NASA/CR-2013-217922 

N~~ ' ) . 

Vandenberg Air Force Base Pressure 

Gradient Wind Study 

Jaclyn A. Shafer 

ENSCO, Inc., Cocoa Beach, Florida 

NASA Applied Meteorology Unit, Kennedy Space Center, Florida 

September 2013 
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NASA/CR-2013-217922 

Vandenberg Air Force Base Pressure 

Gradient Wind Study 

Jaclyn A. Shafer 

ENSCO, Inc., Cocoa Beach, Florida 

NASA Applied Meteorology Unit, Kennedy Space Center, Florida 

National Aeronautics and 

Space Administration 

Kennedy Space Center 

Kennedy Space Center, FL 32899-0001 

September 2013 
Acknowledgements 

The author would like to thank Dr. William Bauman, Ms. Winifred Crawford, and Dr. Leela 

Watson of the Applied Meteorology Unit, Dr. Lisa Huddleston of the Kennedy Space Center 

Weather Office and Mr. William Roeder of the 45th Weather Squadron for lending their time, 

data management, and statistical expertise to this task. Mr. Tyler Brock of the 30th Operational 

Support Squadron and Mr. Ben Kenyon of WROCI/Indyne also played a significant role 

providing historical Vandenberg Air Force Base tower network data for this task. 

2 

Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

This report is also available in electronic form at 

http://science.ksc.nasa.gov/amu/ 
Executive Summary 

Customer: Launch Services Program (LSP) 

Warning category winds can adversely impact day-to-day space lift operations at 

Vandenberg Air Force Base (VAFB) in California. NASA's LSP and other programs at VAFB use 

wind forecasts issued by the 30th Operational Support Squadron Weather Flight (30 OSSWF) to 

determine if they need to limit activities or protect property such as a launch vehicle. For 

example, winds ~ 30 kt can affect Delta II vehicle transport to the launch pad, Delta IV stage II 

attitude control system tank load, and other critical operations. The 30 OSSWF uses the mean 

sea level pressure (MSLP) from seven regional observing stations to determine the pressure 

difference (dP) as a guide to forecast surface wind speed at VAFB. Their current method uses 

an Excel-based tool that is manually intensive and does not contain an objective relationship 

between peak wind and dP. They require a more objective and automated capability to help 

them forecast the onset and duration of warning category winds to enhance the safety of their 

customers' operations. The 30 OSSWF tasked the Applied Meteorology Unit (AMU) to develop 

an automated Excel graphical user interface (GUI) that uses the pressure observations at 

specific observing stations under different synoptic regimes to aid forecasters in determining 

when wind warnings should be issued. The AMU suggested that the tool use pressure gradients 

(PG) instead of dP as it is a more accurate indicator of local wind speed, and the 30 OSSWF 

agreed. Development of such a tool would require that solid relationships exist between the 

peak wind speed and the PG of one or more station pairs. 

In order to determine past high wind events on VAFB and compare the local PGs at the 

time, the AMU required historical wind data from the VAFB wind tower network and MSLP 

observations from weather observing stations used operationally by the 30 OSSWF. The 

30 OSSWF delivered all available data from their 26 VAFB wind towers from October 2007-

November 2012. The AMU processed the observations to develop a database containing 

maximum hourly peak winds for each tower and day in the dataset. Meanwhile, the 45th 

Weather Squadron (45 WS) obtained historical MSLP observations data from the 14th Weather 

Squadron (14 WS). Once received, the AMU developed an MSLP database containing hourly 

observations from each station. These observations were organized by synoptic regime and the 

hourly PGs for each station pair were calculated. 

To better understand the relationship between peak wind and PG at VAFB, the AMU 

created a series of graphs plotting PG and maximum peak wind (MPW) versus time for each of 

the synoptic regimes. These graphs were created for four days in each synoptic regime, each 

day representing a different time of the year in order to have a diverse collection of case 

studies. The initial review of PGs and MPW did not yield a clear qualitative relationship between 

the two variables regardless of the time of year or synoptic regime. Given this result, the AMU 

calculated correlation coefficients between PG and MPW to quantitatively measure the 

relationship between them using the entire 2007-2012 database. Most of the Pearson 

correlation coefficient (PCC) values ranged between -0.1 and 0.4 with occasional outliers. Given 

PCC indicates no relationship when it is equal to zero, these statistics confirm a weak 

relationship between PG and MPW at VAFB. Based on the PG evaluation and calculated PCC 

values, the AMU was unable to determine PG thresholds for the station pairs and therefore did 

not automate the 30 OSSWF wind tool. This report provides a description of the data used and 

the results of the analyses to show the lack of relationship between PG and peak winds at 

VAFB. 

