THE INFLUENCE OF INCLUSIONS ON LIGHT-SCATTERING BY LARGE ICE PARTICLES

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 part icles, and air bubbles. It is shown that a noticeable change in the ic e crystal scattering properties compared to a pure crystal requires ab out 10(3) to 10(4) internal scatterers of a size comparable to the wav elength. While the nonabsorbing ammonium and air bubble inclusions gen erally decrease the asymmetry parameter g, soot provides a strong incr ease in g caused by the additional absorption. An independent superpos ition of the scattering properties of ice crystal and inclusions does not give satisfactory results because of the strong influence of inter nal scatterers on the characteristic ray paths inside the crystal. Mul tiple-scattering calculations show that the strongest changes in the r adiative fluxes are associated with the soot contaminated ice crystals .