1. Intercomparison of satellite retrieved aerosol optical depth over ocean G. Myhre, F. Stordal, M. Johnsrud, A. Ignatov, M.I. Mishchenko, I.V. Geogdzhayev, D. Tanré, J.L. Deuzé, P. Goloub, T. Nakajima, A. Higurashi, O. Torres, B.N. Holben, N.G. Loeb, S. Bailey, G. Feldman, T. Holzer-Popp, M. Schroedter MODIS and MISR data have been downloaded from their web sites. We acknowledge the effort of the two teams Compared 10 satellite retrievals over 3 time periods Main focus on a 40 months period from September 1997 to December 2000. Comparisons made for monthly mean data Two AVHRR retrievals, POLDER, OCTS, TOMS, SeaWiFS, VIRS, GOME/ATSR-2, MODIS, MISR

2. 8-months period, Nov 96 – Jun 97

4. Where are the uncertainties largest? Myhre et al., JAS, 2003, in press

5. Averaged AOD (550 nm) over ocean for the period Sep 97-Dec 00. Maximum AOD is 0.72, 1.00, 0.28, and 1.68, respectively for AVHRR-1, AVHRR-2, SeaWiFS, and TOMS. 40 months period

6. Monthly mean AOD during the 40 months period

7. AOD OVER OCEAN, ZONAL MEAN AVHRR-1(2g), AVHRR-2, TOMS and SeaWiFS for Sep 97-Dec 00, VIRS for Jan-Aug 98, MODIS for Mar-Dec 00.

8. AOD for 11 oceanic regions

9. Spatial correlation between various satellite retrievals for 11 oceanic regions

10. Comparison with AERONET data Alot of data available Generally satellite retrievals compare well with AERONET data No obvious retrieval perform better/worse compared to the AERONET data

12. SCATTER PLOT, SATELLITE RETRIEVALS VS AERONET

13. AOD comparison in events of high AOD or aerosol campaigns

14. Global land and ocean Global land Global ocean

15. Monthly mean AOD over ocean for 9 near coastal regions

16. MISR MODIS

17. Compared 10 satellite retrievals over ocean during 3 time periods Over ocean the satellite retrievals compare best in coastal regions Generally at least a factor of two differences Largest uncertainties over ocean in the southern hemisphere at high latitudes Compared to AERONET observations no retrievals performing obvious worse/better, no large difference in size, and region Some retrievals has upper limits in AOD, which clearly leads to underestimation of AOD for some location and time periods

23. Modis 2001 annual mean AOD Modelled 1996 annual mean AOD