Do Solar Energetic Electrons cross the Heliospheric Current Sheet? - A Statistical Study

TL;DR

This study investigates how solar energetic electrons propagate across the heliospheric current sheet, revealing that cross-HCS transport is inefficient unless sources or observers are near the HCS.

Contribution

It provides a comprehensive classification of SEP events relative to the HCS and offers new insights into particle transport mechanisms across the HCS.

Findings

Opposite-side events are more isotropic.

Both source and spacecraft are closer to the HCS in these events.

Transport across the HCS is inefficient unless near the HCS.

Abstract

Solar eruptive events such as flares and coronal mass ejection (CME)-driven shocks can release solar energetic particles (SEPs) into the heliosphere. The heliospheric current sheet (HCS) is a large-scale structure that separates regions of opposite magnetic polarity, and its influence on SEP propagation remains poorly understood. We classify SEE events into two groups: same-side events, where both the solar source and spacecraft are in the same magnetic sector, and opposite-side events. The magnetic polarities of the solar source region and the spacecraft location are determined comprehensively based on Potential Field Source Surface (PFSS), magnetic field measurements, the pitch angle distribution of strahl electrons, and the first-order anisotropy of energetic electrons. The spacecraft magnetic polarities determined by footpoint positions at the source surface and in-situ observations are consistent for most events, providing a useful methodological reference for future studies. We identify 60 same-side events and 9 opposite-side events. Our results show that opposite-side events tend to be more isotropic, and that both the solar source and the spacecraft are closer to the HCS than in same-side events. This suggests that particle transport across the HCS is inefficient unless the source or the observer is close to the HCS. These preliminary statistical findings advance our understanding of the role of the HCS in shaping SEP transport.