NASA/TM-1998-104606, Vol. 14

Technical Report Series on

Global Modeling and Data Assimilation

Max J. Suarez, Editor

Goddard Space Flight Center, Greenbelt, Maryland

Volume 14

A Comparison of GEOS Assimilated Data

with FIFE Observations

Michael G. Bosilovich, Universities Space Research Association, Greenbelt, Maryland; and

Siegfried D. Schubert, Goddard Space Flight Center, Greenbelt, Maryland

National Aeronautics and

Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

August 1998
NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076-1320

Price Code: A17

Available from:

National Technical Information Service

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Price Code: A10

i II
Abstract

First ISLSCP Field Experiment (FIFE) observations have been used to validate

the near-surface properties of various versions of the Goddard Earth Observing System

(GEOS) Data Assimilation System. The site-averaged FIFE data set extends from May

1987 through November 1989, allowing the investigation of several time scales, including

the annual cycle, daily means and diurnal cycles. Furthermore, the development of the

daytime convective planetary boundary layer is presented for several days. Monthly

variations of the surface energy budget during the summer of 1988 demonstrate the affect

of the prescribed surface soil wetness boundary conditions. GEOS data comes from the

first frozen version of the assimilation system (GEOS-1 DAS) and two experimental

versions of GEOS (v. 2.0 and 2.1) with substantially greater vertical resolution and

other changes that influence the boundary layer.

Two issues must be carefully considered when interpreting the results of this study.

First, the GCM grid space area is much larger than the FIFE site area. This could

lead to differences in local boundary conditions, such as albedo, surface roughness and

soil wetness that lead to differences between the assimilation data and observations.

Secondly, the results may depend on the regional climate and may not apply to all

regions of the globe.

Results indicate several potential systematic problems in the surface properties of

GEOS. First, the surface layer specific humidity is generally too large, especially during

the daytime. This occurs even in cases where the latent heat flux is slightly underestimated (eg. July 1988). This results in a lifted condensation level that is too low to

the surface compared with observations. While the large latent heating in some cases

contributes to the specific humidity bias, the PBL is likely not entraining enough dry

free atmosphere.

The PBL and surface analysis has identified two factors that affect the development

of the assimilated mixed layer. First, the surface sensible heat flux is consistently

underestimated between 12 and 15 UTC. The lack of heat from the surface allows the

stable surface layer to stay in place longer than observed. Second, the observed profiles

indicate that the surface layer stability is too strong in the assimilation system or may

include an elevated stable layer. The stable layer could be related to the slightly cooler

surface temperatures, and too much net upward longwave radiation. As these factors

are overcome by the diurnal heating of the surface, the GEOS 2.1 PBL can develop

quickly, but too late in the diurnal period to catch up with observations.

This report provides a baseline for future versions of the GEOS data assimilation

system that will incorporate a state-of-the-art land surface parameterization. Several

suggestions are proposed to improve the generality of future comparisons. These include

the use of more diverse field experiment observations and an estimate of gridpoint

heterogeneity from the new land surface parameterization.
11I
Contents

List of Figures

List of Tables

Vlll

ix

1 Introduction and Background 1

I.i GEOS DAS .................................... i

1.2 FIFE Observations ................................ 3

1.3 Methodology ................................... 4

Results 4

2.1 Seasonal Cycle .................................. 5

2.2 Surface Daily Mean ................................ 10

2.3 Diurnal Cycle ................................... 17

2.4 Planetary Boundary Layer ............................ 26

2.4.1 GEOS PBL Comparison with FIFE .................. 26

2.4.2 GEOS 2.1 PBL Diurnal Cycle ...................... 27

2.5 1988 Summer (June and July) .......................... 59

2.6 GEOS Grid Point Variability .......................... 66

2

3 Summary and Discussion

Appendix: FIFE Datasets at DAO

References

67

72

75

111
List of Figures

Monthly mean GEOS-1 (solid line) surface variables compared with FIFE

(dashed line), (a) surface presure, (b) wind speed, (c) 2m air temperature,

and (d) 2 m specific humidity ..........................

Monthly mean GEOS-1 (solid line) surface variables compared with FIFE

(dashed line), (a) net downward shortwave radiation, (b) net upward longwave radiation, (c) FIFE surface albedo (Rst/Rs$), and (d) precipitation

(with NOAA precipitation in the bold solid line) ...............

Mean annual cycle of precipitation for GEOS-1 DAS (solid line), FIFE (dashed

line), and NOAA (Higgins et al. 1996, bold line) for May 1987 - Nov 1989.

FIFE IFC2 daily mean comparison to GEOS assimilations for (a) surface

pressure and (b) air temperature at 2m ....................

FIFE IFC2 daily mean comparison to GEOS assimilations for (a) net upward

longwave radiation and (b) net downward shortwave radiation ........

FIFE IFC2 daily mean comparison to GEOS assimilations for (a) total precipitation (with NOAA observations) and (b) cloud fraction .........

FIFE IFC2 daily mean comparison to GEOS assimilations for (a) sensible

heat flux and (b) latent heat flux ........................

FIFE IFC2 daily mean comparison to GEOS assimilations for (a) specific

humidity at 2m and (b) wind speed. FIFE winds were measured at 5.4 m,

GEOS winds are the linear average of 2 m and 10 m levels ..........

FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a)

surface pressure and (b) air temperature at 2m ................

10 FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a) net

upward longwave radiation and (b) net downward shortwave radiation. . .

11 FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a)

total precipitation (with NOAA observations) and (b) cloud fraction ....

12 Vertical distribution of clouds (high, middle and low) for (a) GEOS 2.1 and

(b) GEOS 2.0...................................

13 FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a)

sensible heat flux and (b) latent heat flux ...................

12

13

14

15

16

19

2O

21

22

23

iv
14

15

16

17

18

19

2O

21

22

23

FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a)

heat flux into the surface and (b) surface temperature, where FIFE surface

temperature is measured by a radiometer ...................

FIFE WC2 mean diurnal cycle comparison to GEOS assimilations for (a)

specific humidity at 2m and (b) LCL height above the surface ........

Vertical profiles for 12 UTC 27 JUN for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity ...................

Vertical profiles for 18 UTC 27 JUN for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity .............. .....

Vertical profiles near 00 UTC 28 JUN for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity (note that 24 UTC equates to 00

UTC of the following day) ............................

Vertical profiles for 12 UTC 01 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity ...................

Vertical profiles for 18 UTC 01 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity ...................

Vertical profiles near 00 UTC 02 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity (note that 24 UTC equates to 00

UTC of the following day) ............................

Vertical profiles for 12 UTC 02 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity ...................

Vertical profiles for 18 UTC 02 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity ...................

24

25

29

3O

31

32

33

34

35

36
24

25

26

27

28

29

30

31

32

33

Verticalprofilesnear00UTC03JUL for FIFE PBLobservations(thelegend

indicateslaunchtime) andGEOSPBL profilesof (a) potentialtemperature,

(b) specifichumidity,and (c) wind velocity(notethat 24UTC equatesto 00

UTC of the followingday)............................

Verticalprofilesfor 12UTC 06JUL for FIFE PBL observations(the legend

indicateslaunchtime) andGEOSPBL profilesof (a) potentialtemperature,

(b) specifichumidity,and (c) wind velocity...................

Verticalprofilesfor 18UTC 06JUL for FIFE PBL observations(thelegend

indicateslaunchtime) andGEOSPBL profilesof Ca) potentialtemperature,

(b) specifichumidity,and (c) wind velocity...................

Verticalprofilesnear00UTC07JUL for FIFE PBL observations(thelegend

indicateslaunchtime) andGEOSPBL profilesof Ca) potentialtemperature,

(b) specifichumidity,and (c) wind velocityCnotethat 24UTC equatesto 00

UTC of the followingday)............................

Verticalprofilesfor 12UTC 07JUL for FIFE PBL observations(the legend

indicateslaunchtime) andGEOSPBL profilesof (a) potentialtemperature,

(b) specifichumidity,and (c) wind velocity...................

Verticalprofilesfor 18UTC 07JUL for FIFE PBL observations(the legend

indicateslaunchtime) andGEOSPBL profilesof (a)potentialtemperature,

(b) specifichumidity,and (c) wind velocity...................

Verticalprofilesnear00UTC 08JULfor FIFEPBL observations(thelegend

indicateslaunchtime) andGEOSPBL profilesof (a)potentialtemperature,

(b) specifichumidity,and(c) wind velocity(notethat 24UTC equatesto 00

UTC of thefollowingday)............................

Vertical profilesfor 12UTC 09JUL for FIFE PBL observations(thelegend

indicateslaunchtime) andGEOSPBL profilesof (a) potentialtemperature,

(b) specifichumidity,and (c) wind velocity...................

Verticalprofilesfor 18UTC 09JUL for FIFE PBL observations(thelegend

indicateslaunchtime) andGEOSPBL profilesof (a) potentialtemperature,

(b) specifichumidity,and (c) windvelocity...................

Verticalprofilesnear00UTC 10JUL for FIFE PBL observationsCthelegend

indicateslaunchtime) andGEOSPBL profilesof (a) potentialtemperature,

(b)specifichumidity,and (c) wind velocity(notethat 24UTC equatesto 00

UTC of the followingday)............................

37

38

39

4O

41

42

43

44

45

46

vi

11Ii
34

35

36

37

38

39

4O

41

42

43

Vertical profiles for 12 UTC 10 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity ...................

Vertical profiles for 18 UTC 10 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity ...................

Vertical profiles near 00 UTC 11 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature,

(b) specific humidity, and (c) wind velocity (note that 24 UTC equates to 00

UTC of the following day) ............................

Vertical potential temperature gradient (-A_/Ap) near the surface at 12

UTC. FIFE data is computed in the lowest 10 mb. GEOS-1 data is computed over the lowest two sigma levels (Ap=-22 mb). GEOS 2.0 and 2.1 are

computed over the lowest three sigma levels (Ap=-ll mb) ..........

FIFE PBL observations for 27 JUN 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 27 JUN 87 of (c) potential

temperature and (d) specific humidity ......................

FIFE PBL observations for 01 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 01 JUL 87 of (c) potential

temperature and (d) specific humidity ......................

FIFE PBL observations for 02 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 02 JUL 87 of (c) potential

temperature and (d) specific humidity ......................

FIFE PBL observations for 06 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 06 JUL 87 of (c) potential

temperature and (d) specific humidity ......................

FIFE PBL observations for 07 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 07 JUL 87 of (c) potential

temperature and (d) specific humidity ......................

FIFE PBL observations for 09 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 09 JUL 87 of (c) potential

temperature and (d) specific humidity ......................

47

48

49

5O

51

52

53

54

55

56

vii
44

45

FIFE PBL observationsfor 10JUL 87of (a) potentialtemperatureand (b)

specifichumidity. GEOS2.1 PBL profilesfor 10JUL 87 of (c) potential

temperatureand (d) specifichumidity......................

GEOS2.1 IFC2 meandiurnal cycleof turbulent kinetic energy(m28-2).

Plot is in modelsigmacoordinates,with meanpressurefor eachsigmalevel

labeledon theleft........... . ....................

46 Daytimemeanevaporativefraction for JuneandJuly 1988(EF, definedin

thetext). Daytimemeanis from 12UTC to 00UTC.............

47

48

49

5O

51

Meandiurnal cycleof sensible heat flux for (a) June 1988, and (b) July 1988.

Mean diurnal cycle of latent heat flux for (a) June 1988, and (b) July 1988.

Mean diurnal cycle of two meter temperature for (a) June 1988, and (b) July

1988 .........................................

Mean diurnal cycle of two meter specific humidity for (a) June 1988, and (b)

July 1988 ......................................

Vertical profiles of potential temperature at each of the closest grid points to

the FIFE site ...................................

57

58

61

62

63

64

65

68

viii

Iili
List of Tables

Lowest 13 vertical sigma levels and the corresponding pressure of GEOS-1

DAS and GEOS 2.x, assuming a surface pressure in the FIFE regions of 963

mb. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

June and July 1988 monthly mean evaporative fraction and soil wetness

for GEOS and FIFE. Note that FIFE soil wetness is in volumetric units

(m3m-3), while the GEOS wetness is the fraction of potential evapotranspiration ........................................ 59

3 IFC2 mean data from GEOS 2.1. Horizontal averages and standard deviations are computed for the four grid points closest to the FIFE site. These

are then averaged in time, for 21 UTC data only ................ 66

ix
-11I]
1 Introduction and Background

The surface of the Earth directly affects the weather and climate. Hence, improved representation of the surface boundary in atmospheric numerical models can positively affect

the simulation (or assimilation) of the weather and climate.

Recent studies (eg. Betts et al. 1993, 1996 and 1998) have compared point field experiment

data with global reanalysis data. These studies have shown strengths and weaknesses in

the reanalysis systems and have contributed to the improvement of the surface physical

parameterizations. Here, the output from several recent versions of the Goddard Earth Observing System (GEOS) Data Assimilation System (DAS) is validated against surface and

Planetary Boundary Layer (PBL) observations from the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE, Sellers et al. 1988). This

exercise represents an important step in the evolution of the GEOS DAS, and a benchmark

for the incorporation of a detailed Land Surface Model (LSM, Koster and Suarez 1996).

Betts et a1.(1993) used the FIFE observational data to validate the European Center for

Medium-range Weather Forecasting (ECMWF) global atmospheric numerical model. Since

then, both the ECMWF and National Centers for Environmental Prediction (NCEP) reanalyzed data were also compared to the FIFE observations (Betts et al. 1996, 1998). In this

section, we describe the GEOS DAS and FIFE observations, summarize the results of the

previous comparison studies, and outline the methodology of this comparison.

1.1 GEOS DAS

The GEOS-1 DAS has produced a multi-year global atmospheric data set for use in climate

and weather studies (Schubert et al. 1993). The GEOS-1 General Circulation Model

(GCM) is described by Takacs et al. (1994) and Molod et al. (1996). Pfaendtner et al.

