Relationship between Interplanetary Sector Structure and Geomagnetic Storm
Effects of interplanetary sector structure on geomagnetic storm have been investigated for the decreasing portion of the solar cycle in 1970, 1971 and 1972. The average structure of geomagnetic activity with respect to a sector boundary has been investigated by use of the superposed epoch technique.
In the present study the tendency for K at Kakioka, Kn and Ks in each hemisphere to become higher after the passage of a sector boundary can be seen. Also a sudden commencement has occurred near a sector boundary and it has been observed to reach a maximum occurrence frequency after the passage of a sector boundary.
A sudden commencement is not necessarily associated with a flare-induced shock wave, but may also be caused by a corotating sector boundary.