Laboratory Studies of Ice Vapor Growth in Static and Changing Environments

Cirrus and other high-altitude clouds are made of ice crystals that form at extremely cold temperatures. The crystals form and grow from water vapor, but the rate of growth and the different shapes that are formed are difficult to observe in nature. This award will allow researchers to control ice crystal growth in a laboratory setting, resulting in new knowledge about the role of changes in ice crystals due to environmental changes in temperature and humidity and impurities in the crystals. The primary societal impact of this research is through new data that can be used to improve numerical weather modeling. Additionally, there are training activities for students, new educational materials, and public outreach components of the project. This award will address questions that have arisen from prior research on ice crystal growth at temperatures colder than -20°C. The research team will use several laboratory chambers to make time-series measurements of growing crystals. A diffusion chamber and one vertical flow chamber will be used to grow isolated ice particles under precisely controlled conditions. The chambers will be used to determine the growth rates, and poorly known surface parameters, of crystals grown at temperatures between -20 to -70°C at atmospherically relevant supersaturations. The measured growth time-series will be used to critique and improve theories of ice growth, and improved theories will be used in cloud model parameterizations to explore the atmospheric consequences of laboratory-determined quantities. In particular, the research team will focus on questions related to: 1) The influence of solutions and heterogeneous nuclei on the growth of crystals, 2) Substrate crystal growth in a constant environment, and 3) Substrate crystal growth in a changing environment. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.