Coherence of Geomagnetic <i>DP</i> 2 Fluctuations with Interplanetary Magnetic Variations

From the comparison of the worldwide geomagnetic data with IMP 1 magnetic records obtained in the interplanetary space, it is found that the DP 2 fluctuations, which are thought to be the geomagnetic counterpart of intensity fluctuations of the magnetospheric onvective system, are coherent with variations in the north-south component of the interplanetary magnetic field. This coherence is observed irrespective of whether this component is directed northward or southward. Average time delay between the crossing of an interplantary magnetic structure across the nose of the bow shock and the associated magnetic variation on the ground is 7 minutes at the pole and 9 minutes at the midday equator. Applicability of the proposed models of the magnetospheric electric field to this phenomenon is critically examined, and the penetration of the interplanetary electric field into the magnetosphere is suggested as the origin of the DP 2 phenomenon.