A New Aspect of Snowflake Aggregation Theory

Abstract

A new theoretical approach to snowflake aggregation is presented which accounts for the fact that snowflakes of the same mass can have a spectrum of fallspeeds. The essence of the approach is to define a modified kernel which can be used in the stochastic collection equation exactly as one would use a standard kernel computed by assuming that snowflakes of the same mass have a unique fallspeed. The modified kernel approach predicts more rapid aggregation than the standard kernel approach, the degree of enhancement being critically dependent on the width of the fallspeed spectrum. For the case of aggregates of dendrites, measurements made by a number of investigators suggest that the width of the fallspeed spectrum is of the same order as the variation in the mean fallspeed over the typical range of snowflake sites. Thus the effect of including the fallspeed spectrum in calculations of aggregation is large, and may even dominate the aggregation process.