Effects of an optically thin Rayleigh atmosphere on the absorption ofsolar radiation by a Lambert surface.

The absorption analyzed is under an optically thin plane-parallel scattering layer. Since point-symmetry of the scattering is assumed, the study applies directly to a Rayleigh atmosphere. The scatterers produce two opposite effects, namely a decrease in the absorption resulting from backscattering to space out of the solar beam and an increase resulting from scattering back to the surface of the fluxes reflected from it. An equation is given for the hemispheric reflectivity of the surface atmosphere system. With this equation, the way in which the Rayleigh atmosphere mitigates the change in the absorption at the surface that follows from a change in the surface spectral albedo is analyzed. The analysis of the mitigating effects seen when a large change in albedo (from snow to vegetation) occurs suggests that an adequate specification of a Lambert surface for climate studies requires at least two parameters, namely the visible and the infrared albedo.