Lattice Boltzmann simulation of snow crystal growth in clouds

[1] The Lattice Boltzmann (LB) method can be used to simulate aspects of chemical reactions such as mineral precipitation from a fluid phase or condensation from a vapor phase. The LB method has the advantage of allowing the shape of the condensing phase to evolve depending on local conditions rather than being specified, so that the controls on condensed phase grain shape can be studied simultaneously with the controls on chemical composition and growth rate. We have used the LB approach to simulate the growth of ice crystals from water vapor-oversaturated air as a first step in developing methods for treating more complex chemical reaction problems, including isotopic effects. The formation of ice crystals (i.e., snow) in air is a classic problem in diffusion-limited crystal growth. There are many complexities, but the process is attractive for modeling purposes because it involves only one chemical component and there is abundant information on reaction kinetics and the relationships between crystal morphology and growth conditions. In this paper we describe the LB approach used, and address strategies for properly conserving mass at a surface of a growing ‘‘crystal,’’ the scaling of the calculations to the actual physical problem, and the conditions for growth of dendritic versus compact crystals.