NASA/Goddard Space Flight Center, Greenbelt, MD

We studied the causes of recurrent geomagnetic activity by analyzing interplanetary magnetic field and plasma data from Earth-orbiting spacecraft in the interval from November 1973 to February 1974. This interval includes the start of two long sequences of geomagnetic activity and two corresponding corotating interplanetary stream. In general, the geomagnetic activity was related to an electric field which was primarily due to two factors: (1) the ordered, mesoscale pattern of the stream itself, and (2) random, smaller-scale fluctuations in the southward component of the interplanetary magnetic field B_Z. The geomagnetic activity in each recurrent sequence consisted of two successive stages. The first stage was usually the most intense, and it occurred during the passage of the interaction region at the front of a stream. It was related to a V x B electric field which was large primarily because the amplitude of the fluctuations in B_Z was large in the interaction region. It is suggested that these large amplitudes of B_Z were primarily produced in the interplanetary medium by compression of ambient fluctuations as the stream steepened in transit to 1 A.U. The second stage of geomagnetic activity immediately following the first was associated with the highest speeds in the stream. It was, among other things, related to a V x B electric field which was large mainly because of the high speeds.

Planet. Space Sci., 25, 1151-1160, 1977