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List of Abstracts 76P-Chemistry Climate.33 ID:4559 15:35Ice Crystal Number Concentration Sensitivity Heterogeneous Freezing: A Global Modeling StudyDonifan Barahona, Athanasios NenesGeorgia Institute of TechnologyContact: donifan@gatech.eduThis study presents the sensitivity of ice crystal concentration, N c , to the competition between homogeneousand heterogeneous freezing using predictions of ice nuclei (IN) concentration derived from theoreticalconsiderations and field campaign data. For this, a physically-based, analytical, ice microphysicsparameterization is implemented into the NASA Global Modeling Initiative (GMI) chemical and transportmodel. When competition between homogeneous and heterogeneous freezing is considered, global mean N cvary by factor of 20 depending on the heterogeneous freezing spectrum used. IN effects on N c are highlydependent on local dust and black carbon concentrations and most important under conditions of weakupdraft and high temperature. Regardless of the heterogeneous spectrum used, dust is an importantcontributor of IN over large regions of the northern hemisphere. Black carbon aerosol have an appreciableeffect on N c for freezing fractions greater than 1%. It was found that only cloud formation scenarios wherecompetition between homogeneous and heterogeneous freezing is the dominant feature would result in aglobal distribution of maximum supersaturation consistent with observations.P-Chemistry Climate.34 ID:4130 15:35A one dimensional cloud model with trimodal convective outflowIan FolkinsDalhousie UniversityContact: Ian.Folkins@dal.caConvection has a strong impact on the distribution of chemical species, especially in the tropics. In mostglobal models, the effects of convection are parameterized rather than explicitly simulated. The results of anew one-dimensional convective cloud model, intended to be used as a convective parameterization, aresummarized. The relationships between penetrative downdrafts, congestus outflow, and stability in the lowertropical troposphere are discussed, as well as some of the implications for the transport of trace species.P-Chemistry Climate.35 ID:4372 15:35Climatic impact of Saharan dust Aerosol on a west Africa/ tropical east Atlantic regionFabien Solmon 1 , Nellie Elguindi 1 , Marc Mallet 1 , Ashraf Zakey 2 , Filippo Giorgi 21 Laboratoire d'Aérologie CNRS/UPS2 Abdus Salam ICTPContact: solf@aero.obs-mip.frWe investigate the climatic impact of shortwave and longwave radiative forcing of Saharan dust on the WestAfrican monsoon and Sahel precipitation using a regional climate model interactively coupled to a dustmodel and running for the period 1996-2006. Two competing effects are found. First a reduction of monsoonintensity in the lower troposphere induced by the dust surface cooling causes a reduction of precipitation,and second an ‘elevated heat pump effect’ in the higher troposphere induced by the dust diabatic warmingcauses an increase of precipitation. The net impact of these effects is a reduction of precipitation over mostof the Sahelian region (by about 8 % on average) except over a Northern Sahel - Southern Sahara band,where precipitation increases. This pattern is shown to be very sensitive to dust absorbing properties. Overthe Atlantic ocean (dust outflow region), the heat pump effect is predominant resulting in a northward shiftiCACGP-IGAC 2010 12 July, 2010