A series of global radiation at Wageningen for 1928-1992

A series of daily total incoming radiation measured at Wageningen, The Netherlands, for the period 1928–1992 is described. These data are presented as relative global radiation (K_r), which is defined as the global radiation divided by the corresponding extraterrestrial value. Both the year-to-year variation and the mean annual cycles of K_r averaged over a year, season, month, decade (10 days), and a day are considered. Also, frequency distributions are evaluated. It is found that the maximum of K_r does not occur in June, when the solar elevation is highest, but in May. This is due partly to the west European monsoon, causing a decline of K_r in the last decade of June and second decade of July. Also, it is found that ‘sunny’ weather (K_r relatively large) appears to be significantly persistent in May especially. The persistence of ‘cloudy weather’ (K_r relatively small) is less pronounced. (author)