(1995) document the analysis system. While these data have proven valuable in many

research projects, the system evolves to address new and different problems. An important

component of the GEOS DAS evolution concerns the incorporation of detailed land surface

processes. All the GEOS data presented in this note were generated with the same simplified

land surface parameterization (Takacs et al. 1994 and Schubert et al. 1995) revisited below.

The surface temperature and soil wetness representations in the GEOS system are most

important to this discussion. An energy balance determines the ground temperature of a

bulk layer. The layer's heat capacity recognizes the diurnal oscillation and the influence

of soil wetness (details in the DAO ATBD, 1996). A simple model specifies the monthly

mean soil wetness of[line. The model uses monthly mean observations of precipitation and

temperature as input (Schemm et al. 1992). The advantage of this method is that the
specifiedsoil wetnessprovidesrepeatableand fixedforcing (with respectto atmospheric

interactions)at thesurface,analogousto the useof specifiedseasurfacetemperatures.The

modeledprecipitationmaybebiased,but the biasdoesnot feedbackinto the atmospheric

system.The lackof interactionbetweenthe surfaceandatmosphere,however,introduces

errorinto the hydrologybudget,becausethelongterm integrationof evaporationnolonger

dependson the modeledprecipitation.

The PBL andits diurnal oscillationinteractwith the surface.HelfandandLabraga(1988)

discussthe detailsof the PBL turbulenceparameterization.In short, the turbulenceis

modeledby a MellorandYamadalevel2.5closure.In addition to the standardprognostic

variables,the turbulent kinetic energy(TKE) is also predicted. The vertical turbulent

fluxesof momentum,moisture,and heatarediagnosedfrom meanverticalgradientsand

diffusioncoefficients.Similarity theoryprovidesthe surfaceboundaryvaluesof the fluxes

and diffusioncoefficients.Roughnesslength alsocharacterizesthe surface. Sellersand

Dorman (1989)data specify the annuallyvaryingsurfaceroughness(seealso,Molod et

al. 1994and Helfandand Schubert1995). Additionally, the atmosphericsurfacelayer

parameterizationincludesa viscoussub-layerabovethe roughnesselements.

GEOS 2.0 wasdevelopedas a baselinefor GEOS-3(the systemto support EOSAM1). Scientificimprovementswereimplementedin GEOS2.0 to correctsomedeficiencies

in GEOS-1(Schubertet al. 1996). GCM improvementsincluded the tuning of cloud

parameterizations,gravity wavedrag,new surfacealbedoand higher verticalextent and

resolution(throughthe stratosphereand roughlydoublethe grid pointsin the PBL).See

Table 1 for the PBL vertical levels. The OI analysissystem (Bloomet al. 1996)was

replacedbythephysical-spacestatisticalanalysissystem(PSAS)whichallowstheflexibility

to incorporatenon-statevariablesandeliminatesthe needfor data selection(Cohnet al.

1998,DAO ATBD 1996).

The validationof GEOS2.0 indicateda drastic increaseof daytimeprecipitationduring

the summer,especiallyoverthe centralUnitedStates.Severalmodificationsto the GCM

(in GEOS2.1) havepartially amelioratedthis problem.First, a variablesub-cloudlayer

wasadded.Theheightof the sub-cloudlayeris specifiedat onelevelbelowa critical level.

Thecritical levelis determinedby the lowestlevelwhereturbulent kinetic energy(TKE)

is 10%of the maximumTKE in the PBL.Secondly,a relativehumiditycriteria wasimplementedin the convectiveprecipitationparameterization.The criteria permits convective

adjustmentonly whenthe relativehumidityexceeds85%.In addition,somechangesin the

radiationparameterizationwereimplemented.Shortwaveradiationwasinvokedmorefrequently(everyonehourinsteadof everythree).Also,the longwaveradiationwasmodified

to incorporatetheeffectsof surfacetemperaturechangesthat occurbetweenradiationtime

steps.

1IIiI
Table 1: Lowest 13 vertical sigma levels and the corresponding pressure of GEOS-1 DAS

and GEOS 2.x, assuming a surface pressure in the FIFE regions of 963 mb.

Level

1

2

3

4

5

6

7

8

9

10

11

12

13

GEOS-1 GEOS 2.x

a p (mb)

0.998548 961.60

0.994248 957.46

0.987150 950.62

0.977200 941.04

0.964250 928.57

0.948115 913.03

0.928565 894.20

0.905322 871.82

0.878157 845.66

0.846935 815.60

0.811635 781.60

0.772457 743.87

a p (mb)

0.993935 957.22

0.971300 935.64

0.929925 896.21

0.874137 843.05

0.807833 779.86

0.734480 709.95

0.657114 636.23

0.578389 561.20

0.500500 486.97

0.424750 414.78

0.352000 345.45

0.283750 280.41

0.222750 222.28 0.729920 702.91

1.2 FIFE Observations

The main purpose of FIFE was to develop remote sensing algorithms of the land surface

and PBL. To accomplish this task, the FIFE scientists made comprehensive observations

of the surface properties, meteorology and energy balance. The resulting data set has

helped develop detailed parameterizations of the surface processes, and, more recently, has

validated the surface properties of data assimilation systems (Betts et al. 1996, 1998).

The FIFE data archived on CD-ROM is used in this study (Sellers et al. 1988, Strebel et al.

1994, and Betts and Ball 1998). The FIFE site is located in Manhattan, Kansas (approximately 39.05 o N, 96.53 ° W). The surface in-situ observations consist of approximately 20

- 30 meteorological and energy flux stations. Some observations are available continuously

from May 1987 through November 1989. The flux measurements, however, were taken only

during summer. Intensive Field Campaigns (IFCs) are periods of more extensive of data

collection. Four IFCs in 1987 encompassed various stages of vegetation growth (see Sellers

et al. 1992 for details).

During IFCs, the PBL was observed with radiosonde balloons, but observation were restricted to mostly clear sky conditions during the daytime. Also, balloon launches were at
irregulartime intervals.Thecurrent studyusesradiosondeobservations analyzed to 5 mb

pressure levels (Strebel et al. 1994). The FIFE surface meteorological and energy observations have been site-averaged and quality checked by Betts and Ball (1998). These data

include standard deviations of the site-average at each time period. Betts and Ball (1998)

provide a detailed description of the data and the quality checking. The Appendix of the

present report gives information on further processing of the data.

1.3 Methodology

While the GEOS GCM represents the atmosphere on a global 2° x 2.5°grid, the FIFE

site represents essentially a point measurement within the entire globe. The GEOS DAS

data used in the comparison comes from a nearby grid point (38°N, 97.5°W). The present

GCM grid does not include sub-grid scale surface heterogeneity, such as variations in the

vegetation cover. Within the FIFE site, a variety of vegetation cover and topography exists.

As Betts et al. (1993, 1996, 1998) point out, the goal of such a study is not to search for

exact agreement between the model and observations, but to identify potential systematic

biases in the DAS.

The standard deviation of the site-average is included in the analysis when available. These

data are interpreted as a representation of FIFE site heterogeneity and the realistic range

of values given the geographical region and prevailing synoptic weather. Hence, GEOS

DAS data outside the bounds of the observed heterogeneity may indicate a model bias. To

evaluate the choice of gridpoint, a brief comparison of the four closest model grid points

will also be presented.

Two issues must be carefully considered when interpreting the results of this study. First,

the GCM grid space area is much larger than the FIFE site area. This could lead to

differences in local boundary conditions, such as albedo, surface roughness and soil wetness

that lead to differences between the assimilation data and observations. Secondly, the results

may depend on the regional climate and may not apply to all regions of the globe.

2 Results

The Betts and Ball (1998) site-averaged FIFE dataset report observations at 30 minute

intervals (centered on 15 and 45 minutes past the hour). The data were processed to

monthly means and 3 hour backward mean (see the Appendix) for comparison to GEOS

standard output format. The Appendix describes the processed data in more detail.

All GEOS data are from assimilation experiments, as opposed to simulation experiments

which implement only the GCM. This is a crucial point, because we will be comparing
observationsto the GEOSgridpoint data. GEOS-1refersto the first frozenGEOS DAS

(Schubert et al. 1993). GEOS 2.0 was intended to be the baseline system for future development of the GEOS system that will support EOS. Validation of this system indicated

several significant problems, and prompted a focused development effort (called the "reconciliation" experiment) to fix the most severe problems. The validated reconciliation system

is identified by GEOS 2.1. At the time of this writing, GEOS 2.1 is the most recent validated

system.

The present comparison covers various time scales. The seasonal cycle is examined in terms

of monthly means for the FIFE period. Only the GEOS-1 seasonal cycle is compared to

FIFE because assimilations with the more recent GEOS versions have, to date, been limited

to no more than a season. The analysis focuses on FIFE's IFC2 for daily variations and

mean diurnal cycle. Likewise, the diurnal evolution of the convective PBL is presented

during IFC2. Lastly, monthly variations of the surface energy balance are examined during

the summer of 1988 (chosen because the validation effort of GEOS 2.0 and 2.1 coincide

here).

When available, the standard deviations of the FIFE site-average will be included. This

can be interpreted as a representation of heterogeneity and the observed variability of the

observations. This should provide a range of acceptable values for the GEOS comparison.

Of course, the results presented for FIFE should not be applied generally across the globe.

GEOS variability around the FIFE site (at the grid point level) will also be investigated.

2.1 Seasonal Cycle

While the GEOS-1 reanalysis encompasses the entire FIFE period, the experimental GEOS

2.0 and 2.1 systems reanalyzed only several months for special periods. Figure 1 compares

monthly mean GEOS-1 surface variables for the entire period of FIFE (May 1987 - November

1989). The mean FIFE elevation (410 4- 29 m) was approximately 30 m lower than the

GEOS-1 DAS grid point (439 m) during the summer of 1987. This causes the difference in

surface pressure during 1987 and 1988. The mean altitude of FIFE sites increases in 1989

to 420 4- 28 m due to a lower number (and some shifting) of stations. Despite the mean

difference of the model and observed surface pressure, the assimilation follows the observed

time series quite well.

GEOS-1 2 meter (2 m) and 10 meter (10 m) winds were averaged together (linearly) to

compare with the FIFE 5.4 meter wind speed (Fig. lb). The GEOS wind speeds consistently

underestimate the observed monthly mean. This may indicate surface roughness length that

is biased high. The variability of the wind speed within the FIFE site is very large, but the

GEOS winds still tend to be small.

The GEOS-1 temperature follows the observations reasonably well. The most notable dif5
ferencesoccurin winter,whenthe modelis too cold (documentedby Schubertet al. 1995),

anda smallerbiasin July 1988whenthe modelis too warm (Fig. lc). A moresubstantial

problemoccursin the surfacelayerspecifichumidity (Fig. ld). Spring,Fall andespecially

Summerspecifichumidityaregreatlyoverestimated( 3 - 4 g kg-1). Thedifferencerepeats

regularlyin eachof the threeyears.The implicationsof this biasandits interactionwith

the PBL will bediscussedin thefollowingsections.

Figure2ashowsthe generaloverestimationof netincomingshortwaveradiationby GEOS.

TheGEOS-1albedovariesannually(0.09in July to 0.10in January)forthisgrid point. The

FIFE site albedo,determinedby the incomingand reflectedshortwaveradiation (Fig. 2c,

andBettsandBall 1998),is approximately0.18duringthesummertime,and largerin the

winter. In general,GEOS-1 overestimates net upward longwave radiation with the largest

differences occurring in winter (Fig. 2b). Note that the April and May 1988 FIFE radiation

observations have some bias (see the Appendix). The minimal representation of snow

(snow occurs when the surface temperature is less than zero) in the GEOS-1 system may

contribute to this overestimate, which likely affects the aforementioned surface temperature

biases (Fig. lc).

The GEOS precipitation shows some general inter-annual variations that parallel the observations (Fig. 2d). For example, the 1988 summer precipitation tends to be lower than

the 1989 precipitation. The average GEOS precipitation for the entire period exceeds the

FIFE observations by 0.43 mm day -1. The monthly differences, however, can be near 3 mm

day -1 for June and July 1987 and May 1989. In general, the spring and summer precipitation is overestimated, especially May, June, and July while fall precipitation is slightly

underestimated (Fig. 3) compared to the FIFE site. The NOAA precipitation is almost

always less than the GEOS for this time period.
a

974/ : : : : . : :/. / : :

962 . . ! . ----: ....... :....... :......

960 i ; ; , .: : : : i

JUL OCT JAN APR JUL OCT JAN APR JUL OCT

1987 1988 1989

5 (b

4

3

O9

_2

E_1

0

: i i if hi k i :_

JUL OCT JAN APR ,IUL OCT JAN APR JUL OCT

1987 1988 1989

305 (o)

o.0

300

295

290

285

280

275

27O

265

._iiiiiiiiiiiiiiiiiiil}i ' 'iiiiiiiiiiiiiiiiiiii; ..... iiii;

JOL OCT L_N APR ,IUL OCT J,_N At_R JUL OCT

1907 1988 1989

21 (d)

I

18 -]

12-

9 ..i....x: ...... !...... i iiiiiiiiiiiiii: .... :i

3

0 JlJ] OCT JAN A15R"' $1JL OCT JAN AISR JI)L OCT

1987 1988 1989

Figure 1: Monthly mean GEOS-1 (solid line) surface vari£bles compared with FIFE (dashed

line), (a) surface presure, (b) wind speed, (c) 2m air temperature, and (d) 2 m specific

humidity.
¢q

I

ok/

3OO

2?0 -

240 -

210 -

180 -

150-

120

90 _

60 -

3O !

0

100'

90'

80'

?0

I 80

5O

4O

30

20

10

0

0.4

0.35

0.3

0.25

0.2

?

