Calculations of Hailstone Growth and Trajectories in a Simple Cloud Model

Abstract

A hailstone model is developed which simulates both wet and dry hailstone growth and partial or complete melting as the hailstone falls to the ground. The simulation is obtained by a consideration of the mass and heat budgets of the hailstone as a function of its size and of the environmental conditions. Competition among hailstone embryos is not treated in this model. The hailstone model has been run in over 50 versions of a one-dimensional, time-dependent cloud model to derive estimates of maximum hailstone size from a wide variety of convective storms. The model suggests that hailstone diameter at the ground is determined closely by the strongest updraft encountered by the stone and the temperature at that level. In the model, most hailstones spend some time above the maximum updraft and significant growth occurs during descent from that level to the freezing level. A comparison of model predictions to hailstone observations in the Rapid City area during 1968 and 1969 shows fair agreement. The model has been used to test the concept of hail suppression through artificial glaciation of cloud water and rainwater. It suggests that results would vary with temperature at the level of maximum updraft, but that artificial cloud glaciation would lead in a majority of cases to a reduction in maximum hailstone size at the ground.