Evolution of Shapes, Sizes and Impurity Contents of Ice Particles in Cirrus Clouds

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Baker/Abstract 9704156 The PI plans to use a single crystal evolution model developed in collaboration with Dr. J. Nelson to investigate the vapor growth and sublimation of individual ice crystals in realistic atmospheres. This model produces steady state growth shapes and predicts the conditions under which the crystals are hollow. The model will be run with SO2 as well as water vapor in the particle environment to study the simultaneous takeup of the two gases. The chemical composition of the ensuing particles will be examined as a function of assumed ice nucleus content as well as environmental gas concentrations, temperature and pressure. After the single study is completed, the results will be used in a Lagrangian parcel study of the evolving characteristics (size and chemical composition distributions) of ice particle populations in realistic atmospheres This work will be carried out in informal collaboration with Dr. Nelson (U. Arizona), with Dr. T. Peter and his colleagues at the MPI fur Chemie in Mainz, who are studying takeup of SO2 on single crystals in the laboratory, and with Dr. Noone and his collaborators rom Stockholm University, who will be collecting in situ data on microphysical evolution in cirrus clouds. These studies will be useful in providing a self-consistent picture of cirrus particles, and will add physical realism to the models now used, which are based largely on spherical particle analogues and do not incorporate modern ideas on the crystal/vapor interface. The final stage of the study will be the comparison of the new models with the parameterizations used in GCM's to assess the usefulness of the parameterizations.