Solar Radiative Heating in the Presence of Aerosols

A theoretical study is carried out to evaluate the effects of aerosols on the shortwave flux divergence in the lower troposphere (0–2 km) by using four computational methods: Gauss-Seidel iteration, a reference method by which all orders of scattering are accounted for, and three approximations, primary scattering, no-scattering and median wavelength. By using these procedures, the radiative transfer equation is solved for a cloudless plane parallel atmosphere of infinite extent in the horizontal, but of finite extent in the vertical. The Gauss-Seidel procedure is taken as a standard and comparisons of the flux divergence are made by using various combinations of solar zenith angle, aerosol size frequency distribution and aerosol refractive index. In many of the simulations the median wavelength approximation gives accuracies comparable to those of the no-scattering approximation, in which case the choice of method is based on the required computational time. However, inaccuracies appear with all the approximations and the degree of superiority of one method over another depends on the aerosol and gaseous constituents of the model atmosphere.