Structures and Formation Mechanisms of Snow Polycrystals

Abstract

On the basis of the three dimensional Coincidence-Site Lattice (CSL) concept and the formation of an ice germ with a cubic structure in nucleation process, structures and formation mechanisms of a variety of snow polycrystals in nature are systematically explained.
When each component of poly initial-crystal, which is originated from a cubic ice germ and the subsequent growth in hexagonal structure on its { 111 } faces grows independently, snow polycrystals are formed as a "regular" assemblage of single crystals. While, under the conditions of low temperature and low supersaturation, growth of the initial-crystal may be controlled by a new growth mechanism in which a CSL boundary acts as a successive source of growth steps, so that the formation of snow polycrystals with a specific boundary as a crossed-plate crystal becomes more preferential.