Sudden commencement absorption events at the edge of the polar cap

Examination of riometer records from a 5-year period (1967–1971) at Godhavn, Greenland (77.2° invariant latitude), shows the presence of sudden commencement absorption on two occasions, both during the late spring and early summer months in the northern hemisphere. One event occurred during quiet geomagnetic conditions when the interplanetary field was northward; the other event occurred during disturbed conditions when the predicted position of the equatorward boundary of the polar cusp was 2° equatorward of the observing site.