A Numerical Study of the Nature of the Glaciation Process

Abstract

A model is presented which simulates the glaciation of a cloud. In this model both vapor transfer and accretion processes are computed, the latter being treated stochastically. Two model clouds have been examined, one a modified continental cloud and the other a maritime cloud. These clouds have been seeded with ice crystal concentrations of 0.5, 10 and 500 liter?1. In all numerical experiments the resulting shape of the ice particle spectrum was a function of the initial water drop spectrum. At the lowest ice crystal concentration the rate of formation of ice in the clouds is relatively slow. The importance of the vapor transfer processes in the calculation is discussed and a comparison is made between this model and one that uses a continuous formulation for the accretion processes. From the point of view of the production of precipitation-size particles it appears that seeding a cloud with 10 ice crystals per liter would be the most productive of the three ice crystal concentrations tested. For the assumed cloud liquid water content of ?1 gm m?3 it is unlikely that even the largest seedings used in the experiments would initiate marked dynamical changes in the cloud by the glaciation process.