PoS - Proceedings of Science
Volume 444 - 38th International Cosmic Ray Conference (ICRC2023) - Solar & Heliospheric Physics (SH)
Observations of Extremely 3He-Rich Solar Energetic Particle Events from Parker Solar Probe
R. Leske*, E. Christian, C. Cohen, A.C. Cummings, A. Davis, G.A. De Nolfo, M. Desai, J. Giacalone, M. Hill, A. Labrador, D. McComas, R.L. McNutt Jr., R.A. Mewaldt, D.G. Mitchell, J.G. Mitchell, J. Rankin, N. Schwadron, T. Sharma, M. Shen, J. Szalay, M. Wiedenbeck, A. Vourlidas, S. Bale, M. Pulupa, J. Kasper, D. Larson and P. Whittleseyet al. (click to show)
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Pre-published on: July 25, 2023
Published on: September 27, 2024
Abstract
Since its launch in 2018, the Integrated Science Investigation of the Sun (ISOIS) instrument suite on Parker Solar
Probe has observed numerous periods of $^{3}$He-rich solar energetic particle (SEP) events. Notable among them are
some very small events that occurred on 21 January 2021 and 30 May 2022, in both cases when Parker was within 0.2 AU of the Sun.
In these events the $^{3}$He/$^{4}$He ratio was greater than 10 at $\sim$1 MeV/nucleon but rapidly decreased with increasing
energy since $^{3}$He had softer spectra than $^{4}$He. Although unusual, similar extreme enrichments of $^{3}$He have
occasionally been observed at 1 AU in other events. The events seen by Parker were anisotropic, had velocity dispersion
yielding inferred pathlengths longer than expected for scatter-free transport along a nominal Parker spiral, and were associated
with type III radio emission detected by Parker/FIELDS. We present the Parker observations of the time profiles, spectra, composition,
velocity dispersion, and anisotropies of these events and compare them with previous $^{3}$He-rich SEP events detected much
farther from the Sun.
DOI: https://doi.org/10.22323/1.444.1251
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