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List of Abstracts 72P-Chemistry Climate.26 ID:4186 15:35Aerosol-climate interactions over southern Africa: interannual variability and the role of ENSOFiona Tummon 1 , Fabien Solmon 2 , Cathy Liousse 2 , Mark Tadross 3 , Bruce Hewitson 31 Laboratoire d'Aerologie / Climate Systems Analysis Group2 Laboratoire d'Aerologie3 Climate Systems Analysis GroupContact: tumf@aero.obs-mip.frSouthern Africa is a region that experiences high interannual climatic variability. It is also a region that, ingeneral is under-developed, has high population growth and is at times politically unstable. As a whole, theregion is extremely vulnerable to climatic changes, with a large proportion of the population depending onrain-fed agriculture as a source of income and subsistence. It is well known that the El Niño/SouthernOscillation contributes significantly to climate variability over much of southern Africa. This in turn effectsvegetation growth, and as a result the extent of biomass burning in the following dry season; with aboveaveragewet seasons leading to increased burning, and drier than average seasons being followed by lessextensive burning.The savannas of Africa experience some of the most extensive burning in the world, and contribute asignificant portion of the aerosol loading over southern Africa during the austral winter season, from Junethrough October. At present, the climatic impact of these aerosols over southern Africa is poorly understood,particularly in terms of their interannual variability. In order to further investigate these impacts, theRegCM3 model is used in conjunction with emissions developed at the Laboratoire d’Aerologie.Preliminary results indicate that the impacts of the direct aerosol effect on regional temperature, precipitationand circulation patterns vary between El Niño and La Niña years. Surface temperature decreases during thepeak biomass burning season in all years, but more significantly in years with increased burning (generallyfollowing La Niña years). Climatic signals are also visible away from the major aerosol source regions, inthe so-called 'river of smoke', the main exit passage of air from the region out to the Indian Ocean. Thisoutflow pathway shifts northwards during La Niña periods, and southwards during El Niño periods, with theassociated climatic impacts shifting correspondingly.P-Chemistry Climate.27 ID:4245 15:35A global modeling study on carbonaceous aerosol microphysical characteristics and radiative forcingSusanne BauerNASA GISSContact: sbauer@giss.nasa.govRecently, attention has been drawn towards black carbon aerosols as a short-term climate warmingmitigation candidate. However the global and regional impacts of the direct, cloud-indirect and semi-directforcing effects are highly uncertain, due to the complex nature of aerosol evolution and the way that mixed,aged aerosols interact with clouds and radiation. A detailed aerosol microphysical scheme, MATRIX,embedded within the GISS climate model is used in this study to present a quantitative assessment of theimpact of microphysical processes involving black carbon on aerosol cloud activation and radiative forcing.Our best estimate for net direct and indirect aerosol radiative forcing between 1750 and 2000 is -0.56 W/m2.However, the direct and indirect aerosol effects are quite sensitive to the black and organic carbon sizedistribution and consequential mixing state. The net radiative forcing can vary between -0.32 to -0.75 W/m2depending on these carbonaceous particle properties at emission. Assuming that sulfates, nitrates andsecondary organics form a coating around a black carbon core, rather than forming a uniformly mixediCACGP-IGAC 2010 12 July, 2010