A Simple Method to Compute the Change in Earth-Atmosphere Radiative Balance Due to a Stratospheric Aerosol Layer

Abstract

A simple three-layer model of the earth-atmosphere system, including the ground, troposphere and stratosphere, with their interactions, is developed. The model permits the radiative characteristics of both the troposphere and stratosphere to be separately adjusted to describe any atmospheric state. The accuracy is tested against the more precise computations of Herman et al. (1976), which take into account the aerosol profile and the angular variation of reflectance at the top of the troposphere. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. The physical procedures are outlined, as well as the influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal albedo and the planetary radiation balance due to a stratospheric aerosol layer of background H2SO4 droplets and of volcanic ash. The resulting ground temperature perturbation is evaluated, using a Budyko type climate model.