MeV magnetosheath ions energized at the bow shock

A causal relationship between midlatitude magnetosheath energetic ions and bow shock magnetic geometry was previously established for ion energy up to 200 keV e(-1) for the May 4, 1998, storm event. This study demonstrates th at magnetosheath ions with energies above 200 keV up to 1 MeV simply extend the ion spectrum to form a power law tail. Results of cross-correlation an alysis suggest that these ions also come directly from the quasi-parallel b ow shock, not the magnetosphere. This is confirmed by a comparison of energ etic ion fluxes simultaneously measured in the magnetosheath and at the qua si-parallel bow shock when both regions are likely connected by the magneti c field lines. We suggest that ions are accelerated at the quasi-parallel b ow shock to energies as high as 1 MeV and subsequently transported into the magnetosheath during this event.