Numerical Simulation of Dry Ice Cloud Seeding Experiments

Abstract

The application of a two-dimensional, time-dependent cloud model to describe the effects of dry ice cloud seeding is demonstrated. A conservation equation and associated auxiliary equations for the mixing ratio of dry ice (CO2) are presented. The importance of identical time steps in both seeded and unseeded cases is discussed. Small convective clouds are seeded at about the ?10°C level and the seeding agent (CO2) traced as it falls through the cloud creating a mass of cloud ice in its trail. The cloud ice transforms to snow and the snow to graupel/hail which then melts into rain as it falls below the zero degree isotherm level. Precipitation starts about 6 min earlier in the seeded cloud and the timing of the rain fallout affects the interaction with a second cell. Approximately 20% more rain falls from the seeded cell in a very light shower.