Radiative Forcing of a Tropical Direct Circulation by Soil Dust Aerosols

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Abstract
The effect of soil dust aerosols upon the tropical climate is estimated by forcing a simple model of a tropical direct circulation. The model consists of a region vertically mixed by deep convection and a nonconvecting region, for which budgets of dry static energy and moisture are constructed. Dynamical effects are included implicitly, by prohibiting horizontal temperature contrasts above the boundary layer. Dust aerosols absorb sunlight to a greater extent than industrial sulfate and sea-salt aerosols. In a companion study, where the climate response to dust is calculated using an atmospheric general circulation model, the global-average dust radiative forcing is negligible at the top of the dust layer, in comparison to the large reduction of the net flux at the surface. Thus, dust aerosols redistribute radiative heating from the surface into the dust layer, unlike industrial sulfates and sea salt, which through reflection reduce the total radiative energy gained by the column. The simple model... Abstract The effect of soil dust aerosols upon the tropical climate is estimated by forcing a simple model of a tropical direct circulation. The model consists of a region vertically mixed by deep convection and a nonconvecting region, for which budgets of dry static energy and moisture are constructed. Dynamical effects are included implicitly, by prohibiting horizontal temperature contrasts above the boundary layer. Dust aerosols absorb sunlight to a greater extent than industrial sulfate and sea-salt aerosols. In a companion study, where the climate response to dust is calculated using an atmospheric general circulation model, the global-average dust radiative forcing is negligible at the top of the dust layer, in comparison to the large reduction of the net flux at the surface. Thus, dust aerosols redistribute radiative heating from the surface into the dust layer, unlike industrial sulfates and sea salt, which through reflection reduce the total radiative energy gained by the column. The simple model...

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