Investigating GLE73, the first Ground Level Enhancement of solar cycle 25
Athanasios Papaioannou, National Observatory of Athens, IAASARS, Penteli, Greece
Athanasios Kouloumvakos, The Johns Hopkins University Applied Physics Laboratory, Maryland, USA
Alexander Mishev, Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
Rami Vainio, Department of Physics and Astronomy, University of Turku, Turku, Finland
Ilya Usoskin, Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
Konstantin Herbst, Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany
Alexis P. Rouillard, IRAP, Université Toulouse III—Paul Sabatier, CNRS, CNES, Toulouse, France
Anastasios Anastasiadis, National Observatory of Athens, IAASARS, Penteli, Greece
Jan Giesler, Department of Physics and Astronomy, University of Turku, Turku, Finland
Robert Wimmer-Schweingruber, Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany
and Patrick Kuhl, Institut 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). he 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.
Oral