Laboratory and Modeling Studies of the Growth Efficiency of Vapor Grown Ice

Cirrus clouds exist in extremely cold conditions where there is very little moisture. The pathways for the growth of ice particles that make up cirrus and other cold clouds is complex, and there are gaps in the understanding of how these crystals increase in size and mass. This award will focus on vapor growth, which is the process in which water vapor is deposited onto ice crystals. The research team runs a very specialized cloud chamber that allows for the testing of the growth of individual crystals at extremely cold temperatures. The main benefit of this research is to provide a check on numerical models that simulate cold clouds and to provide input parameters to those models. This will have an impact on societally-relevant weather forecasts and climate projections. The project will also help to train the next generation of scientists and provide interesting outreach opportunities to increase public science literacy. The research team will continue their studies into the growth of ice crystals in atmospheric cold clouds. The focus of the work is on addressing a critical gap in the understanding of the deposition coefficient at very cold temperatures. The work will make use of a levitation diffusion chamber and vertical flow levitation chamber to grow ice crystals in different conditions. The lab data will be used synergistically with existing and new theoretical models to derive input parameters for cloud models. The specific objectives of the work are to determine: 1) Whether it is a robust result that the deposition coefficients cover a larger range for homogeneously frozen drops than heterogeneously frozen drops, 2) Whether characteristic supersaturations extracted from the levitation diffusion chamber follow the values estimated from prior measurements at temperatures below -40C, 3) If growth transitions are unique to homogeneously frozen drops and whether a model of the process can be constructed, and 4) Whether a power law parameterization of kinetics-diffusion limited growth can be constructed based on fits to laboratory data. 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.