RADIATIVE PROPERTIES OF WATER CLOUDS - SIMPLE APPROXIMATIONS

A polynomial approximation for Mie scattering characteristics is appli ed in the long and shortwave regions. Expressions for the absorption, scattering and extinction coefficients, single scattering albedo and a symmetry factor are obtained. The integration over the droplet size di stribution is done analytically and the resulting expressions are foun d to be sufficiently accurate (within 3% for the tenth order polynomia l approximation in the IR region) and computationally fast. When only the first two terms are kept in the polynomial expansions, the resulti ng expressions reduce to the Slingo parameterization of the radiative properties of clouds in the shortwave region. It is shown that this pa rameterization is more accurate than approximations based on geometric al optics and anomalous diffraction theory.