2004/04/02 GIST 21, Boulder M. Viollier et al. 1

Time sampling bias: combination of CERES with Meteosat narrow-bands

and beginning a comparison with GERB

Michel Viollier, Patrick Raberanto, Robert Kandel

Laboratoire de Météorologie Dynamique, IPSL/CNRS, Ecole Polytechnique

Palaiseau, France

2004/04/02 GIST 21, Boulder M. Viollier et al. 2

Important issue on the SW monthly means …

can the low 1999-2002 SW flux be explained by diurnal effects ? linked to the 10:30 observation local time ?

1985-89 Radiative Anomaly (Wm-2)- Wielicki etal. 2002

ScannersTropical Means

0

20

40

60

80

100

120

1985 1990 1995 2000

Flu

x S

W (

Wm

-2)

CERES

ScaRaB

NOAA-ERBS

2004/04/02 GIST 21, Boulder M. Viollier et al. 3

Outline objective: to search for a possible diurnal bias in the Terra alone computations:

- comparison of diurnal cycles and monthly means from Terra and Aqua

- combination of Meteosat-5 with CERES/Terra, July 2002, July 2002, and comparison with Terra+Aqua ; second example: March 2000March 2000

- beginning GERB/CERES comparisons and diurnal variations over selected areas

2004/04/02 GIST 21, Boulder M. Viollier et al. 4

CERES SW : Aqua minus Terra, 2002 July, Sep, Dec.

Compared to Terra, Aqua misses morning reflected flux from marine stratus,but is sensitive to afternoon convective activity on continents, and vice versa.[December/Antartic: instrument/angular differences are amplified by the very large solar incident flux]

Jul

Sep

Dec

2004/04/02 GIST 21, Boulder M. Viollier et al. 5

Aqua, Terra ES 9 differences: Min and Max (Wm-2)

Minimum differences near western continent

coast

Maximum differences

inland areas

ERBE Region Wm-2 ERBE Region Wm-2

Jul 2002

4901Cameroon

-303126

New Mex. US44

Sep 2002

5622Angola

-395126

Lake Victoria33

Dec 2002

6306off Peru

-316211

Madagascar22

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Aqua, Terra ES 9 regional instantaneous albedo

July 2002

Cameroon/east Atlanticsw flux monthly m.Aqua –Terra= - 30 Wm-2

New Mexico USA/inland area Aqua –Terra= + 44 Wm-2

Red=monthly mean

Terra Aqua

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CERES Aqua, Terra : SW 20°S-20N Means (Wm-2)

2002 AquaFM3 Ed1

TerraEd2

S9(Aq+Te) Ed1

Aqua minus Terra

Aqua minus S9(Aq+Te)

Jul 90.45 89.76 90.02 +0.7 -0.3

Aug 94.23 93.63 93.88 +0.6 -0.2

Sep 93.93 92.03 92.53 +1.9 -0.5

Oct 94.27 92.57 92.98 +1.7 -0.4

Nov 93.85 94.75 94.81 -0.9 -0.1

Dec 91.51 92.55 92.43 -1.0 +0.1

< 0.5 Wm-2Combination of Terra and Aqua don’t changesignificantly the tropical SW mean.

2004/04/02 GIST 21, Boulder M. Viollier et al. 8

Compare ES9 Terra and Aqua with contemporaneous Meteosat-5 : JULY 2002

SW LW

Study over the INDOEX area (1999 study following-on )

2004/04/02 GIST 21, Boulder M. Viollier et al. 9

SW Monthly Means Computations with CERES/Meteosat-5 combinations

- estimate instantaneous fluxes from Meteosat-5- average the fluxes (2.5°x2.5°) and fill the 24x31 day-hour table

(applying cos SZA corrections between observation time and local half-hour, eliminating spurious data,

twilight and night-time data) - use ‘our ERBE-type’ code, with CERES flux estimates

- use the GEO observed diurnal albedo variation shapein place of the ERBE modeled albedo

basically the same approach as the GEO interp. of CERES/SRBAVG

2004/04/02 GIST 21, Boulder M. Viollier et al. 10

Estimation of Meteosat-5fluxes by comparison to CERES. Examples: July 2002

FM2 (Terra) FM4 (Aqua)

Meteosat flux conversion: based on ScaRaB 1999 (Viollier et al., JGR 2004)

