AbstractNearly 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 30MeV ( F 30 ) and above 200MeV ( F 200 ) 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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    Title :

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


    Contributors:
    Asvestari, E. (author) / Willamo, T. (author) / Gil, A. (author) / Usoskin, I.G. (author) / Kovaltsov, G.A. (author) / Mikhailov, V.V. (author) / Mayorov, A. (author)

    Published in:

    Advances in Space Research ; 60 , 4 ; 781-787


    Publication date :

    2016-08-30


    Size :

    7 pages




    Type of media :

    Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English





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