Tailward energetic ion streams observed at ∼100 RE by GEOTAIL‐EPIC associated with geomagnetic activity intensification

The authors report energetic particle (EPIC instrument) and magnetic field (MGF instrument) measurements collected onboard GEOTAIL located at {approximately} 100 R{sub E} downstream in the magnetotail during a 13-hour long active period on January 20-21, 1993. During this period, a series of 6 geomagnetic activity intensifications (breakup or pseudo-breakup) have been studied with ground magnetograms and energetic particle data at geosynchronous orbit. They show that: (1) as a general trend, the level of the energetic ion fluxes was related to the intensity of the westward electrojet; (2) a systematic temporal (within a few minutes) correlation exits between energetic ion flux enhancements observed by GEOTAIL/EPIC in the distant tail and near-Earth geomagnetic activity intensification onsets; and (3) for 5 of 6 cases, these energetic ion flux enhancements corresponded to strong tailward streams which included particles of both solar wind and ionospheric origin. Their amplitude seemed also to be related to the electrojet intensity change. 6 refs., 4 figs.