Direct Radiative Effect of Major Aerosol Types Derived From MODIS Over Ocean

Accurate calculation of direct radiative effect of aerosol (DREA) at the top of atmosphere (TOA) is important to understand climate effect of aerosol. It is thought that the DREA is cooling effect at TOA in global average, however, DREA efficiency defined by DREA of unit aerosol optical thickness (AOT) is different for aerosol optical properties and even the sign could be opposite depending on aerosol optical properties and underlying surface albedo. To quantify accurately these effects from nadir-viewing satellite observation, aerosol classification algorithm should be taken into account in aerosol remote sensing algorithm. In this study, aerosol remote sensing algorithm including aerosol type classification procedure is proposed and DREA of major aerosol types, that is dust, black carbon, seasalt, and sulfate, at TOA is derived from Moderate Resolution Imaging Spectroradiometer (MODIS) over ocean. The derived annual mean DREAs show distinctly large negative value over west coast of Africa, the circumference of the Asian continent and the Antarctic continent. The west coast of Africa is affected by dust and black carbon aerosol from Sahara Desert and biomass burning from South Africa, the circumference of the Asian continent is affected by dust, black carbon, and sulfate from desert, biomass burning, and huge anthropogenic activity, and near the Antarctic continent is affected by enhanced seasalt by strong wind in boreal winter. The DREA efficiency show seasonal variation due to different fraction of aerosol types in each season. The DREA of major aerosol types derived in this study could help to understand more the climate effect of each aerosol type.