Sunward Streaming 3He-rich SEP Events Observed by Solar Orbiter and Parker Solar Probe during Perihelion Passage

Samuel T. Hart; George C. Ho; Michael R. Terres; Gabriel C. Muro; Robert C. Allen; Maher A. Dayeh; Radoslav Bučík; Glenn M. Mason; Athanasios Kouloumvakos; Abdullah A. Shmies

arXiv · 2601.20624

Sunward Streaming 3He-rich SEP Events Observed by Solar Orbiter and Parker Solar Probe during Perihelion Passage

Samuel T. Hart·George C. Ho·Michael R. Terres·Gabriel C. Muro·Robert C. Allen·Maher A. Dayeh·Radoslav Bučík·Glenn M. Mason·Athanasios Kouloumvakos·Abdullah A. Shmies

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Abstract

We report on two 3He-rich solar energetic particle (SEP) events observed by Solar Orbiter (SO) and Parker Solar Probe (PSP) during the April 1 - 4, 2024 conjunction when both spacecraft are within 0.3 AU near their respective perihelion passage. The two 3He-rich SEP events, originating from active region (AR) 13615, exhibit two key anomalies: (1) sunward streaming SEPs and (2) SEP travel path lengths exceeding 2 - 8 times the nominal Parker spiral expectations. Remote observations suggest these SEPs have been redirected by a slow coronal mass ejection (CME) that also originated from AR 13615 two days prior on March 30, 2024 at 21:04 UT. Using the near-Sun CME speed and width measurements, we estimate its size and location at the onset time of the first 3He-rich SEP event. Based on our estimates, SEPs propagating around the ICME front have travelled between 0.76 - 0.95 AU when they arrive at SO, increasing to 0.94 - 1.1 AU at PSP, consistent with our observed SEP arrival times. These findings constitute the first multi-spacecraft observation of sunward streaming 3He-rich SEPs. We discuss the implications of this phenomenon on 3He-rich seed material and the rare widespread 3He-rich SEP events (see Section 5.4).

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Samuel T. Hart, George C. Ho, Michael R. Terres, Gabriel C. Muro, Robert C. Allen, Maher A. Dayeh, Radoslav Bučík, Glenn M. Mason, Athanasios Kouloumvakos, Abdullah A. Shmies. 2026-01-28. Sunward Streaming 3He-rich SEP Events Observed by Solar Orbiter and Parker Solar Probe during Perihelion Passage. https://arxiv.org/abs/2601.20624

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