speed, and surface roughness length at VRM, 

July 30 through August 1, 1999 

SMI

Estimated Wave Height and Period, Wind Speed, 

and Surface Roughness Length

Estimated wave height and period, wind speed, and surface roughness length at SMI, 

July 30 through August 1, 1999
D-199

VRM

COARE and Eta Latent and Sensible Heat Fluxes

COARE and Eta latent and sensible heat fluxes at VRM, July 30 through August 1, 1999 

Note: the four-digit number after Eta in the key indicates the 

forecast period (i.e., 0612 is the 6- to 12-hr forecast). 

SMI

COARE and Eta Latent and Sensible Heat Fluxes

COARE and Eta latent and sensible heat fluxes at SMI, July 30 through August 1, 1999 

Note: the four-digit number after Eta in the key indicates the 

forecast period (i.e., 0612 is the 6- to 12-hr forecast).
D-200

VRM

COARE and Eta Friction Velocity and z/L

COARE and Eta friction velocity and z/L at VRM, July 30 through August 1, 1999 

Note: the four-digit number after Eta in the key indicates the forecast period 

(i.e., 0612 is the 6- to 12-hr forecast and 3036 is the 30- to 36-hr forecast). 

SMI

COARE and Eta Friction Velocity and z/L

COARE and Eta friction velocity and z/L at SMI, July 30 through August 1, 1999 

Note: the four-digit number after Eta in the key indicates the forecast period 

(i.e., 0612 is the 6- to 12-hr forecast and 3036 is the 30- to 36-hr forecast). 
D-201

VRM

Hourly Air and Skin Temperatures, Wind Speed, and 

Relative Humidity

0

5

10

15

20

25

30

35

40

7/30/99 0:00

7/30/99 3:00

7/30/99 6:00

7/30/99 9:00

7/30/99 12:00

7/30/99 15:00

7/30/99 18:00

7/30/99 21:00

7/31/99 0:00

7/31/99 3:00

7/31/99 6:00

7/31/99 9:00

7/31/99 12:00

7/31/99 15:00

7/31/99 18:00

7/31/99 21:00

8/1/99 0:00

8/1/99 3:00

8/1/99 6:00

8/1/99 9:00

8/1/99 12:00

8/1/99 15:00

8/1/99 18:00

8/1/99 21:00

8/2/99 0:00

Time (CST)

Other variables

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

RH

Air Temperature (Degrees C) 

Wind Speed (m/sec)

Skin temperature (Degrees C) 

RH (Fraction)

Hourly air and skin temperatures, wind speed, and relative humidity at VRM, July 30 through August 1, 1999

SMI

Hourly Air and Skin Temperatures, Wind Speed, and 

Relative Humidity

0

5

10

15

20

25

30

35

40

7/30/99 0:00

7/30/99 3:00

7/30/99 6:00

7/30/99 9:00

7/30/99 12:00

7/30/99 15:00

7/30/99 18:00

7/30/99 21:00

7/31/99 0:00

7/31/99 3:00

7/31/99 6:007/31/99 9:00

7/31/99 12:00

7/31/99 15:00

7/31/99 18:00

7/31/99 21:00

8/1/99 0:00

8/1/99 3:00

8/1/99 6:00

8/1/99 9:00

8/1/99 12:00

8/1/99 15:00

8/1/99 18:00

8/1/99 21:00

8/2/99 0:00

Time (CST)

Other variables

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

RH

Air Temperature (Degrees C) 

Wind Speed (m/sec)

Skin temperature (Degrees C) 

RH (Fraction)

Hourly air and skin temperatures, wind speed, and relative humidity at SMI, July 30 through August 1, 1999
D-202

SMI, July 31, 1999

0900 UTC 1300 UTC 1700 UTC 2100 UTC

Winds at SMI, July 31, 1999
D-203

July 31, 1999, Summary

• In general, mixing heights were about 750 to 850 m. 

Mixing heights remained fairly constant with 

relatively little variation.

