The Role of Ice Growth/Evaporation Processes on the Ice Economy of Clouds

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This project consists of a broad range of laboratory experiments on the growth and evaporation of ice crystals and the analysis of existing cloud data collected by aircraft. One set of experiments will simulate the conditions of crystal growth in cirrus clouds. Modifications to an existing cloud chamber will permit temperatures as cold as -100 C, pressures as low as 1 mb, and supersaturations with respect to ice as high as 200%. The chamber will be modified to permit the examination of impurities, in particular oxides of nitrogen, on crystal habit. Results for these experiments will contribute to the understanding of crystal growth at the extreme conditions in cirrus clouds in the high atmosphere. Another set of experiments at temperatures around 0 C will be designed to study aspects of particle growth, melting, and evaporation relevant to the melting layer of snow. Emphasis will be on conditions with high supersaturations with respect to water, to simulate ice as it falls and melts in air with and without cloud droplets. Electrical effects and secondary ice production will be monitored. Data from the CALJET and SHEBA projects using the airborne "cloudscope" instrument will be compared with laboratory results on both the cirrus cloud and the melting layer simulations.