On the Theory of Formation of a Sandwich Structure of a Spherical Hailstone

Abstract

The paper analyzes the motion of the crystallization front under laminar and turbulent conditions of film motion on a hailstone surface. It is shown that the transition from one structure of ice to another is determined by both the equilibrium critical thickness of the film and the generalized Maclean parameter. A relation between them has been established. An expression for Kachurin's critical water content q _K defining the dry–wet transition of the hailstone growth has been obtained. It is shown that the Schumann–Ludlam critical water content q _Sch–L gives only that value of the critical content at which droplets settled on the hailstone freeze. If q _Sch–L < q < q _K, then a film is formed on the hailstone surface, but it is in an unstable state and, in the course of time, disappears, and the wet regime of the hailstone changes into the dry one. The hailstone will grow in the wet regime only at q > q _K.