• The Tv data revealed stable profiles throughout the 

day, with the exception of a shallow layer at 

1300 UTC below about 150 m.

• Winds within the lowest 1000 m at SMI were 

primarily moderate southwesterly; however, a wind 

shift to light southerly began around 2200 UTC. The 

depth through which the southwesterly winds were 

observed was greater than the previous day, 

extending to above 2000 m. 

VRM

Hourly Air and Skin Temperatures, Wind Speed, and 

Relative Humidity

0

5

10

15

20

25

30

35

40

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Other variables

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

RH

Air Temperature (Degrees C) 

Wind Speed (m/sec)

Skin temperature (Degrees C) 

RH (Fraction)

RH is estimated, w hich w ill influence the Latent Heat

Hourly air and skin temperatures, wind speed, and relative humidity at VRM, September 18 through 20, 2001 
D-204

SMI

Hourly Air and Skin Temperatures, Wind Speed, and 

Relative Humidity

0

5

10

15

20

25

30

35

40

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Other variables

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

RH

Air Temperature (Degrees C) 

Wind Speed (m/sec)

Skin temperature (Degrees C) 

RH (Fraction)

Hourly air and skin temperatures, wind speed, and relative humidity at SMI, September 18 through 20, 2001 

VRM

COARE Latent and Sensible Heat Fluxes 

and Friction Velocity

COARE latent and sensible heat fluxes and friction velocity at VRM, September 18 through 20, 2001 

0

50

100

150

200

250

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Other variables

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Friction Velocity

Latent Heat (w/m**2)

Sensible Heat (w/m**2)

Friction Velocity (m/sec)
D-205

SMI

COARE Latent and Sensible Heat Fluxes and Friction Velocity

0

50

100

150

200

250

9/18/01 0:009/18/01 3:00

9/18/01 6:009/18/01 9:00

9/18/01 12:00

9/18/01 15:009/18/01 18:009/18/01 21:00

9/19/01 0:009/19/01 3:009/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:009/19/01 18:009/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:009/20/01 15:009/20/01 18:009/20/01 21:00

9/21/01 0:00

Time (CST)

Other variables

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Friction Velocity

Latent Heat (w/m**2)

Sensible Heat (w/m**2)

Friction Velocity (m/sec)

COARE latent and sensible heat fluxes and friction velocity at SMI, September 18 through 20, 2001

VRM

Estimated Wave Height and Period, Wind Speed, 

and Surface Roughness Length

0

1

2

3

4

5

6

7

8

9

10

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Other variables

0

0.00005

0.0001

0.00015

0.0002

0.00025

0.0003

0.00035

0.0004

0.00045

0.0005

0.00055

0.0006

0.00065

0.0007

0.00075

0.0008

0.00085

0.0009

0.00095

0.001

Roughness

Estimate Wave Height (m)

Estimate Wave Period (sec)

Wind Speed (m/sec)

Roughness (m)

Estimated wave height and period, wind speed, and surface roughness length at VRM, 

September 18 through 20, 2001
D-206

SMI

Estimated Wave Height and Period, Wind Speed, 

and Surface Roughness Length

0

1

2

3

4

5

6

7

8

9

10

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Other variables

0

0.00005

0.0001

0.00015

0.0002

0.00025

0.0003

0.00035

0.0004

0.00045

0.0005

0.00055

0.0006

0.00065

0.0007

0.00075

0.0008

0.00085

0.0009

0.00095

0.001

Roughness

Estimate Wave Height (m)

Estimate Wave Period (sec)

Wind Speed (m/sec)

Roughness (m)

Estimated wave height and period, wind speed, and surface roughness length at SMI, 

September 18 through 20, 2001

VRM

COARE and Eta Latent and Sensible Heat Fluxes

0

50

100

150

200

250

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Latent and Sensible Heat 

Latent Heat (w/m**2)

Sensible Heat (w/m**2)

Eta0612 Sensible Heat (w/m**2)

Eta0612 Latent Heat (w/m**2)

COARE and Eta latent and sensible heat fluxes at VRM, September 18 through 20, 2001 

Note: the four-digit number after Eta in the key indicates the 

forecast period (i.e., 0612 is the 6- to 12-hr forecast). 
D-207

SMI

COARE and Eta Latent and Sensible Heat Fluxes

0

50

100

150

200

250

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Latent and Sensible Heat 

Latent Heat (w/m**2)

Sensible Heat (w/m**2)

Eta0612 Sensible Heat (w/m**2)

Eta0612 Latent Heat (w/m**2)

COARE and Eta latent and sensible heat fluxes at SMI, September 18 through 20, 2001 

Note: the four-digit number after Eta in the key indicates the 

forecast period (i.e., 0612 is the 6- to 12-hr forecast). 

