A Multisensor satellite-based assessment of biomass burning aerosol radiative impact over Amazonia

Using spatially and temporally collocated multispectral, multiangle and broadband data sets from the Terra satellite, the role of biomass burning ( BB) smoke particles on cloud-free top of atmosphere (TOA) direct shortwave aerosol radiative forcing (SWARF) is examined. A 5- year analysis during the peak biomass burning months of August and September is presented over South America (0 degrees-20 degrees S and 45 degrees W-65 degrees W). Our results indicate that over 5 years, the TOA diurnally averaged SWARF (DSWARF) from the Clouds and the Earth's Radiant Energy System (CERES) scanner ranges between -5.2 Wm(-2) and -9.4 Wm(-2) with a mean value of -7.6 Wm(-2) and an estimated uncertainty of +/- 1.4 Wm(-2). The corresponding Multi Angle Spectroradiometer (MISR) aerosol optical thickness (AOT at 0.558 mu m) ranged from 0.15 to 0.36 with a mean value of 0.24. The estimated mean TOA aerosol radiative forcing efficiency ( Et) is -44.2 Wm(-2)tau(-1) and is in good agreement with previous studies. We also examined the beta versions of the MISR data products such as the angstrom exponent (AE) and fraction of AOT in different size bins to assess the role of BB aerosol particle properties on SWARF. Our analysis indicates that the MISR retrieved 5 year mean AE is 1.54. Contribution to total AOT from small, medium and large particles is 66%, 16% and 18% respectively. This is the first multiyear assessment of SWARF for biomass burning aerosol particles using satellite observations alone and should serve as a useful constraint for numerical modeling simulations that estimate SWARF.