Longitudinal Extent of 3He-rich Solar Energetic Particle Events Near 1 au

Abstract

Multispacecraft observations of 3He-rich solar energetic particle (SEP) events are scarce, but much needed in order to understand and properly constrain the source and transport of these remarkably enriched 3He SEP events. In this paper, we report 15 3He-rich SEP events that were detected by the Advanced Composition Explorer, the Solar Terrestrial Relations Observatory, and Solar Orbiter near 1 au during Solar Orbiter’s aphelion pass at the end of 2022 and early 2023. Three (five) of these events were detected simultaneously by at least two (three) spacecraft at up to ∼40° longitudinal separation, while seven events were detected by only a single spacecraft, even though an adjacent spacecraft was less than 20° apart. Using a magnetic connectivity tool, we show statistically that there is a >50% probability of detection when the spacecraft-modeled footpoints have an angular separation angle of <24° to the potential source region back at the Sun. This supports previous studies suggesting that the source of these 3He-rich SEP events is narrow in longitudinal extent. On the other hand, the magnetic connectivity due to the presence of coronal mass ejections, footpoint motion, and/or field-line meandering may also lead to difference in a detection at 1 au.