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SUMMARY:Hard spectra of extreme Ground Level Enhancements
DTSTART;VALUE=DATE-TIME:20161011T101500Z
DTEND;VALUE=DATE-TIME:20161011T103000Z
DTSTAMP;VALUE=DATE-TIME:20260717T084735Z
UID:indico-contribution-586@cern.ch
DESCRIPTION:Speakers: Ilya Usoskin (University of Oulu)\nGround Level Enha
 ncement (GLE) is a significant increase of the count rate registered on gr
 ound-based neutron monitors (NMs). So far\, 72 GLEs have been recorded by 
 the worldwide neutron monitor network since the 1950s. The energy spectrum
  of solar energetic particles (SEP) for these events varied quite a lot be
 tween the events\, as measured directly and indirectly. Here we studied a 
 statistical relation between the event-integrated intensity of a GLE (expr
 essed in percent-hours) and the 'hardness' of the solar particle energy sp
 ectra\, quantified as the ratio of the the integral omnidirectional event-
 integrated fluences of particles with energy above 30 MeV ($F_{30}$) and a
 bove 200 MeV ($F_{200}$). We specifically analyzed the event-integrated en
 ergy spectrum for the GLE 71 (17-May-2012)\, the only directly measured by
  PAMELA over the entire span. We found no clear relation between the inten
 sity and the spectral hardness for weak and moderate GLE events\, but all 
 extreme GLE events were characterized by a very hard spectrum. This implie
 s that a hard spectrum can be securely assumed for all extreme GLE events\
 , e.g.\, those studied using cosmogenic isotope data in the past.\n\nhttps
 ://indico.particle.mephi.ru/event/4/contributions/586/
LOCATION:Milan Hotel Vivaldi-Boccerini
URL:https://indico.particle.mephi.ru/event/4/contributions/586/
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