MeV magnetosheath ions energized at the bow shock

Abstract

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 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.