Drop Freezing Through Drop Breakup

Abstract

Evidence supporting the hypothesis that the first particles of ice in small cumulonimbus clouds way form as a result of a mechanism involving the violent breakup of drops is presented. The hypothesis is supported by observations that: (1) ice nucleation occurs at relatively warm temperatures if a supercooled drop is subjected to a shock wave; (2) the bag mode of drop breakup occurs when drops are subjected to a shock wave; (3) and, the bag mode of drop breakup may occur in natural clouds even though the air is motionless except for turbulence introduced by the cloud drops themselves (i.e., shock waves or unnatural forms of turbulence are not required to promote the bag mode of drop breakup). The mechanism can only he effective in cases when clouds contain large supercooled drops. It is believed that the hypothesized mechanism may supply a critical link in the understanding of cloud glaciation by providing a means of triggering the avalanche mechanism involving ice splinter formation during drop freezing.