Hail Formation via Microphysical Recycling

Abstract

It is suggested that alternation of low-density riming and wet growth processes play a role in hailstone formation. Such alternation of growth processes, which has been called microphysical recycling, is envisioned to operate in the following manner. During low-density riming growth, hailstones require reduced updraft velocities as compared to hailstones growing via classical high-density ice acquisition. During subsequent wet growth, water soaks into the previously acquired porous rime and on freezing produces hard, dense hailstones compatible with samples collected at the surface. Such a two-stage process lessens the dynamical requirements of hail formation. This article elucidates the microphysical recycling mechanism, cloud conditions necessary to initiate it, evidence that it is operational in the atmosphere, and the possible consequences of its existence with regard to hail suppression.