The spontaneous crystallization of supercooled water

Abstract

Abstract It is shown theoretically that the rate of nucleation of the ice phase in supercooled water changes very rapidly with temperature in the neighbourhood of −40°C. Thus, in chilling a supercooled water cloud below this temperature one would expect to observe a rapid increase in the number of ice crystals which appear as the temperature falls. This is verified by observations made in a cold chamber. The different critical temperatures for the spontaneous appearance of ice crystals quoted by Schaefer (−39°) and the Oxford workers (−41°C) probably arise as the result of differences in the experimental conditions. It is tentatively suggested that the parts of mother‐of‐pearl clouds showing iridescence at temperatures around −80°C consist of spheres of ‘glassy’ ice, which may eventually crystallize spontaneously to form ice crystals towards the leeward edges of the cloud.