Do spaceborne aerosol observations limit the accuracy of modeled surface solar irradiance

Aerosols play a primary role in the global climate system and the solar radiation budget at the Earth surface. Here we analyze the role of spaceborne aerosol observations and their uncertainties in the expected accuracy of the modeled cloudless surface shortwave downward radiation using a state-of-the-art numerical weather prediction model over the continental U.S. We compare five different modeling approaches for the aerosol optical effects with differing sophistication. Overall, we show that, counterintuitively, the direct and diffuse irradiances predicted by solar radiation models that use empirically adjusted fixed aerosol extinction may be more accurate than more sophisticated radiative transfer models that require inputs of aerosols. We conclude that, compared to ground observations, the mean absolute error in satellite-retrieved aerosol optical depth over the U.S., and possibly elsewhere, should be reduced to less than 0.025 aerosol optical depth unit to assure improvement over the predictions of a simpler, aerosol-insensitive radiation model.