Sunshine and sky cloudiness over Iran

Abstract

Using data provided by the Iranian Meteorological Organization (IMO) obtained from 36 stations for a period of 11 years (1965-1975 ), spatial distribution of the averaged monthly sustained winds relative duration of sunshine over country is studied; also, averaged annual variations of the relative sunshine and sky clearness are investigated for every station, and assuming linear correlation between the two quantities, the regression and correlation coeffieients are computed for each of the stations.

It is clearly seen that a major part of the country has relative duration of sunshine less than 60 percent during half a year (December to May), and more than that in the second half. It is also shown that the country is actually divided into four different regions from sunshine and cloudiness point of view; the southern region is under substantial influence of the monsoon, remaining parts, but the northern area, being only fairly affected. Moreover, the percentage of sky free from cloud is more or less higher than the percentage of the duration of sunshine in summer, and generally, either lower or identical in winter.