8

_4

_3

_2

1

0

a)

,.._!_ii_  ̧ i_iiii_ _....._i_

........i_ _!i_i::i:_::::i:::i::::ii_....:i:ii_::_ii _

JbL O_T JAN APR' JUL' " OCT' JAN.... APR JUL OCT

1987 1988 1989

(b)

_>i': ...... i...... i...... i/\ :- -:....... :.... ......... ..

ii!i!i:_J!i! iii! i!i!!!iii! :ii!!!!i!!!ii ii

JUL OCT JAN APR JUL OCT JAN APR JUL OCT

1987 1988 1989

(o)

,.,..... iiiiill iiii ii i/ ,ili:ii:i:iiii;

;-LL.> .....'......'\_:L. _!-/ ....i.... ,<.......;..... ,_.

JUL OCT JAN APR JUL OCT JAN APR JUL OCT

19B7 1988 1989

(d)

JUL OCT JAN APR JUL OCT JAN APR JUL OCT

1987 1988 1989

Figure 2: Monthly mean GEOS-1 (solid line) surface variables compared with FIFE (dashed

line), (a) net downward shortwave radiation, (b) net upward longwave radiation, (c) FIFE

surface albedo (Rs¢/RsJ'), and (d) precipitation (with NOAA precipitation in the bold solid

line).
-- GEOS

-- - FIFE

-- NOAA

>,

Annual Precipitation Cycle

\

\

\

\ .....i..........

\

....................................... \i

AN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN

Figure 3: Mean annual cycle of precipitation for GEOS-1 DAS (solid line), FIFE (dashed

line), and NOAA (Higgins et al. 1996, bold line) for May 1987 - Nov 1989.
2.2 Surface Daily Mean

Currently, GEOS 2.0 and 2.1 data assimilations exist for only a fraction of the time period

covered by GEOS-1. All the assimilation systems have data that overlap in time with a

special observing period during FIFE. In order to examine higher frequency variations and

the diurnal cycle, we focus on FIFE's second Intensive Field Campaign (IFC2). The IFCs

concentrated the observational effort into two week periods. IFC2 began on June 24, 1987

and lasted until July 11, 1987. In this section, we examine the daily variation of the FIFE

observations compared with assimilated data generated with GEOS-1, 2.0 and 2.1.

GEOS data is taken from the grid point 38 ° N and 97.5 ° W. While the comparison at any

of the four surrounding grid points may provide similar results (Betts et al. 1996, 1998),

the FIFE site-average surface pressure and altitude above sea level compare most favorably

to this grid point. Aside from a mean bias (probably due to the difference in altitude of

approximately 30 m), the GEOS assimilation surface pressure parallels the observations

(Fig. 4a).

Similarly, the daily variations in 2 m temperature follow the observations reasonably well

(Fig. 4b). While the GEOS values generally do not stay within the observed horizontal

standard deviations, there does not seem to be any significant biases in the daffy mean

temperature. The GEOS assimilations, however, show less day-to-day variability than FIFE

observations. GEOS 2.1 tends to be the warmest assimilation. Most noticeably, the GEOS1 and 2.0 are cold toward the end of the period and all the assimilations are warm on July

1.

Some of the fluctuations in the daily mean temperature and the differences between model

and observation relate (in part) to the radiational heating at the surface (Fig. 5). The

observed cold temperature on July 1 correspond to the reduction of daytime insolation by

clouds. GEOS, on the other hand, has less clouds (Fig. 6b), more insolation, and more net

upward longwave radiation, at this time. Some of the overestimate of net upward longwave

radiation may be compensated for by the overestimate of net downward shortwave radiation.

Some similarities between model and observed cloud fields are evident. The cloudy period at

the end of June is an example. In general, the assimilations seem to have more cloud cover

than the observations, especially GEOS 2.0 (Fig. 6b). Large variations in the observed

cloud cover seem to correlate with net upward longwave radiation, but this seems less clear

in GEOS. Overall, the models coupling between clouds, radiation and surface temperature

is internally consistent, and compares favorably with observations, with the exception that

the observed day-to-day variations tend to be larger than in the assimilations.

Daily mean precipitation is presented in Figure 6a. The GEOS assimilations consistently

show more precipitation than FIFE observations. The large differences are probably not

too surprising given that the FIFE observations are taken over a 15 × 15 km area, while the

10

Till
GEOS data represent 2 ° x 2.5 ° . We have already identified the summer of 1987 as having

large precipitation in the GEOS-1 annual cycle. Also, the GCM grid representation of the

convective scale precipitation may have deficiencies. NOAA precipitation data (Higgins

et al. 1996) that has been averaged to the GEOS grid, indicate three days with heavy

precipitation. The GEOS assimilations, especially GEOS 2.0 and 2.1, have more days with

heavy precipitation. The precipitation time series' must be interpreted cautiously. Even

at the 2 ° x 2.5°resolution, in both the model and observation, the variability between

neighboring grid points or stations can be very large.

For the IFC2 period, the GEOS assimilations show reasonable partitioning of sensible and

latent heat fluxes, with latent heat being generally larger than sensible (Fig. 7). GEOS

latent heat does tend to be biased higher than the observed daily mean. On July 1, when

clouds were underestimated, both turbulent heat fluxes are overestimated in the GEOS

data.

Similar to the monthly mean comparison, GEOS daily mean specific humidity is overestimated (Fig. 8a). Daily mean differences can be more than 3 g kg -1. These differences seem

too large to be simply resolved by the difference in altitude of the model and observations,

as evidenced by the relatively small area standard deviations. While it might be simple

to ascribe the large specific humidity to the high latent heat, Betts et al. (1996) results

indicate that the NCEP high specific humidity bias is related to inadequate PBL top entrainment of dry (free-atmosphere) air and low mixed layer depth. The PBL interactions

in GEOS are investigated later in this chapter.

Near surface wind speeds also appear strongly biased. GEOS seems to systematically underestimate the daily mean wind speed (Fig. 8b). The roughness length for GEOS-1 is 51

cm, and for GEOS 2.0 and 2.1 it is 19.5 cm. While this may explain why GEOS-1 winds

are slightly less than GEOS 2.0 and 2.1, the differences between observation and all GEOS

output are too large. Betts and Beljaars (1993) estimate the FIFE site roughness length

for momentum to be 19 cm and for heat to be 1.2 cm.

In the daily mean, the differences between the three assimilation systems seem to be generally small at the surface, compared to the difference between any one model and the

observations. This likely relates to the prescription of soil water, its lack of interaction with

precipitation, and the strong control that soil water has on the surface energy balance.

11
Surface Pressure, IFC2 Daily Mean(a )

--FIFE 972

GEOS i

--- - OEOS 2.O970

GEOS 2.1968

966

"_ 964

962

960 .....

958 _,z-

\:/z

$,

95625JUN27JUN29JUN 1JIJL 3JUL 5JUL 7JIJL 9JIJL liJUL

i987

2m T, IFC2 Daily Mean (b)

302 I

301

300

299

• .: ........ , .............. : ....... •........ ._ ./:'. \_._ ..-.,:_-: _._":'.

298 i i fl, : _ 1....._'" _"1_,, .......:/)% ....:......__!(iiii

_:_ 296 -.,-, ........... _,,,.......... : ,/,,, .......................... : : :

293

292

291

29025JUN 27JUN 29JUN IJUL 3JUL 5JUL 7JUL 9JUL

i987

11JUL

Figure 4: FIFE IFC2 daily mean comparison to GEOS assimilations for (a) surface pressure

and (b) air temperature at 2m.

12

II1
--FIFE 100

Net LW Rad, IFC2 Daily Mean (.)

-- - GEOS 1

-.-o os

•.:.I ...... :.\-.. >-_, .",,.. ;',/;../.. _-/... :\\.d-.\.'.X':',, ..... :-- ,:,,.-.,

80 / :\ >_": / i\ -v \. _,,..._.._%.,

.,o,o,o ilii 

20

10 , I , ,

25JUN 27JUN 29JUN IJUL 3JUL 5JUL 7JUL 9JUL IIJUL

1987

550

500

450

4OO

¢x/

I

35o

3O0

250

200

150

100

Net SW Rad, IFC2 Daytime Mean (b)

•.. /J-. : ............ ;',, : ;:_".......:........:

., • . ",3 li >:", !...... ,';i "...... !....... !

•" ........ x_ !/'_ i........... .;.::7

\ ,

I

25JUN 27JUN 29JUN IJUL 3JUL 5JUL 7JUL 9JUL IIJUL

1987

Figure 5: FIFE IFC2 daily mean comparison to GEOS assimilations for (a) net upward

longwave radiation and (b) net downward shortwave radiation.

13
--FIFE 40

- GEOS I

36

--'--GEOS 2.0

........GE0S 2.1 32

--NOAA Pr 28

>" 24

_ 20

16

12

8

4

0

Precipitation, IFC2 Daily Mean (,)

I\

• ' i'\....

ii _i

i i/ ,"i,,,. /. \

25iUN27JUN29JUNIJUL3_UL

1987

5JUL

lr

/ _ I.\

• : ....... :-.... '-:-',. l_ _"t _\...........

i'_\ . :. :. V,:, ,I\I, .:., ,.. ,,: :

..,i ............... I_ .... i./.i ../, .... ;t ..........

_i : :\ I]t:'17.1, "

, jl • ,, ' _ f

i ,

; : ,. :

1 .....W%:

7JtSL9JtsLll,iUL

Cloud IFC2 Daily Mean

I

• • ' .i..-.,, ::":_"",,

o.o o.8 ..!.. ............. / ..... ............ i \i.<....._,./< .............. .-i.._.-'- -!

o._ 'i..........//// _1.....i:....... ;'2,/_/ ....b<.j i

0.8 ................ .:.,--/_...._-i....i-p...... i......... 7-A- --:....... :

_o._ !........ / Ixt,..... /,1 ",;// V ............

i

0.2 •

0.I "- "_1. :;' ...... : ....... : ""_i : '"; 7 ': ........ :........ :....... :

: "_ \l : : 7 : "/ : : : :

O I ' I , I

25JUN27JUN29JUN 1JTJL 3JUL 5JUL "tJiJL 9JUL l iJUL

1987

(b)

Figure 6: FIFE IFC2 daily mean comparison to GEOS assimilations for (a) total precipitation (with NOAA observations) and (b) cloud fraction.

14

Ill
--FIFE 60

-- - GEOS i

-----GEOS 2.0 50

........ GEOS 2.I

40

3O I

20

I0

0

Sens. Heat Flux, IFC2 Daily Mean (.)

-i0

-2025JUN 27JUN 29JUN 1JUL 3JbL 5_bL 7JUL 9,IUL

]

IIJUL

1987

Latent Heat Flux, IFC2 Daily Mean(b )

270 .................................................................

240 ......................................................................

I 180

_: 150

120

90

60

30 , ,

25JUN27JUN 29JUN 1JUL 3JUL 5JIJL 7JiJa 9JLTL l lJVa

1987

Figure 7: FIFE IFC2 daily mean comparison to GEOS assimilations for (a) sensible heat

flux and (b) latent heat flux.

15
-- FIFE

-- - GEOS

-----GEOS

........ GEOS

!

2.0

2.1

22

2m q, IFC2 Daily Mean (,)

21

20

19

18

17

16

15

14

13

12

II

I0

............................................... );i,:,.............. i

_.\,, . &. . -x. ,, . /''_ / • _ 1_ / I

. ,[ _ .....

_-_....:J.....-.e%..:......._--i ........i

25JUN 27JUN 29JUN IJUL 3JUL 5JUL 7JUL 9JUL I IJUL

1987

Surface Wind Speed, IFC2 Daily Mea_

7

__:...: ...... _t . . r ..._. . .: ........ ......... . ........

25JUN27JUN29JUN IJUL 3JIJL 5JIJL 7JUL 9JUL IIJUL

1987

Figure 8: FIFE IFC2 daily mean comparison to GEOS assimilations for (a) specific humidity

at 2m and (b) wind speed. FIFE winds were measured at 5.4 m, GEOS winds are the linear

average of 2 m and 10 m levels.

16
2.3 Diurnal Cycle

While the daily mean time series' provide some information on DAS surface representation,

the investigation of the diurnal cycle is also important. Here, we examine the mean diurnal

cycle for the FIFE IFC2 period.

FIFE observed surface pressure varies about 2 mb for the average diurnal cycle (Fig. 9a).

The GEOS assimilations seem to vary slightly less, and there may be a phase difference

compared to observations. The near surface atmospheric temperature minimum of GEOS-1

and GEOS 2.0 tends to be too cold (:1 K), even less than the lowest standard deviation

(Fig. 9b). GEOS 2.1 seems to be cool at night and a little warm during the day, but

represents the diurnal cycle (highs and lows) very well.

Recent changes in the radiation parameterization seem to have improved the phase of the

GEOS 2.1 net upward longwave radiation diurnal cycle (Fig. 10a). GEOS 2.1 longwave

radiation biases are fairly uniform throughout the diurnal period (20 W m-2). The biases

are likely related to the downward radiation from the atmosphere because near surface

temperatures seem to be reasonable (1 K difference in temperature does not lead to 20 W

m -2 differences in upward terrestrial radiation). As discussed earlier, the net downward

shortwave radiation is overestimated, but the diurnal phase in GEOS 2.0 and 2.1 seems

improved over GEOS-1 (Fig. 10b).

Schubert et al. (1995) identify the diurnal oscillation of precipitation in the United States as

being overestimated in GEOS-1 DAS. GEOS 2.0 was found to have an even stronger diurnal

oscillation than GEOS-1 DAS (a primary factor in the modifications to GEOS 2.1). For the

FIFE case, the NOAA observed precipitation (Fig. lla) shows a strong maximum at 15

UTC (NOAA observed precipitation comes from Higgins et al. (1996) at the grid point that

matches the GEOS data). Care must be taken when comparing the model and observed

diurnal precipitation. This maximum is primarily the result of one very strong event. The

GEOS system, on the other hand, tends to overestimate the number of significant events.

