EGU22-5504, updated on 27 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Characteristics of the First Ground Level Enhancement (GLE) of Solar Cycle 25 on 28 October 2021

Athanasios Papaioannou1, Athanasios Kouloumvakos2, Alexander Mishev3, Rami Vainio4, Ilya Usoskin3, Konstantin Herbst5, Alexis P. Rouillard2, Anastasios Anastasiadis1, Jan Giesler4, Robert Wimmer-Schweingruber5, and Patrick Kuhl5
Athanasios Papaioannou et al.
  • 1National Observatory of Athens, IAASARS, 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

We present an overview of the first ground-level enhancement (GLE) event of solar cycle 25, recorded on 28 October 2021 (GLE73), based on the available neutron monitor (NM) network observations and on data from near-Earth spacecraft (GOES, SOHO, SolO). The maximum increase was ~7.3% for DOMC (Dome C NM at Concordia station) and 5.4% for SOPO (South Pole) conventional NMs located on the Antarctic plateau. Bare (lead-free) NMs at the same sites detected a higher response (14.0% for DOMB and 6.6% for SOPB). The Fort Smith (FSMT) NM shows the earliest increase among the high-latitude NMs, indicating a moderate anisotropy in the first phase of the GLE event. The maximum rigidity of accelerated protons did not exceed 2.4 GV. We estimated the solar release time (SRT) of ≥1 GV protons into open magnetic field lines at ~15:40 UT.  In-situ proton observations from near-Earth spacecraft were combined with the detection of a solar flare in soft X-rays (SXRs), a coronal mass ejection (CME), radio bursts and extreme ultraviolet (EUV) observations to identify the solar origin of the GLE. Around the ≥1 GV proton SRT the CME-driven shock was located at a height of ~2.33 Rs. The timing of the EUV wave evolution towards the field lines magnetically connected to Earth seem to be in good agreement with the inferred release time of ≥1 GV protons.

How to cite: Papaioannou, A., Kouloumvakos, A., Mishev, A., Vainio, R., Usoskin, I., Herbst, K., Rouillard, A. P., Anastasiadis, A., Giesler, J., Wimmer-Schweingruber, R., and Kuhl, P.: Characteristics of the First Ground Level Enhancement (GLE) of Solar Cycle 25 on 28 October 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5504,, 2022.

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