Laboratory study of immersion and evaporative droplet freezing in the Leipzig Aerosol and Cloud Interaction Simulator

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Ice formation in clouds influences all major cloud characteristics of interest: precipitation formation, interactions with radiation, latent heat release and cloud dynamics, chemical processes, charge separation, water vapor content, icing potential, gas and particle scavenging water redistribution, and others. Yet, it is poorly understood, because historic measurements in clouds have lacked the resolution to adequately sample early ice in clouds or the nuclei that influence its formation and because particle/droplet histories are not well characterized. Systematic laboratory studies are required to advance our understanding. Whereas such studies cannot elucidate all ice-related cloud processes we expect the new Leipzig Aerosol Cloud Interaction Simulator LACIS to be able to simulate accurately the processes of immersion and evaporative droplet freezing, which is the subject of the present proposal. For the study of these processes dedicated optical sensors need to be developed for LACIS in order to determine droplet freezing and accompanying particle characteristics. Consequently, the first part of the project covers the development of two new optical instruments for LACIS. The second part of the project focuses on the modification of LACIS for the study of immersion and evaporative droplet freezing, experiments with different well-characterized aerosol/cloud systems and the interpretation of the experimental results with a numerical model of LACIS. From these interpretations microphysical expressions and/or parameterizations for immersion and evaporation freezing processes can be evaluated/developed and made available for use in large scale models.