Surface and atmospheric forcing by anthropogenic aerosols: Insights from a model-observation intercomparison

The direct and indirect effects of aerosols have the potential to significantly redistribute energy between the surface and atmosphere. Ground- and satellite-based observations have detected aerosol-driven trends in surface solar radiation (SSR) in many regions of the Northern Hemisphere over the past several decades. In areas with primarily negative trends, such as India and China, observations also indicate that increased atmospheric absorption by aerosols may have played a large role in the attenuation of SSR. Such redistribution of energy between the surface and atmosphere can be expected to have a considerable effect on regional hydrological systems and circulation. Past generations of general circulation models (GCMs), however, have been largely unsuccessful at recreating observed trends in SSR, impeding our ability to investigate the causes and effects of these surface and atmospheric forcings in regional climate.

The IPCC AR5 generation of models, however, presents an advance over previous generations, particularly in aerosol processes. The Geophysical Fluid Dynamics Laboratory's CM3 general circulation model contains an updated aerosol treatment, which includes internal mixing of aerosols and interactive dry and wet deposition. Comparison of CM3 with observational data indicates that it performs better than the previous generation of GCMs at recreating the observed trend in SSR and the contribution of atmospheric absorption. We investigate which processes in the model are responsible for producing the trend and analyze the responses in regional climate to the aerosol-driven redistribution of energy between the surface and atmosphere.