Figure llb indicates that GEOS 2.1 produces the least amount of cloud during the FIFE

IFC2. None of the assimilation systems, however, reproduce the observed diurnal cycle

of clouds. The observations indicate a noticeable diurnal cycle of cloudiness. Low level

clouds that top the developing convective PBL would have a diurnal cycle. The GEOS 2.0

and 2.1 vertical distribution of clouds, however, indicate very little low cloud and mostly

high cloud (Fig. 12), and Molod et al. (1996) show that GEOS-1 DAS has too little low

cloud. GEOS-1 also shows too much high cloud (Pickering et al. 1995; Allen et al. 1997).

Significant differences in the vertical distribution of clouds could have detrimental effects

on the surface radiation.

The sensible heat flux at the surface is reproduced quite well by the GEOS 2.1 assimilation

(Fig. 13a). GEOS-1 sensible heat is too low in the late afternoon. At night, the downward

17
sensibleheat is reproducedby eachassimilation. Latent heat fluxesin the assimilation

systemsareoverestimatedduring the daytime,whichwasto be expected,giventhe daily

meananalysis.GEOS2.1producesmorelatentheatthanGEOS2.0(Fig. 13b).The mean

observednocturnallatentheatflux isslightly positive.GEOS,however,showssomeslightly

negativevalues.Notethat GEOS2.0and 2.1underestimateboth sensibleandlatent heat

at the 15UTC period.

Thenet surfaceheating(Hg) is definedby,

Hg = Rn - Hs - LE,

where Rn is the net radiation, Hs is the sensible heat flux and LE is the latent heat of

evaporation. Figure 14a shows GEOS surface heating is particularly strong at 15 UTC.

The heat capacity of the soil may be larger than observed leading to the differences. Note

the small temperature change between 12 and 15 UTC despite the strong heating (Fig.

14b). Turbulent fluxes are small until the surface layer warms and becomes more thermodynamically unstable. The phase lag of surface heating is a common problem of bulk

surface heat budget models. The phase lag of surface temperature in the ECMWF and

NCEP models was related to thick soil layers (Betts. et al. 1993 and 1997).

As in the previous analyses, the surface layer specific humidity bias is quite apparent (Fig.

15a). The bias maximizes during the daytime coinciding with the diurnal cycle of the

latent heat. While the specific humidity bias may be partly related to the latent heat bias,

at least one other factor is identified later in this paper. The specific humidity bias most

likely affects the lifted condensation level (LCL) in the GEOS system. The LCL identifies

the level at which parcels lifted from the surface begin to condense water vapor. In GEOS,

there are few low clouds considering the low LCL and the specific humidity bias.

In summary, this analysis demonstrates several shortcomings in the present GEOS system

surface fields. In particular, the specific humidity, clouds, longwave radiation precipitation and latent heat flux all show large biases compared with the FIFE site observations.

While some improvement is anticipated by incorporating a more comprehensive land surface parameterization, other parameterizations (eg. radiation, convective precipitation or

cloud microphysics) may require further study and development. Consideration must also

be given to the differences in albedo and the adverse effect that this will pose in the surface

energy balance.

18
Surface

--FIFE 970

-- - GEOS 1

-- •--GEOS 2.0

........ GEOS 2.1968 ..... "

966

964

962

Pressure, IFC2 Diurnal Mea_

960 , ,

12 15 18 2'1 0'0

UTC

03 06 09 12

3O2

2m T, IFC2 Diurnal Mean

(b)

301

300

299

298

297

296

295

294

293

292

291

12 1'5 18 21 00 03 06 0'9 12

UTC

Figure 9: FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a) surface

pressure and (b) air temperature at 2m.

19
-- FIFE

-- - GEOS 1

-- ---GEOS 2.0

........ GEOS 2.I

c_

I

I00

90

80

70

60

Net LW Rad, IFC2 Diurnal Mean (a)

50

40

30

80

12

: / : ./ : "<,,.,'_. : : :

........_;.,' ....._;f...._........"___ ........i........_.......

: / ..+'..._ ..... i. _:,,..\.L ....... i ...............

1'5 1'8 2'1 0'0 0'3 0'6 0'9

UTC

12

700

Net SW Rad, IFC2 Diurnal Mean

_o55o6°° t ............... I_.---,...._,:....................... ::...............

iiii;i;iiiii if: __i'( :1;77::::111111!1 :iii i

............... i................

350 ........

20o ...._ ..... i.x.&....i........ i........i.......

150

I i i

2 15 18 21 O0 03 06 09

UTC

(b)

12

Figure 10: FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a) net

upward longwave radiation and (b) net downward shortwave radiation.

20

111
Sn_E 30

-- - GEOS I

27

--'--GEOS 2.0

........ GEOS 2.1 24

Precipitation, IFC2 Diurnal Mean

.......

........ : ........ :........ ,k........ i ........ :........ : ........ i .......

........ :........ :....... ./.:..'?:....i ........ i........ i........ i.......

! i / ! "% } : :

-- NOAA Pr 21

I_ 15 .....

. _. l : / _[ ' /" ' \ ',, " '

9 4-/--./: \--,"- .:_._..':?,"_ .... :........ :.... _... :':',,,...... !.......

I/ / : X/ ,,¢-........ ":"....."_.:"--/_ \:. ",,,, /%

12 15 18 21 O0 03 06 09 12

UTC

(a)

Cloud, IFC2 Diurnal Mean

0.9

0.8

0.7

0.6

O.5

0.4

0.3

0.2

0.I

0

12

........ :........ :........ :........ !........ !........ i........ i.......

........ !_.<-._ ......... _-- :........ ---_._L. .......... _ "7"/, : ....... _. !___._ :.......

. . ._ - - . . . - - . ................... :-.._. ...........

........ :........ :........ :........ !........ i........ !........ i.......

........ :........ :........ :........ i........ i........ i........ i.......

i

15 1'8 2'i 0'0 0'3 0'6 0'9 12

UTC

(b)

Figure 11: FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a) total

precipitation (with NOAA observations) and (b) cloud fraction.

21
-- - Low

--•--Mid

........ High

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.I

0

GEOS 2.1 Cloud, IFC2 Diurnal Mear{b )

........ '......... i........ _ ........ i ........ '......... : ........ i .......

........ i ........ i........ i ........ i ........ i........ _ ........ i .......

2 I'5 18 2'I O0 0'3 0'6 09

IJTC

12

GEOS 2.0 Cloud, IFC2 Diurnal Mear_a )

1

........ i "_-,', .... i ........ i .... _,"......................................

• i

18 21 O0 0'3 0'6 09

UTC

12

Figure 12: Vertical distribution of clouds (high, middle and low) for (a) GEOS 2.1 and (b)

GEOS 2.O.

22

Ill
--FIFE 100

- GEOS I 90

-----GEOS 2.0 80

........ GEOS 2.i 70

60

50

i

4o

30

i_ 2O

i0

0

-10

-20

-30

-40

Sens. Heat Flux, IFC2 Diurnal Mea%)

iiiiiiiii_ iiii i iiiiii iiiiii iiiii

iiiiii/_ _' ii_,_ ii iiiiii iiliiii iiiii

".........................i....... I........ !....... I ! I ! I !

2 15 18 21 O0 03 06 09 12

UTC

c_

Latent Heat Flux, IFC2 Diurnal Mea_)

600

550

500

450

400

350

300

250

200

150

I00

50

0

-50

................ :...... ,<_e.'.'\ ......................................

•-F_--,'; ........ % ---i ........ :........ _...... : ....

........ _...... I/_ ......Lx< "_,,,...... _ i-..............

12 15 18 21 O0 03 06 09 12

UTC

Figure 13: FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a) sensible

heat flux and (b) latent heat flux.

23
Surface

-- Fn_F. 150

a_,os i2.° 125 --- --GEOS

........ GEOS 2.1100

75

5O

Z5

0

-25

-50

-75

-100

12

Heat Flux, IFC2 Diurnal Me_@

'/! ..../-\,_ _ \ i i i

....... i............... k % i _:

....... !........ i........ :' •-"_:_,-........ :...... .

.......!........ i........ i......<-:-_..._:_..... i........i.......

I

15 1'8 2'1 0'0 0'3 0'6 0'9 12

UTC

Surface Temperature, IFC2 Diurnal M,

3O4

302

300

298

296

294

292

290

12

: -- : :

: ..... .;_. ,. "': ..... . ........ •........ , ...............

" i ! ,,_, \. ":",, i : :

...................i........... \<%:! .....

........ :... /...: ........ : ........ :...... .'_,,,:: ........

I I , ,

15 8 21 O0 03 06 09 12

UTC

Figure 14: FiFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a) heat

flux into the surface and (b) surface temperature, where FIFE surface temperature is measured by a radiometer.

24
--F_E 20

--- GEOS 1

-----GEOS 2.0 19

........GEOS 2.1

18

_o 17

_o 16

15

14

13

2m q, IFC2 Diurnal Mean

,,,!..........._....

........i.....yc:7 ......,..,......:...............

• " " /: ""'4._ :",, i :

........:..... 1/'>,..<............ ...-_,__...._,,...................

I ,',. \\ ',,

,//. ._ ,,

........ :. -../.,,- • .:........ : ........ :........... .,_,. .... ._,-....... : ........

: /,;/: : : "_ :',,,, :

• s/° • •

.,/,:.....i...... i........i............... \:...',,...: ........

i// i 4 T '_ "",:

.......:/,,: __ ....i \. :::.... .....

(.)

12 15 18 21 O0 03 06 09

UTC

12

120

LCL Height, IFC2 Diurnal Mean (b)

110

I00

90

80

70

"_ 60

50

40

30

20

lO

0

12 15 18 21 O0 03 06 09 12

UTC

Figure 15: FIFE IFC2 mean diurnal cycle comparison to GEOS assimilations for (a) specific

humidity at 2m and (b) LCL height above the surface.

25
2.4 Planetary Boundary Layer

Radiosonde balloon observations of the PBL were made on most days during FIFE's IFC2.

Here, we present seven days of FIFE IFC2 PBL observation where the frequency of balloon

launches allows the examination of the daytime part of the diurnal cycle. Two analyses of

the diurnal cycle are presented. First, six hourly intervals of GEOS-1, GEOS 2.0 and GEOS

2.1 are compared to the closest time during FIFE. The standard GEOS assimilation system

data are instantaneous at 12 UTC, 18 UTC, and 00 UTC. GEOS 2.1 profiles, however, are

available at 3 hour intervals. Unless otherwise noted, GEOS profiles are plotted on sigma

levels. The second analysis uses three hourly vertical profiles from GEOS 2.1 to examine

the diurnal cycle with more temporal resolution.

The comparison of PBL observations to the GEOS assimilation systems has several difficulties. First, the observational data are not as regular nor as continuous as the surface

observations. Instantaneous profiles of observation and assimilation must be compared.

The FIFE PBL observations were taken at only one station, and only during clear afternoons. Horizontal heterogeneity within the FIFE site can influence local mesoscale circulations (Smith et al. 1994). Of course, the 2 ° × 2.5 ° GEOS grid cannot resolve these small

features. At any given time, there can be large differences between GEOS and the observations. Furthermore, the GEOS systems can have substantial differences between each other.

Nonetheless, we expect that the assimilation systems profiles and diurnal variation should

bear some likeness to the observations.

2.4.1 GEOS PBL Comparison with FIFE

The comparison of GEOS-1, 2.0 and 2.1 with FIFE PBL profiles of potential temperature,

specific humidity and wind are presented in Figures 16 - 36. We will discuss some of the

generalizations that can be seen in this comparison, rather than a description of each figure.

The GEOS potential temperature profiles at 12 UTC show more thermodynamic stability

near the surface than in the observed profile. The morning of 07 JUL demonstrates this

feature (Fig. 28a). Figure 37 shows that the near-surface temperature gradients are generally larger in the assimilations than the observations. The assimilations and observation

are, however, closer to each other toward the end of the period.

On 10 JUL, the near surface Stability seems more comparable to the observations but there

is an elevated stable iayer::(Fig. 34a) that even persists at 18 UTC (Fig. 35a). The

observed elevated stable layer appears weaker than in GEOS, and the GEOS system does

not penetrate as deep into the free atmosphere. At 18 UTC, the GEOS systems' well mixed

layers are consistently lower than the observed profiles. Furthermore, the GEOS 18 UTC

profiles indicate a sligi_t]y unstable tilt, while the:observati0ns are Closer to neutral stability:

26
At 00UTC (towardthe endof the dayin FIFE observations),all the GEOSassimilations

underestimatethe depth of the mixedlayer. Notethat the last radiosondeballoonlaunch

of eachday can be 1 - 2 hours before00 UTC. In general,the GEOS2.1 assimilation

producesadeepermixedlayerthanGEOS-1and GEOS2.0at 00UTC. Of thesevendays

investigated,theGEOS2.1PBL is notthe deepestonly on01JUL (Fig. 21a).Thediurnal

evolutionof the GEOS2.1PBL will bediscussedfurther in the nextsection.

The wind and specifichumidity observationstend to be noisierthan the potential temperatureprofiles. In particular,the specifichumidity is computedfrom measurementsof

wet bulb temperature.If the bulb driesor freezes,the observationsareerroneous.Most

specifichumidity profilesshowhighervaluesthan theobservationsin thelowerpart of the

PBL, but this is not alwaystrue. This seemsto occurmorefrequentlyin the GEOS2.1

systemdespitethe generallydeeperlate afternoonPBL. The wind profilesaredifficult to

drawconclusionsfrom dueto somevariabilityin theobservationsandwith theassimilation

systems.Someprofilesarequitecomparableto theobservations(09-10JUL, Figs. 31- 36).

Theredoesnot seemto bea consistentlow wind biasin the PBL that mightexplainthe

low surfacewinds(throughverticalmomentumtransport)notedin the discussionsof the

surfacediurnal cyclesand daily means.

2.4.2 GEOS 2.1 PBL Diurnal Cycle

The GEOS 2.1 assimilation archived data at three hour intervals. This permits further

investigation of some of the features of GEOS 2.1 discussed in the previous section. Specifically, the higher time resolution profiles of GEOS 2.1 are compared to all the FIFE profiles

for the same days shown in the previous section (Figs. 38 - 44).

