THE 1990 MAY 24 SOLAR COSMIC-RAY EVENT

This paper presents an integrated analysis of GOES 6, 7 and neutron mo nitor observations of solar cosmic-ray event following the 1990 May 24 solar flare. We have used a model which includes particle injection a t the Sun and at the interplanetary shock front and particle propagati on through the interplanetary medium. The model does not attempt to si mulate the physical processes of coronal transport and shock accelerat ion, therefore the injections at the Sun and at the shock are represen ted by source functions in the particle transport equation. By fitting anisotropy and angle-average intensity profiles of high-energy (>30 M eV) protons as derived from the model to the ones observed by neutron monitors and at GOES 6 and 7, we have determined the parameters of par ticle transport, the injection rate and spectrum at the source. We hav e made a direct fit of uncorrected GOES data with both primary and sec ondary proton channels taken into account. The 1990 May 24-26 energeti c proton event had a double-peaked temporal structure at energies simi lar to 100 MeV. The Moreton (shock) wave nearby the 'flare core' was s een clearly before the first injection of accelerated particles into t he interplanetary medium. Some (correlated with this shock) accelerati on mechanism which operates in the solar corona at a 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 spectru m during this increase is found to be hard (spectral index gamma appro ximate to 1.6) at lower energies (similar to 30 MeV) with a rapid stee pening above 300 MeV. Large values of the mean free path (lambda appro ximate to 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 in crease was presumably produced by acceleration/injection of particles by an interplanetary shock wave at height of approximate to 10 solar r adii. Our analysis of the 1990 May 24-26 event is in favour of the gen eral idea that a number of components of energetic particles may be pr oduced while the flare process develops towards larger spatial/tempora l scales.