Multi-spacecraft Analysis of Energetic Heavy Ion and Interplanetary Shock Properties in Energetic Storm Particle Events near 1 au

Abstract

We examine the longitude distribution of and relationship between interplanetary (IP) shock properties and ∼0.1-20 MeV nucleon^-1 O and Fe ions during seven multi-spacecraft energetic storm particle (ESP) events at 1 au. These ESP events were observed at two spacecraft and were primarily associated with low Mach number, quasi-perpendicular shocks. Key observations include the following: (I) the Alfvén Mach number increased from east to west of the coronal mass ejection source longitude, while the shock speed, compression ratios, and obliquity showed no clear dependence; (II) the O and Fe time intensity profiles and peak intensities varied significantly between longitudinally separated spacecraft observing the same event, the peak intensities being larger near the nose and smaller along the flank of the IP shock; (III) the O and Fe peak intensities had weak to no correlations with the shock parameters; (IV) the Fe/O time profiles showed intra-event variations upstream of the shock that disappeared downstream of the shock, where values plateaued to those comparable to the mean Fe/O of solar cycle 23; (v) the O and Fe spectral index ranged from ∼1.0 to 3.4, the Fe spectra being softer in most events; and (VI) the observed spectral index was softer than the value predicted from the shock compression ratio in most events. We conclude that while the variations in IP shock properties may account for some variations in O and Fe properties within these multi-spacecraft events, detailed examination of the upstream seed population and IP turbulence, along with modeling, are required to fully characterize these observations.