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, http://dx.doi.org/10.1016/j.asr.2016.08.043. (http://www.sciencedirect.com/science/article/pii/S0273117716304963) 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
Persistent link: http://urn.fi/urn:nbn:fi-fe201708097929
Language: English
Published: Elsevier, 2017
Publish Date: 2019-08-15
Description:

Abstract

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
OADOI: https://oadoi.org/10.1016/j.asr.2016.08.043
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Subjects:
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.