ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-9819-2010 Direct and semi-direct impacts of absorbing biomass burning aerosol on the climate of southern Africa: a Geophysical Fluid Dynamics Laboratory GCM sensitivity study Randles C. A. 1 3 Ramaswamy V. 1 2 Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, USA NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA now at: Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore County and NASA GSFC Code 613.3, Greenbelt, Maryland, USA 19 10 2010 10 20 9819 9831 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/9819/2010/acp-10-9819-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/9819/2010/acp-10-9819-2010.pdf

Tropospheric aerosols emitted from biomass burning reduce solar radiation at the surface and locally heat the atmosphere. Equilibrium simulations using an atmospheric general circulation model (GFDL AGCM) indicate that strong atmospheric absorption from these particles can cool the surface and increase upward motion and low-level convergence over southern Africa during the dry season. These changes increase sea level pressure over land in the biomass burning region and spin-up the hydrologic cycle by increasing clouds, atmospheric water vapor, and, to a lesser extent, precipitation. Cloud increases serve to reinforce the surface radiative cooling tendency of the aerosol. Conversely, if the climate over southern Africa were hypothetically forced by high loadings of scattering aerosol, then the change in the low-level circulation and increased subsidence would serve to decrease clouds, precipitation, and atmospheric water vapor. Surface cooling associated with scattering-only aerosols is mitigated by warming from cloud decreases. The direct and semi-direct climate impacts of biomass burning aerosol over southern Africa are sensitive to the total amount of aerosol absorption and how clouds change in response to the aerosol-induced heating of the atmosphere.

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