On the physical meaning of the critical equilibrium thickness of a film on the hailstone surface

The currently available theories of hailstone growth explain the layered structure of hailstones in two ways. Kachurin has shown that the layered structure of ice covering an object placed in the flow of a supercooled water aerosol is determined by the equilibrium thickness of the film. The other approach is based on solving the equation of heat balance on the hailstone surface and uses the notion of the critical liquid water content in a cloud. The meaning of the critical equilibrium thickness of the film is elucidated, and a relation between two existing criteria for the dry-wet hailstone growth transition is established.