Authors: Samuel T. Hart (The University of Texas at San Antonio), Maher A. Dayeh (Southwest Research Institute), Radoslav Bučík (Southwest Research Institute)

³He-rich solar energetic particle (SEP) events, also known as impulsive SEP events, are characterized by their enhanced ³He/⁴He abundance ratio over 10⁴ times the typical solar wind values. ³He-rich SEPs are believed to be accelerated by magnetic reconnection occurring near the boundary between solar active regions (closed magnetic loops) and coronal holes (open magnetic field lines), producing extreme ultraviolet jets that signify the injection of accelerated SEPs into interplanetary space. The common acceleration mechanism of magnetic reconnection would theoretically produce similar spectral profiles between events and between ion species. However, case studies have shown that ³He-rich SEP events exhibit a considerable amount of interevent spectral variability. Some events have a low energy roll-over spectra, while others are better described by single and classic double power laws. In this work, we survey ³He-rich events from Sept. 1997 – Jan. 2023 (solar cycles 23, 24, and rise phase of 25) that were observed by the Ultra-Low Energy Ion Spectrometer (ULEIS) onboard the Advanced Composition Explorer (ACE). We categorize each event based on the spectral shape (single power law, roll-over) of ³He, ⁴He, Fe, & O, and we correlate each category with other relevant characteristics associated with the SEP event (e.g., ion fluence, ³He/⁴He, associated CMEs, flare class, solar cycle phase) in conjunction with concurring interplanetary magnetic field conditions to narrow down on the cause of the spectral variability of ³He-rich SEP events.