On 27 JUN (Fig. 38a and c) and 01 JUL(Fig. 39a and c), both observations and assimilation

show the presence of a near-neutral residual layer above the surface stable layer at 12 UTC.

Once the model mixes through the surface stable layer, the mixed layer deepens rapidly. On

27 JUN, the assimilation PBL becomes deeper than observed late in the day. The profile

above the PBL on 01 JUL is more stable than 27 JUN and the entrainment and deepening

of the PBL is also lessened in the assimilation.

In general, the observations clearly show that the PBL can deepen rapidly between 12 UTC

and 18 UTC. GEOS 2.1 is not able to consistently reproduce this feature. However, the

previous section showed that GEOS 2.1 produces the deepest (compared to the previous

versions) late afternoon PBL. Here, with three hourly data we see that on five of the seven

days (excluding 02 JUL, Fig. 40, and 07 JUL, fig. 42), the GEOS 2.1 PBL deepens rapidly

between 18 UTC and 21 UTC. Most of these days show that the model has mixed through

a very stable layer during this period. Entrainment from above this layer allows the PBL to

deepen, and become drier. The IFC2 mean diurnal cycle of TKE shows the drastic increase

in turbulence from 18 to 21 UTC (Fig. 45) when the surface sensible heat flux is more

27
comparablewith observed(Fig. 13). Also, the GEOS2.1 morningsurfacetemperatures

tendto beslightlywarmerthan the previousGEOS versions.

This analysis has identified two factors that affect the development of the assimilated mixed

layer. First, the surface sensible heat flux is consistently underestimated between 12 and 15

UTC. The lack of heat from the surface allows the stable surface layer to stay in place longer

than observed. Secondly, the observed profiles indicate that the surface layer stability is

too strong in the assimilation system or may include an elevated stable layer. The stable

layer could be related to the slightly cooler surface temperatures, and too much net upward

longwave radiation. As these factors are overcome by the diurnal heating of the surface,

the GEOS 2.1 PBL can develop quickly, but too late in the diurnal period to catch up with

observations.

28
i i ! !.......... :i............ f

iiiiiiiiiiii iiiii_ :

¢_ 0 0 0 0 0 0

_0 0 _ 0 LO 0

CO

o .-._-_.-_ ...... _ .......... ---"

o_

1 IiI! ........................._.............. _I

i

Figure 16: Vertical profiles for 12 UTC 27 JUN for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

29
Z : : :

_: "_ ............ i iiiiiii i:: ........... __v!i+"-,-,--.----_!>.7.. "_ ...... i}2"_

cO

_ g . _ _ _ -

r.T.a . I _"-----.,.._--_-, J I_'_

: K';"Y::::7':_.................. i........................ t°

F.,.,T..I o t_ _ i.t,-a _ tg-a

L1,g

i_,egg--'__: ....:............ ;..................... I_..

I _-- - -:.-_ ........ bo

I __"..._-_..---__ I

l _;;a

0 tea 0 tO ¢_ tO 0

Figure 17: Vertical profiles for 18 UTC 27 JUN for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

30
Z

E-_

" T \ L,_i

_ ", . . ,

"_(.._-_.m _ ...... :............. ",- ..................._,_. :,.......................... :

lil! : ............ : ............ :............ : ...... _.: ............. o

' o * ' ' _°c_

Figure 18: Vertical profiles near 00 UTC 28 JUN for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity (note that 24 UTC equates to 00 UTC of the following

day).

31
?_i... ' £ A i

I _

02 1 : ""-."---. : : I-"" : l

l i .......h: i _--'" : I

. .......,A--_\_-:--, .................

,1[.rio

_F ! T -T T - T-

/ i i i _. _._<: _ /

. • - . .... :..... ._.._...._-::-:-::-.-,-::-::... I

/ _ --.. --.L / J.'_/ : : : /

_i_l .... .. ,: i i i I

I

p_ • ?, . •

I fa [..)_"%\.,., : : : i I

_.) _ _: _ : : : :

-_i_i .."Q'_,_.

/ -_"" _ __,--_-.-_. i /

/ l,l R_M-- --- ....... .:........ _ /_

................. i........................ 7............::.....

Figure 19: Vertical profiles for 12 UTC 01 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

32
+ t

I t i O

o_1-........... i............ !.._ ........ _........ -t

r-q ./ i i / i // _ i /

Figure 20: Vertical profiles for 18 UTC 01 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

33
! o , ,

cO

I : : .. :......... _.......... .._...4,. L',_

i ' ' " _ _'_ '.-J-_..... _ i

o;= I........... :............ _FY ','_.......... "............ :........... ["

r_ . i i / / ! i i o I........... :........... :V /.v:............ :............ :........... -F_

(]2 : : .,2' : : :

_,_ ......... ,,_/...._ ............ _............ _........... _o

I

E-,

'_(__:............ _............ i............ _............ -C_-_

_,_..__._......... _,_ _ -,_ . . .

.-_._-__......_: _,_ : : : _.

--_R_._, ..........]_....._...:............ :............ :............

._ o o o 1 ",,,__ . -

--?.?-?-?i, Ii ............ i......... _]:F_.,........ i............ i............ o

Figure 21: Vertical profiles near 00 UTC 02 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity (note that 24 UTC equates to 00 UTC of the following

day).

34

Ill
qJ

E'-,

Figure 22: Vertical profiles for 12 UTC 02 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

35
0

I+\

(I,) I P,A \ _'. ....

_ I-i- -:k,---"......... _"-_.......... :........ _ "_......... A :............. <o

I..i

r..#'2 """:...." : _ ___I_ : • _I_---

.:................. \.... ...........

• . "--_.,_,

_:.-J

, , o

_I i ! : : ........ $, I

c_ I............ i............ ,............. :............ _._;,,/;_ .......... Io A I : i i .;....i'/i l_,

I : .-_'/ i : / : . /

• • .._ ./.: ....................... :............

I>e#_ II'_ .-. -.....-.- _:.......... !i i......! !......FII_>

v

_...:__ .....•..... :;.... _ ........... o

i_

_. o

- CO

Figure 23: Vertical profiles for 18 UTC 02 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

36

illl]
..... "'" "" .:.h' "' _ "': .................................................

o o o ';0 ,g o oo

O0

_'_ . ' " • /" " I co

o = i ............i.......:.:;/_:"-- ........._.............Z

........... :............ ,.....;./-/_// .... i ............ :.............. ,_,

........... :........ .>,5..j<--_,/- ......... ! ............ :..............

d__ : ........ _I ;__ ............ !. : <,>

..........;;_ -..: .......... : ............ :.............

I"x_ "'-,'-. i

...... t "_." .............................................. 0

_

,....7• --,.,,:,,., . . _,_,,._-_..

' .<,,._ .......... _ ............ .<.,...................................

_- _-._i i _i "_:Z'k- ......4-. ._

_000: : : _ : -4,.,.,-", co

I_I _ r_ _ .....

..... TIT ' ............ '.......... ' °-0

, I _ , 0

II &' o o o o o<",

Figure 24: Vertical profiles near 00 UTC 03 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity (note that 24 UTC equates to 00 UTC of the following

day).

37
q)

,.Izl

E_

0

.... •'_ ....... _ _"'2_- ........ :............. o

l,_ _ 00" : "_ • _"_,...._ .

_ : : _ ,_ •

i I I _ : ............ : ........... i............ i ............ :)............

Ili! : : : !

Figure 25: Vertical profiles for 12 UTC 06 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

38

III
¢_ 0 0 0 0 0

eF " - - - - T_

o .......... i............ i............ i.......... i_i ....=

C-_/ : r -_" _'- ........:............r-_

/ • / " _.'" _f • . /-- v

I .....f"-_-./........ _ ....................... I-_

_ lZl4/ I : - : _'_ : i : /

>_ I........ _2.;_: ......... _............ _............ ::............ _=

!_r"<-s"7 i i i i J

Figure 26: Vertical profiles for 18 UTC 06 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

39
CO

i i ! i i

i " _ i i o

cO

__ *I........... :_............ _............ _..... _ ......... ......... ://...... IN

o_I i ; f : .,." !/ i L_._

_ ,..........:............,.-_ ....................... r.-_

c) I ........... :........ _ ........ :.........F-_'-"

Figure 27: Vertical profiles near 00 UTC 07 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity (note that 24 UTC equates to 00 UTC of the following

day).

4O

Ill
.,r-4

_ _ _-___--._-.._.- _ ...... i _-

-_--_:- .... -,,..\_. ............ _o -- mmm , ' ',\_ "

°°,_:............ :............ :.............................°

I II :

/li ! !\_ ©

i u

Figure 28: Vertical profiles for 12 UTC 07 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

41
"4+

: : i i : |

: : i- ' ,'_,/ % r II 02

. _ _..___...."__..,-.;.._:.._;; ........._"_,,_Y \':,\ %: II "" I_

............-_-!i'i!i............ !_! i ............ :............iii i!ii _............ iii i-)!'i_ i/:............. o_

c_

_N .... +............+............+....._i...+ [..+............ :m -

_ : : _ - ..,.,,_..+., . ,._

+ _ ...........+.........$I_+_?; +.-........i......................... "+

,- _ ........... :..... +:_ ......... :.............

gm _:" :: + +

_ , , , , "_

Z",.. P"- C_ _ 0'+ 0'_ 0

IJ+j

"" _"+_ _ _ _ 17+

-_'_ .... i ............. _'_._ -+_ .... , ............ : ............ •............

_.i ""."__..-.... i -_.._.+'. ....... _-'-',, i i

mmm ! ! ! _ ! o

I:T=C,,,1r..3 _ , , ' \ ' ,,.-a

_ ?.+_ .... \ .i.............

II I i: : : : : +

i ..... + : + : : _

Figure 29i VerticalProfiles for 18 UTC 07 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of:(a) potential temperaturel (b) specific

humidity, and (c) wind velocity.

42
"C'_

............ ir i i _ ! : "-' "_"

............ :............ _............ ............. : ............ :............ CO

0

t .'°_ 0

_ ..";__/ I _

"-" ,"._.: ..... L_

............ ............. : ............ ............ : .... • ....... ............. | ,,,,,_

o_ ................ _i _...... i ........... ,-,

• _ - ..----j_- .......... . . . .

,2

E--,

.............. •,_.:,,_ ...... :. ............ :.......... : :

. __ "-,_ ._ \ ......... ";'..->.. ....... :........... ; ............ :.............

,-' - _ & _ ---: : "--...--..../ . .

,,_,, _ _"_ _"_ _. _ . ".. . \ '

.......:...........r

- O0 0: ............ :

..........

..................... _ 2.'-., "'_ ............

• ,_

r

/lii ! /_

¢_ 0 0 0 0 0 ¢:_ ¢'0

0 LO _ LO 0 Lt_ 0

_ ¢0 _ _ (_ 0

Figure 30: Vertical profiles near 00 UTC 08 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity (note that 24 UTC equates to 00 UTC of the following

day).

43
....

{X],_

"_ ii'. ...... i.... ' "..... i............ i............ i............ !,'_._ I I "_

•

: : _ :_.,..! : "-'

• ¢_ ....... _,..'_E.:..._, _-r_ .......... :.............

o o o & & & o

v

E-,

- ,w,-,,,i

Figure 31: Vertical profiles for 12 UTC 09 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

44
•._ I......................... :............:............ :......_-.--_ ..........

I

............ i............ i............ i............ i............ :............. I

I :, i i :, i o

'-_ ""_........... i............ i........ i............ i......r_:':':_::':.,_.......

_ .. .:......_......... :_-/.. ...... :.......... _._.

-- _ : : _ i/.,:I i I;::::2 i..I-0 " " L,-.-"----7 _...._.-"... ...... ........:_ ._

r.Do :_ ........_...... _,_,_

.......... _.- ........... : ............ "............ : ............ "............. _,D _._ . --_

Figure 32: Vertical profiles for 18 UTC 09 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

45
............ :............ ;............ i............ i............ i............ i-_

o

,JO .... °°_°"

D

i , c',z

0 0 0 o 0 <_ o

Figure 33: Vertical profiles near 00 UTC 10 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity (note that 24 UTC equates to 00 UTC of the following

day).

46

111
_j !j.--:::_ i ,-I : : \',. \

•-_ ..._/_,.,-:... :

I , '

0o

o . I............__ ..... t_-

r-.< . I i i / 4.'"./ i Io'_

...... ...........F

0 0 0 0 0 0 0 ''_

.-_.._._ . . _ k"O

_-_ _ ............ _; ......... i' "_R ....... :........... o

I_??i I if: ..............................................

............::............ ............i............_.......... o_

I I I i

0 0 0 0 0 0 0

0 k_ 0 _ 0 _'_ 0

Figure 34: Vertical profiles for 12 UTC 10 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

47
"lzl

(D

(D

ID.,

"el

, , O

I_ _ . m m u m m m O

e _ i _ _ _ I_

o ............i............ !............i............ i?'/- i/ ..... [-

"Ei ............ i............ i......... ...._ .......I_

o__'-'=............_............i_............::/ ......._ ......i............I-_-._

• . / _

6 : _ ....... i.......... Lo_

" : : i ./...." _w' : i "'

............ ........................ 1-o

:> ._ _..'C__..:-_":''r : : : I

rm ._:------;""i.: ............._:............."........................ i.......... "_

3

,..el

E-,

i.,l..i

f.-, : : . ". . : .

",,i i <,=,

._ ooo: .....

I", t....l t.,.1 r.,.1..... , \ ,

_?,ii ............ !............i............ :....._:"--_ .......... _°

<:) uP o u5 0 u5 o

Figure 35: Vertical profiles for 18 UTC 10 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity.

48

II1
i

_I i ! i i i.. I _

I

|

"_:__'_.. : :

O,2

._._._._.._ ........... ..._.._.\ ...... _.'_.. ....... : ........................

