The Fragmentation of Freezing Water Droplets in Free Fall

Abstract

The fragmentation of water droplets during freezing has not been previously established under conditions which resemble those in natural clouds. In laboratory experiments designed to investigate this phenomenon it is important that the droplets be close to the equilibrium state with their environment prior to nucleation. In this paper theoretical expressions are derived which may be used to calculate the degree to which a droplet is in equilibrium with its environment as it falls through a gas which has a vertical gradient of temperature. Experiments are described in which the fragmentation of freezing droplets from 50?100 ? in diameter have been observed under conditions which are close to those in natural clouds. The fragmentation appeared to be independent of the nucleation temperature over the range investigated (?20 to ?32C) and it also occurred for droplets nucleated at ?8C by silver iodide in supension. Droplets from 20?50 ? in diameter were not observed to fragment during freezing.