Snow Formation and Processes in the Atmosphere that Influence its Chemical Composition

Abstract

The chemical composition and physical form of snowfall is controlled by a range of complex physical and chemical processes occurring on spatial scales ranging from the atomic dimensions of a water molecule (10−10 m) to the size of precipitating cloud system (105 to 106 m) and on temporal scales ranging from the time to grow ice particles by diffusion (1 to 102 s) to the lifetime of a precipitating cloud system (104 to 105s). The processes occur in a turbulent atmosphere and involve three phases of water. In the last thirty years, the cloud physics research community has made major advances in our understanding of snow formation. In particular, the role of the ice phase has received considerable attention since in extra-tropical regions, it plays a key role. There are several comprehensive texts in this field (Mason, 1971; Hobbs, 1974; Pruppacher and Klett, 1980) as well as symposia proceedings(e.g. Cloud Physics, 1990) which the reader is encouraged to consult as background to this review.