OSCILLATIONS OF MAGNETOSPHERIC BOUNDARIES DRIVEN BY IMF ROTATIONS

The arrival of the magnetic cloud on January 10, 1997, 01:05 UT, was p receded by a 12-hour interval of increased fluctuations in the IMF ori entation, which drove boundary oscillations in the magnetosphere. The GEOTAIL spacecraft, initially located near the dawnside magnetopause, experienced multiple crossings of the magnetopause; at the geosynchron ous distance, GOES 9 observed weak perturbations associated with these oscillations. During this time, the POLAR spacecraft, encountered the dense high-latitude boundary layer, followed by several rapid encount ers with the tenuous lobe. The boundary between the mantle and the lob e was observed to be thin as the crossings lasted only 30 seconds. The source of these boundary oscillations is magnetosheath pressure varia tions produced by rapid IMF directional changes.