Development and analysis of an ice crystal scattering database for remote sensing applications and cloud model evaluation

An ice crystal (ice dendrites, plates and columns) scattering database at radar wavelengths (W-, Ka-, Ku- and X-bands) is created to facilitate radar retrievals and cloud model evaluations of ice cloud properties. The ice crystals in the database are modeled as clusters of closely-packed tiny spheres and their scattering properties calculated with the Generalized Multi-particle Mie-method (GMM). Radar observables, such as effective radar reflectivity factor at hh- and vv-polarizations (Z hh and Zvv), differential reflectivity (Zdr), specific differential phase (KDP) and specific attenuation at h- and v-polarizations (Ah and Av), are created from the database using gamma size distributions with various parameters. For the four radar wavelengths considered, ice water content retrievals based purely on radar backscattering cross sections are highly uncertain while KDP shows greater promise.;Using the concepts of resonance and internal electric field strength across an ice crystal, a modified Rayleigh-Gans (MRG) theory is developed that captures most of the variability in the single ice crystal scattering properties within the database. Radar observables are also estimated using the MRG theory and compared to GMM results. Zhh, Zvv, Zdr and KDP estimated using the MRG theory show good agreement with GMM results. The errors for Ah and Av are large but not important because attenuation at radar wavelengths is generally small for ice crystals. As such, this MRG theory may be useful in radar applications.;In the representing ice crystals as clusters of tiny spheres with air gaps between them, the dielectric constant of the tiny spheres/air gaps mixtures is smaller than that of solid ice. To make the mixture electromagnetically equivalent to solid ice, the dielectric constant of the tiny spheres in the clusters is artificially increased by an amount dictated by the Maxwell-Garnett approximation. This approach leads to computations that more accurately represent the scattering properties of the original solid ice crystals as compared to increasing the thicknesses of the clusters of tiny spheres so that their total masses match that of the original solid ice crystals.