On the role of solar flare generated ions in producing high energy (> 300 keV) ion events upstream from the Earth's bow shock

Abstract

We performed a further statistical analysis of the 125 ion events detected by IMP-7/8 upstream from the Earth's bow shock and analysed in /1,2/. We found a strong negative correlation between the relative flux increase (peak-to-background flux ratio) and the background flux level of the 290–500 keV ions. Such a statistical behaviour suggests that the role of the acceleration processes taking place at the bow shock and its environment (Shock Drift and Fermi acceleration) is not decisive in the formation of the high energy (E≥300 keV) upstream ion events selected for this study. The statistic is consistent with an acceleration mechanism that accelerates ions to high energies independently from the presence of an ambient energetic ion population of solar origin, and confirms that magnetospheric acceleration processes during substorm activity and propagation of high energy ion to the upstream region are responsible for the high energy tail (E≥300 keV) of upstream proton spectra.