LIGHT-SCATTERING BY ABSORBING HEXAGONAL ICE CRYSTALS IN CIRRUS CLOUDS

An improved ray-optics theory for single scattering and polarization o f hexagonal columns and plates randomly oriented in space has been dev eloped by considering absorption and by using the Chebyshev solution f or diffraction integrals. The vector-tracing method and statistics tec hnique of random sampling are employed. The equivalent forms of Snell' s law and Fresnel formulas for absorbing ice crystals are derived, and two equivalent optical constants, m' and m '', are obtained. Comparis on is made of the computed results of our model and the Takano and Lio u model for asymmetry factors, single-scattering albedos, and scatteri ng phase matrix elements. Some characteristics of our model are discus sed, and these analyses demonstrate that our ray-optics model is pract ical and much improved.