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Published February 2025 | Version Published
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Solar energetic particles injected inside and outside a magnetic cloud. The widespread solar energetic particle event on 2022 January 20

Creators

  • 1. ROR icon European Space Astronomy Centre
  • 2. ROR icon University of Alcalá
  • 3. ROR icon University of Turku
  • 4. ROR icon Goddard Space Flight Center
  • 5. ROR icon George Mason University
  • 6. ROR icon Predictive Science (United States)
  • 7. ROR icon Johns Hopkins University Applied Physics Laboratory
  • 8. ROR icon Leibniz Institute for Astrophysics Potsdam
  • 9. ROR icon University College London
  • 10. ROR icon University of Science and Technology of China
  • 11. ROR icon University of Central Lancashire
  • 12. ROR icon University of California, Berkeley
  • 13. ROR icon California Institute of Technology
  • 14. ROR icon Southwest Research Institute
  • 15. ROR icon National Observatory of Athens

Abstract

Context. On 2022 January 20, the Energetic Particle Detector (EPD) on board Solar Orbiter measured a solar energetic particle (SEP) event showing unusual first arriving particles from the anti-Sun direction. Near-Earth spacecraft separated by 17° in longitude to the west of Solar Orbiter measured classic anti-sunward-directed fluxes. STEREO-A and MAVEN, separated by 18° to the east and by 143° to the west of Solar Orbiter, respectively, also observed the event, suggesting that particles spread over at least 160° in the heliosphere.

Aims. The aim of the present study is to investigate how SEPs are accelerated and transported towards Solar Orbiter and near-Earth spacecraft, as well as to examine the influence of a magnetic cloud (MC) present in the heliosphere at the time of the event onset on the propagation of energetic particles.

Methods. We analysed remote-sensing data, including flare, coronal mass ejection (CME), and radio emission to identify the parent solar source of the event. We investigated energetic particles, solar wind plasma, and magnetic field data from multiple spacecraft.

Results. Solar Orbiter was embedded in a MC erupting on 16 January from the same active region as that related to the SEP event on 20 January. The SEP event is related to a M5.5 flare and a fast CME-driven shock of ∼1433 km s−1, which accelerated and injected particles within and outside the MC. Taken together, the hard SEP spectra, the presence of a Type II radio burst, and the co-temporal Type III radio burst being observed from 80 MHz that appears to emanate from the Type II burst, suggest that the shock is likely the main accelerator of the particles.

Conclusions. Our detailed analysis of the SEP event strongly suggests that the energetic particles are mainly accelerated by a CME-driven shock and are injected into and outside of a previous MC present in the heliosphere at the time of the particle onset. The sunward-propagating SEPs measured by Solar Orbiter are produced by the injection of particles along the longer (western) leg of the MC still connected to the Sun at the time of the release of the particles. The determined electron propagation path length inside the MC is around 30% longer than the estimated length of the loop leg of the MC itself (based on the graduated cylindrical shell model), which is consistent with the low number of field line rotations.

Copyright and License

© The Authors 2025.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

LRG acknowledges support through the European Space Agency (ESA) research fellowship programme. The UAH team acknowledges the financial support by the Spanish Ministerio de Ciencia, Innovación y Universidades FEDER/MCIU/AEI Projects ESP2017-88436-R and PID2019-104863RB-I00/AEI/10.13039/501100011033 and by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 101004159 (SERPENTINE). ND is grateful for support by the Research Council of Finland (SHOCKSEE, grant No. 346902). ND, CP, AW, and RV acknowledge funding by the European Union’s Horizon Europe research and innovation program under grant agreement No. 101134999 (SOLER). LAB acknowledges the support from the NASA program NNH17ZDA001N-LWS (Awards Nr. 80NSSC19K0069 and 80NSSC19K1235). EP acknowledges support from NASA’s LWS (grant no. 80NSSC19K0067) and LWS-SC (grant no. 80NSSC22K0893) programmes. AK acknowledges financial support from NASA NNN06AA01C (SO-SIS Phase-E) contract. ICJ acknowledges the support of Academy of Finland (SHOCKSEE, grant 346902). AW acknowledges support by the German Space Agency (DLR), grant numbers 50 OT 2304. JG thanks the support from National Natural Science Foundation of China (Grant Nos. 42188101, 42130204, 42474221. TL acknowledges support from the UK Science and Technology Facilities Council (STFC) through grants ST/V000934/1 and ST/Y002725/1. COL acknowledges support from the NASA LWS program (grant no. 80NSSC21K1325) and the MAVEN project funded through the NASA Mars Exploration Program. RV also acknowledges funding by the Research Council of Finland (FORESAIL, grant No. 352847). The authors acknowledge the different SOHO, STEREO instrument teams, and the STEREO and ACE science centers for providing the data used in this paper. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. This research has used PyThea v0.7.3, an open-source and free Python package to reconstruct the 3D structure of CMEs and shock waves (GCS and ellipsoid model). ENLIL simulation results have been provided by the CCMC at NASA Goddard Space Flight Center (GSFC) through their public Runs on Request system (http://ccmc.gsfc.nasa.gov; run ID Laura_Rodriguez-Garcia_121523_SH_1). The WSA model was developed by N. Arge, currently at GSFC, and the ENLIL Model was developed by D. Odstrcil, currently at George Mason University.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2409.04564 (arXiv)

Funding

European Space Agency
Ministerio de Ciencia, Innovación y Universidades
ESP2017-88436-R
Ministerio de Ciencia, Innovación y Universidades
PID2019-104863RB-I00
European Union
101004159
Research Council of Finland
SHOCKSEE 346902
European Union
SOLER 101134999
National Aeronautics and Space Administration
NNH17ZDA001N-LWS
National Aeronautics and Space Administration
80NSSC19K0069
National Aeronautics and Space Administration
80NSSC19K1235
National Aeronautics and Space Administration
80NSSC19K0067
National Aeronautics and Space Administration
80NSSC22K0893
National Aeronautics and Space Administration
NNN06AA01C
Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
50 OT 2304
National Natural Science Foundation of China
42188101
National Natural Science Foundation of China
42130204
National Natural Science Foundation of China
42474221
Science and Technology Facilities Council
ST/V000934/1
Science and Technology Facilities Council
ST/Y002725/1
National Aeronautics and Space Administration
80NSSC21K1325
National Aeronautics and Space Administration
MAVEN Project -
Research Council of Finland
FORESAIL 352847

Dates

Accepted
2024-12-05
Accepted
Available
2025-02-04
Published online

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