2 
Table of Contents 

Executive Summary ... ...... .. ......... ..... ......... ... .. ....................... .. .. ......... ....... .......... ... .. ..... .............. 2 

Table of Contents ......... .... .. ... .......................... .. ... ..... ..... .. .. .. ........ ... ....................... ......... ... ........ 3 

List of Figures ...... .... .. .......... .................. ....... ................... .................... ... .... ....... ....... ... ... .. .......... 4 

List of Tables ........... ............ ........... .. ...................... ... ............ .. ............ ............................ .... ....... 5 

1 Introduction ..... .... .... ....... ..... ................... ............ ..... ...... ..... ... ............... ............ ................ ..... 6 

2 Data Acquisition and Processing ......... ... ... ............... ... ......... ................ ...... ... ...................... . 7 

2.1 VAFB Synoptic Regimes ... .............. ... .. ......... ................ ... .... .. ... ........... ... ........ ........ ..... 7 

2.2 VAFB Wind Tower Data ....... ... ........... .. .................. ....... .. .... .. ........ ..... .. ........................ 9 

2.3 Regional Observing Station Data ... ............. .. .. ...... ... ...... ... ... ......... ........... ....... .. ......... 11 

3 Data Analysis .. ..... .. ................................. .. ... .................................. ....... .. ......... .... .. ............. 13 

3.1 Pressure Gradient Evaluation: Full Base ................. ........... ................ .. ...... ... ... ... ... ... . 13 

3.2 Pressure Gradient Evaluation: North and South Base ... ... ................................... ....... 16 

3.3 Correlation ....... ... .......... ........... ......... ... .................. .. .. .... ............... ............................. 21 

4 Summary ... .. .. ........ ... .. ... ...... ........... ............. ......... ........ .. ..... ...................... ..... ........ ........... . 24 

List of Acronyms ......... .................. .... .. ............... .. .......................... ........................... ..... ........... 25 

3 
List of Figures 

Figure 1. Charts depicting the synoptic conditions for each of the regimes included in this 

study. The red solid line indicates the location of the PFJ. The blue H indicates a 

high pressure area, the red L indicates a low pressure area . ......... ......... ............ ...... 8 

Figure 2. Locations of the 26 wind towers in the VAFB network (KVBG in Figure 3) .......... .... 10 

Figure 3. Locations of the seven observing stations used to calculate PG. KVBG is VAFB .... 11 

Figure 4. Example PG/MPW versus time graph for the~ 40 kt wind event on 14 July 2011 with 

a CH regime. The MPW values are on the left y-axis, the PG values between all the 

station pairs in the legend are on the right y-axis, and the time in UTC is on the xaxis . .................... ... ............................. ..... .... .. .. ............................................. ...... .... 14 

Figure 5. Same as Figure 4 except ABS(PG) replaces PG on the right y-axis . ............ .......... 14 

Figure 6. Same as Figure 5, except for 25 January 2008 in the UT regime ...... ...................... 15 

Figure 7. Same as Figure 5, except for 4 November 2008 in the NPL regime ... ...... ... ..... ....... 16 

Figure 8. All VAFB wind towers designated as North Base (yellow) and South Base (light 

blue) .... .................... .......... ..... ...... .... ........................... ..................... ................. ...... 17 

Figure 9. Example ABS(PG)/MPW versus time graph with PH regime. The MPW is on the left 

y-axis, the ABS(PG) is on the right y-axis, and time is on the x-axis ..... .. ..... ............ 18 

Figure 10. Same as Figure 9 except for NB/SB ABS(PG)/MPW. NB-MPW are the solid black 

line with diamonds, the SB-MPW are the dashed line with circles ..... ................ ..... . 18 

Figure 11 . Same as Figure 10 except for 22 August 2010 ....... ........ ........ .. ..... ............... ...... ..... 19 

Figure 12. Same as Figure 10 except for 18 July 2011 and for a CL regime ........ .. .................. 20 

Figure 13. ABS(PG) PCC versus synoptic regime for the full base from 2007-2012. The solid 

black line highlights where PCC equals zero. The PCC is on the y-axis and the 

synoptic regime on the x-axis. The "ALL" category on the x-axis includes all of the 

days in the 2007-2012 database regardless of synoptic regime and the solid black 

horizontal line highlights where PCC equals zero ........ ................... .. ........ ............... 22 

Figure 14. Same as Figure 13 except for NB towers ........ ...... ................... ......................... .. .... 22 

Figure 15. Same as Figure 13 except for SB towers ............. ....... .............. .............................. 23 

Figure 16. Same as Figure 13 except for dP ................ ... ..... .. ....... ............... .. ....... ............ ..... .. 23 

4 
List of Tables 

Table 1. Number of days with peak winds 2: 40 kt for each synoptic regime ................ .......... 10 

Table 2. List of the 30 OSSWF-identified station pairs and distance (km) between them used 

in the PG calculations. The station pairs below the green line were added by the 

AMU ....... .. ............... ................. ............ .. ... ........................................ ... ............... .. .. 12 

Table 3. List of the 30 OSSWF towers classified by NB/SB and their respective elevations in 

feet. .. ..... ................ ......................................................... ....... .................. .......... ...... 21 

5 
1 Introduction 

Warning category winds can adversely impact day-to-day space lift operations at 

Vandenberg Air Force Base (VAFB) in California. NASA's Launch Services Program (LSP) and 

other programs at VAFB use wind forecasts issued by the 30th Operational Support Squadron 

Weather Flight (30 OSSWF) to determine if they need to limit activities or protect property such 

as a launch vehicle. For example, winds <:: 30 kt c.an affect Delta II vehicle transport to the 

launch pad, Delta IV stage II attitude control system tank load, and other critical operations. The 

30th Operational Support Squadron Weather Flight (30 OSSWF) at VAFB uses the mean sea 

level pressure (MSLP) from seven regional observing stations to determine the pressure 

difference (dP) as a guide to forecast surface wind speed at VAFB. Their current method uses 

an Excel-based tool that is manually intensive and does not contain an objective relationship 

between peak wind and dP. They require a more objective and automated capability to help 

them forecast the onset and duration of warning category winds to enhance the safety of their 

customers' operations. The 30 OSSWF tasked the Applied Meteorology Unit (AMU) to develop 

an automated Excel graphical user interface (GUI) that uses the pressure observations at 

specific observing stations under different synoptic regimes to aid forecasters in determining 

when wind warnings should be issued. 

