The Effect of Dry-Ice Pellet Velocity on the Generation of Ice Crystals

Abstract

The influence of fall velocities of dry-ice pellets on the nucleation of slightly supercooled clouds is discussed and the conditions necessary for the production of ice crystals are examined. A theoretical argument is presented, which suggests that when cloud temperatures are warmer than about ?5C, the number of ice crystals produced by a pellet of dry ice moving at its terminal velocity decreases rapidly as the temperature approaches 0C. In contrast to the pellet moving at terminal velocity, it is shown that the ice-crystal productivity of a slowly moving pellet remains high up to 0C. An experimental verification of this predicted dependence upon pellet velocity is described, data are presented, and the implications of these findings for future seeding experiments are discussed.