A SIMPLE SOLAR, SPECTRAL MODEL FOR STUDYING THE EFFECTS OF CLOUD COVER AND SURFACE ALBEDO ON THE INCOMING SOLAR RADIATION

The effect of cloud cover and surface albedo on the solar insolation at the surface of the Earth was investigated. The model uses Bird's (1984) clear sky model for direct-normal and diffuse horizontal irradiance as its basis. Bird's model was modified to include inclined surfaces and cloud cover. The clouds were modelled using parameterizations developed by Welch, Cox and Davis (1980) and a weighting technique to account for cloud shape using plane-parallel calculations suggested by Welch and Wielicki (1984). The radiative transfer in the cloud was modelled by a two stream approximation known as the Shuster-Schwarzchild method. The model results were compared with clear sky broadband and spectral observations, and cloudy broadband observations. The clear sky spectral observations were obtained from the Solar Energy Research Institute (SERI) in Golden, Colorado. The broadband observations were obtained from the Solar and Meteorological Research Program at the University of Michigan. The effects of cloud amount, cloud thickness, cloud type, and surface albedo are demonstrated. Cloud amount and cloud thickness are the predominant cloud factors affecting insolation. High surface albedos tend to slow the decrease in insolation due to increasing cloud cover; while low surface albedos cause greater variation in insolation under the same circumstances. The model has the capability to simulate simple mountain obstructions. However, no cases with obstructions are presented. The model produces terrestrial spectra between 0.28 and 4.0 micrometers with a resolution of approximately 10 nm. The goal of this work is to provide researchers with the capability to calculate spectral irradiance for different atmospheric conditions and different collecting surface geometries.