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-e on 14 January 199 6. The bursts appeared in the recovery phase of a moderate storm. One of th em was singly ionized oxygen burst which lasted about 150 min and had a pea k energy of about 250 keV. The oxygen event is characterised by strong impu lsive increases in the oxygen flux with a nearly constant IMF orientation a ngle (-45 degrees), whereas the energetic proton and helium ions essentiall y disappeared. The oxygen burst exhibited strong field aligned streaming (a ntiparallel to the magnetic field vector) whereas the hydrogen and helium b ursts have a broad azimuthal angle distribution. These ion bursts exhibit l ayer structures, the oxygen ions exist outside the layer of proton and heli um ion. These observations suggest that energetic ions from the ring curren t may leak out of the magnetosphere into the magnerosheath during storm rec overy phase. (C) 1998 Elsevier Science Ltd. All rights reserved.