Theoretical aspects of modeling backscattering by cirrus ice particles at millimeter wavelengths

This research attempts to understand how nonspherical ice particles backscatter electromagnetic radiation at millimetric wavelenghts. The discrete dipole approximation (DDA) is employed to examine backscattering by single particles. It is shown that spheroids are reasonable models of cirrus ice particles at wavelengths of 3 and 8 mm. Furthermore, with careful consideration of optical size it is possible to exploit the Rayleigh approximation for spheroids under many circumstances. The sensitivity of backscattered radiation to variations in microphysical properties is examined, based on DDA calculations for ensembles of ice particles. The most important factor in the ice crystal size distribution is found to be the median diameter (D_m) of the ice crystal volume distribution.