University of Oulu

Papaioannou, A., Kouloumvakos, A., Mishev, A., Vainio, R., Usoskin, I., Herbst, K., Rouillard, A. P., Anastasiadis, A., Gieseler, J., Wimmer-Schweingruber, R., & Kühl, P. (2022). The first ground-level enhancement of solar cycle 25 on 28 October 2021. Astronomy & Astrophysics, 660, L5.

The first ground-level enhancement of solar cycle 25 on 28 October 2021

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Author: Papaioannou, A.1; Kouloumvakos, A.2; Mishev, A.3;
Organizations: 1Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing (IAASARS), National Observatory of Athens, I. Metaxa & Vas. Pavlou St., 15236 Penteli, Greece
2IRAP, Université Toulouse III-Paul Sabatier, CNRS, CNES, Toulouse, France
3Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
4Department of Physics and Astronomy, University of Turku, 20500 Turku, Finland
5Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3.9 MB)
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Language: English
Published: EDP Sciences, 2022
Publish Date: 2023-03-07


Aims: The first relativistic solar proton event of solar cycle 25 was detected on 28 October 2021 by neutron monitors (NMs) on the ground and particle detectors on board spacecraft in near-Earth space. This is the first ground-level enhancement (GLE) of the current cycle. A detailed reconstruction of the NM response together with the identification of the solar eruption that generated these particles is investigated based on in situ and remote-sensing measurements.

Methods: In situ proton observations from a few MeV to ∼500 MeV were combined with the detection of a solar flare in soft X-rays, a coronal mass ejection, radio bursts, and extreme ultraviolet (EUV) observations to identify the solar origin of the GLE. Timing analysis was performed, and a relation to the solar sources was outlined.

Results: GLE73 reached a maximum particle rigidity of ∼2.4 GV and is associated with type III, type II, and type IV radio bursts and an EUV wave. A diversity of time profiles recorded by NMs was observed. This points to the event having an anisotropic nature. The peak flux at E > 10 MeV was only ∼30 pfu and remained at this level for several days. The release time of ≥1 GV particles was found to be ∼15:40 UT. GLE73 had a moderately hard rigidity spectrum at very high energies (γ ∼ 5.5). Comparison of GLE73 to previous GLEs with similar solar drivers is performed.

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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 660
Article number: L5
DOI: 10.1051/0004-6361/202142855
Type of Publication: B1 Journal article
Field of Science: 115 Astronomy and space science
Copyright information: © ESO 2022