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Published February 2020 | Supplemental Material + Published
Journal Article Open

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


The Integrated Science Investigation of the Sun (IS⊙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 ³He-rich solar energetic particle (SEP) events under very quiet solar minimum conditions. On 2019-110–111 (April 20–21), ³He-rich SEPs were observed at energies near 1 MeV 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 ³He-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 ³He-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⊙IS did not observe any other ³He-rich SEPs during orbits 1 and 2.

Additional Information

© 2020. The American Astronomical Society. Received 2019 October 6; revised 2019 October 29; accepted 2019 October 30; published 2020 February 3. Early Results from Parker Solar Probe: Ushering a New Frontier in Space Exploration We thank the large team of people responsible for developing the IS☉IS instruments and, particularly, the lead IS☉IS/EPI-Hi engineers, including Rick Cook, Branislav Kecman, Greg Dirks, and Nigel Angold. We gratefully acknowledge the test and calibration support provided by Michigan State University's National Superconducting Cyclotron Laboratory, Texas A&M University's Cyclotron Institute, and the Lawrence Berkeley National Laboratory's 88-inch Cyclotron Laboratory. PSP was designed, built, and is now operated by the Johns Hopkins Applied Physics Laboratory as part of NASA's Living with a Star (LWS) program (contract NNN06AA01C). Support from the LWS management and technical team has played a critical role in the success of the Parker Solar Probe mission. This study benefited from discussions within the International Space Science Institute (ISSI) team on "Origins of ³He-Rich Solar Energetic Particles." The ACE work was supported under NASA grant 80NSSC18K0223, and the PSP work was supported under NASA contract NNN06AA01C. The work of R.B. was supported by DFG grant BU 3115/4-1. S.D.B. acknowledges the support of the Leverhulme Trust Visiting Professorship program. The IS☉IS data and visualization tools are available to the community at: https://spacephysics.princeton.edu/missions-instruments/isois; data are also available via the NASA Space Physics Data Facility (https://spdf.gsfc.nasa.gov/).

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