Title : Clear-sky climatology of Greece
A new methodology for classifying sky conditions at any location on Earth in overcast, intermediate and clear has been published (Kambezidis et al., Appl. Sci. 2021). This methodology is applied in the present study in order to identify clear-sky conditions at 33 sites in Greece. Clear-sky conditions are synonymous to sunshine duration because of the criterion of the direct-normal solar radiation to exceed 120 Wm-2 (World Meteorological Organisation-WMO) applies to both parameters. The methodology is based on the diffuse fraction, kd, defined as the ratio of diffuse to global solar radiation, and being equal or less than 0.26. The data used is solar radiation (global, diffuse, direct) as ingredient of the typical meteorological years (TMY) derived for the sites. The analysis of the 33 data bases aims at finding the hours when the direct-normal solar radiation exceeded 120 Wm-2 (WMO directive) and providing a map of Greece showing the distribution of those hours at annual and seasonal basis. Such an analysis is done for the first time in Greece.