Solar radiation transfer in inhomogeneous stratiform clouds

Two previously unsolved problems are considered: (1) In which way does a horizontally distributed absorber (for example, soot) affect the albedo and transmittance of a stratiform cloud with a given horizontally averaged optical thickness? (2) How important is the vertical structure of a cloud with a given horizontal distribution of the optical thickness in calculations of its albedo and transmittance? Calculations of albedo and transmittance are based on perturbation solutions of the equation of radiative transfer. A model of a cloud whose optical characteristics vary horizontally by a simple harmonic law is considered. This is the main model for clouds with optical characteristics representable in a horizontal plane as a trigonometric series. It is found that the horizontally averaged albedo and transmittance increase in passing from a homogeneous distribution of a nonscattering absorber to a horizontally inhomogeneous distribution with the same horizontally averaged optical thickness. The sensitivity of albedo and transmittance to the vertical structure of clouds decreases as the characteristic sizes of horizontal inhomogeneities increase from 0.16 to 5.58 km. It is suggested that these results are valid for horizontal inhomogeneities of arbitrary shapes.