P1.5 QUANTIFYING DROPLET CLUSTERING IN CLOUDS

A great deal of work has been devoted in the last decade to identify whether or not the spatial posi-tions of cloud particles are statistically correlated. If, in fact, spatial correlations do exist there could be consequences in radiation attenuation (Kostinski (2001) and Shaw et al. (2002a)) and collision rates (note the assumption of independent and identically distributed spatial positions of droplets in Saffman & Turner (1956)). Although quite varied theoretical tools have been utilized in attacking this problem, many of them are fundamentally related in ways that have not been explicitly noted. In studying the ana-lytic connections between these methods, a great deal of physical intuition and knowledge about the limita-tions of the statistics in question can be acquired. More specifically, the tools of the pair-correlation function [η(r)], clustering index [CI(r)], volume-averaged pair-correlation function [η(r)], autocorre-lation function [ρ(r)], and power spectral density [P (k)] are analyzed here. Most of these methods have been used recently to characterize correlations in spatial positions of cloud droplets. In the inter-ests of brevity, the relative merits of these statistics will not be addressed here. A more thorough litera-ture review and careful analysis can be found in Shaw et al. (2002b). Representative papers are: Kostin