The contrast and brightness of halos in crystalline clouds

Numerical calculations of the halo brightness and contrast using the discrete ordinate method of the integro-differential radiative transfer equation solution have been carried out for a typical phase function of crystalline clouds exhibiting halo at 22 and 46°. The dependence of halo brightness and contrast on the cloud optical thickness has been investigated. A simple technique to determine the Ci cloud optical thickness from the halo contrast measurements is proposed.