A model for polarization effects in remote probing of clouds

Abstract

A computer model is described which has been developed to aid in the interpretation of polarization data obtained by electromagnetic remote probing of mixed phase ice crystals and waterdrop clouds. Such clouds can contain many possible crystal forms, most notably thin long cylinders, bullets, and flat plate crystals, and the intent of the measurements is to characterize the ice crystal population by the polarization changes caused by these highly nonspherical shapes. The present work is a partial investigation of the theoretical aspects of this problem using flat circular disks as models of flat plate ice crystals randomly oriented over all rotation angles about axes perpendicular to the flat faces of the crystals. Mixtures of such disks and spherical particles to simulate waterdrops are considered. It is expected to include other crystal shapes in future work. Mie theory is used for the waterdrops, which are modeled as spheres, and a numerical procedure especially designed for dielectric disks is used for the flat plate crystals. Numerical results are presented to illustrate the sensitivity of the different Stokes parameters to ice crystal size and orientation distribution and variables such as the relative number density of ice crystals to waterdrops.