Comparison of the Numerically Simulated Time-intensity Profile and Pitch-angle Distribution of GeV Solar Protons with the Unusual GLE Event of 22 OCT 1989.

Intense solar proton can sometimes be observed by ground-level based Neutron Monitors (NMs), and these are known as GroundLevel Enhancements (GLE). GLE events typically show a sharp rise in the count rate of NMs, followed by a gradual decay primarily associated with outward moving protons; however, in the GLE event of 22 OCT 1989, the initial outward sharp rise was followed by a rapid decay, and later followed by a second bi-directional spike with a slow decay. Such behavior cannot be explained using a model in which the GeV-energy protons are released impulsively at the Sun and move in the nominal Parker magnetic field. Other attempts considered two separate injections at the Sun (Shea and Smart, 1997; Makhmutov, 2002), or injection in the foot-point of the two legs of a large-scale closed magnetic flux tube, (Ruffulo 2006). In this study, we investigate if the transport of the GeV solar protons in the meandering IMF (Giacalone 2004), due to large-scale turbulence, can explain the unusual time-intensity profile and the pitch-angle distribution of GLE event of 22 OCT 1989. In our model, 1 GeV solar energetic protons are released near the Sun and the time-intensity profile and pitch-angle distributions of the SEPs crossing one AU are obtained using a fully relativistic 3D test particle simulation which solves the equations of motion for 3 million test particles. Our model also includes pitch-angle scattering. We find results that are qualitatively similar to the observations.