The 1990 May 24 solar cosmic-ray event

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 does not attempt to simulate the physical processes of coronal transport and shock acceleration, therefore the injections at the Sun and at the shock are represented by source functions in the particle transport equation. By fitting anisotropy and angleaverage intensity profiles of high-energy (>30 MeV) 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 particle transport, the injection rate and 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 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 spectrum during this increase is found to be hard (spectral index "7 ~ 1.6) at lower energies (,-~ 30 MeV) with a rapid steepening above 300 MeV. Large values of the mean free path (), ~ 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 height 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.

Injection of energetic protons during solar eruption on 1999 May 9: Effect of flare and coronal mass ejection

“…Furthermore, these authors assume that posteruptive soft X-ray arcades are the main candidate for coronal acceleration, antithetical to the CME bow shock acceleration in the interplanetary medium. It is surprising that we are listed among the authors who have suggested this, referring to Kocharov et al (1994) and Torsti et al (1996Torsti et al ( , 1998. The assumption that posteruptive arcades should produce significant SEP events even when the associated CMEs are too slow to drive shocks, was formulated and tested by Kahler et al (2000).…”

“…Also in the case of well-connected SEP events with a double-peak structure, coronal shocks may contribute to the early component, whereas the last production is caused by the interplanetary shock wave driven by the CME (Torsti et al 1996;Laitinen et al 2000).…”

Observation of a Moreton Wave and Wave-Filament Interactions Associated With the Renowned X9 Flare on 1990 May 24

“…Besides prominent microwave ) and hard X-ray (HXR; Pelaez et al 1992) emission, this renowned X9/1B flare simultaneously produced energetic neutrons, protons, and γ -rays, and has since been studied extensively (Shea et al 1991;Debrunner et al 1992Debrunner et al , 1993Debrunner et al , 1997Kocharov et al 1994Kocharov et al , 1996Torsti et al 1996;Vilmer et al 2003). The γ -ray lightcurve up to 95 MeV measured by the PHEBUS detector on the GRANAT spacecraft shows two peaks at 20:48:12 and 20:48:36 UT, respectively (Debrunner et al 1997).…”

ERNE observations of energetic particles associated with Earth-directed coronal mass ejections in April and May, 1997

“…CMEs faster than the ambient solar wind are decelerating, and CMEs slower than the solar wind are accelerating during their passage through the heliosphere (e.g., Gosling, 1996). The IP transport of the particles is treated numerically by using Monte Carlo simulations of Green's functions as described by Torsti et al (1996). The interplanetary transport is calculated from the pitch angle distribution integrated over the whole event.…”

“…We obtained values k r (1 GV) = 0.37 AU for the April 7 event and k r (1 GV) = 0.15 AU for the May 12 event. The best ®t for the observed intensity at 1 AU was then obtained by convoluting the Monte Carlo simulated IP transport Green's function with the source function q(E,t) (Torsti et al, 1996;Anttila et al, 1998).…”