A New Parameterization of Single Scattering Solar Radiative Properties for Tropical Anvils Using Observed Ice Crystal Size and Shape Distributions

Abstract

Parameterizations of single scattering properties currently used in cloud resolving and general circulation models are somewhat limited in that they typically assume the presence of single particle habits, do not adequately account for the numbers of ice crystals with diameters smaller than 100 m, and contain no information about the variance of parameterization coefficients. Here, new parameterizations of mean single scattering properties (e.g., single scatter albedo, asymmetry parameter, and extinction efficiency) for distributions of ice crystals in tropical anvils are developed. Using information about the size and shape of ice crystals acquired by a twodimensional cloud probe during the Central Equatorial Pacific Experiment (CEPEX), a self-organized neural network defines shape based on simulations of how the particle maximum dimension and area ratio (ratio of projected area to that of circumscribed circle with maximum dimension) vary for random orientations of different idealized shapes (i.e., columns, bullet rosettes, rough aggregates, and particles represented by Chebyshev polynomials). The size distributions for ice crystals smaller than 100 m are based on parameterizations developed using representative samples of 11 633 crystals imaged by a video ice particle sampler (VIPS). The meanscattering properties for distributions of ice crystals are then determined by weighting the single scattering properties of individual ice crystals, determined using an improved geometric ray-tracing method, according to number concentration and scattering cross section.