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Important issue on the SW monthly means …

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. ScaRaB. NOAA-ERBS. CERES.

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Important issue on the SW monthly means …

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  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 GIST 21, Boulder M. Viollier et al.

  2. ScaRaB NOAA-ERBS CERES Important issue on the SW monthly means … Scanners 1985-89 Radiative Anomaly (Wm-2)- Wielicki etal. 2002 can the low 1999-2002 SW flux be explained by diurnal effects ? linked to the 10:30 observation local time ? 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, and comparison with Terra+Aqua ; second example: March 2000 • beginning GERB/CERES comparisons and diurnal variations over selected areas GIST 21, Boulder M. Viollier et al.

  4. CERES SW : Aqua minus Terra, 2002 July, Sep, Dec. Sep Jul 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] Dec GIST 21, Boulder M. Viollier et al.

  5. Aqua, Terra ES 9 differences: Min and Max (Wm-2) GIST 21, Boulder M. Viollier et al.

  6. Aqua, Terra ES 9 regional instantaneous albedo July 2002 Cameroon/east Atlanticsw flux monthly m.Aqua –Terra= - 30 Wm-2 New Mexico USA/inland areaAqua –Terra= + 44 Wm-2 Red=monthly mean Terra Aqua GIST 21, Boulder M. Viollier et al.

  7. CERES Aqua, Terra : SW 20°S-20N Means (Wm-2) Combination of Terra and Aqua don’t changesignificantly the tropical SW mean. < 0.5 Wm-2 GIST 21, Boulder M. Viollier et al.

  8. Compare ES9 Terra and Aqua with contemporaneous Meteosat-5 : JULY 2002 Study over the INDOEX area (1999 study following-on ) SW LW GIST 21, Boulder M. Viollier et al.

  9. SW Monthly Means Computations with CERES/Meteosat-5 combinations basically the same approach as the GEO interp. of CERES/SRBAVG • 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 shape • in place of the ERBE modeled albedo 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) GIST 21, Boulder M. Viollier et al.

  11. DIURNAL EXTRAPOLATION Ethiopia ERBE-type extrapolation with Meteosat Diff= 120-102=18 Wm-2 GIST 21, Boulder M. Viollier et al.

  12. Ocean W. Australia ERBE-type extrapolation with Meteosat Diff= 70.7-74.8=-4 Wm-2 GIST 21, Boulder M. Viollier et al.

  13. Red Sea ERBE-type extrapolation with Meteosat Diff= 60.6-61.8=-1,2 Wm-2 GIST 21, Boulder M. Viollier et al.

  14. Terra/Meteosat-5 correction - July 2002 Area of predominant afternoon cloudiness, Ethyopia Difference betweenM5-Terra SW combination and ERBE-type extrapolation Mean ~ + 3,35 Wm-2 Area of predominant morning cloudiness: over ocean west of Australia GIST 21, Boulder M. Viollier et al.

  15. ES9(2 sat) - ES9(Terra) Terra/Meteosat-5 correction Mean=0.74 3.35 but 27-31 July Meteosat data are available to us from Aqua –Terra (Takmen Wong, Oct. 15) same but # colors, grid, interp. GIST 21, Boulder M. Viollier et al.

  16. 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) Same but for region of predominant afternoon cloudiness, over ocean northwest of Madagascar (long.=56°E, lat.=6°S) SW Monthly Means Computations with CERES/Meteosat-5 combinations, March 2000 Difference betweenM5-Terra SW combination and ERBE-type extrapolation Mean ~ + 4 Wm-2 (Viollier et al., JGR 2004) GIST 21, Boulder M. Viollier et al.

  17. 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) GIST 21, Boulder M. Viollier et al.

  18. CERES/GERB flux intercomparison LW day LW night SW mean difference < ~2%, (preliminary result for 2003 Dec 23,approximate GERB observation time= 00:07:30, 00:22:30,.. ) GIST 21, Boulder M. Viollier et al.

  19. Diurnal variations using GERB (preliminary) – 2003, Dec. 19 Clear Ocean (Arabian Gulf) Clear Land (S. Africa) GIST 21, Boulder M. Viollier et al.

  20. Diurnal variations using GERB (preliminary) – 2003, Dec. 19 off Angola Africa low cloud area convective cloud area GIST 21, Boulder M. Viollier et al.

  21. 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 GIST 21, Boulder M. Viollier et al.

  22. back up slides GIST 21, Boulder M. Viollier et al.

  23. 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,… 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 GIST 21, Boulder M. Viollier et al.

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