_ooo: : : ", : \.

I_ r_ r_ r_ ' • ', • _ • x

• _o,,._:............:...........:........... :.....__,_<_--_..:-"-

',,-4

Figure 36: Vertical profiles near 00 UTC 11 JUL for FIFE PBL observations (the legend

indicates launch time) and GEOS PBL profiles of (a) potential temperature, (b) specific

humidity, and (c) wind velocity (note that 24 UTC equates to 00 UTC of the following

day).

49
-- FIFE

---GEOS i 0.8

-----GEOS 2.0

........GEOS 2.1 0.7

Near Sfc. Vert. Theta Grad. (12 UTC)

0.9

I \ .... "

....... • , ,,;........ :........ :........ : ....... : ....... : ....... :.......

.:.1k':,, : : : : :

0.6 • :---,/--:- , ..... :........ :........ : ....... :; ..... : ....... :.......

: ;. : , : : : :INN: :

..._ o.5 i / i _,,/,.i i....i/,../ i i

0.4 _..:.j?,,</,;x\ ....... ,;>'_:7-7!:-->"_:_.-_"i\.:x, ...... i.......

...... _ _. ;, . \ , I \, ..-'\ ._ ,,,. •

.'-"'. 0.3 --:--/-x-_'_-',,'_,:\,/": .... ._-:--__:".-"-',,:',_-: .......

/ i _, ,.,, . , , • " .

--'>" ' \ ",: )"Z _ ', k _

0.2 ---:.......:-\ ....,:\.>'J/"_: .......:.......:',,....:_ ....

: : \ .'., .' / "x. : :'t,_,,---k_.;-",\

0 -i .....

-O.1 , ,

25JUN 27JUN 29JUN iJUL 3JUL 5JUL 7JUL 9JUL i iJUL

i987

Figure 37: Vertical potential temperature gradient (-,_6/Ap) near the surface at 12 UTC.

FIFE data is computed in the lowest 10 mb. GEOS-1 data is computed over the lowest two

sigma levels (Ap=-22 mb). GEOS 2.0 and 2.1 are computed over the lowest three sigma

levels (Ap=-ll mb).

5O

III]
FIFE 27JUN87 (a) FIFE 27JUN87 (b)

700 I : '.. _1_ _ _.

/ .... 1832 UTC! i V I'/_F:: I I : : ...'_.'..4'1

75ot..........:_958UTC;...........i... t _'_._-'-I 7504 i...._-\'_i._ ..................._....._.....

/--"- 2ta5 UTC: : : / //;'"" I

/......=""u"_'//f_i.,"I / ,,a""_

I : i -" i . : i i

.oo ..........i...... 9oo i..... '_......:......;.....i.....

I i i i :ii ! ! i

I

) GEOS 2.1 27JUN87 (d)

700-

" -12uTC _ _ _ _ _;t, _. _ i ii/_\ . i _: :: :: --*--'15UTC I

--;18UTC i : ! II/, _ : : i,/_\ _ ; _ :

750-"__i-----:21UTC 24 UTC i; i : i/lll _ !1

...._..... ,.... //// .. ,,. i.......... '_,,_).I - ) ....... !............ i...... _.

=oo-........ i....... i............ ---Y'--i //k':.... _oo............ '_. __._.<.-_ ..... :,........ i....

i .. : ,.

950

1000

0

....i!............... i I ..... i.......

_so ........ ....; _ }L .... ::...... i....

: i : i

IOOC_-9o_9__9_,_96_.98360 35_ 3o4 _o6356 3io 3t_

r_eta (K)

4 8 1'0 12 14 16 16 20

Specific Humidity (_/k_)

i\ .........i.....

Figure 38: FIFE PBL observations for 27 JUN 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 27 JUN 87 of (c) potential temperature and

(d) specific humidity.

51
700-

FIFE 01JUL87 (a)

!1212 UTCi i

1411 UTC

" 1530 UTC

-----:1735 UTCi

750 ...... :..... i 2002 OTCi .......... i....

214 0 .UTCi

2250 UTC ,L:_' i

i

:

i ! : :

ili

850 ":.... : ...... !-fl .......................

iil

ooo :-'i .........................

!.( l: :

i .?

i * • [

_. : ) "'"|.'1 :

! : i :

292 294 298 298 300 302 304 306 308 310 312

Theta (K)

GEOS 2.1 01JUL87 (c)

700,

i 12 !UTC

15 UTC

18:UTC

-----! 21 !UTC

750 ...." ....P,A:UTC. _....

800 .......................... :....

: i

850 ........

900 .................

950 •

! /.I

7OO

750"

800"

FIFE O1JUL87 (b)

• • , ,. .......

.._. /.:....;....:....:...,.:....:...;....: ....

900"

950-

I000

::::::::

i i i i : . : i ....

0 I 2 3 4 5 8 7 8 9 10 11 12 13 14

Specific Humidity (g/kg)

GEOS 2.1 OlJUL87 (d)

7O0 i i i i : : : : : - -

: : i i ! ! : i ! : :

750 .... _" : _"':'"'_'":'!"?'":'"':':""

:i

500 ............ ....!.--.i.,-,!.-_, ! ! :

850 ..... :---:- :--:--: "_:..Z. : :

::: ..... :_1

!i!iiii:i

900 ....... i--.-i----i--- i .. Z .

950' " .....

1000 tO00

290 292 294 298 298 300 302 304 306 308 310 312 0

Theta (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Specific Humidity (g/kg)

Figure 39: FIFE PBL observations for 01 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 01 JUL 87 of (c) potential temperature and

(d) specific humidity.

52
FIFE 02JUL87

800

850'

900'

950

700 •

_4---- 1403 UTC i

i _1540 UTC i

-----i1709 UTCI z

750 ...... i..... 61838 UTCi

•2o02 UTCi ::

i ! i ! i

......... }..... i ..... !.... i.... :

" ! ' " i

-;..... i ..... _ .... J

(a)

292 294 296 298 300 302 304 306 308 310 312

Th,t° (K)

GEOS 2.1 02JUL87 (c)

700

12 iUTC

_--- 15:UTC

" 18 UTC

+--{ 21 iUTC

750 --'.-#,_i 24 i UTC

800

850 ..............

900 ...........

..... ....... ...

7OO

950-

750"

800"

1000

FIFE 02/UL87

........... i.

.... _...... ,...... :. |

. I

, i i i ! i

\ !

850.

900 .... : ...... i...... i...... _ _: "_""?" '_...... i...........

2 i 8 8 {o f2 1'4 i'8 t'8

Specific Humidity (g_g)

GEOS 2.1 02JUL87

700

!\

750 ...........i

800 .................. ::-

............ ....... ....... L..

850 ............................ n, ..............

900"

950"

1000"

292 294290298300302304306308310312 0 2 4 6 8 10 12 14 18 18

Theta (K) Specific Humidity (_/kg)

(b)

2O

(d)

2O

Figure 40: FIFE PBL observations for 02 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 02 JUL 87 of (c) potential temperature and

(d) specific humidity.

53
7O0

FIFE 06JUL87

•.----_1155 0TC!

1358 UTC

750 ..... i..... i1834 OTCi .... :....

i

2136 UTC

800 .................. •..........

900

950"

(a)

298 300 362 304 308 308 310 312 314 318 3i8

7beta (K)

E_EOS 2.1 06JUL87 (o)

700.

.12UTC

-- 15 UTC

• "18 :UTC

--÷--;21;UTC

750 ..... _,_, 24 UTC .........

800 .................

850 ........

900 .......

100(

i i i _ ii

: .... i : fli

: ..... i .......... ! :,_..........

: (

.... i ........................ ' ....

: i

: ]

298 300 302 304 306 308 310 312 314 310 318

Theta (g)

950"

700'

750'

FIFE OBJUL87

800 .... !.-

i

850 .......... " ...................

900 .......................

: ! i

950............................ i..... ,... i--i!

I000

i :

0 2

700

(b)

750

800

850

4 6 8 10 12 14 16 18 20 22

Specific Humidity (g/kg)

OEOS 2.10BJUL87 (d)

900 ........................

2 4 8 8 10 12 14 IB 18 20 22

Specific Humidity (g/kg)

950 .... :..... _..... ;..... :............

i ! i i

1000,

0

Figure 4h FIFE PBL observations for 06 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 06 JUL 87 of (c) potential temperature and

(d) specific humidity.

54

II1
FIFE 07JUL87

700

1203 UTC i " "

--" 1449 UTC

1558 UTC

- --i.1802" UTC

750 ..... !.... !, 1854 :UTC.

2044 UTC

--..i-.._- 2246UTC ! "

800" : : : :

/

e5o................ _!

/ /: .....

/: i i i

900......... .:'I- ....................

950- i.... rtO00- " ........

(a)

294 296 298 300 302 304 306 308 310 312 314 316 318

Theta (K)

GEOS 2.1 07JUL87 (c)

700-

1000

i 12 urc " i i i

15 UTC

18 UTC

-----' 2_ UTC : i

750 ...... .-_,_4....UTC " . ! !

- ! i i i i i

800 .......... "....."..._...;...._....:

. : : i i i

..... i

i i i i : :

850 i : : .: .......

i i : i ! : !

900 ........ :.....;................... •

.... i

i i i ! : !

950 ..... i..... i..... i !ii

294 _95 298 300 302 304 306 308 310 312 314 316 318

Theta (K)

: "1⁄2,

750 ...... ; ....

900 "........... ' "

950

1000

0 2

700"

750-

(b)

i i i i i

10 12 14 16 18 20 22

Specific Humidity (g/kg)

GEOS 2.1 07JUL87 (d)

800 ................

850 ................:

l

900 .......................

950 .................. :..... i ..... :

. ! :

1000

0 2 4 6 8 10 12 14 16 18 20 22

Specific Humidity (g/kg)

Figure 42: FIFE PBL observations for 07 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 07 JUL 87 of (c) potential temperature and

(d) specific humidity.

55
FIFE 09JUL87

700'

1209 UTCl

1417 UTC.

i 1535 UTC

---. --{ 1717 UTCI

750 ...... i..... i-1-841 UTCi ..... i_.

-'_----': 2005 UTC: i

-"_'"= 2137 UTC

2255 UTC :

800. --:.....:....._....:....._....

i i i : :

! : i

: i : I

850. ..::.... i... :-..... i (

: i I

900"

950'

(a)

: !

298 300 302 304 308 308 310 312 314 318 318

Theta (K)

GEOS 2.1 09JUL87 (c)

700,

12'UTC

15 UTC

' 18:UTC

--+--_21_UTC

750 ...._'_---"24i UTC .......... _-"

800

1

. ...... . ..... : ..... :.....

850

900 .................

/

/ . .!....._.....:...... :..

!

298 300 302 304 308 308 310 312 314 316 318

Theta (K)

950

700"

FIFE 09JUL87 (b)

750 ..............

800 --_...........

\

i /

850- i ................... _._,.i ..... i.

,%

9OO ....................... i ..... i ..... i.h

t

................................... -...... i2 4 8 tO 12 14 18

Specific Humidity (g/kg)

GEOS 2.1 09JUL87

950

tO00

900

18 2O

(d)

950 ....................................... :

1000

0 2 8 8 10 12 14 18

Specific Humidity (g/kg)

18 20

Figure 43: FIFE PBL observations for 09 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 09 JUL 87 of (c) potential temperature and

(d) specific humidity.

56

] !1
FIFE lOJUL87 (a)

700 700

750

8OO

850"

!1150 UTCi

_---- 1424 UTC

1542 UTC]

+--_ 1716 UTCi

.......... i t638 OTci ..............

•2004 .l_TCi

2154 UTC

• 2301 UTC _

z ; ._ ..... i..... ( ..... ....... .

: i i :

: : i i

: i i i

. .i ..... : ..................

/

/

900"

//

/

750

BOO

850-

900-

950. 950 ................. :...... :

":?i

i . _ i ! i

..... 100C 29830030,304306308310312314318318

_,t, (K)

GEOS 2.1 10JUL87 (c)

700 700

_121UTC

15 UTC

18_UTC

_i21!UTC

750 .... _,--,i.24UTC

800

850 ...............

75O

800

850"

950- 950 •

FIFE lOJUL87

. ? , i .......:,

i :. I

4. (3 8 1'0 1'2 14 1'6 1'8

Specific Humidity (g/kg)

GEOS 2.1 10JUL87

900 ......

1000

0 2 4 6 8 10 12 14 16 18 20

Specific Humidity (g/kg)

(b)

2O

(d)

Figure 44: FIFE PBL observations for 10 JUL 87 of (a) potential temperature and (b)

specific humidity. GEOS 2.1 PBL profiles for 10 JUL 87 of (c) potential temperature and

(d) specific humidity.

57
p(mb)

GEOS 2.1 IFC2 Mean TKE

781

0.84 •

815 0._;

s45 0.88 ................................

871

894

912

9280.96

940

0.92 .........................

I ! I

06 09 12 15 18 2'1 O0 03 06

UTC

O9

Figure 45: GEOS 2.1 IFC2 mean diurnal cycle of turbulent kinetic energy (rn2s-2). Plot is

in model sigma coordinates, with mean pressure for each sigma level labeled on the left.

58
2.5 1988 Summer (June and July)

GEOS 2.0 and 2.1 validation experiments were also performed for the summer of 1988,

specifically June and July. These were going to be included in the previous discussions on

the daily mean and diurnal cycles. Analysis of the data, however, yielded some substantially

different results compared to that of IFC2. It is important to note that the quantity of FIFE

observations during the summer of 1988 is lower than 1987 or 1989. There were no IFCs

or PBL observations during 1988. The fewer number of stations during likely influence

the site-averages. We note that the the central United States experienced severe drought

conditions during the spring and summer of 1988 with especially dry conditions during May

and June.

During the analysis of the 1988 GEOS assimilations, a significant difference was identified

in the monthly mean June and July energy budgets. The differences are quite apparent

in the time series of daytime mean (from 12 UTC - 00 UTC) evaporative fraction (Fig.

