Latitudinal variation of the polar cusp during a geomagnetic storm

Large amplitude latitudinal variation of the polar cusp position was observed during the intense geomagnetic storm of 15--16 February 1980. The observation of the polar cusp, identified as the region of intense but extremely soft electron precipitation, was made by two nearly noon-midnight orbit DMSP satellites over both northern and southern hemispheres. The latitudinal shift of the polar cusp is observed to be related to the intensity variation of the ring current indicated by the hourly Dst values. The polar cusp region moved from its normal location at approx.76/sup 0/ gm lat down to approx.62/sup 0/ gm lat at the peak of this storm. This movement took about 5 hours and was detected over both hemispheres. A drastic variation in the width of the cusp region was also observed; it is very narrow (approx.1/sup 0/) during the equatorial shift and expands to > or approx. =5/sup 0/ during the poleward recovery. Variation of the polar cusp latitude with that of the Dst index was also seen during the period before the intense storm.

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