Atmos. Chem. Phys. Discuss., 10, 9731-9752, 2010
www.atmos-chem-phys-discuss.net/10/9731/2010/
doi:10.5194/acpd-10-9731-2010
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under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Impacts of absorbing biomass burning aerosol on the climate of southern Africa: a Geophysical Fluid Dynamics Laboratory GCM sensitivity study
C. A. Randles1,* and V. Ramaswamy1,2
1Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, USA
2NOAA 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

Abstract. 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. Warming from cloud decreases mitigates surface cooling associated with scattering-only aerosols.

Citation: Randles, C. A. and Ramaswamy, V.: Impacts of absorbing biomass burning aerosol on the climate of southern Africa: a Geophysical Fluid Dynamics Laboratory GCM sensitivity study, Atmos. Chem. Phys. Discuss., 10, 9731-9752, doi:10.5194/acpd-10-9731-2010, 2010.
 
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