46, where EF = LE/(LE + Hs)). During June of 1988, the magnitude of GEOS daytime

mean EF resembles that of the observations. However, the observed EF maintains a steady

magnitude into July, while the GEOS EF continues a downward trend (see also table 2).

Closer examination of the turbulent fluxes shows that the GEOS sensible heating is slightly

larger than FIFE in June, and increases dramatically in July (Fig. 47). The GEOS latent

heat flux, on the other hand, is too large during June, and smaller in July (Fig. 48). This

affects the near surface atmospheric temperature so that it is too cold in June (especially

at night) and too warm during July, especially during the day (Fig. 49).

Table 2: June and July 1988 monthly mean evaporative fraction and soil wetness for GEOS

and FIFE. Note that FIFE soil wetness is in volumetric units (m3m-3), while the GEOS

wetness is the fraction of potential evapotranspiration.

EF June July

FIFE 0.77 0.78

GEOS 2.1 0.76 0.54

GEOS 2.0 0.75 0.55

GEOS 1 0.76 0.54

Wetness

FIFE 0.21 0.24

GEOS 0.26 0.076

The differences between the GEOS monthly mean energy budgets corresponds to variations

in the monthly mean prescribed soil wetness. FIFE gravimetric observations of soil water

59
(BettsandBall, 1998)indicateonly a slight increasefrom Juneto July (table 2). This is

consistentwith thesmallvariationof FIFE monthlymeanEF.GEOSsoilwetness,however,

undergoesa sharpreductionof soilwetnessfromJuneto July,not only at this grid point,

but acrossthe wholeregion.This isconsistentwith thecontrastingJuneandJuly monthly

meantemperature,sensibleheatandlatentheat. It is interestingto notethat asthe GEOS

soil wetnessbecomesverysmall,the latentheatflux doesdecrease,but is still quite large.

Eventhough the July latent heatis only slightly lessthan observations,the surfacelayer

specifichumidity is still quite large(Fig. 50). We mustconcludethat the overestimateof

GEOSspecifichumidityispot entirely relatedto thesurfacelatent heat.Theseresultsand

the similarity betweeneachGEOSsystemdemonstratetheeffectthat prescribedsoilwater

hasonthe GEOSsurfaceprocesses.

6O
Evaporative

FIFE 1

-- - GEOS 1

--- -- GEOS 2.0 0.9

........ GEOS2.

Fraction, Daytime Mean

.5 ............................................

01JUN88 11JUN 21JUN 01JUL 11JUL 21JUL 01AUG

Figure 46: Daytime mean evaporative fraction for June and July 1988 (EF, defined in the

text). Daytime mean is from 12 UTC to 00 UTC.

61
June BB MM Sensible Heat

--FIFE 300

-- - GEOS 1

----- GEOS 2.0250 ........:........:........;................. :.........................

........ GEOS 2.1

200 ................ :........-.........................................

I00 -/.':"'I......."_\_',,:........:........:........:.......

so )

o -,/.// :_"

-50 , , __ )

2 i'5 18 21 00 03 06 09 12

UTC

(a)

300

July 88 MM Sensible Heat (b)

250

200

i 150

100

5O

0

-5O !

12 15

................. /_.-._"_.g_\............... :......;................

: , ..... k- : : : :

: If./ :\': : : : :

........ :..... Ii./ ...... _ _(- .... :........ :........ _........ :.......

• i.1. . \: ....

: /-: : -. ....

• ... . \ ....

.............l,.,,............. _.............................i.......

' //. , _...... :/,,1 / _:,,, : : :

:i/'"/,,,!'_:_ //i.... K- !",:_:,;, ...... :i........ :i........ !:.......

,//,/ ¢ J- \T%, - : :

....... 4'2"...... :........ !...... "I,: "_. "i ........ _........ :.......

f ',',. ......i

8 21 00 0'3 0'6 0'9 12

UTC

Figure 47: Mean diurnal cycle of sensible heat flux for (a) June 1988, and (b) July 1988.

62
June 88 MM Latent Heat (al

r_, 500

-GEOS 1 450 ................: ::....../,,,,,,_.^_"- ..................................... : : : :

........--" GEosGEOS 2.14002'0 ........ .......... : /.,,,,:, ./m.\\ ,,,,,.:........ :........ _........:.......

? 300 ........ i.......... i........ ; ........ i.......

25o /, ii>,,,

_: 200 1

...... %:i.......i.... iii

100 7"-_-_ t

-50 !

12 15 18 21 O0 03 06 09 12

UTC

5O0

July 88 MM Latent. Heat (b)

450

400 ........ . ........ ,................ ........ ......... : ........ •.......

350

300

'_ 250

200

100 ._..__ I

50 ............

-500 :.. : .......... :........ i ........ : ................ _F?:_:_. _--.,-,.--_

2 15 18 21 O0 03 06 09 12

UTC

Figure 48: Mean diurnal cycle of latent heat flux for (a) June 1988, and (b) July 1988.

63
FIFZ 308

June 88 MM 2m Temperature

GEOS 12.o306 --- --GEOS

........ GEOS 2.1304

302

300

298

296

294

292

290

288

12 1'5 1'8 2'1 0'0 0'3 O'6 0'9

UTC

(a)

13

July 88 MM 2m Temperature

3O8

3O6

304

3O2

........ i........ i>"./. "/! ........ i _:-:, i........ !........ !.......

a°°/t : /),2_: i i -,% -<.: : 1

298 ....... _: ...... _ :<h_.:.... :.......

296

294

292 I

290

288

12 1'5 1'8 2'1 00 0'3 0'6 0'9 12

UTC

(b)

Figure 49: Mean diurnal cycle of two meter temperature for (a) June 1988, and (b) July

1988.

64
_ FIF_. 24

June 88 MM Specific Humidity

- GEOS i

---- GEOS 8.0 22

........ GEOS 2.1

20

18

16

14

12

10

18

......... { ....!.......... :---_

'! /_i.J_i --'-_':_-!-_ ....i........!.......

• i ,,'_ . . : \'-,%. : :

........ i..-,,./,,i ........ !........ !........ :.... •\:,...- ....... :.......

...... • -_'"..... i........ ! ........ !........ !........ !...."':_...: ....

,,_.-.--._'" : : : : : : "--....

_ !'_ : • ,. T ._]:,...... __'. . .: : .. ._"

15 18 21 00 03 06 09 12

UTC

24

22

20

_o 18

16

14

12

I0

12

July 88 MM Specific Humidity

/ ........ !....-_-_ ._._

/ ._. __\

: ,,?-/" -,._: • .. .... :<,,.,, \: :

........ :..ft..: ........ :........ :........ :.....<......_\ ......:.......

..............::......; ....... ....

_..-.- ....... ......... ..,................ ..... _ .... .-,,

.......................................................... i .......

15 18 21 O0 03 06 0'9

UTC

Figure 50: Mean diurnal cycle of two meter specific humidity for (a) June 1988, and (b)

July 1988.

65
2.6 GEOS Grid Point Variability

Betts et ah (1996) and Betts et al. (1998) justify the use of a single point from the

reanalysis system because the larger, synoptic scale fields are smoothly varying over GCM

grid spaces. Therefore, comparing any one of the nearby grid points with FIFE would lead

to the same conclusions. This should be acceptable; however, any horizontal variations of

surface properties (eg. soil wetness, roughness or aibedo) could cause a mean bias in the

results. Here, we examine the variability of the surface and PBL data of GEOS 2.1 during

IFC2 for the four grid points nearest the FIFE site.

In the present analysis, the GEOS grid point at 38°N, 97.5°W is compared with FIFE

observations. This point was chosen because its surface pressure corresponded more closely

to the observed surface pressure than any of the other grid points. Furthermore, the surface

type in GEOS is prescribed as grassland which corresponds to the observed FIFE vegetation

cover.

Table 3:IFC2 mean data from GEOS 2.1. Horizontal averages and standard deviations

are computed for the four grid points closest to the FIFE site. These are then averaged in

time, for 21 UTC data only.

Variable

t2m 301.00 ± 0.77 K

q2m 19.48 -]- 1.01 g kg -1

ps 967.02 ± 8.61 mb

preacc 6.23 ± 6.72 mm dy -1

pbl 98.82 ± 15.35 mb

cldfrc 0.490 ± 0.138

hfiux 72.35 ± 27.48 W m -2

efiux 511.99 ± 80.05 W m -_

radlwg 96.43 ± 12.36 W m -2

radswg 678.18 ± 87.94 W m -2

tg 302.71 ± 1.38 K

U 1.87±0.69 ms -1

We have analyzed the surface data at each of the grid points near the FIFE site (many

figures not included). In general, the results presented in this report do hold for each grid

point and the grid point mean. For example, the diurnal cycles of the ground heat flux,

specific humidity and net shortwave radiation all show similar patterns at each grid point.

The diurnal maxima and minima have some variability, but not enough to drastically alter

66

lII]
the conclusions. Table 3 presents the IFC2 mean data from GEOS 2.1 at 21 UTC (generally

the diurnal maximum for many of the variables). The area average of the four closest grid

points and the standard deviation were computed then time averaged for 21 UTC.

The grid point variability seems reasonable considering that this is area averaged over four

2° × 2.5 ° grid points. The latent heat flux variability seems large, but even the smallest values

are still somewhat larger than the observations. Also, one of the gridpoints is prescribed to

be forest (38°N, 95°W) while the rest are grassland. Notice that precipitation variability is

very large. The mean diurnal cycle of precipitation tends to be similar for each point, but

the timing and magnitude on each day may vary.

The grid point variability of the PBL is more difficult to ascertain. Problems arise from the

topography and its impact on data at sigma level coordinates. Each grid point will vary

in pressure similar to that at the surface. This is demonstrated in Figure 51. The effects

of the topography are very apparent within the PBL. Also, at this time, a substantial

horizontal temperature gradient exists above (and likely, within) the PBL. While there

may be some substantial variation between each grid point at any given time, the general

conclusions discussed in this report should be applicable at each nearby grid point. The

global generality of these conclusions will be addressed in future studies.

3 Summary and Discussion

First ISLSCP Field Experiment (FIFE) observations have been used to validate the surface

properties of various versions of the Goddard Earth Observing System (GEOS) Data Assimilation System. This work follows that of Betts et al. (1996 and 1998) for the NCAR/NCEP

and ECMWF reanalysis projects. The primary assumption is that we can learn something

of the global system's surface parameterization from comparing point observations with

gridpoint data. Two issues must be carefully considered when interpreting the results of

this study. First, the GCM grid space area is much larger than the FIFE site area. This

could lead to differences in local boundary conditions, such as albedo, surface roughness

and soil wetness that lead to differences between the assimilation data and observations.

Second, the results may depend on the regional climate and may not apply to other regions

of the globe.

Results indicate several potential systematic problems in the surface properties of GEOS.

First, the surface layer specific humidity is generally too large, especially during the daytime.

This occurs even when the latent heat flux is slightly underestimated (July 1988). The result

is a lifted condensation level that is too low compared with observations. While the large

latent heating in some cases contributes to the specific humidity bias, the PBL is likely not

entraining enough dry free atmosphere. The improper dirunal cycle of specific humidity

could influence the diurnal cycle of precipitation (Betts et al. 1996).

67
700

75O

800

85O

9OO

950 .............

I000298 3oo

GEOS 2.1, Theta (18ZO9JUL87)

(38N, 97.5W)

_40N, 97.5W_

.... _ (38 N. 95.0W_.

(40N. 95.0W)

---FIFE 1717 UTC

/

/

/

3o8 3io 3i2 _4

Figure 51: Vertical profiles of potential temperature at each of the closest grid points to

the FIFE site.

68

 llli
The analysis of PBL and surface data has identified two factors that affect the development

of the assimilated mixed layer. First, the surface sensible heat flux is consistently underestimated between 12 and 15 UTC. The lack of heat from the surface allows the stable surface

layer to stay in place longer than observed. Secondly, the observed profiles indicate that the

surface layer stability is too strong in the assimilation system or may include an elevated

layer that is more stable than observed. The stable layer could be related to the slightly

cooler surface temperatures, and too much net upward longwave radiation. As these factors

are overcome by the diurnal heating of the surface, the GEOS 2.1 PBL can develop quickly,

but too late in the diurnal period to catch up with observations.

The comparison of GEOS data to FIFE IFC2 seems mostly favorable. However, the June

and July 1988 comparison demonstrates that soil wetness has substantial control over the

surface energy budget. Likewise, this explains the relatively close correlation of each GEOS

system (at the surface), but may also imply that the IFC2 comparison is favorable because

the GEOS soil wetness happens to be comparable to FIFE.

As discussed previously, Betts et al. (1993, 1996 and 1998) have had considerable success

in evaluating NCEP's and ECMWF's reanalyses products with FIFE observations. There

appear to be several similarities between their comparisons and the present study.

Betts et al. (1996) compare the FIFE observation with the NCEP/NCAR forty year reanalysis (Kalnay et al. 1996). This reanalysis has a horizontal spectral resolution of T-62

and 28 vertical layers. The surface parameterization includes two interactive soil layers and

transpiration (Pan 1990).

For both clear and cloudy conditions, shortwave radiation appears too large in the NCEP

/ NCAR data. The model clouds were updated every three hours leading to significant

problems in the surface energy budget. The GEOS system has had several adjustments to

the radiation parameterization, but a similar bias seems to exist. In GEOS, it is related in

part to the albedo and in part to the representation of cloud.

Summertime precipitation amounts produced by the NCEP/NCAR reanalysis are larger

than observation. Betts et al. (1996) results suggest a feedback between too much evaporation and too low Lifted Condensation Level (LCL) pressure, and the interaction with

the PBL development. The GEOS system clearly exhibits too much surface layer specific

humidity which reduces the LCL. While several scientific modifications have partially ameliorated the problem, the system still produces too much precipitation in the central United

States.