As stated previously, the 30 OSSWF forecasters use dP as their guide for forecasting peak 

winds. The AMU suggested that the tool use pressure gradients (PG) instead of dP as it is a 

more accurate indicator of local wind speed, and the 30 OSSWF agreed. Therefore, the AMU 

used the PG between the regional observing stations and VAFB wind tower data, both stratified 

by synoptic-scale flow regimes, to determine relationships between PG and peak winds at 

VAFB. 

The goal of this task, then, was to develop an automated tool that would use relationships 

between PG values and peak winds to determine PG thresholds under different synoptic 

regimes that would provide objective peak wind forecast guidance to the 30 OSSWF. 

Development of such a tool would require that solid relationships exist between the peak wind 

speed and the PG of one or more station pairs. The AMU conducted subjective and objective 

analyses to discern such relationships, but found there were none. As a result, the requested 

GUI could not be developed. This report provides a description of the data used and the results 

of the analyses to show the lack of relationship between PG and peak winds at VAFB. 

6 
2 Data Acquisition and Processing 

The goal of this task as stated in the previous section required identification of past high 

wind events and calculating the local PG values between regional observing station pairs under 

different synoptic regimes at the times of those peak winds. These two parameters were used to 

identify PG thresholds related to the occurrence of the peak winds. In order to identify past high 

wind events on VAFB and compare the PGs between observing stations at the same time, the 

AMU required historical wind data from the VAFB wind tower network and MSLP observations 

from weather observing stations used operationally by the 30 OSSWF. The AMU acquired and 

processed VAFB wind tower network data and MSLP observations from seven 30 OSSWFidentified weather observing stations in the period 2007-2012. 

2.1 VAFB Synoptic Regimes 

Overall, there are 11 synoptic regimes that affect the weather at VAFB. For the days 

included in this study, seven of them were observed. Each regime is summarized below and 

illustrated in Figure 1. 

Pacific High (PH): This is a semi-permanent summer regime that develops in late May and lasts 

through late September. It may extend beyond the standard time frame when the upper-level 

pattern remains unchanged for extended periods of time. The high is generally recognized as a 

well-established surface feature and is located hundreds of miles off the California coast. 

North Pacific Low (NPL): This is most recognizable in fall through winter low pressure regimes 

that affect California. It is usually quick moving and highly dependent on the speed and position 

of the polar front jet (PFJ). This feature is usually very cold, originates from the Gulf of Alaska 

and is evident from the surface up to 200 mb. Depending on dynamics and moisture content, 

thunderstorms are possible. 

North Pacific High (NPH): This regime typically begins as a post-frontal ridge that extends from 

the Pacific into the western portion of the continental United States. It typically follows the NPL 

regime and is most common through the early fall to late spring. 

California High (CH): This is not a typical high pressure regime but, when present, the surface 

feature is easily recognized off the northern coast of California during the fall to early spring. 

Northwest flow is dominant in this system and often brings stronger winds to VAFB. 

California Low (CL): This is the most powerful system common to the West Coast because it is 

located farther south and exhibits tremendous upper-level support for widespread precipitation 

and severe weather. It is most common during the winter to early spring south of 42° N. Cooler 

mid-level temperatures are common with these systems and lead to thunderstorm development. 

These systems usually move quickly and are followed by the CH regime. 

Upper Trough (UT): This is defined by an upper-level feature that becomes more barotropic with 

time and cut off from the main portion of the PFJ. These features can be distinguished from 

200-300 mb down to the surface before they dissipate. When they move over California they 

bring unsettled weather with the strongest winds around the base of the low. These systems 

bring the best chance for thunderstorm development at VAFB. 

Great Basin High (GBH): The Great Basin is defined as the area between the Sierra Nevada, 

Cascades and Rocky Mountains. This high pressure system is caused by cold air that becomes 

trapped by the Rocky Mountains on the east and the Sierra Nevada Mountains on the west. The 

GBH remains a shallow feature that is mostly confined to 700 mb and below. This system brings 

dry conditions, larger temperature fluctuations and generally clear skies at VAFB. 

7 
8 

H 

GBH 

Figure 1. Charts depicting the synoptic conditions for each of the regimes 

included in this study. The red solid line indicates the location of the PFJ. The 

blue H indicates a high pressure area, the red L indicates a low pressure area. 
2.2 VAFB Wind Tower Data 

The 30 OSSWF delivered all available data from their 26 VAFB wind towers (Figure 2) for 

the October 2007-November 2012 time period. Each tower reports observations at three 

different sensor heights (2, 4 and 16 m) with the exception of tower 0087, which only had 

observations at 16 m. Since the 30 OSSWF verifies their wind warnings from the 4 m sensors, 

the AMU identified all 4-m one-minute average peak wind observations and confirmed all values 

fell within valid meteorological ranges. The hourly averages at each tower were then calculated 

using Peri scripts. 

