Improving GCM Aerosol Climatology using Satellite and Ground-Based Measurements

A physically based aerosol climatology is essential to address the questions of global climate changes. We use available satellite and ground-based measurements, i.e., moderate-resolution imaging spectroradiometer (MODIS), multiangle imaging spectroradiometer (MISR), Polarization and Directionality of the earth’s Reflectance (POLDER), advanced very high resolution radiometer (AVHRR), and Aerosol Robotic Network (AERONET) data, to characterize the geographic distribution and seasonal variability of aerosol optical depth and size. The Ångström exponent is used as a measure of aerosol size. Although large discrepancies exist between different datasets, particularly for the Ångström exponent, the measurements point to a need for reducing the aerosol effective radii specified in the global climate model (GCM) from the nearly 1.0 micron average value to about 0.2 or 0.3 microns, as suggested by the observed Ångström exponent. Incorporating this change in aerosol effective radius also improves the agreement for the aerosol optical depth between satellite measurements and the Goddard Institute for Space Studies (GISS) GCM aerosol climatology. As a consequence, the radiative forcing due to aerosol under clear-sky conditions is increased by about 30%.