We propose a comprehensive validation and refinement of the GISS GCM aerosol climatology using global satellite data from MODIS, MISR, AVHRR, POLDER, and TOMS together with ground-based AERONET measurements. The GCM aerosol climatology consists of the principal tropospheric aerosol species (sulfate, nitrate, dust, sea salt, organic carbon, and black carbon) with their geographic, vertical, and seasonal distributions and variability obtained from chemistry-transport model simulations. The chemistry-transport model results are in the form of mass density distributions derived from emission rate inputs, incorporating the effects of atmospheric chemistry, simulated winds, and wet and dry deposition. The GCM treatment of aerosol radiative properties is based on Mie scattering results using laboratory measured refractive indices for individual aerosol species, including the effects of relative humidity for hygroscopic aerosols. Accordingly, the global values of aerosol optical depth, single scattering albedo, and asymmetry parameter, though strongly constrained by Mie scattering, are distinctly dependent on aerosol size - a parameter that is poorly constrained. The current GCM treatment relies on specified aerosol dry sizes to yield reasonable agreement with available observational constraints. A comparison of GCM aerosol optical depths and Angstrom exponent to MODIS, MISR, POLDER, and AVHRR data has shown that in the current GCM aerosol climatology the specified sizes are too large. In our earlier study of this problem, we found that although there are large differences in retrieved aerosol optical depth between the different stellite instruments, there is more or less general agreement on the seasonal variability of aerosol optical depth, and that the observed seasonal variability in aerosol optical depth and Angstrom exponent can be used as a powerful constraint to critically evaluate the chemistry-transport model results. This proposal emphasizes the intercomparison of data from MODIS, MISR, POLDER, and AVHRR measurements and a least-squares application of the seasonal variability of aerosol optical depth and Angstrom exponent variability to constrain chemistry-transport model results on a regional basis.