VRM

COARE and Eta Friction Velocity and z/L

COARE and Eta friction velocity and z/L at VRM, September 18 through 20, 2001 

Note: the four-digit number after Eta in the key indicates the forecast period 

(i.e., 0612 is the 6- to 12-hr forecast and 3036 is the 30- to 36-hr forecast). 

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:00

9/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Friction Velocity

-2

-1

0

10

20

30

40

50

60

70

Friction Velocity (m/sec)

Eta3036 Friction Velocity (m/sec)

Eta0612 Friction Velocity (m/sec)

ZL
D-208

SMI

COARE and Eta Friction Velocity and z/L

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

9/18/01 0:00

9/18/01 3:00

9/18/01 6:00

9/18/01 9:00

9/18/01 12:00

9/18/01 15:009/18/01 18:00

9/18/01 21:00

9/19/01 0:00

9/19/01 3:00

9/19/01 6:00

9/19/01 9:00

9/19/01 12:00

9/19/01 15:00

9/19/01 18:00

9/19/01 21:00

9/20/01 0:00

9/20/01 3:00

9/20/01 6:00

9/20/01 9:00

9/20/01 12:00

9/20/01 15:00

9/20/01 18:00

9/20/01 21:00

9/21/01 0:00

Time (CST)

Friction Velocity

-40

-35

-30

-25

-20

-15

-10

-5

0

Z/L

Friction Velocity (m/sec)

Eta3036 Friction Velocity (m/sec)

Eta0612 Friction Velocity (m/sec)

ZL

COARE and Eta friction velocity and z/L at SMI for September 18 through 20, 2001 

Note: the four-digit number after Eta in the key indicates the forecast period 

(i.e., 0612 is the 6- to 12-hr forecast and 3036 is the 30- to 36-hr forecast). 

Tv at VRM, September 18, 2001

0900 UTC 1300 UTC 1700 UTC 2100 UTC

Reflectivity data did not reveal a specific mixing height during this period 

at either site.
D-209

Winds at VRM, September 18, 2001

September 18, 2001, Summary

• No Cn

2, RASS, or wind data for SMI were 

available.

• Winds within the lowest 1500 m were light to 

moderate southerly.

• The Tv data showed an adiabatic profile with 

the exception of the lowest 100 m, which 

showed a superadiabatic layer because the 

air temperature was cooler than the skin 

temperature on this day.
D-210

Case Study Summary (1 of 5)

• January 20-24, 2000, was an active synoptic period, 

with frequent moderate winds, large fluctuations in air 

temperature, and large swings in latent and sensible 

heat. 

• January 5-6, 2001, was a relatively cool period but 

with the air temperature warmer than the skin 

temperature most of the time, leading to frequent 

stable conditions. 

• The July 1999 and September 2001 periods were 

typical summertime periods with air temperature 

usually cooler than skin temperature (i.e., unstable 

conditions) and with light to moderate winds. 

• During most periods with an unstable 

temperature gradient, the COARE latent heat 

fluxes are about 5 to 10 times larger than the 

sensible heat fluxes. At these times, both 

latent and sensible heat fluxes are roughly 

proportional to u*. 

• Skin temperature is greater than air 

temperature most of the time in the four years 

of Gulf of Mexico data, as it is at most ocean 

sites at low to mid-latitudes.

Case Study Summary (2 of 5)
D-211

Case Study Summary (3 of 5)

• Latent heat is about 100 to 200 W/m2 when air 

temperature is greater than skin temperature during 

typical summertime periods. 

