Note on the occurrence of world-wide S.S.C.'s during the onset of negative bays at College, Alaska

World-wide sudden commencements which appear during the night hours at College, Alaska, are found to occur most frequently during the onset, or decreasing H stage, of negative bays. As this stage of magnetic disturbance accompanies a distinct change from homogeneous to rayed aurora, it is suggested that s.s.c.'s have an atmospheric source which is related to sudden changes in auroral activity.