A New Aspect of Snowflake Aggregation Theory

A new theoretical approach to snowflake aggregation is presented, which considers 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 that can be used in the stochastic collection equation exactly as a standard kernel, computed by assuming that snowflakes of the same mass have a unique fallspeed, would be used. The modified kernel approach predicts more rapid aggregation than the standard kernel approach, the degree of enhancement being critically dependent upon 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 sizes. Thus, the effect of including the fallspeed spectrum in calculations of aggregation is large and may even dominate the aggregation process.