Energetic particles bursts in the near-earth magnetosheath during a storm recovery phase

Several energetic ion bursts were observed in the near-Earth magnetosheath when the spacecraft was located at (-4.5, 18.6, -1.3) R, on 14 January 1996. The bursts ap- peared in the recovery phase of a moderate storm. One of them was singly ionized oxygen burst which lasted about 150 min and had a peak energy of about 250 keV. The oxy- gen event is characterised by strong impulsive increases in the oxygen flux with a nearly constant IMF orientation angle (-45O), whereas the energetic proton and helium ions essen- tially disappeared. The oxygen burst exhibited strong field aligned streaming (antiparallel to the magnetic held vector) whereas the hydrogen and helium bursts have a broad az- imuthal angle distribution. These ion bursts exhibit layer structures, the oxygen ions exist outside the layer of proton and helium ion. These observations suggest that energetic ions from the ring current may leak out of the magnetosphere into the magnetosheath during storm recovery phase. 0 1998