Hydrodynamic Behavior and Growth Processes of Large Ice Particles in Clouds

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Accurate knowledge of the fall behavior and the growth of large ice hydrometeors are necessary for understanding the thunderstorm processes and the numerical modeling of them. They are also of fundamental importance to the study of cloud physics. These processes include the riming growth of graupel and hail, collision between graupel/hail and ice crystals, and the aggregation of snowflakes. They occur in deep convective clouds and it influences the further development of such clouds due to its thermodynamic and dynamic effects. The ice crystal-graupel collision is known to be connected with the electrification of thunderclouds. Hail damage costs billions of dollars annually to agriculture and properties. Snow aggregates dominate the anvil process in storms. Quantitative knowledge of these processes is necessary for accurate weather and climate predictions, but so far this is poorly understood.Intellectual Merit:This project will perform a numerical study to investigate the fall behavior and diffusion and collisional growth of large ice particles (graupel, hail, rimed crystals and snow aggregates) for a wide variety of ice particle types, shapes and sizes. Numerical models will be developed to simulate the fall behavior of these large ice particles as they accrete other particles while changing their shapes. Collision growth models will also developed to study the collision growth rates of them due to accretion of supercooled droplets or ice particles. The former involves solving numerically the relevant Navier-Stokes equations to obtain the flow field of the falling particle that may perform complex motions such as translation, vibration, rotation, etc. The equation of motion of the supercooled droplets or ice particles around the falling ice particle will be solved so as to determine the trajectory and hence the collision efficiency. The computation of the ventilation coefficient of the falling ice particle will be conducted and the convective diffusion equation of water vapor around the ice particles will be solved to determine their diffusion growth rates.The results from the study will fill a major gap in this fundamental area of cloud physics and provide necessary quantitative information on how these processes operate in clouds.Such information can be used by a cloud resolving model to design better ice growth parameterizations to understand better the convective cloud dynamics. They can also be used by larger scale weather/climate models to improve their parameterizations to minimize the prediction uncertainties. Better models will allow forecasters to make better forecasts on severe storms.Broader Impacts:The results of the study will have direct impact to our society as they will be applicable to enhance our capability of weather and climate predictions through the use of mesoscale cloud resolving models and larger scale numerical weather/climate prediction models. The research activity will help training graduate students and young scientists who will contribute to atmospheric science research. The research results will be disseminated in scientific journals, meetings, and public lectures so that wider audience becomes aware of them.