A study of atmospheric transparency over Qena/Upper Egypt

Abstract

Atmospheric transparency over Qena/Egypt has been studied for direct solar radiation values, which were calculated from global and diffuse solar radiation measurements. The monthly mean of the instantaneously transparency coefficient has been analyzed in clear-. cloudy-. and mixed days. In general, the value of the transparency coefficient was found to decrease towards the sunset hours, owing to the high aerosol content expected in the afternoon time. The clouds deplete significantly the solar energy passed through them and then lead to an obvious decreasing in the transparency coefficient. A try to calculate the transparency coefficient has been done with the aid of the more available global solar radiation measurements. The results are in a good agreement with those obtained for direct solar radiation. The relation between the daily average of the trail transparency coefficient and the corresponding mean diffuse fraction has been investigated. High correlation were found between them in all months and empirical formulae were obtained.