Solar activities associated with 3He-rich solar energetic particle events observed by Solar Orbiter

Abstract

A series of 3He-rich solar energetic particle (SEP) events was observed by Solar Orbiter in May 2021 at a radial distance of 0.95 AU. An isolated active region AR 12824 was likely the ultimate source of these SEP events. The period of the enhanced flux of 3He was also a period of frequent type III bursts in the decametric-hectometric range, confirming their close relationship. As in past studies, we try to find the solar activities possibly responsible for 3He-rich SEP events, using the type III bursts close to the particle injection times estimated from the velocity dispersion. But this exercise is not as straightforward as in many of the past studies since the region produced many more type III bursts and jet-like eruptions than the SEP injections. We may generalize the solar activities for the 3He-rich SEP events in question as coronal jets, but their appearances do not necessarily conform to classic jets that consist of a footpoint and a spire. Conversely, such jets often did not accompany type III bursts. The areas that produced jet-like eruptions changed within the active region from the first to the second set of 3He-rich SEP events, which may be related to the extended coronal mass ejection that launched stealthily.

Element Abundances in Impulsive Solar Energetic-Particle Events

“…We could begin to identify, with greater certainty, which of the many small type III burst or X-ray peaks in Figure 1 goes with which 3 He-rich event and ask why some events contribute electrons and 3 He while others, from the same active region, apparently do not. There are already interesting studies, mainly of the electron, i.e., type III, timing and spatial distributions [108,109].…”

Solar Active Region Coronal Jets. III. Hidden-onset Jets

“…For this eight-hour period, we have inspected all nine of the EUV and UV AIA channels at full cadence. This region was also responsible for expulsion of a series of 3 He-rich solar energetic particle (SEP) events, with the jets discussed here likely being the sources of those SEPs (Nitta et al 2023).…”