ON THE RADIATIVE PROPERTIES OF CONTRAIL CIRRUS

Using the observed ice crystal size distribution in contrail cirrus fr om SUCCESS, we have carried out the scattering and absorption calculat ions based on a unified theory for light scattering by ice crystals co vering all sizes and shapes. We illustrate the effects of ice crystal size and surface roughness on the scattering phase function features f or remote sensing applications. The extinction coefficient and single- scattering albedo exhibit a minimum feature at 2.85 mu m, referred to as the Christiansen effect, which is particularly pronounced for cloud s consisting of a significant number of small ice crystals. Based on a line-by-line equivalent solar model, we show from spectral curves tha t cloud reflection increases as ice crystal sizes become smaller, but the cloud absorption increase is only evident for wavelengths longer t han about 2.7 mu m. The ice crystal shape has a substantial effect on the cloud reflection and absorption for a given size; more complex ice particles reflect more solar radiation. Finally, we propose a contrai l cirrus cloud model consisting of a combination of bullet rosettes (5 0%), hollow columns (30%), and plates (20%), with sizes ranging from 1 to 90 mu m in association with radiation perturbation studies.