Freezing Nucleus Measurements in January 1957

Abstract

It is well known that the appearance of the ice phase in supercooled clouds is one of the more important phenomena leading to the formation of rain. The formation of ice crystals is itself dependent on the freezing nucleus content of the atmosphere. Little is known about the nature and origin of natural freezing nuclei, but daily measurements of freezing nucleus concentration made in different parts of the world during the month of January in the three years 1954, 1955, and 1956 have suggested that some fraction of them might be of extraterrestrial origin (Bowen 1956). The present note describes a further series of measurements made during January 1957.