DELTA-EDDINGTON APPROXIMATION FOR RADIATIVE FLUX TRANSFER.

Abstract

A rapid yet accurate method, the ″dela-Eddington″ approximation, is presented for calculating monochromatic radiative fluxes in an absorbing-scattering atmosphere. By combining a Dirac delta function and a two-term approximation, it overcomes the poor accuracy of the Eddington approximation for highly asymmetric phase functions. Comparisons of delta-Eddington albedos, transmissivities and absorptivities with more exact calculations reveal typical differences of 0 to 0. 02 and maximum differences of 0. 15 over wide ranges of optical depth, sun angle, surface albedo, single-scattering albedo and phase function asymmetry factor. Delta-Eddington fluxes are in error, on the average, by no more than 0. 5%, and at the maximum by no more than 2% of the incident flux. This computationally fast and accurate approximation is potentially of utility in applications such as general circulation and climate modeling.