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Cloud trends from GOME, SCIAMACHY and OMI Ping Wang, Mark Kroon, Piet Stammes, Ronald van der A

OMI science meeting, Helsinki, 24-27 June 2008. Cloud trends from GOME, SCIAMACHY and OMI Ping Wang, Mark Kroon, Piet Stammes, Ronald van der A KNMI, De Bilt, the Netherlands. Overview. Importance of clouds Satellite instruments Method Global frequency distributions of cloud properties

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Cloud trends from GOME, SCIAMACHY and OMI Ping Wang, Mark Kroon, Piet Stammes, Ronald van der A

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  1. OMI science meeting, Helsinki, 24-27 June 2008 Cloud trends from GOME, SCIAMACHY and OMI Ping Wang, Mark Kroon, Piet Stammes, Ronald van der A KNMI, De Bilt, the Netherlands

  2. Overview • Importance of clouds • Satellite instruments • Method • Global frequency distributions of cloud properties • Trends in global cloud properties • Conclusions

  3. Importance of clouds for climate 1. Clouds dominate the radiative budget of the atmosphere: • Clouds contribute about 75 % to Earth’s albedo. • Height of clouds determines their temperature. 2. Clouds play a central role in the hydrological cycle. 3. Current understanding of clouds is limited: • Global climate models have to be validated with global observations of clouds.

  4. Satellite spectrometers INSTRUMENT /SATELLITE SPECTRAL RANGE PIXEL SIZE GOME / ERS-2: 240 – 800 nm 320x40 km2 SCIAMACHY / Envisat: 240 – 2380 nm 60x30 km2 GOME-2 / Metop-A: 240 – 800 nm 80x40 km2 OMI/AURA: 270 – 500 nm 24x13 km2 Spectral resolution: 0.2 - 0.4 nm SCIA GOME/GOME-2 OMI Raman O2-O2 O2 A

  5. O2 A-band simulation O2 A-band measurement Spectral resolution: 1 pm Spectral resolution: 0.4 nm

  6. Cloud retrieval algorithm FRESCO Reality Retrieval model Ac = 0.8 pc ceff 1-ceff • Geometrical cloud fraction • Cloud optical thickness • Cloud top pressure • Cloud bottom pressure • Cloud phase • ……… ps, As • FRESCO algorithm produces: • Effective cloud fraction: ceff • Cloud pressure pc

  7. Simulation of O2 cloud pressure Sneep et al. JGR 2008

  8. O2 A-band cloud results compared to ISCCP data Data selection: GOME (FRESCO): 1996-2003 SCIAMACHY (FRESCO): 2003-2005ISCCP D2 data: 1996-2005 Area: 60° N – 60° STime: 10:OO hr local time Monthly averages

  9. Comparison between GOME and ISCCP land ocean 1997 ISCCP 09:00

  10. Time series of global mean cloud pressure

  11. Time series of NH and SH cloud pressure GOME

  12. OMI global mean cloud pressure

  13. OMI global mean effective cloud fraction

  14. Global mean cloud pressure 1996-2008

  15. Global mean effective cloud fraction 1996-2008

  16. O2-O2 cloud fraction across track The larger ceff at the edges of the swath might contribute to the larger global mean ceff July 2007

  17. O2-O2 ceff, Pc vs. lat. July 2007

  18. Conclusions • O2 absorption provides unique height information about clouds, since visible light penetrates into clouds. • O2 methods are complementary to IR methods which give mostly the top of the cloud. • O2 cloud pressure has a clear bimodal distribution unlike ISCCP. • The global average O2 A-band cloud pressure has a clear seasonal dependence, which is missing in ISCCP. .OMI O2-O2 global averaged cloud pressure and effective cloud fraction show less seasonal variation than GOME and SCIA FRESCO cloud products.

  19. Trend in global cloud pressure from GOME and SCIAMACHY

  20. Use of O2 absorption band:direct measure of cloud pressure

  21. Cloud pressure distributions from GOME land ocean Global mean, 1997

  22. O2-O2 FRESCO comparison Maarten et al. 2008 • FRESCO+ cloud fraction and pressure monthly average, perhaps not all the data • Differences in the FRESCO and OMI cloud average. • Cloud effect on climate • ISCCP data new version? • How to explain the seasonal variation • Check the SZA dependence? • Make FRESCO cloud trend plot using excel ?

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