Laboratory Studies of Vapor Grown Ice at Low and High Supersaturations

Clouds that consist of ice crystals, such as cirrus, have a significant impact on weather and climate because of their role in interacting with incoming or outgoing radiation. However, there is still a significant amount of uncertainty about the processes that impact ice crystal growth from water vapor at very high altitudes and cold temperatures. This project will conduct laboratory-based measurements of ice crystal growth at temperatures of colder than -40 degrees to reduce uncertainties and provide information that can be used in weather and climate models. This award will also support multiple students and the creation of software for classroom use, thereby training the next generation of scientists. The research team will continue their studies of the growth of ice in laboratory chambers. The overarching goal of the work is to use measurements to estimate characteristic supersaturations and effective densities at low temperatures, and at low to high supersaturations. The resulting growth data will reduce uncertainties in calculating vapor growth rates at low temperatures and could be used to develop new parameterizations suitable for microphysical models. Specifically, the research plan is to: 1) Measure the dimensional growth rates of ice crystals grown from the tip of a single capillary at temperatures below -40°C and at a range of supersaturations using a diffusion chamber constructed for capillary studies. This would result in characteristic supersaturation and effective density measurements for faceted growth under -40°C. 2) Explore high supersaturation growth through the use of a levitation diffusion chamber and capillary diffusion chamber. This would result in a measure of growth rates that result from branching and hollowing of ice as it forms. 3) Measure the rate of facet development on the surface of frozen water droplets using a new growth chamber. 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.