Betts et al. (1996) indicate that the daytime development of the NCEP/NCAR system's

convective PBL is within reason. The entrainment at the top of the PBL, however, was

too small. The depth of the PBL tended to be lower than observed. This is also noted in

the analysis of the GEOS assimilations. Similarly, the NCEP Eta operational model, which

also uses a level 2.5 turbulence parameterization, has very limited PBL top entrainment

69
(Bettset al. 1997).

Bettset al. (1996)point out that by underestimating the entrainment of dry air from above

the PBL, near surface specific humidity can be too large. The NCEP / NCAR diurnal cycle

of near surface specific humidity, particularly the daytime maximum in summer, is larger

than observed in FIFE. The biases were especially strong during June 1987, similar to the

GEOS assimilations.

Further analysis of the NCEP assimilation shows that the surface layer vertical temperature

gradient tended to be smaller than FIFE, possibly a result of too large roughness length.

The near surface (2 meter) temperature data was used to determine the gradient. In GEOS,

we find that the early morning near-surface vertical temperature gradients tend to be too

stable. However, the winds in GEOS also appear to be too low (close to the surface).

Betts et al. (1993) used 48 hour forecasts from the ECMWF global model (T-106, 19 levels,

Cycle 39) to compare with FIFE. These experiments provided a preliminary evaluation of

the ECMWF surface and boundary layer parameterizations. Betts et al. (1998) updated

the results for the ECMWF global reanalysis (Gibson et al. 1997). The model used T-106

horizontal resolution and 31 vertical layers. The years 1979 - 1993 were assimilated. One

important component of the ECMWF reanalyses is that the soil water prognostic equation

includes a nudging term, based on the near Surface atmospheric specific humidity.

In ECMWF's reanalysis, the diurnal temperature maximum was comparable to observation,

but the minimum temperature was too low. This was related to a low bias of incoming longwave radiation. The low morning temperature corresponded to a strong surface inversion.

These factors slowed the development of the convective PBL. The lag of the diurnal cycle

of surface temperature in ECMWF was related to the thick soil layer (Betts et al. 1993

and 1997). The GEOS DAS exhibits similar features, except that an unrealistic phase of

surface heating compounds the problems.

Similar to both NCEP and GEOS, the development of ECMWF's PBL affects the bias of

near-surface specific humidity. The diurnal cycle of ECMWF's specific humidity improved

drastically, however, due to the inclusion of nudging in the soil water content. The summertime bias of mixing ratio was only +0.5 g kg -1. Without soil water nudging in the

GCM simulations, the diurnal cycle of the surface layer specific humidity was too large.

Interestingly, ECMWF's June evaporation was too low.

The GEOS comparison to FIFE yields conclusions similar to those for both ECMWF's and

NCEP's reanalyses. Some of the underlying processes, however, show subtle differences. The

limited representation of the GEOS surface parameterization may degrade the comparison

with these observations; however, the PBL turbulence parameterization seems to improve

the comparison. Regardless, the results do indicate several areas where improvements in

the parameterization are needed.

7O
While the resultspresentedin this reportaregenerallyconsistentwith previousanalysesof

the GEOSDAS,someeffortmustbetakento makethemmorerobust.Severalpossibilities

existthat mayimprovefutureexperimentsandanalysesof thesurfaceandPBL parameterizations.First, field experimentdatafrom a varietyof regionswill helpto generalizesome

of theseresults.This will betterhelpidentify modeldeficiencies.Secondly,futureversions

of theGEOSDASwill includetheMosaicLSM.This surfaceparameterizationincorporates

grid spaceheterogeneity.This will allow the comparisonof the appropriateland type to

theobservations,aswellasprovideanestimateof grid box variability.

71
Appendix: FIFE Datasets at DAO

For this report, surface data of Betts and Ball (1998) and PBL data from the FIFE CDROM (Strebel et al. 1994) were used. Both data sets have been converted into a binary

format for use in Grads because the GEOS data is readily available in that format.

Betts and Ball's data has also been time averaged in order to compare with the GEOS

output. In particular, a monthly mean data set is available as well as a 3 hourly mean

data set. The standard output of the GEOS DAS surface data is in a 3 hourly backward

mean. Therefore, the data at 03 UTC is the average of data from 00 - 03 UTC. For further

discussion, see Schubert et al. (1995). Betts and Bali's data files and their Grads equivalent

are available at 15 and 45 minutes past the hour (30 minute centered means).

There are two sets of radiation data. The portable area mesonet (PAM) stations recorded

net radiation and several component radiation terms, while flux stations recorded all radiation terms in addition to the turbulent heat fluxes. The flux station data is only available

during the summers, and the radiation data from the flux station is preferable to the PAM

radiation data. There is a bias that exists between the two radiation measurements which

can be very large during the daytime (see Smith et al. 1992; Betts and Ball 1998; Bosilovich

and Sun 1998).

A typical FIFE surface table file includes:

sfcp

ta

tw

prec

u

v

tsurf

tslO

tsSO

rsdn

rsup

rnet

rldn

q

tocl

met2

LE

Hs

Surface Pressure (mb)

Atmospheric Temperature at 2 m (C)

Wet Bulb Temperature at 2 m (C)

Rain Rate (mm/3 hr)

East-West Wind Component 5.4 m (m/s)

North-South Wind Component 5.4 m (m/s)

Radiometric Surface Temp (C)

I0 cm deep soil temperature (C)

50 cm deep soil temperature (C)

Incoming Shortwave Radiation (W/m2)

Reflected Shortwave Radiation (W/m2)

Net Radiation (W/m2)

Incoming IR Radiation (W/m2)

Atmospheric Mixin E Ratio (g/Kg)

Total Cloud cover (Eighths) (1987 only)

Net Rad. (different from rnet) (W/m2)

Latent Heat Flux (W/m2)

Sensible Heat Flux (W/m2)

72
Hg

rsdn2

rsup2

rldn2

rlup2

Soil Heat Flux (W/m2)

Incomin E Shortwave Radiation (W/m2)

Reflected Shortwave Radiation (W/m2)

Incoming IR Radiation (W/m2)

Reflected IR Radiation (W/m2)

Note that all the variables up to the total cloud cover (tocl) are from surface PAM stations,

and are generally available for the whole period. The rest are flux station observations

which were generally taken only during summer periods and IFCs. Also, Betts and Bali's

flux station data in 1988 report the reflected shortwave radiation (rsup2) as a negative

number, but positive in other years. This has been corrected in the Grads files.

The Grads PBL data files are defined between 1000 mb and 505 mb at 5 mb intervals. The

data has been separated into one file for each day, because of the irregular time intervals of

balloon launches.

Use the PBL data with caution. The time intervals that Grads will default to are likely

not correct. This is due to the irregular launch time of the soundings. A time variable is

included in the Grads data file. Check this variable for each profile used. Also, the wind

variables tended to show some very unrealistically large values. In some of the profile, these

were marked as undefined. All PBL data files, however, were not screened.

PBL data files include the following variables:

time

pres

hgt

ta

tw

q

theta

uwind

vwind

Decimal time (UTC) (Check this for each profile)

Atmospheric Pressure (mb)

Balloon Height AGL (m)

Atmospheric Temperature (C)

Atmospheric Wet Bulb Temperature (C)

Atmospheric Mixing Ratio (g/Kg)

Atmospheric Potential Temperature (K)

East-West Wind (m/s)

North-South Wind (m/s)

The raw FIFE data can be acquired through the Oak Ridge National Laboratory data

archive, or from FIFE CD-ROM (Strebel et al. 1994). See Betts and Ball (1994) for

information on the processing of the FIFE site-averaged data.

73
Illi
References

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in the Goddard Chemical Transport Model using International Satellite Cloud Climatology Project cloud parameters.J. Geophys. Res., 102, No. D21, 25467-25476.

Betts, A. K., and A. C. M. Beljaars, 1993: Estimation of effective roughness length for heat

and momentum from FIFE data. Atmos. Res., 30, 251 - 261.

Betts, A., and J. H. Ball, 1998: FIFE surface climate and site-averaged dataset 1987 - 1989.

J. Atmos. Sci., 55, 1091-1108.

Betts, A., J. H. Ball, and A. C. M. Beljaars, 1993: Comparison between the land surface

response of the ECMWF model and the FIFE-1987 data. Q. J. R. Meteorol. Soc.,

119, 975- 1001.

Betts, A., S.-Y. Hong, and H.-L. Pan, 1996: Comparison of the NCAR-NCEP reanalysis

with 1987 FIFE Data. Mon. Wea. Rev., 124, 1480 - 1498.

Betts, A., F. Chen, K. E. Mitchell, and Z. I. Jani5, 1997: Assessment of the land surface

and boundary layer models in two operational versions of the NCEP Eta model using

FIFE data. Mon. Wea. Rev., 125, 2896 - 2916.

Betts, A., P. Viterbo, and A. C. M. Beljaars, 1998: Comparison of the land-surface interaction in the ECMWF reanalyses model with the 1987 FIFE data. Mon. Wea. Rev.,

126, 186- 198.

Blackadar, A.K.,1977: High Resolution Models of the Planetary Boundary Layer. Advances

in Environmental Science and Engineering, Vol 1 Editors Pfafflin and Zeigler, Gordon and Breach, Scientific Publishers.

Bloom, S.C., L.L. Takacs, A. M. da Silva, and D. Ledvina, 1991: Data assimilation using

incremental analysis updates. Mon. Wea. Rev., 124, 1256-1271.

Bosilovich, M. G., and W.-Y. Sun, 1998: Monthly simulation of surface layer fluxes and soil

properties during FIFE. J. Atmos. Sci., 55, 1170-1184.

Cohn, S. E., A. da Silva, J. Guo, M. Sienkiewicz and D. Lamich, 1998: Assessing the effects

of data selection with the DAO Physical-space statistical analysis system. Mon.

Wea. Rev., In Press.

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Gibson, J. K., P. Kallberg, S. Uppala, A. Hernandez, A. Nomura, and E. Serrano, 1997:

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77
III
Previous Volumes in This Series

Volume 1

September 1994

Documentation of the Goddard Earth Observing System

(GEOS) general circulation model - Version 1

L.L. Takacs, A. Molod, and T. Wang

Volume 2

October 1994

Direct solution of the implicit formulation of fourth order

horizontal diffusion for gridpoint models on the sphere

Y. Li, S. Moorthi, and J.R. Bates

Volume 3

December 1994

An efficient thermal infrared radiation parameterization for

use in general circulation models

M.-D. Chou and M.J. Suarez

Volume 4

January 1995

Documentation of the Goddard Earth Observing System

(GEOS) Data Assimilation System - Version 1

James Pfaendtner, Stephen Bloom, David Lamich,

Michael Seablom, Meta Sienldewicz, James Stobie,

and Arlindo da Silva

Volume 5

April 1995

Documentation of the Aries-GEOS dynamical core: Version 2

Max J. Suarez and Lawrence L. Takacs

Volume 6

April 1995

A Multiyear Assimilation with the GEOS-1 System:

Overview and Results

Siegfried Schubert, Chung-Kyu Park, Chung-Yu Wu,

Wayne Higgins, Yelena Kondratyeva, Andrea Molod,

Lawrence T_Lkacs, Michael Seablom, and Richard

Rood

Volume 7

September 1995

Proceedings of the Workshop on the GEOS-1 Five-Year

Assimilation

Siegfried D. Schubert and Richard B. Rood

79
Volume 8

March 1996

Documentation of the Tangent Linear Model and Its Adjoint

of the Adiabatic Version of the NASA GEOS-1 C-Grid GCM:

Version 5.2

Weiyu Yang and I. Michael Navon

Volume 9

March 1996

Energy and Water Balance Calculations in the Mosaic LSM

Randal D. Koster and Max J. Suarez

Volume 10

April 1996

Dynamical Aspects of Climate Simulations Using the GEOS

General Circulation Model

Lawrence L. Takacs and Max J. Suarez

Volume 11

May 1997

Documentation of the Tangent Linear and its Adjoint Models

of the Relaxed Arakawa-Schubert Moisture Parameterization

Package of the NASA GEOS-1 GCM (Version 5.2)

Weiyu Yang I. Michael Navon, and Ricardo Todling

Volume 12

August 1997

Comparison of Satellite Global Rainfall Algorithms

Alfred T.C. Chang and Long S. Chiu

Volume 13

December 1997

InterannualVariabilityand PotentialPredictabilityin ReanalysisProducts

Wie Ming and Siegfried D. Schubert

8O

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4. TITLE AND SUBTITLE

Technical Report Series on Global Modeling and Data Assimilation

Volume 14---A Comparison of GEOS Assimilated Data with FIFE

Observations

6. AUTHOR(S)

Michael G. Bositovich and Siegfried D. Schubert

Max J. Suarez, Series Editor

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13. ABSTRACT (Maximum 200 words)

First ISLSCP Field Experiment (FIFE) observations have been used to validate the near-surface properties of various versions of the Goddard Earth Observing System (GEOS) Data Assimilation System. The siteaveraged FIFE data set extends from May 1987 through November 1989, allowing the investigation of several

time scales, including the annual cycle, daily means and diurnal cycles. Furthermore, the development of the

daytime convective planetary boundary layer is presented for several days. Monthly variations of the surface

energy budget during the summer of 1988 demonstrate the affect of the prescribed surface soil wetness

boundary conditions. GEOS data comes from the first frozen version of the assimilation system (GEOS- 1

DAS) and two experimental versions of GEOS (v. 2.0 and 2.1) with substantially greater vertical resolution

and other changes that influence the boundary layer.

This report provides a baseline for future versions of the GEOS data assimilation system that will incorporate a state-of-the-art land surface parameterization. Several suggestions are proposed to improve the

generality of future comparisons. These include the use of more diverse field experiment observations and an

estimate of gridpoint heterogeneity from the new land surface parameterization.

14. SUBJECT TERMS

data assimilation, GCM, FIFE, planetary boundary layer, land surface

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