Dependence on latitude of the relation between the diffuse fraction of solar radiation and the ratio of global-to-extraterrestrial radiation for monthly average daily values

Abstract

An approach for the prediction of the monthly average daily diffuse radiation, H d , was proposed by Page in 1961. The Page method is based on the use of the linear correlation H d H = c + d H H o , where H and H o are, respectively, the monthly average daily values of global and extraterrestrial radiation, both on a horizontal surface. The values of c and d are a function of atmospheric conditions. cloud cover conditions/types, as well as latitude. In the present work we study the dependence on latitude of c and d for European locations with 36°N < (γ) < 61°N (longitudes between 29°E and 11°W). The dependence is first studied using 28 values of c and d obtained using experimental values of H and H d . Next the dependence on γ is studied using experimental values of H for 64 European locations, obtained for the period 1966–1975, and corresponding values of H d estimated using the European Community Solar Radiation Model (E.C.S.R.M.). In both cases a minimum for c vs. γ and a maximum for d vs. γ are obtained for similar values of γ. Using the E.C.S.R.M. it is shown that both, the minimum and the maximum can be explained by the way H d H and H H o vary with γ.