PoS - Proceedings of Science
Volume 358 - 36th International Cosmic Ray Conference (ICRC2019) - SH - Solar & Heliospheric
Occurrence of $^3$He-rich Solar Energetic Particles near Earth and Closer to the Sun
M.E. Wiedenbeck*, G.M. Mason, C.M.S. Cohen, D.J. McComas, E.R. Christian and  for the Advanced Composition Explorer SIS and ULEIS Teams and the Parker SolarProbe ISIS Team
Full text: pdf
Pre-published on: August 29, 2019
Published on: July 02, 2021
Abstract
$^3$He-rich solar energetic particle (SEP) events, which result from the acceleration of energetic particles in association with reconnection events on the Sun, are identified on the basis of 3He/4He enhancements of at least several orders of magnitude over the solar coronal value of ~0.04%. The ULEIS and SIS instruments on the Advanced Composition Explorer (ACE) have been measuring the occurrence of SEP $^3$He in the interplanetary medium near Earth over nearly two full solar cycles. The $^3$He isotope has been observed nearly 90% of the time at solar maximum, but no more than a few % of the time at solar minimum. NASA’s Parker Solar Probe (PSP) spacecraft was launched in August 2018 on a mission designed to include 24 close flybys of the Sun over seven years. PSP’s scientific objectives include the study of the acceleration and transport of $^3$He-rich SEPs, and the spacecraft carries a two-instrument suite, ISOIS, that has the capability to perform these studies. The first two orbits of PSP occurred under extremely quiet solar-minimum conditions, which will provide an opportunity to search for small $^3$He-rich SEP events in the previously unexplored region <0.2 AU from the Sun under conditions with extremely low energetic-particle backgrounds. We present an update of the long-term record of SEP $^3$He occurrence near 1 AU and, with this context, discuss some advances that can be expected from PSP.
DOI: https://doi.org/10.22323/1.358.1171
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