The AMU filtered the wind tower data into a database containing maximum hourly peak 

winds for each tower and day in the period, and then determined all days where peak winds ~ 

30 kt were observed. As previously mentioned, the 30 OSSWF agreed to organize the AMUidentified high wind event days by synoptic regime. Considering the number of ~ 30 kt peak 

wind days was over 1 ,200, the 30 OSSWF requested the peak wind threshold be increased to 

~ 40 kt to reduce the number of days in the database. Per this request, the AMU identified all 

days where peak winds~ 40 kt were observed, 745 in all, and provided a list of these dates to 

the 30 OSSWF. Table 1 shows the number of~ 40 kt days in each of the synoptic regimes 

described in the previous section. 

9 
10 

Figure 2. Locations of the 26 wind towers 

in the VAFB network (KVBG in Figure 3). 

Table 1. Number of days with peak winds <:: 40 kt for each 

synoptic regime. 

Synoptic Regime Number of;::: 40 kt days 

Pacific High (PH) 141 

North Pacific Low (NPL) 153 

North Pacific High (NPH) 141 

California High (CH) 81 

California Low (CL) 81 

Upper Trough (UT) 64 

Great Basic High (GBH) 84 
2.3 Regional Observing Station Data 

In addition to the wind tower data, the AMU also required historical MSLP observations. The 

45th Weather Squadron (45 WS) obtained the MSLP observations from the seven weather 

stations identified by 30 OSSWF for calculating PGs (Figure 3) from the 14th Weather Squadron 

(14 WS). Once received, the AMU wrote Peri scripts to develop an MSLP database containing 

hourly observations from each station on the days when peak winds ~ 40 kt were observed in 

the VAFB wind tower network. These observations were stratified by the synoptic regimes 

described previously, and the hourly PGs for each station pair were calculated in Microsoft 

Excel. The 30 OSSWF station pairs, distance between stations, and PG formula are in Table 2. 

The two station pairs listed below the green line are additional pairs the AMU included to further 

evaluate the relationship between peak wind and PG at VAFB. 

Figure 3. Locations of the seven observing stations used to calculate PG. 

KVBG is VAFB. 

11 
12 

Table 2. List of the 30 OSSWF-identified station pairs and 

distance (km) between them used in the PG calculations. The 

station pairs below the green line were added by the AMU. 

Station Pair Distance (km) 

KVBG- KBFL 159.0 

KBFL- KLAS 359.6 

KVBG-KLAS 514.4 

KACV- KSFO 402.1 

KSFO- KPRB 266.7 

KPRB-KVBG 104.1 

KVBG-KLAX 218.5 

KACV- KPRB 663.3 

KPRB-KLAX 279.4 

KACV- KVBG 759.6 

KSFO-KVBG 358.5 

KACV- KLAX 929.6 

KPRB- KLAS 495.3 

KLAX- KLAS 380.0 

Pressure Gradient (PG) formula: 

PG = (d;) * 100 

Where:dP =Pressure difference (mb) between two stations 

D =Distance (km) between two stations 
3 Data Analysis 

The AMU analyzed peak wind and PG values stratified by synoptic regime subjectively and 

objectively to determine if relationships existed between them. If a relationship could be found, 

the AMU would then determine PG thresholds that could be used to forecast warning-level 

winds on VAFB. 

3.1 Pressure Gradient Evaluation: Full Base 

In order to better understand the relationship between peak wind and PG at VAFB, the AMU 

created a series of graphs plotting PG and maximum peak wind (MPW) versus time for each of 

the synoptic regimes. The MPW was the maximum peak wind of all 4 m peak wind speeds 

observed at the 26 towers in each hour. The AMU created a PG/MPW versus time graph for 

four days in each of the seven synoptic regimes, each day representing a different time of the 

year in order to have a diverse collection of case studies. Figure 4 is an example of the 

PG/MPW versus time graph for 14 July 2011 with a CH synoptic regime. The MPW is on the left 

y-axis, PG is on the right y-axis, and the time in UTC is on the x-axis. Included in the graph are 

the PGs from each of the 14 station pairs used in the task. The AMU also plotted the absolute 

value (ABS) of the PGs versus time to better highlight potential trends and/or relationships 

between PG and MPW. Figure 5 is an example ABS(PG)/MPW versus time graph for the same 

day and regime as Figure 4. 

The reason why the AMU created the ABS(PG)/MPW versus time graphs is shown by 

comparing the trends in Figure 4 and Figure 5. For example, compare the PG and ABS(PG) 

trends for the KPRB-KVGB station pair (blue line with +s) to MPW in both figures. The AMU 

noticed this PG series appeared to mirror MPW in Figure 4, which made it difficult to determine 

how well PG truly trended with MPW for this station pair and the others. By comparing the 

ABS(PG) to MPW instead, the AMU could more easily see how these variables trended 

together and qualitatively compare the relationship (Figure 5). Considering this example, the 

AMU created the ABS(PG)/MPW versus time graphs for the 28 days included in the evaluation 

to see if they would further assist in the analysis. Unfortunately, for the days selected, the AMU 

discovered most PG and ABS(PG) trends did not follow the MPW trends. The initial review of 

the PGs and MPW also did not yield a clear qualitative relationship between the two variables. 

13 
10 

14 July 2011 ~Wind Speed - KVBG-KBFL _.,_ KBFL-KLAS ~ KVBG-KLAS --+- KACV-KSFO 

-+--- KSFO-KPRB --+- KPRB-KVBG - KVBG-KLAX - KACV-KPRB --+- KPRB-KLAX 

- KACV-KVBG -.-KSFO-KVBG - KACV-KLAX 0 KPRB-KLAS 0 KLAX-KLAS 

5 ~~--------------------------------~~~ 

0 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Hour (UTC) 

-4.00 

Figure 4. Example PG/MPW versus time graph for the ;:: 40 kt wind event on 14 

July 2011 with a CH regime. The MPW values are on the left y-axis, the PG values 

between all the station pairs in the legend are on the right y-axis, and the time in 

UTC is on the x-axis. 

35 

~30 

-

"'0 g: 25 

a. 

II) 20 

"'0 

c 

~ 15 

10 

5 

14 July 2011 ~Wind Speed - KVBG-KBFL _.,_ KBFL-KLAS - KVBG-KLAS -I-KACV-KSFO 

-+--- KSFO-KPRB --+- KPRB-KVBG - KVBG-KLAX - KACV-KPRB --+- KPRB-KLAX 

- KACV-KVBG _.,_ KSFO-KVBG - KACV-KLAX KPRB-KLAS 0 KLAX-KLAS 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Hour (UTC) 

0.50 

Figure 5. Same as Figure 4 except ABS(PG) replaces PG on the right y-axis. 

Even though the PG/MPW and ABS(PG)/MPW versus time graphs did not reveal a clear 

relationship between the variables, the preliminary findings suggested there may be a link 

14 
between synoptic regime, MPW, and the PG orientation: north-south (NS) versus east-west 

(EW). As an example, Figure 6 is the ABS(PG)/MPW versus time graph for 25 January 2008 

with a UT synoptic regime and winds generally out of the southeast (130 degrees) on VAFB. 

When the ABS(PG)s for each station pair were compared, the KVBG-KLAX (red line with 

dashes) and KPRB-KLAX ABS(PG)s (purple line with diamonds) with a northeast-southwest 

orientation followed the MPW trend and had greater magnitudes than the other pairs at the 

same times. Another example, Figure 7, is from 4 November 2008 with an NPL synoptic regime 

and winds generally out of the north-northwest (345 degrees) on VAFB. After comparing the 

ABS(PG)s, there were four with higher magnitudes; KBFL-KLAS (green line with triangles), 

KVBG-KLAS (purple line with Xs), KPRB-KLAS (pink line with circles) and KLAX-KLAS (green 

line with circles). All of these station pairs had EW oriented PGs on this day, consistent with the 

north-northwest wind direction. 

25 January 2008 Wind Speed - KVBG-KBFL _._ KBFL-KLAS - KVBG-KLAS KACV-KSFO 

-+- KSFO-KPRB ~ KPRB-KVBG - KVBG-KLAX - KACV-KPRB -+-KPRB-KLAX 

- KACV-KVBG --.- KSFO-KVBG KACV-KLAX 0 KPRB-KLAS 0 KLAX-KLAS 

Figure 6. Same as Figure 5, except for 25 January 2008 in the UT regime. 

15 
70 

60 

- so g 

~ 40 

4 November 2008 .._Wind Speed - KVBG-KBFL .....,.._ KBFL-KLAS - KVBG-KLAS __._ KACV-KSFO 

-+-KSFO-KPRB -+- KPRB-KVBG - KVBG-KLAX - KACV-KPRB -+- KPRB-KLAX 

- KACV-KVBG KSFO-KVBG KACV-KLAX 0 KPRB-KLAS 0 KLAX-KLAS 

~ flt!!~t;;;;a.-t"i. Cll 30 r-..:::._..v -a 

c 

~ 20 ~irfC 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Hour (UTC) 

4.00 

0.50 

0.00 

Figure 7. Same as Figure 5, except for 4 November 2008 in the NPL regime. 

Unfortunately, the NS and EW oriented PG and MPW relationship was not consistent for all 

the case study days included in the evaluation. Given the inconsistencies, the AMU could not 

determine PG threshold values from these charts. 

3.2 Pressure Gradient Evaluation: North and South Base 

Considering LSP and other programs at VAFB often launch from the south portion of VAFB, 

the AMU decided to investigate the relationship between PG and the MPW on the North Base 

(NB) and South Base (SB) individually to see if any additional information would be revealed 

and aid in determining PG threshold values. The AMU divided the VAFB wind tower data into 

two sections: NB and SB. The NB-MPW and SB-MPW were determined per hour for the same 

four days in each regime discussed previously. The AMU then created ABS(PG)/MPW versus 

time graphs that included both NB-MPW and SB-MPW. The NB and SB towers are identified by 

the yellow and light blue diamonds in Figure 8, respectively. 

16 
Figure 8. All VAFB wind towers 

designated as North Base (yellow) and 

South Base (light blue). 

The AMU compared the NB-MPW and SB-MPW trends to those of the ABS(PG) to see if a 

stronger qualitative relationship could be found. Figure 9 shows the ABS(PG)/MPW for all 

towers on VAFB versus time graph for 29 April 2008 with a PH synoptic regime. The MPW is on 

the left y-axis, the ABS(PG) is on the right y-axis, and time is on the x-axis. Included in the 

graph are the ABS(PG)s from each of the 14 station pairs used in the task (Table 2). The MPW 

remains between 40 and 45 kt during the time period until 1000 UTC when it then began a slight 

upward trend. This same upward trend is not evident in most of the ABS(PG) trends. For 

instance, the KBFL-KLAS (green line with triangles), KPRB-KLAS (pink line with large outlined 

circles), KVBG-KLAS (purple line with Xs), and KLAX-KLAS (green line with large outlined 

circles) ABS(PG)s gradually increased over the entire time period while the KVBG-KBFL 

ABS(PG) decreased. Figure 10 shows the same ABS(PG) data, but MPW is divided into NBMPW and SB-MPW. It is clear in this graph that the higher maximum winds on this day were 

observed on the SB towers. This graph also shows the NB-MPW followed the ABS(PG) trends 

more closely than the SB-MPW. 

