Anthropogenic Aerosol Effects on Cirrus Clouds

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This study examines the effects of anthropogenic aerosols on ice processes in the atmosphere. The PIs will use a global atmospheric general circulation model (GCM) coupled with an aerosol model. Parameterizations of heterogeneous ice nucleation processes (immersion freezing and deposition nucleation) will be developed and implemented together with an existing parameterization for homogeneous freezing in the climate model. The climate forcing due to the anthropogenic effects on cirrus clouds will be estimated, and the importance of heterogeneous versus homogeneous ice nucleation in the upper troposphere will be addressed. The effect of aircraft emitted soot particles will be studied in comparison with soot and other sources of ice nuclei from the earth's surface. The broader impacts of this project include: (1) that this is a policy-relevant study that will be widely disseminated because of its direct relevance to uncertainties in climate forcing and, hence, climate change, and will thereby benefit society; (2) that results learned here will be incorporated into the aerosol microphysics course offered by Dr. Penner; and (3) that graduate students will be trained through the project.