Effect of Aerosols on the Transfer of Solar Energy Through Realistic Model Atmospheres. Part I: Non-Absorbing Aerosols

Abstract

Extensive calculations aimed at determining the effect of aerosols on the solar energy absorbed, reflected and transmitted by cloudless, nonhomogeneous, plane-parallel atmospheric models were recently carried out with the object of treating the radiation transfer in as comprehensive a manner as possible consistent with reasonable computing time. The concentration of aerosol (spherical particles with size distribution and refractive index independent of height), ozone and water vapor were specified for 160 layers of varying thickness from the surface to 45 km. The solar spectrum (0.285?2.5 ?m) was divided into 83 intervals with appropriate functions representing the scattering and absorption of gases and aerosol assigned to each, the index of refraction of the aerosol taken to be wavelength-independent. Upward and downward fluxes for each spectral interval at each level were computed taking into account all orders of scattering. Results will be presented for four model atmospheres to show the absorbed, diffusely reflected, and diffusely as well as directly transmitted (spectrally integrated) solar flux for a range of Lambert ground reflectivities and solar zenith angles. The first model (A) is free of aerosols and absorbing gases. The remaining models contain carbon dioxide, ozone and water vapor representative of average summer mid-latitude conditions. Model B contains no aerosol; Model C contains an aerosol distribution typical of average clear sky conditions; and Model D has increased aerosol concentration near the ground and in the Junge layer located in the lower stratosphere.