17 
29 April 2008 ~Wind Speed - KVBG-KBFL ...,._ KBFL-KLAS - KVBG-KLAS ~ KACV-KSFO 

-+-KSFO-KPRB ~ KPRB-KVBG - KVBG-KLAX - KACV-KPRB -+- KPRB-KLAX 

- KACV-KVBG KSFO-KVBG KACV-KLAX 0 KPRB-KLAS 0 KLAX-KLAS 

70 ~ 4.00 

60 3.50 

-::- so " 

..:tl. 

-

0 

0.50 

~ 0.00 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Hour (UTC) 

Figure 9. Example ABS(PG)/MPW versus time graph with PH regime. The MPW is 

on the left y-axis, the ABS(PG) is on the right y-axis, and time is on the x-axis. 

70 

~NBASEWIND 

- KVBG-KLAS 

- KVBG-KLAX 

KSFO-KVBG 

29 April 2008 ..... SBASEWIND 

- KACV-KSFO 

- KACV-KPRB 

KACV-KLAX 

- KVBG-KBFL 

-+-KSFO-KPRB 

--+-- KPRB-KLAX 

0 KPRB-KLAS 

...,._ KBFL-KLAS 

KPRB-KVBG 

- KACV-KVBG 

0 KLAX-KLAS 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Hour (UTC) 

4.00 

Figure 10. Same as Figure 9 except for NB/SB ABS(PG)/MPW. NB-MPW are the 

solid black line with diamonds, the SB-MPW are the dashed line with circles. 

Unfortunately, these trends were not consistent in other test cases. For example, Figure 11 

is a NB/SB ABS(PG)/MPW versus time graph for 22 August 2010 with a PH synoptic regime. 

Similar to Figure 10, the highest maximum winds were again observed on the SB towers. 

18 
However, neither the NB-MPW or SB-MPW followed the ABS(PG) trends this day. Another 

example is shown in Figure 12 from 18 July 2011 with a CL synoptic regime. The SB-MPW 

gradually increased during the time period while the NB-MPW increased from 0600-1400 UTC 

and then decreased. The ABS(PG)s from KVBG-KBFL (red line with squares) and KPRB-KVBG 

(blue line with +s) show the opposite trend where they decreased until 1500 UTC and then 

experienced a steep increase through the rest of the time period. The remaining ABS(PG)s 

remained fairly constant or decreased in general. Overall, for the case studies selected, 

regardless of the time of year or synoptic regime, the NB-MPW and SB-MPW did not follow the 

same trends as the ABS(PG)s. 

NBASEWIND 

KVBG-KLAS 

- KVBG-KLAX 

KSFO-KVBG 

so I 

45 

22 August 2010 --SBASE WIND 

-+- KACV-KSFO 

- KACV-KPRB 

KACV-KLAX 

- KVBG-KBFL 

KSFO KPRB 

-+-- KPRB-KLAX 

0 KPRB-KLAS 

-.-KBFL-KLAS 

-+- KPRB-KVBG 

- KACV-KVBG 

0 KLAX-KLAS 

~ 4.00 

t 3.50-

., ............. ---- < -;: 

~~ 3.00 -~ ----"1 --. "C 

2.50 ~ 

Ql 

-- _g 2.00 ~ 1.50 Ql 

10 ~~ ~~~;~~~~~i~~ ~~~~~~~~i 0l.OO .50 ~ <[ 5 ~~-- ----~ 

0 0.00 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Hour (UTC) 

Figure 11 . Same as Figure 10 except for 22 August 2010. 

19 
...... NBASEWIND 

- KVBG-KLAS 

- KVBG-KLAX 

KSFO-KVBG 

18 July 2011 ~SBASEW ND 

-+-KACV-KSFO 

- KACV-KPRB 

KACV-KtAX 

- KVBG-KBFL 

KSFO KPRB 

-+- KPRB-KLAX 

KPRB-KlAS 

-.-KBFL-KLAS 

-+- KPRB-KVBG 

- KACV-KVBG 

0 KLAX-KtAS 

3.50 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Hour (UTC) 

Figure 12. Same as Figure 10 except for 18 July 2011 and for a CL regime. 

When creating the NB/SB ABS(PG)/MPW graphs, the AMU noticed most of the maximum 

winds were observed over the SB portion of VAFB. Of the 28 case study days evaluated, 26 

showed SB-MPW values greater than NB-MPW for the majority of the 24-hour time period. The 

reason is likely due to the elevations of the towers on NB versus SB. At the start of this task the 

30 OSSWF provided the AMU detailed information about the VAFB tower network including 

NB/SB classification, latitude/longitude points and the elevation of each tower. The elevation of 

each tower is listed in Table 3. The network has 26 towers, 12 on NB and 14 on SB. The 

elevations of the NB range from 64 to 920 ft while the SB towers range from 27 to 2170 ft. Of 

the SB towers, five of them have elevations that exceed 1 ,200 ft. Since wind speeds tend to 

increase with altitude, the higher altitudes of the SB towers are more likely to observe higher 

wind speeds. This may impact LSP and other programs that mainly launch from SB on VAFB 

with vehicles or activities that are sensitive to higher wind speeds. Operations could be delayed 

or scrubbed if the winds exceed specific constraints. 

