Aggregation and Scaling of Ice Crystal Size Distributions

Ice particle size distributions (PSDs) can be scaled onto a single exponential distribution for a wide range of observed conditions as demonstrated using data from Atmospheric Research Measurement (ARM) cirrus uncinus, Tropical Rainfall Measurement Mission (TRMM) tropical anvils, and First International Satellite Cloud Climatalogy Project (ISCCP) Regional Experiment (FIRE1) midlatitude cirrus field programs. The successful scaling of the PSDs is the result of the dominance of the aggregation process. The PSD is found to be a function of mean particle size and precipitation rate only. A correlation between precipitation rate and particle mass and fall speed relations is demonstrated and made use of in a semiempirical model of ice cloud that predicts the evolution of PSDs.