University of Oulu

Owens, M.J., Barnard, L.A., Pope, B.J.S. et al. Solar Energetic-Particle Ground-Level Enhancements and the Solar Cycle. Sol Phys 297, 105 (2022).

Solar energetic-particle ground-level enhancements and the solar cycle

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Author: Owens, Mathew J.1; Barnard, Luke A.1; Pope, Benjamin J. S.2;
Organizations: 1Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading, RG6 6BB, UK
2School of Mathematics and Physics, University of Queensland, St Lucia, QLD, 4072, Australia
3Space Physics and Astronomy Research Unit and Sodankyla Geophysical Observatory, University of Oulu, 90014, Oulu, Finland
4Department of Physics, University of Helsinki, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.3 MB)
Persistent link:
Language: English
Published: Springer Nature, 2022
Publish Date: 2023-01-27


Severe geomagnetic storms appear to be ordered by the solar cycle in a number of ways. They occur more frequently close to solar maximum and the declining phase, are more common in larger solar cycles, and show different patterns of occurrence in odd- and even-numbered solar cycles. Our knowledge of the most extreme space-weather events, however, comes from spikes in cosmogenic-isotope (14C, 10Be, and 36Cl) records that are attributed to significantly larger solar energetic-particle (SEP) events than have been observed during the space age. Despite both storms and SEPs being driven by solar-eruptive phenomena, the event-by-event correspondence between extreme storms and extreme SEPs is low. Thus, it should not be assumed a priori that the solar-cycle patterns found for storms also hold for SEPs and the cosmogenic-isotope events. In this study, we investigate the solar-cycle trends in the timing and magnitude of the 67 SEP ground-level enhancements (GLEs) recorded by neutron monitors since the mid-1950s. Using a number of models of GLE-occurrence probability, we show that GLEs are around a factor of four more likely around solar maximum than around solar minimum, and that they preferentially occur earlier in even-numbered solar cycles than in odd-numbered cycles. There are insufficient data to conclusively determine whether larger solar cycles produce more GLEs. Implications for putative space-weather events in the cosmogenic-isotope records are discussed. We find that GLEs tend to cluster within a few tens of days, likely due to particularly productive individual active regions, and with approximately 11-year separations, owing to the solar-cycle ordering. However, these timescales would not explain any cosmogenic-isotope spikes requiring multiple extreme SEP events over consecutive years.

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Series: Solar physics
ISSN: 0038-0938
ISSN-E: 1573-093X
ISSN-L: 0038-0938
Volume: 297
Issue: 8
Article number: 105
DOI: 10.1007/s11207-022-02037-x
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was part-funded by the Science and Technology Facilities Council (STFC) grant numbers ST/R000921/1 and ST/V000497/1, and the Natural Environment Research Council (NERC) grant numbers NE/S010033/1 and NE/P016928/1. I.U. acknowledges the Academy of Finland (projects ESPERA No. 321882). E.A. acknowledges support from the Academy of Finland (Postdoctoral Researcher Grant 322455), and the Finnish Centre of Excellence in Research of Sustainable Space (Academy of Finland grant number 312390).
Academy of Finland Grant Number: 321882
Detailed Information: 321882 (Academy of Finland Funding decision)
Dataset Reference: Sunspot data are provided by the Royal Observatory of Belgium SILSO and available from The GLE database can be accessed here: The aaH-geomagnetic index data are available from All analysis and visualisation code is packaged with all required OMNI data here:
Copyright information: © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit