University of Oulu

E. Asvestari, T. Willamo, A. Gil, I.G. Usoskin, G.A. Kovaltsov, V.V. Mikhailov, A. Mayorov, Analysis of Ground Level Enhancements (GLE): Extreme solar energetic particle events have hard spectra, Advances in Space Research, Volume 60, Issue 4, 2017, Pages 781-787, ISSN 0273-1177, ( Keywords: Solar energetic particles; Cosmic rays

Analysis of Ground Level Enhancements (GLE) : extreme solar energetic particle events have hard spectra

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Author: Asvestari, E.1; Willamo, T.2; Gil, A.1,3;
Organizations: 1ReSoLVE Centre of Excellence, University of Oulu, FIN-90014 Oulu, Finland
2University of Helsinki, FIN-00014 Helsinki, Finland
3nstitute of Mathematics and Physics, Siedlce University, Stanislawa Konarskiego 2, 08-110 Siedlce, Poland
4Sodankylä Geophysical Observatory, University of Oulu, FIN-90014 Oulu, Finland
5Ioffe Physical-Technical Institute, Politechnicheskaya St. 26, 194021 St. Petersburg, Russia
6National Research Nuclear University “MEPhI”, Kashirskoye Sh. 31, 115409 Moscow, Russia
Format: article
Version: accepted version
Access: embargoed
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Language: English
Published: Elsevier, 2017
Publish Date: 2019-08-15


Nearly 70 Ground Level Enhancements (GLEs) of cosmic rays have been recorded by the worldwide neutron monitor network since the 1950s depicting a big variety of energy spectra of solar energetic particles (SEP). Here we studied a statistical relation between the event-integrated intensity of GLEs (calculated as count-rate relative excess, averaged over all available polar neutron monitors, and expressed in percent-hours) and the hardness of the solar particle energy spectra. For each event the integral omnidirectional event-integrated fluences of particles with energy above 30 MeV (F30) and above 200 MeV (F200) were computed using the reconstructed spectra, and the ratio between the two fluences was considered as a simple index of the event’s hardness. We also provided a justification of the spectrum estimate in the form of the Band-function, using direct PAMELA data for GLE 71 (17-May-2012). We found that, while there is no clear relation between the intensity and the hardness for weak events, all strong events with the intensity greater 100 %∗h are characterized by a very hard spectrum. This implies that a hard spectrum can be securely assumed for all extreme GLE events, e.g., those studied using cosmogenic isotope data in the past.
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Series: Advances in space research
ISSN: 0273-1177
ISSN-E: 1879-1948
ISSN-L: 0273-1177
Volume: 60
Issue: 4
Pages: 781 - 787
DOI: 10.1016/j.asr.2016.08.043
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was supported by the Center of Excellence ReSoLVE (Project No. 272157)
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Copyright information: © 2016 COSPAR. Published by Elsevier Ltd. All rights reserved.