Light scattering by mixed-phase clouds

Abstract

The main optical characteristics of light scattering by mixed-phase clouds (the phase scattering function, the scattering, absorption and extinction efficiencies) were investigated. A theoretical study using a particle size spectrum of a mixed-phase cloud microstructure under the assumption of its spatial homogeneity is presented. The calculations of optical characteristics for the droplets of the mixed-phase cloud were made with the Mie theory and for the crystalline fraction the calculation methods connected with the geometrical optics and diffraction were used. For the mixed-phase cloud particle size spectrum the expressions were used that connect the ratio of droplets liquid water content to the crystals ice content (t) with the ratio of scattering coefficients for these fractions (q) for mixed- phase clouds. This made it possible to use the known expressions for calculations of the t values depending on the cloud layer temperature T to calculate the dependence of q on T.. The parameter q determines unambiguously basic optical characteristics for a mixed-phase cloud medium. It depends on the parameters of a particle size spectrum for water droplet and ice crystal fractions of a mixed-phase cloud and significantly depends on the incident radiation wavelength.