3He-rich Solar Energetic Particle Observations at the Parker Solar Probe and near Earth

Abstract

The Integrated Science Investigation of the Sun (IS circle dot IS) instrument suite on the Parker Solar Probe (PSP) spacecraft is making in situ observations of energetic ions and electrons closer to the Sun than any previous mission. Using data collected during its first two orbits, which reached perihelion distances of 0.17 au, we have searched for He-3-rich solar energetic particle (SEP) events under very quiet solar minimum conditions. On 2019-110-111 (April 20-21), He-3-rich SEPs were observed at energies near 1MeV nucleon(-1) in association with energetic protons, heavy ions, and electrons. This activity was also detected by the Ultra-Low-Energy Isotope Spectrometer and the Electron, Proton, and Alpha Monitor instruments on the Advanced Composition Explorer (ACE) spacecraft located near Earth, 0.99 au from the Sun. At that time, PSP and ACE were both magnetically connected to locations near the west limb of the Sun. Remote sensing measurements showed the presence of type III radio bursts and also helical jets from this region of the Sun. This combination of observations is commonly associated with He-3-rich SEP acceleration on the Sun. AR 12738, which was located at Carrington coordinates from which numerous X-ray flares were observed over a period of more than 6 months, was identified as the source of the He-3-rich events. This region was also the source of several other SEP events detected at PSP or ACE. Aside from the period in 2019 April, IS circle dot IS did not observe any other He-3-rich SEPs during orbits 1 and 2.