March 21, ‘06 comp

May 5, ‘06 comp

Summary ~4% swath angle dependent difference Up to 9% difference over clouds Differences correlate with snow/ice maps Known issue in OMTO3: O 3 underestimation by up to 3% at large SZAs due to straylight at 313 nm.

Comparison of OMTO3 v1, OMDOAO3 v and OMDOAO3 v1 Zonal Means Er-Woon Chiou And Daniel Kahn SSAI

Monthly Gridded Map Criteria 1 degree x 1 degree grid using all 60 pixels OMTO3 screening criteria (1)Total ozone > 0 (2)Error flag = 1, 1, 2 OMDOAO3 screening criteria (1)Total ozone > 20 (2)Precision ÷ (total ozone) < 90% (3)Ascending part of the orbit

January 2005 Gridded Maps

March 2005 Gridded Maps

May 2005 Gridded Maps

July 2005 Gridded Maps

September 2005 Gridded Maps

November 2005 Gridded Maps

8-Weekly Zonal Means Uses the nadir pixel only 5-degree zones 8-week period –Week 1: 3/19 – 3/25 –Week 8: 5/13 – 5/17 OMTO3 screening criteria: 1.50 < total ozone < Error flag 0, 1, 2, 8, 9, 10 OMDOAO3 screening criteria both versions: 1.50 < total ozone < 700

DOAS v0.942  DOAS v1.01  OMTO3

DOAS v0.942  DOAS v1.01  OMTO3

DOAS v0.942  DOAS v1.01  OMTO3

Summary For 60 S through 60 N, OMDOAO3 v is larger than OMTO3 by about 8 ~ 9 DU For 50 S through 50 N, OMDOAO3 v1 is very close to OMTO3 for all 8 weeks with differences of 1 ~ 2 DU Differences between OMDOAO3 v1 and OMTO3 are larger during the first 4 weeks at 60 N and the last 2 weeks at 60 S For 30 S to 30 N, OMDOAO3 v1 is always slightly less than OMTO3

Cloud-top pressure climatology assumed by OMI Total O 3 Products OMTO3 January (R>0.6) OMDOAS January ‘05 (f c >0.75) Cloud hts are lower

Comparison of Cloud-top Pressures Raman clouds are higher than O 2 -O 2, but similar to THIR except in downwelling areas of the tropics. THIR O 2 -O 2 Raman

Comparison of IR Cloud Heights Nimbus-7 THIR (R>0.6) Note: color scales are different Aqua MODIS Jan ‘05 (all R) MODIS clouds are somewhat lower, particularly over water. Similar features were seen in THIR without R cutoff.

Summary O 2 -O 2 derived cloud hts are generally too low compared to both IR and Raman. Raman values are similar to IR (after removing low reflecting clouds from the IR climatology) except in the downwelling areas of the tropics.

Possible Improvements to OMTO3 Replace cloud climatology with OMI-”measured” cloud-top pressures. Fix (apparent) straylight related problem at large SZAs. Improve O 3 climatology using MLS data. Improve Raman scattering table. Improve profile correction scheme. –optimal estimation using several wavelengths? Degrade OMI resolution to 1-2 nm before doing retrieval. –To reduce noise and Ring signal Replace Bass & Paur (1981) with Malicet, Daumont et al. (1995) O 3 cross-section.