20 
Table 3. List of the 30 OSSWF towers classified by NB/SB and their respective 

elevations in feet. 

North Base South Base 

Tower ID Number Elevation Tower ID Number Elevation 

0068 459 0070 1446 

0069 920 0074 309 

0072 125 0077 90 

0073 303 0078 450 

0075 401 0080 2170 

0082 375 0081 296 

0083 226 0085 504 

0084 120 0086 1200 

0089 215 0087 2053 

0093 64 0088 27 

0096 573 0091 387 

0097 330 0092 380 

0094 349 

0095 1539 

3.3 Correlation 

As previously mentioned, regardless of the time of year or synoptic regime, the analysis 

described in section 3.1 did not yield a clear qualitative relationship between PG and MPW for 

the 28 selected case study days. Given this result, the AMU calculated correlation coefficients 

between the two variables to quantitatively measure the relationship between them using all 

days in the 2007-2012 database. The PEARSON function in Microsoft Excel was used to 

determine the Pearson Correlation Coefficient (PCC). This value is a measure of the linear 

correlation between two variables ranging from -1 to +1 . A result of -1 means there is a perfect 

negative correlation between the two variables, while a result of +1 means there is a perfect 

positive correlation. A value of zero indicates there is no relationship between the two datasets. 

The AMU calculated this value for each station pair stratified by synoptic regime for the full 

VAFB, NB and SB towers. Figure 13, Figure 14 and Figure 15 show the ABS(PG) PCC versus 

synoptic regime for the full base, NB and SB, respectively When comparing the figures, the 

values in Figure 13 and Figure 15 are nearly identical. This result was expected considering 

most of the MPWs were observed on the SB towers. When comparing Figure 13 and Figure 14, 

there are some minor differences among station pairs and corresponding synoptic regimes, but 

overall the patterns are very similar. These figures show most PCC values range between -0.1 

and 0.4 with only a few outliers close to 0.5. Such low values indicate a very weak relationship 

between ABS(PG) and MPW at VAFB and should not be the lone data source when forecasting 

MPW. 

21 
22 

ABS(PG} PCC vs Synoptic Regime 

Full Base 2007 - 2012 

• KVBG-KBFL • KBFL-KLAS & KVBG-KLAS KACV-KSFO I KSFO-KPRB e KPRB-KVBG + KVBG-KLAX 

- KACV-KPRB - KPRB-KLAX • KACV-KVBG • KSFO-KVBG KACV-KLAX KPRB-KLAS KLAX-KLAS 

0.70 

+ 

u 

0.50 +---

+ u 

!!:. 0.30 

c 

0 

Ill 0.10 ... 

IV 

Qj 

~ -0.10 

-0.30 

-0.50 _L_ 

All NPl NPH CH Cl UT PH GBH 

Synoptic Regime 

Figure 13. ABS(PG) PCC versus synoptic regime for the full base from 2007-

2012. The solid black line highlights where PCC equals zero. The PCC is on the 

y-axis and the synoptic regime on the x-axis. The "ALL" category on the x-axis 

includes all of the days in the 2007-2012 database regardless of synoptic regime 

and the solid black horizontal line highlights where PCC equals zero. 

ABS(PG} PCC vs Synoptic Regime 

North Base 2007 - 2012 • KVBG-KBFL • KBFL-KLAS A KVBG-KLAS KACV-KSFO t KSFO-KPRB e KPRB-KVBG + KVBG-KLAX 

- KACV-KPRB - KPRB-KLAX • KACV-KVBG • KSFO-KVBG KACV-KLAX KPRB-KLAS KLAX-KLAS 

0.70 ~ 

0.50 

0' • .. 

u 0.30 i * !!:. • t 5 0.10 - Ill 

... X c:- ~ -0.10 -,---+ ~ ~ • 

-0.30 

-0.50 

All NPl NPH CH Cl UT PH GBH 

Synoptic Regime 

Figure 14. Same as Figure 13 except for NB towers. 
ABS(PG) PCC vs Synoptic Regime 

South Base 2007 - 2012 

+ KVBG-KBFL • KBFL-KLAS & KVBG-KLAS KACV-KSFO I KSFO-KPRB e KPRB-KVBG + KVBG-KLAX 

- KACV-KPRB - KPRB-KLAX + KACV-KVBG • KSFO-KVBG KACV-KLAX KPRB-KLAS KLAX-KLAS 

0.70 

0.50 

g 0.30 ~ 

-c 0.10 0 

., 

.. 

~ -0.10 ~ 

-0.30 

-0.50 ~ 

+ 

ALL NPL NPH CH CL 

Synoptic Regime 

Figure 15. Same as Figure 13 except for SB towers. 

+ 

• 

UT PH 

+ 

• 

GBH 

The tool currently used by the 30 OSSWF to predict MPW examines dP between the station 

pairs instead of PG. As a comparison, the AMU created a graph displaying the dP PCC versus 

synoptic regime for the full base (Figure 16). Compared to the ABS(PG) PCC results, dP PCC 

has a smaller range per synoptic regime and values closer to zero. The North Pacific High 

(NPH) and PH regimes show the highest PCC values however, they are mainly between zero 

and 0.5 with the exception of KVBG-KBFL in PH where PCC is -0.14. This graph confirms dP 

also performs poorly as a predictor for MPW at VAFB. 

