On the effect of latitude and season on the relation between the diffuse fraction of solar radiation and the ratio of global to extraterrestrial radiation

Data sets of global and diffuse irradiance at Sede Boqer, Israel, for clear, hazy and overcast conditions have been used to simulate the behavior of the relation between the diffuse fraction of solar radiation and the ratio of global to extraterrestrial radiation (D/G-K_T) as a function of latitude and season. It was found that in the summer solstice the latitude dependence is very small, and in the winter solstice very large. For the equinox the latitude dependence is closer to that of the summer. At a fixed latitude the seasonal dependence is large for high latitudes and negligible near the equator. Some consequences of these findings are discussed.