• During the January 20-25, 2000, case study, there 

was a period with a large skin temperature-minus-air 

temperature difference and large wind speed, which 

led to an exceptionally large latent heat flux of about 

500 W/m2. 

• Rarely does the latent heat flux become negative. 

During periods when skin temperature is less than air 

temperature and RH is high, its magnitude is less 

than 10 W/m2. 

Case Study Summary (4 of 5)

• Sensible heat flux is usually positive upward with 

magnitudes of 50 W/m2 or less when skin temperature is 

greater than air temperature (i.e., most of the time). 

• When skin temperature is less than air temperature, it 

becomes negative but has a magnitude less than 10 

W/m2. 

• Sensible heat flux is negative more often than latent heat 

flux because the sensible heat is negative whenever skin 

temperature is less than air temperature, but latent heat 

becomes negative only when skin temperature is less than 

air temperature and the RH of the air near the surface is 

very high.

• On average, the Eta-predicted u*s are about 50% to a 

factor of 2 larger than the COARE u*s. 
D-212

Case Study Summary (5 of 5)

• COARE latent and sensible heat fluxes agree fairly well 

with Eta forecasts of these fluxes. 

• Agreement is best during warm summer periods for which 

COARE was derived and calibrated, and Eta also does 

well with these periods. 

• Despite the fact that Eta appears to match the average 

and the maximum COARE latent and sensible heat fluxes 

well, the time variations are not well-simulated, especially 

at VRM. 

• Part of the reason for the diurnal fluctuations forecasted 

by Eta may be that the grid cell in which VRM is located 

includes a large fraction of land surface. 

Follow-on work involving collaboration with outside 

organizations:

• Work with NCEP to better understand over-water wind 

differences between the Eta model and observed 

profiler winds. Analysis has shown that Eta model 

winds are biased from the profiler winds.

• Compare Eta 12-km gridded predictions to observed 

data; compare the comparisons done with EDAS 40-

km predictions/observations. The results will help 

guide how 

finer-resolution Eta model data should be used in 

high-resolution modeling efforts.

Recommendations: Collaboration (1 of 2)
D-213

• Work with NOAA ETL to design a scheme to remove sea-clutter 

from profiler data so that mixing heights can be automatically 

estimated for this study and future studies using existing mixing 

height algorithms.

• Work with Christopher Fairall at NOAA to improve COARE 

predictions at high surface roughness. Roughness increases 

under very low wind speeds, which influences estimations of the 

boundary layer parameters.

• Make better use of BL measurements/analyses in other MMSsponsored projects by reviewing plans and progress and 

recommending ways to incorporate BL data and 

analysis/modeling results.

Recommendations: Collaboration (2 of 2)

Plan a special issue (of JAM, JGR, or ?) on BL issues in the Gulf and 

prepare specific papers on the following:

• Eta/profiler wind comparisons.

• 3-year climatology of surface boundary layer parameters 

calculated using COARE in a shallow water ocean and 

modifications made to COARE (joint with NOAA?).

• Modeled and estimated mixing heights in the Gulf of Mexico.

• Results from other related MMS-sponsored projects.

Recommendations: Publish
D-214

• Compare satellite-derived sea-surface temperatures to 

radiometer temperatures and buoy temperatures collected during 

this study. Accurate spatial sea-surface temperatures are 

important for accurate modeling.

• Compare estimates of sea-surface temperatures to the 

radiometer temperatures when clouds obscure the satellite’s view

of the Gulf (currently estimated using hole-filling techniques).

• Identify several additional periods of super-stable conditions in 

the existing data set (i.e. a period of southerly flow after a cold 

outbreak has cooled the water in the shallow portion of the Gulf) 

and perform a BL case study similar to other case studies.

Recommendations: Analysis (1 of 2)

• Determine the best scheme for estimating wave height and 

frequency as a function of water depth from wind speed alone. 

When wave data is not available at the platforms, inaccurate 

estimations of wave characteristics can result in inaccurate 

estimations of surface roughness, which influence boundary layer

parameterizations. Evaluate the roughness estimations estimated

from wind speed alone; compare to observed wave data.

