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
Flux
SW
(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 areasERBE Region Wm-2 ERBE Region Wm-2
Jul 2002
4901Cameroon -30 3126
New Mex. US 44
Sep 2002
5622Angola -39 5126
Lake Victoria 33
Dec 2002
6306off Peru -31 6211
Madagascar 22
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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 )
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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
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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)
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Ethiopia
ERBE-type extrapolation
with Meteosat
Diff= 120-102=18 Wm-2
DIURNAL EXTRAPOLATION
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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,.. )
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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,…
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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