Letter to the Editor

The 18–19 March 2022 series of ³He-rich events observed by Solar Orbiter at 0.36 au compared with EUV, X-ray, and radio observations^⋆

¹ Johns Hopkins Univ. Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD, USA
e-mail: Glenn.Mason@jhuapl.edu
² Lockheed Martin Advanced Technology Center, Dept/A021S, B/252, 3251 Hanover Street, Palo Alto, CA, 94304, USA
³ Southwest Research Institute, 6220 Culebra Road, Sal Antonio, TX, 78238, USA
⁴ Universidad de Alcalá, Space Research Group, 28805 Alcalá de Henares, Madrid, Spain
⁵ Goddard Planetary Heliophysics Institute, University of Maryland, Baltimore County, Baltimore, MD, 21250, USA
⁶ Heliophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD, USA
⁷ University of Applied Sciences and Arts Northwestern Switzerland, 5210 Windisch, Switzerland
⁸ Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA, 94720, USA
⁹ Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Leibnizstrasse 11, Kiel, Germany
¹⁰ Radboud Radio Lab – Department of Astrophysics, Radboud University, Nijmegen, The Netherlands
¹¹ LESIA, Observatoire de Paris, Universite PSL, CNRS, Sorbonne Universite, Universite de Paris, 5 Place Jules Janssen, 92195 Meudon, France

Received: 29 November 2022
Accepted: 29 December 2022

Abstract

Context. During the first close perihelion pass of Solar Orbiter, a series of impulsive ³He-rich solar particle events was observed on 18–19 March 2022 from a distance of 0.36 au. In addition to the energetic particle, radio, and X-ray data from Solar Orbiter, the events were observed in radio and/or extreme ultraviolet by STEREO-A, SDO, Wind, and Parker Solar Probe.

Aims. Observations of the event series along with remote sensing of flaring and radio emission with only small timing delays due to the close distance allow the association with energetic particles to be determined with much higher accuracy than previously possible from 1 au.

Methods. By comparing the onsets of type-III bursts with the arrival of electrons of tens of keV at Solar Orbiter only a few minutes later, it can be seen that, overall, each of the more intense type-III bursts was associated with an electron and ion injection. Extreme ultraviolet data show that the times of the type-III bursts coincide with emission from a small (approximately Earth-sized) loop to the west of a nearby active region.

Results. The energetic particle spectra and abundances show typical properties of impulsive ³He-rich flares and, when combined with the remote sensing observations, establish that the particle-accelerating mechanism in this series of events operates near the solar surface in association with magnetic loops, and in the absence of other phenomena such as jets and small coronal mass ejections.