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

Abstract

Multispacecraft observations of ^3 He-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 ^3 He SEP events. In this paper, we report 15 ^3 He-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 ^3 He-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.

Keywords

• Solar energetic particles
• Interplanetary particle acceleration
• Solar active regions