Wednesday, 5 June 2002
Single and multiple scattering/absorption properties of pristine Ice crystals and polycrystals in the terrestrial window region
In a previous study, we showed that the vertical inhomogeneity of both particle habit (shape) and particle size distribution in cirrus clouds can have a substantial effect on the scattering properties at visible and near-infrared wavelengths. In this study we investigate two problems pertaining to cirrus cloud retrieval efforts using wavelengths in the terrestrial window region (8-12 Ám), specifically the effect of ice crystal habit on the cirrus single-scattering properties and the bulk radiative characteristics of cirrus. A pristine geometry and a polycrystal morphology are assumed for ice crystals. Particle habit is shown to have a significant effect on the scattering properties for particles with sizes below 100 Ám, but not for larger particle sizes. Calculations were performed assuming two vertical habit distributions within the cloud. The single-scattering albedo and asymmetry factor are sensitive to the assumed vertical distribution of habits, but not the extinction efficiency. Furthermore, the emission at cirrus cloud top and cloud base at 8.5 Ám is insensitive to the vertical habit distributions within the cloud layer.