On the scattering phase-function of non-symmetric ice-crystals

Theoretical phase-functions representing randomly oriented fractal ice-crystals, bullet-rosettes, ice aggregates, and an ensemble of ice crystals are compared to measured phase-functions using a Polar Nephelometer located in the Antarctic. The Polar Nephelometer operated at a wavelength of 0.80 mu m and measured the scattering phase-functions of individual ice-crystals between the scattering angles of 5.86 degrees and 167 degrees. The Polar Nephelometer was operated in tandem with a Cloud Particle Imager (supplied by SPEC Inc.) both were situated at the South Pole Amundsen-Scott base station during January 2002. In this paper we report on a sample of Polar Nephelometer data obtained over a time interval of 2000 seconds consisting of 3256 phase-functions measured from individual ice-crystals. The 3256 measured phase-functions were averaged to produce an ensemble-averaged phase-function. The theoretical phase-functions have been compared to the measured ensemble-averaged phase-function. The paper demonstrates that phase functions representing single ice-crystal geometries do not reproduce the measured data well. However, the theoretical phase-function representing scattering from an ensemble of ice crystals is found to be the best description of the measured phase-function over all scattering angles.