The physical causes of DSD variability

A disdrometer collocated with a vertically pointing radar is used to establish a relationship between observed drop size distributions and the dominant microphysical processes occurring aloft, particularly in snow. From the fall velocity of snow and its reflectivity change with height it is possible to separate cases where snow growth is dominated either by deposition, by riming or by aggregation. The resulting classification of cases leads to distinct distributions that can be represented by different values of a scaling constant in a context of single moment DSD normalization.

Theory and results of simulations of the evolution of drop size distributions by the quasi-stochastic growth equation provide a conceptual model for the causes of DSD variability in that fits well the observations.