Field and Laboratory Observations of Ice Crystal Growth from the Vapor

Abstract

The temperature dependence of the habit of ice crystals growing in a water vapor diffusion chamber is related to the growth rate of ice crystals in a supercooled cloud. The rates of growth occurring between ?4 and ?6C as needles or between ?12 and ?16C as dendrites may be in excess of those at intermediate temperatures by as much as a factor of 100. The effect of seeding a supercooled cloud will therefore depend critically on its temperature. Growth of crystals at large supersaturation between ?4 and ?6C takes place as spikes growing along a direction 25° to the c axis. These crystals have been observed in the diffusion chamber, and also as frost near hot springs in Yellowstone Park. The molecular processes responsible for these habit changes are discussed.