Comparison of the onset times and decay rates of the MeV-GeV Solar Energetic Hydrogen and Helium Ions at various observer locations at 1au

Authors: Ashraf Moradi (University of Arizona), Joe Giacalone (University of Arizona)

We numerically simulate the transport of the 0.1-1GeV/n solar energetic helium ions and protons into the interplanetary space using a 3D fully relativistic test particle model and present the intensity profile at various observer locations at 1au. In the model, we include pitch-angle scattering by using ad hoc scattering with parallel mean free paths relevant to “weak” pitch-angle scattering. The interplanetary magnetic field (IMF) model includes a flat heliospheric current sheet (HCS) which is placed at the Ecliptic plane, and cases of both A- and A+ IMF polarity are considered. We release the test particles impulsively near the Sun in locations both close and far from the HCS, and numerically integrate the trajectory of each particle separately as they move into the inner heliosphere, and record their locations when they arrive at 1 AU. In this study, we particularly focus on the differences in the time-intensity profile of each species at each observer location. We find that the magnetic connectivity and gradB and curvature drifts can lead to significant differences in the onset times and the decay rates of each ion species.