A Numerical Investigation of Collision Efficiencies of Simple Ice Plates Colliding With Supercooled Water Drops

Abstract

The hydrodynamic interaction between simple ice plates, idealized as oblate spheroids of axis ratio 0.05, and water drops, assumed to be spherical, was numerically investigated for atmospheric conditions of ?10C and 700 mb. The ice plates had semi-major axis length between 147 and 404 µm and the water drops had radii up to 53 µm. Since the ratio of the mass of the drop to the mass of the crystal was small, the superposition model was found to be satisfactory. The flow fields around drops were those of LeClair et al., and the flow fields around oblate spheroids were those of Pitter et al. From the trajectories of the water drops relative to the ice crystals, collision efficiencies were determined. The model predicts preferential riming of the drops at the edges of crystals under certain conditions, in agreement with field observations in atmospheric clouds.