2004/04/02 GIST 21, Boulder M. Viollier et al. 11

Ethiopia

ERBE-type extrapolation

with Meteosat

Diff= 120-102=18 Wm-2

DIURNAL EXTRAPOLATION

2004/04/02 GIST 21, Boulder M. Viollier et al. 12

Ocean W. Australia

ERBE-type extrapolation

with Meteosat

Diff= 70.7-74.8=-4 Wm-2

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Red Sea

ERBE-type extrapolation

with Meteosat

Diff= 60.6-61.8=-1,2 Wm-2

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Terra/Meteosat-5 correction - July 2002

Area of predominant morning cloudiness: over ocean west of Australia

Difference betweenM5-Terra SW combinationand ERBE-type extrapolation

Mean ~ + 3,35 Wm-2

Area of predominant afternoon cloudiness, Ethyopia

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ES9(2 sat) - ES9(Terra) Terra/Meteosat-5 correction

but 27-31 July Meteosat data are available to us

from Aqua –Terra (Takmen Wong, Oct. 15)same but # colors, grid, interp.

Mean=0.74 3.35

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SW Monthly Means Computations with CERES/Meteosat-5 combinations, March 2000

Difference betweenM5-Terra SW combinationand ERBE-type extrapolation

Mean ~ + 4 Wm-2

Same but for region of predominant afternoon cloudiness, over ocean northwest of Madagascar (long.=56°E, lat.=6°S)

Area of predominant morning cloudiness: monthly means of the diurnal cycle for albedo (left) and LW flux (right), over ocean west of Australia (long.= 104°E, lat.=29°S) (Viollier et al., JGR 2004)

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preliminary GERB comparisons

- GERB data: 19, 23 Dec. 2003 (ex. G2_SEV1_L20S_20031223_130000_V002.hdf)

- CERES : ES8 (ex CER_ES8_Aqua-FM3_Edition1_025023.20031223)

- average data over 2.5 x 2.5° regions

- keep region with more than 80 (CERES) and 20 (GERB) observations

- compare GERB and CERES flux regional means with time condition: ± 10 minutes (LW), ± 2 minutes (SW),

- other comparisons: radiance, reflectance, albedo

- observe selected regional diurnal cycles (albedo, LW flux)

2004/04/02 GIST 21, Boulder M. Viollier et al. 18

CERES/GERB flux intercomparison

LW day LW night SWmean difference < ~2%, (preliminary result for 2003 Dec 23,approximate GERB observation time= 00:07:30, 00:22:30,.. )

2004/04/02 GIST 21, Boulder M. Viollier et al. 19

Diurnal variations using GERB (preliminary) – 2003, Dec. 19

Clear Ocean (Arabian Gulf) Clear Land (S. Africa)

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Diurnal variations using GERB (preliminary) – 2003, Dec. 19

off Angola Africa low cloud area convective cloud area

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Conclusions

• SW differences of tropical monthly means between computations from one (Terra) or two satellites (Terra+Aqua, Ed1) are not significant (0.5 Wm-2)

the addition of Aqua in the monthly means calculations doesn't show any sufficient diurnal bias to explain the low SW fluxes observed by Terra since 2000

• over INDOEX area : combination with Meteosat suggests Terra monthly means might be underestimated by ~4 Wm-2 , and then diurnal bias could partly explain the low CERES SW fluxes

• further analysis of GERB and of the CERES geo-interpolations are necessary to confirm this conclusion

• with still several issues: inter-calibration and radiance-to-flux

conversions

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back up slides

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Beside presentation : AMMA as a potential GERB data user (1/2)

African Monsoon Multidisciplinary Analyses(http://medias.obs-mip.fr/amma/index.en.html)

multidisciplinary project on the West African Monsoon and its impacts

Atmospheric Dynamics, Continental Water Cycle, Atmospheric Chemistry, Oceanic and Continental Surface Conditions.

Sponsors : French Agencies CNES, CNRS/INSU, IRD, and Meteo-France . International participation: Africa, Germany, the UK, and the United States,…

2004/04/02 GIST 21, Boulder M. Viollier et al. 24

AMMA as a potential GERB data user (2/2)

Long Term Observation Period : … 2009

Special Observing Period (SOP): various key stages of the rainy season during three periods in 2005: (i) monsoon onset, (ii) peak monsoon and (iii) late monsoon

AMMA-SAT : the satellite data component of AMMA

http://ammasat.lmd.polytechnique.fr/WelcomeE.html

In this project : we emphasize the value of CERES and GERB data