A Numerical Study of the Growth of Large Ice Hydrometeors

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The growth of large ice hydrometeors is a central problem in cloud physics and one that potentially has great impacts on a wide variety of atmospheric processes, particularly in the context of deep convective (thunderstorm-type) clouds. These impacts include the rate and location of riming growth of graupel and hail and the aggregation of snowflakes, which in-turn influence cloud development and ensuing production of precipitation ultimately reaching the ground. The growth of graupel is known to be connected with the electrification of thunderclouds, while costs of hail damage to property and agriculture runs into billions of dollars annually. Snow-related processes impact thunderstorm anvil structures, which have important downstream radiative impacts. Quantitative knowledge of all of these processes and their interactions are required for accurate weather and climate predictions, yet understanding of these processes on the scale of individual particles and their interactions remains limited.This investigator will utilize a commercially available computational fluid dynamics package to solve the Navier-Stokes equation for flow around a target ice particles whose surfaces are defined by an analytical expression, and thereby gain improved descriptions of the collisional growth of large ice particles (in particular graupel and snow aggregates). Numerical models of the fall behavior of these large ice particles as they are accreting other particles (either supercooled droplets or another ice particle) and hence changing their shapes will be developed, as will collisional-growth rate models. Complex combinations of various modes of particle motion including as translation, vibration, and rotation will be explicitly represented so as to more accurately characterize particle trajectories, ventilation coefficients and associated collision efficiencies applicable to real clouds. The intellectual merit of this work centers on an improved understanding of cloud microphysical interactions applicable to convective clouds. Broader impacts will include student education and, ultimately, the potential for improved interpretation of cloud observations through a variety of operational and anticipated research-mode measurements including storm-penetrating aircraft.