The 2021 October 28 solar energetic particle (SEP) event was a rare ground level enhancement (GLE) event, where secondary particles from the interactions of SEPs with the Earth's atmosphere were detected by neutron monitors on the ground. A number of papers have examined the solar signatures, neutron monitor observations, and the characteristics of the SEP protons and electrons for this event. Here we describe the heavy ion signatures, specifically O and Fe, observed by multiple spacecraft. Parker Solar Probe, Solar Terrestrial Relations Observatory-Ahead, and Advanced Composition Explorer were distributed over nearly 60° in solar longitude and 0.4 au in heliocentric distance. Despite their separations, all three spacecraft measured event-integrated O and Fe spectra, well represented by power laws, with nearly the same power-law index of approximately −1.7, which is significantly harder than most large SEP events and many GLE events. Moreover, the Fe/O abundance ratio determined from these spectra was also found to be spatially invariant over the 60° in longitude and 0.4 au in heliocentric distance. Such near uniformity is highly unusual, and only one similar occurrence was found in a previous multispacecraft. The observed Fe/O ratio of 0.39 is higher than typical for large SEP events but not unusual for GLE events.
Longitudinal Dependence of Heavy Ion Composition in the 2021 October 28 Ground Level Enhancement Event
- Creators
- Cohen, C. M. S.1
- Mason, G. M.2
- Christian, E. R.3
- Cummings, A. C.1
- de Nolfo, G. A.3
- Desai, M. I.4, 5
- Giacalone, J.6
- Hill, M. E.2
- Labrador, A. W.1
- Leske, R. A.1
- McComas, D. J.7
- McNutt Jr, R. L.2
- Mitchell, D. G.2
- Mitchell, J. G.3
- Muro, G. D.1
- Rankin, J. S.7
- Schwadron, N. A.7, 8
- Shen, M. M.7
- Wiedenbeck, M. E.9
- Xu, Z. G.1
- Ho, G. C.4
- Wimmer-Schweingrüber, R. F.10
- 1. California Institute of Technology
- 2. Johns Hopkins University Applied Physics Laboratory
- 3. Goddard Space Flight Center
- 4. Southwest Research Institute
- 5. The University of Texas at San Antonio
- 6. University of Arizona
- 7. Princeton University
- 8. University of New Hampshire
- 9. Jet Propulsion Lab
- 10. Kiel University
Abstract
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins Applied Physics Laboratory (JHU/APL) 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. Solar Orbiter is a mission of international cooperation between ESA and NASA, operated by ESA. The Suprathermal Ion Spectrograph (SIS) is a European facility instrument funded by ESA under contract number SOL.ASTR.CON.00004. We thank ESA and NASA for their support of the Solar Orbiter and other missions whose data were used in this letter. Solar Orbiter post-launch work at JHU/APL and the Southwest Research Institute is supported by NASA contract NNN06AA01C and at CAU by German Space Agency (DLR) grant # 50OT2002. The UAH team acknowledges the financial support by the Spanish Ministerio de Ciencia, Innovacion y Universidades MCIU/AEI Project PID2019–104863RBI00/AEI/10.13039/501100011033. C.M.S.C. acknowledges additional partial funding from NASA grants 80NSSC22K0893, 80NSSC21K1327, 80NSSC20K1815, and 80NSSC19K0067.
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Additional details
- European Space Agency
- SOL.ASTR.CON.00004
- National Aeronautics and Space Administration
- NNN06AA01C
- Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
- 50OT2002
- Ministerio de Ciencia, Innovación y Universidades
- PID2019- 104863RBI00/AEI/10.13039/501100011033
- National Aeronautics and Space Administration
- 80NSSC22K0893
- National Aeronautics and Space Administration
- 80NSSC21K1327
- National Aeronautics and Space Administration
- 80NSSC20K1815
- National Aeronautics and Space Administration
- 80NSSC19K0067
- Accepted
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2024-12-20Accepted
- Available
-
2025-01-08Published
- Publication Status
- Published