Four-Stream Isosector Approximation for Solar Radiative Transfer

Abstract

For radiative transfer in a thin atmosphere, an analytical four-stream isosector approximation for solar radiative transfer is presented. This approximation method is based on the assumption of four spherical sectors of isotropic intensities. Calculations show that the four-stream isosector approximation model substantially improves the accuracy in reflection, transmission, and absorption with respect to the Coakley?Ch?lek model. For an optical thickness less than unity, the four-stream isosector approximation has errors mostly under 5%, in contrast to errors up to 20% or higher for the Coakley?Ch?lek model. This four-stream isosector approximation can be applied to atmospheric aerosol layers or thin cirrus clouds.