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The 1990 May 24 Solar Cosmic-Ray Event

  • Authors: Torsti, J.; Kocharov, L. G.; Vainio, R.; Anttila, A.; Kovaltsov, G. A.
  • Publication: Solar Physics, v. 166, p.135, 1996
  • Solar event of 1990 May 24
  • Case study
  • ADS link
  • Abstract: This paper presents an integrated analysis of GOES 6, 7 and neutron monitor observations of solar cosmic-ray event following the 1990 May 24 solar flare. We have used a model which includes particle injection at the Sun and at the interplanetary shock front and particle propagation through the interplanetary medium. The model doesnot attempt to simulate the physical processes of coronal transport and shock acceleration, therefore the injection at the Sun and at the shock are represented by source functions in the particle transport equations. By fitting anisotropy and angle-average intensity profiles of high energy (> 30 MeV) protons as derived from the model to the ones observed by the neutron monitors and at GOES 6 and 7, we have determined the parameters of particle transport, the injection rate and the spectrum at the source. We have made a direct fit of uncorrected GOES data with both primary and secondary proton channels taken into account.

The 1990 May 24-26 energetic proton event had a double-peaked temporal structure at energies ~100 MeV. The Moreton (shock) wave nearby the 'flare core' was seen clearly before the first injection of accelerated particles into the interplanetary medium. Some (correlated with this shock) acceleration mechanism which operates in the solar corona at the height up to one solar radius is regarded as a source of the first (prompt) increase in GOES and neutron monitor counting rates. The proton injection spectrum during this increase is found to be hard (spectral index γ~1,6) at lower energies (~30 MeV) with a rapid steepening above 300 MeV. Large values of the mean free path (λ~1.8 AU for 1 GV protons in the vicinity of the Earth) led to a high anisotropy of arriving protons. The second (delayed) proton increase was presumably produced by acceleration/injection of particles by an interplanetary shock wave at hight of ~ 10 solar radii. Our analysis of the 1990 May 24-26 event is in favour of the general idea that a number of components of energetic particles may be produced while the flare process develops towards larger spatial/temporal scales.


Created by mevali. Last Modification: Wednesday 23 of May, 2007 09:43:58 UTC by mevali.