A comment about the seasonal cycle of solar radiation
The field of global radiation for March shows a primarily zonal pattern, that is, one in which radiation decreases with latitude. This occurs because in March, the amount of solar radiation at the top of the atmosphere decreases sharply with increasing latitude. From April through August, latitudinal variations in solar radiation at the top of the atmosphere are less pronounced, so that cloud cover plays a strong role in determining the flux reaching the surface. Consequently, radiation patterns from April through August are very asymmetric. Fluxes are lowest over the Atlantic sector, where cloud cover is greatest. Fluxes peak over central Greenland from May through August. In large part, this illustrates the tendency for the high central portions of the ice sheet to be above the bulk of cloud cover. The highest fluxes are found in June because radiation at the top of the atmosphere peaks in June. Note for June the rather high fluxes over the central Arctic Ocean. This is largely explained in that cloud cover over this region is comparatively limited. From July onwards, radiation fluxes decline. September shows a zonal pattern, which as with March, arises from the strong latitudinal variation in solar flux at the top of the atmosphere for this month.