Given these PCC values and those of the PG evaluations described in sections 3.1 and 3.2, 

the AMU was unable to determine PG thresholds or trends that could be used to forecast 

warning-level winds in the VAFB wind tower network. 

dP PCC vs Synoptic Regime 

Full Base 2007- 2012 

+ KVBG-KBFL • KBFL-KLAS & KVBG-KLAS KACV-KSFO I KSFO-KPRB e KPRB-KVBG + KVBG-KLAX 

- KACV-KPRB - KPRB-KLAX + KACV-KVBG • KSFO-KVBG KACV-KLAX KPRB-KLAS KLAX-KLAS 

0.70 

0.50 

u u 0.30 

~ 

5 0.10 ., 

... 

~ -0.10 ~ 

-0.30 

-0.50 

ALL NPL NPH CH CL 

Synoptic Regime 

Figure 16. Same as Figure 13 except for dP. 

UT PH GBH 

23 
4 Summary 

Warning category winds can adversely impact day-to-day space lift operations at VAFB in 

California. NASA's LSP and other programs at VAFB use wind forecasts issued by the 

30 OSSWF to determine if they need to limit activities or protect property such as a launch 

vehicle. The 30 OSSWF tasked the AMU to develop an automated Excel GUI that includes PG 

thresholds between specific observing stations under different synoptic regimes to aid 

forecasters when issuing wind warnings. This required an analysis to determine if relationships 

between the MPW and PG trends and threshold values existed. To conduct the analysis, the 

AMU obtained historical VAFB wind tower and regional MSLP observations. The 30 OSSWF 

delivered all available data from their 26 VAFBwind tower network in the period October 2007-

November 2012. The AMU processed the observations and then developed a database 

containing MPWs for each tower and day in the dataset. The AMU identified all days where 

peak winds ;:: 40 kt were observed and provided a list of these dates to the 30 OSSWF for them 

to stratify by synoptic regime. The 45 WS obtained MSLP observations from the seven regional 

weather stations identified by the 30 OSSWF from the 14 WS to calculate the PGs. Once 

received, the AMU developed an MSLP database containing hourly observations from each 

station on the days when peak winds ;:: 40 kt were observed. These observations were also 

stratified by synoptic regime and the hourly PGs for each station pair were calculated. 

In order determine if relationships exist between MPW at VAFB and PG trends and/or 

values, the AMU created a series of graphs plotting ABS(PG) and MPW versus time for four 

days in each of the seven synoptic regimes, each day representing a different time of the year in 

order to have a diverse collection of case studies. The initial review of the ABS(PG)s and MPW 

did not yield a clear relationship between the two variables. For the days selected, most 

ABS(PG) trends did not follow the MPW trends. The AMU investigated the potential relationship 

between PG orientation and MPW but found it was inconsistent. Considering these results, and 

that LSP mainly launches out of the SB portion of VAFB, the AMU further investigated the PG 

and MPW relationship by dividing VAFB into two sections: NB and SB. The NB-MPW and SBMPW were determined per hour for the same four days in each regime discussed previously 

and ABS(PG)/MPW versus time graphs were created, including graphs for NB-MPW and SBMPW. Unfortunately, for the 28 selected case study days, stratifying VAFB this way did not 

reveal a stronger qualitative relationship between PG and MPW regardless of the time of year or 

synoptic regime, therefore PG threshold values could not be determined. 

The AMU then calculated correlation coefficients between PG and MPW to quantitatively 

measure the relationship between them using all days in the 2007-2012 database. These values 

were calculated for each station pair stratified by synoptic regime for the full VAFB, NB and SB. 

Most PCCs ranged between -0.1 and 0.4 with very few outliers near 0.5. Such low PCC values 

show a very weak relationship between PG and MPW at VAFB. Therefore, PG should not be 

the lone data source when forecasting MPW. Based on the subjective PG review of trends and 

values and the objective PCC values, the AMU determined there was no relationship between 

PG and MPW and therefore did not develop an automated GUI for the 30 OSSWF. 

24 
14WS 

30 OSSWF 

45WS 

ABS 

AMU 

CH 

CL 

dP 

EW 

GBH 

GUI 

MPW 

MSLP 

NB 

NPH 

NPL 

NS 

PCC 

PG 

PH 

SB 

UT 

VAFB 

List of Acronyms 

14th Weather Squadron 

30th Operational Support Squadron Weather Flight 

45th Weather Squadron 

Absolute Value 

Applied Meteorology Unit 

California High 

California Low 

Pressure Difference 

East-West 

Great Basin High 

Graphical User Interface 

Maximum Peak Wind 

Mean Sea Level Pressure 

North Base 

North Pacific High 

North Pacific Low 

North-South 

Pearson Correlation Coefficient 

Pressure Gradient 

Pacific High 

South Base 

Upper Trough 

Vandenberg Air Force Base 

25 
NOTICE 

Mention of a copyrighted, trademarked or proprietary product, service, or document does 

not constitute endorsement thereof by the author, ENSCO Inc., the AMU, the National 

Aeronautics and Space Administration, or the United States Government. Any such 

mention is solely for the purpose of fully informing the reader of the resources used to 

conduct the work reported herein. 

26