• Integrate onshore and offshore air quality data into the 

meteorological data set and analyses performed during this project. 

This will expand the applicability of the results and provide further 

evaluation of the methods used.

• Revise the NEGOM Met Statistical Expert System to use improved 

model output and now-available data; this will result in a more 

accurate tool for visualization of meteorological data and of estimates 

of transport and dispersion from specific locations offshore.

Recommendations: Analysis (2 of 2)
D-215

• Update the Calmet model to better estimate mixing heights and 

perform additional comparisons of observation-based estimations 

of mixing heights to model mixing heights. Currently, CALMET 

does a poor job estimating mixing heights in the Gulf of Mexico.

• Update the CALPUFF dispersion runs using new CALMET output 

created with an improved mixing height scheme. Compare the 

new runs to those created as part of this project.

• Compare CALMET diagnostic model runs to MM5 prognostic 

model runs and observational data and create best estimates of 

gridded mixing heights and winds.

• Modify the way diagnostic and prognostic models treat the diffuse 

shoreline of the Gulf; operate the models and compare results 

with observations.

Recommendations: Modeling

• Collocate a radiometer and underwater temperature sensor to determine 

the relationship and the accuracy of the COARE estimated warm layer 

and cool skin effect. This effect is used to estimate skin temperature at 

buoys, an important parameter for the estimation of boundary layer 

parameters and for model initial conditions. Work with NOAA to adjust 

COARE as needed.

• On a platform, operate temperature, relative humidity, and wind sensors 

at two heights within the surface layer, as well as a solar radiometer. 

Use this data to verify COARE estimations of boundary layer parameters 

that used surface boundary layer data at only one level. 

Recommendations: Measurements (1 of 2)
D-216

• Continue routine operations of surface and upper-air meteorological 

parameters at the IMPROVE site in the Mississippi River Delta.

• Routinely operate a mini-Sodar, a profiler/RASS system, and a surface 

meteorological monitoring system on a platform to obtain wind and 

temperature measurements through the depth of the surface layer and 

boundary layer. This data could be used for routine comparisons with 

Eta, for routine estimates of BL characteristics, for real-time modeling, 

and for special research studies involving BL gradients on- and offshore, etc. The addition of the mini-Sodar would fill the measurement 

hole that exists from 30 m to about 200 m; this hole is often the location 

of plumes.

Recommendations: Measurements (2 of 2)
The Department of the Interior Mission

As the Nation's principal conservation agency, the Department of the Interior has responsibility 

for most of our nationally owned public lands and natural resources. This includes fostering 

sound use of our land and water resources; protecting our fish, wildlife, and biological diversity; 

preserving the environmental and cultural values of our national parks and historical places; 

and providing for the enjoyment of life through outdoor recreation. The Department assesses 

our energy and mineral resources and works to ensure that their development is in the best 

interests of all our people by encouraging stewardship and citizen participation in their care. 

The Department also has a major responsibility for American Indian reservation communities 

and for people who live in island territories under U.S. administration. 

The Minerals Management Service Mission 

As a bureau of the Department of the Interior, the Minerals Management Service's (MMS) 

primary responsibilities are to manage the mineral resources located on the Nation's Outer 

Continental Shelf (OCS), collect revenue from the Federal OCS and onshore Federal and Indian 

lands, and distribute those revenues. 

Moreover, in working to meet its responsibilities, the Offshore Minerals Management Program 

administers the OCS competitive leasing program and oversees the safe and environmentally 

sound exploration and production of our Nation's offshore natural gas, oil and other mineral 

resources. The MMS Minerals Revenue Management meets its responsibilities by ensuring the 

efficient, timely and accurate collection and disbursement of revenue from mineral leasing and 

production due to Indian tribes and allottees, States and the U.S. Treasury. 

The MMS strives to fulfill its responsibilities through the general guiding principles of: (1) being 

responsive to the public's concerns and interests by maintaining a dialogue with all potentially 

affected parties and (2) carrying out its programs with an emphasis on working to enhance the 

quality of life for all Americans by lending MMS assistance and expertise to economic 

development and environmental protection.