3He-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 3He in the interplanetary medium near Earth over nearly two full solar cycles. The 3He isotope has been observed nearly 90% of the time at solar maximum, but no more than a few percent 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 3He-rich SEPs, and the spacecraft carries a two-instrument suite, IS☉IS, 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 3He-rich SEP events in the previously unexplored region <0.2AU from the Sun under conditions with extremely low energetic-particle backgrounds. We present an update of the long-term record of SEP 3He occurrence near 1AU and, with this context, discuss some advances that can be expected from PSP.
|Original language||English (US)|
|Journal||Proceedings of Science|
|State||Published - Jul 2 2021|
|Event||36th International Cosmic Ray Conference, ICRC 2019 - Madison, United States|
Duration: Jul 24 2019 → Aug 1 2019
All Science Journal Classification (ASJC) codes