MeV Magnetosheath Ions Energized at the I Bow Shock 1 1 August 2001 I Prepared

A causal relationship between mid-latitude magnetosheath energetic ions and bow shock magnetic geometry was previously established for ion energy up to 200 keV/e for the May 4, 1998, storm event. This study demonstrates that 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 analysis suggest that these ions also come directly from the quasi-parallel bow shock, not the magnetosphere. This is confirmed by a comparison of energetic ion fluxes simultaneously measured in the magnetosheath and at the quasi-parallel bow shock when both regions are likely connected by the magnetic field lines. We suggest that ions are accelerated at the quasi-parallel bow shock to energies as high as 1 MeV and subsequently transported into the magnetosheath during this event.