The effects of surface roughness on the light scattering properties of ice crystals

The effects of surface roughness on light scattering by ice crystals are systematically investigated. The pseudo-spectral time domain method (PSTD) and the improved geometry-optics method (IGOM) are combined to calculate the optical properties of particles with rough surfaces, over the whole range of size parameters from the Rayleigh to the geometric-optics regimes. The extinction efficiency, single-scattering albedo, asymmetry factor, and scattering phase matrix of randomly oriented hexagonal columns with rough surfaces are calculated. A surface roughness model for sea surface is applied to ice crystals in the PSTD and IGOM calculations. With the rough surfaces generated, it is straightforward for the PSTD to define the particles in the discretized spatial domain. Meanwhile, as an improvement to the previous IGOM that represents a rough surface by tilted facets, this study defines the rough surface exactly by triangular facets, and considers multiple reflections and refractions on the surface. The optical properties calculated using the new IGOM analyzed in comparison with those computed with the previous one.