Including Surface Kinetic Effects in Simple Models of Ice Vapor Diffusion

Abstract

model for kinetically limited vapor growth and aspect ratio evolution of atmospheric single ice crystals is presented. The method is based on the adaptive habit model of J. Chen and D. Lamb but is modified to include the deposition coefficients through a theory that accounts for axis-dependent growth. Deposition coefficients are predicted for each axis direction based on laboratory-determined critical supersaturations and therefore extends the adaptive habit approach and the capacitance model to low ice supersaturations. The new model is used to simulate changes in single-crystal primary habit in comparison to a hexagonal growth model. Results show that the new model captures the first-order features of axis-dependent, kinetically limited growth. The model reproduces not only the strong reductions in growth as supersaturations decrease but is also able to reproduce the near cessation of minor axis growth as saturations decline. While the new model reproduces the qualitative features of kinetically limited growth, relative errors are generally between 5% and 20% but can become larger than 50%. Parcel model simulation comparisons show that the new growth method reproduces the general features of axis-dependent growth in a changing temperature environment. The method also produces relatively accurate estimates of mass evolution with spherical particles, indicating that it may have broad applicability. Although the model compares well to a detailed method, uncertainties remain in the knowledge of surface kinetics that future studies need to unravel.