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 (Kr), 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 Kr 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 Kr 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 Kr in the last decade of June and second decade of July. Also, it is found that ‘sunny’ weather (Kr relatively large) appears to be significantly persistent in May especially. The persistence of ‘cloudy weather’ (Kr relatively small) is less pronounced.