The Influence of Radiative Transfer on the Mass and Heat Budgets of Ice Crystals Failing in the Atmosphere

Abstract

A theoretical study was carried out to investigate the effect of radiative heating and cooling on the mass and heat budgets of an ice crystal. Equations describing the radiative budget of an ice crystal were derived and particle absorption efficiencies were calculated from the scattering theories for spherical and cylindrical particles. The radiation budget equation was solved in terms of upper limits of warming and cooling. By the introduction of the cloud blackbody depth, these limits were shown to apply over depths of several kilometres for typical ice clouds. The effects of radiation on the growth and evaporation rates of ice crystals were shown to be significant. Particle growth (evaporation) is enhanced (suppressed) in a radiatively cooled (heated) environment. It was further demonstrated that the effects of radiative cooling in the upper regions of the cloud greatly enhances the particle fall distances. In addition, particle growth and evaporation with and without radiation exchange are discussed in terms of their effect on the total expected heating of the cloud environment. It is demonstrated that radiation is the principal component in the diabatic heating of the cloud environment especially when the ice particle dimensions are large.