Tuesday, 4 June 2002: 4:00 PM
Parameterization of cloud optical properties for a mixture of ice particles
Based on the single-scattering optical properties that are pre-computed using an improve geometric optics method, the bulk mass absorption coefficient, single-scattering albedo, and asymmetry factor of ice particles have been parameterized as a function of the mean effective particle size of a mixture of ice habits. The parameterization has been applied to compute fluxes for sample clouds with various particle size distributions and assumed mixtures of particle habits. Compared to the parameterization for a single habit of hexagonal column, the solar heating of clouds computed with the parameterization for a mixture of habits is smaller due to a smaller co-single-scattering albedo. Whereas the net downward fluxes at the TOA and surface are larger due to a larger asymmetry factor. The maximum difference in the cloud heating rate is ~ 0.2 °C day–1, which occurs in clouds with an optical thickness > 3 and the solar zenith angle < 45°. Flux difference is < 10 W m-2 for the optical thickness ranging from 0.6 to 10 and the entire range of the solar zenith angle. The maximum flux difference is ~ 3%, which occurs around an optical thickness of 1 and at high solar zenith angles. .