The influence of inclusions on light scattering by large ice particles

Abstract

The scattering of visible light by ice crystals containing scattering and absorbing inclusions is calculated by a combination of ray‐tracing and Monte Carlo techniques. Results are shown for a randomly oriented hexagonal ice column containing ammonium sulfate particles, soot particles, and air bubbles. It is shown that a noticeable change in the ice crystal scattering properties compared to a pure crystal requires about 10 3 to 10 4 internal scatterers of a size comparable to the wavelength. While the nonabsorbing ammonium and air bubble inclusions generally decrease the asymmetry parameter g , soot provides a strong increase in g caused by the additional absorption. An independent superposition of the scattering properties of ice crystal and inclusions does not give satisfactory results because of the strong influence of internal scatterers on the characteristic ray paths inside the crystal. Multiple‐scattering calculations show that the strongest changes in the radiative fluxes are associated with the soot contaminated ice crystals.