1. A four year record of Aerosol Absorption measurements from OMI near UV observations Omar Torres Department of Atmospheric and Planetary Sciences Hampton University, Hampton, Va, 23668 Changwoo Ahn SSAI, Inc, Lanham, MD, USA Santiago Gasso GEST Center University of Maryland Baltimore County, Baltimore, MD Outline: -An update on validation of C3 product -The emerging OMI record on aerosol absorption -Use of OMI near UV aerosol product in climate-related studies OMI Science Team Meeting Finland, Helsinki June 24-27, 2008

2. Validation of Collection 3 OMAERUV Product

3. Evaluation of extinction AOT using AERONET observations (absorbing aerosols) Under miminum sub-pixel cloud contamination conditions the OMI near-UV algorithm (OMAERUV) performs reasonably well.

4. Evaluation of extinction AOT using AERONET observations (non-absorbing aerosols) Retrievals of non-absorbing aerosols are significantly noisier. Overestimates and underestaimates are associated to the OMI large footprint.

5. OMAERUV-Aeronet Comparison Monthly Averages Absorbing Aerosols Non-absorbing aerosols Noise level significantly reduced when comparing monthly averaged data

6. Absorption by Brazilian and African Savanna smoke RMS=0.03 ( Africa ) (Brazil) Assessment of OMI Aerosol Absorption Product Comparison to AERONET Retrievals

7. Emerging OMI record on Aerosol Absorption

8. DJFMAMJJASON Seasonal Averages of Aerosol Absorption (OMI 2006) Single Scattering Albedo Absorption Optical Depth

9. Combined TOMS-OMI Record on Aerosol Absorption (Preliminary Results) Larger OMI values are the result of algorithmic differences. TOMS record will be re-processed using OMI algorithm

10. Eastern Europe Western Europe OMI Multiyear record on Aerosol Absorption: A Regional Analysis Solid line: 388 nm Aerosol Extinction Optical Depth (AOD)/10. Dashed line: 388 nm Aerosol Absorption Optical Depth

11. Southeast United States OMI Multiyear record on Aerosol Absorption: A Regional Analysis

12. Brazil Central Africa OMI Multiyear record on Aerosol Absorption: A Regional Analysis

13. Use of OMI near-UV aerosol product in Climate studies

14. Figure from Keil & Haywood (JGR, 108, 2003) Aerosol- cloud Interaction The relative vertical distribution of absorbing aerosol and clouds determines the net aerosol radiative forcing effect

15. Use of OMI near UV aerosol product for climate studies OMI Aerosol Index OMI’s near UV capability to detect absorbing aerosols over clouds is an excellent tool for the study of aerosol-cloud interactions: -Direct Effect -Semi-direct effect

16. Cloud fraction TOA forcing (Wm -2 ) Direct forcing effect of aerosols over clouds 0.86 0.90 0.93 SAFARI 2000 September Keil and Haywood, JGR,2003 The net radiative forcing effect of absorbing aerosols changes from cooling over cloud-free conditions to warming over cloudy scenes.

17. The semi-direct aerosol effect Aerosols absorb solar radiation  Evaporation of the cloud! Absorbing aerosols in and around a cloud Absorbing aerosols may reduce low cloud cover This would warm the climate as low clouds scatter solar radiation back to space.

18. Direct Radiative Forcing Effect of Absorbing Aerosols as seen by the A-train Aqua-CERES Aura-OMI Shortwave TOA FluxAerosol Index Reduced levels of SW Flux are observed in the CERES data associated with the presence of absorbing aerosols as indicated by OMI data April 14, 2006

19. Global Distribution of Stratocumulus Clouds Associated with cool ocean surfaces & subtropical anticyclones.

20. Summary OMI near UV algorithm performing reasonably well in spite of instrumental limitations. Best results obtained over arid and semi-arid regions where sub-pixel cloud contamination is minimum. The emerging multi-year OMI data set extends the TOMS record on aerosol Absorption. Work is needed to homogenize the combined TOMS-OMI record. Future Work -Integration of observations by other A-train sensors (Calipso, Modis) to improve accuracy of retrieval products. -New near-UV algorithm to retrieve aerosol absorption in the presence of clouds. -Reprocessing of TOMS and OMI records (same algorithm). -Evaluation of direct effect of absorbing aerosols over clouds. -Evaluation of semi-direct effect.