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Great Storm Particle Event on 2000 August 11 Observed by SOHO ERNE

  • Author: Torsti, J.; Mäkelä, P.; Riihonen, E.; Saloniemi, O.
  • Publication: The Astrophysical Journal, Volume 638, Issue 1, pp. 530-538, 2006
  • Solar event of 2000 August 11
  • Case study
  • ADS link
  • Abstract: We report on an energetic storm particle event on 2000 August 11 observed by ERNE on board SOHO. A large-intensity enhancement started simultaneously in all energy channels between 2 and 50 MeV at 11 UT. The concurrence of the onsets indicates the local nature of the particle event. Intensities increased 100-fold from the background level before 11 UT to the maximum of the event around 15:30 UT. Three hours after the maximum, at 18:19 UT, the SOHO CELIAS Proton Monitor observed the passage of an interplanetary shock. Our analysis of the proton energy spectrum during the event indicates that the interplanetary shock was capable of accelerating particles up to energies of an order of 50 MeV. Assuming that the energy spectrum prevailing in the event describes the seed particle population for shock reacceleration, we find that the energy spectrum during major phases of the energetic storm particle event matches well with the assumption of a constant energy conversion power by the shock over the whole energy range from 2 to 50 MeV. We analyze the evolution of anisotropy of the proton flux in the 16-20 MeV channel of ERNE. The distribution of the directional intensity was observed to be relatively flat in the beginning of the event. Then the upstream distribution developed into a loss-cone-like distribution, and the intensity along the magnetic field relative to the intensity in the perpendicular direction was systematically reduced. At the shock passage, the distribution resembled a pancake.


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