A Study of Cirrus Ice Particle Size Distribution Using TC4 Observations

An analysis of two days of in-situ observations of ice particle size spectra, in convectively generated cirrus, obtained during the NASA's TC4 (Tropical Composition, Cloud and Climate Coupling) mission is presented. The observed spectra are examined for their fit to the exponential, gamma and lognormal function distributions. Characteristic particle size and concentration density scales are determined using two (for the exponential) or three (for the gamma and lognormal functions) moments of the spectra. It is shown that transformed exponential, gamma and lognormal distributions should collapse onto standard curves. An examination of the transformed spectra, and of deviations of the transformed spectra from the standard curves, shows that the lognormal function provides the best fit to the observed spectra. The implication of the results to radar retrieval of cirrus cloud properties will be discussed.