CAREER: Laboratory Studies of Small-Scale Processes in Clouds

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The research component of this CAREER grant consists of laboratory investigations of two kinds of small-scale processes that are important for the formation and growth of water droplets in natural clouds: (1) kinetic effects, as characterized by the accommodation coefficient and the condensation coefficient, that determine the rates of exchange of heat and mass between a drop and its environment; (2) effects of small-scale turbulence on the interactions between drops and the humidity of their environment. The study of kinetic effects are conducted using an electrodynamic levitation cell coupled with an environmental control chamber that enables the observation of individual cloud particles. The effects of turbulence are carried out using an expansion chamber that includes provision for creating turbulence of variable intensity using internally mounted fans. Objectives of the research include (1) independent measurement of the accommodation coefficient and the condensation coefficient of pure water drops and solution drops over a range of temperature and pressure corresponding to conditions in the atmosphere; (2) studies of turbulence-induced humidity fluctuations on the growth rates of drops, using observed efflorescence of solution droplets as indicators of humidity fluctuations below a predetermined threshold. Results of the experiments will be a better understanding of the small scale processes in clouds that are precursors to the formation of precipitation. The educational component of the grant emphasizes undergraduate research. It consists of (1) working with teams of undergraduate students in the design, construction, and deployment of simple instruments for atmospheric measurements as part of the Midwest Rockets for Schools Program of Michigan Technical University and (2) mentoring upper-level undergraduates in laboratory research projects in cloud physics as part of the physics department's senior thesis program.