A four year record of Aerosol Absorption measurements from OMI near UV observations

Omar TorresDepartment of Atmospheric and Planetary Sciences

Hampton University, Hampton, Va, 23668

Changwoo AhnSSAI, Inc, Lanham, MD, USA

Santiago GassoGEST 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 MeetingFinland, HelsinkiJune 24-27, 2008

Validation of Collection 3 OMAERUV Product

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.

Evaluation of extinction AOT using AERONET observations(non-absorbing aerosols)

Retrievals of non-absorbing aerosols are significantly noisier. Overestimates andunderestaimates are associated to the OMI large footprint.

OMAERUV-Aeronet ComparisonMonthly Averages

Absorbing Aerosols Non-absorbing aerosols

Noise level significantly reduced when comparing monthly averaged data

Absorption by Brazilian and African Savanna smoke

RMS=0.03

(Africa)(Brazil)

Assessment of OMI Aerosol Absorption ProductComparison to AERONET Retrievals

Emerging OMI record on Aerosol Absorption

DJF MAM JJA SON

Seasonal Averages of Aerosol Absorption (OMI 2006)Single Scattering Albedo

Absorption Optical Depth

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

Eastern EuropeWestern 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

Southeast United States

OMI Multiyear record on Aerosol Absorption:A Regional Analysis

Brazil Central Africa

OMI Multiyear record on Aerosol Absorption:A Regional Analysis

Use of OMI near-UV aerosol product in Climate studies

Figure from Keil & Haywood (JGR, 108, 2003)

Aerosol- cloud Interaction

The relative vertical distribution of absorbing aerosol and cloudsdetermines the net aerosol radiative forcing effect

Use of OMI near UV aerosol product for climate studies

OMI Aerosol Index

OMI’s near UV capability to detect absorbing aerosols over clouds isan excellent tool for the study of aerosol-cloud interactions:

-Direct Effect-Semi-direct effect

Cloud fractionTO

A fo

rcin

g (W

m-2)

Direct forcing effect of aerosols over clouds

0.860.90

0.93

SAFARI 2000September

Keil and Haywood, JGR,2003

The net radiative forcing effect of absorbing aerosols changes from coolingover cloud-free conditions to warming over cloudy scenes.

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.

Direct Radiative Forcing Effect of Absorbing Aerosols as seen by the A-train

Aqua-CERES Aura-OMI

Shortwave TOA Flux Aerosol Index

Reduced levels of SW Flux are observed in the CERES data associated with thepresence of absorbing aerosols as indicated by OMI data

April 14, 2006

Global Distribution of Stratocumulus Clouds

Associated with cool ocean surfaces & subtropical anticyclones.

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 aerosolAbsorption. 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.