Effects of Natural Dust and Sulfate on Atmospheric Circulation and Radiation in CESM 1.0: Comparison of Prescribed v. Interactive Emissions Schemes

Atmospheric aerosols originate from a variety of natural and anthropogenic sources, and induce significant changes to Earth's radiative budget. These changes can be realized directly (when aerosols scatter, reflect and absorb solar radiation) or indirectly (when aerosols seed clouds, thereby influencing cloud albedo and cloud lifetime). Using CESM 1.0, a fully-coupled climate model with a uniquely realistic multi-modal aerosol scheme embedded in its atmospheric component, we analyze two new 150-year pre-industrial control runs with different aerosol emissions schemes. The first run treats aerosol emissions at each timestep interactively (allowing aerosols to interact in the atmosphere), while the second run prescribes aerosol emissions at each timestep using climatological fields as model input. Our comparative analysis focuses on the relationship between aerosol concentrations and emissions to cloud properties in each run, including cloud droplet number concentration, and to subsequent precipitation. In addition, we examine changes in atmospheric circulation associated with high and low aerosol months and years in each run. Finally, we relate regional aerosol properties in each run to lower frequency coupled ocean-atmosphere phenomena, with particular focus on decadal fluctuations of Pacific circulation and sea surface temperature.