Diffusion analysis of the GLE (ground-level enhancement) of September 29, 1989 | CU Experts

On September 29, 1989, neutron monitors and muon telescopes around the world recorded a significant increase in their count rate. This ground-level enhancement affords a unique opportunity to study the rigidity dependence of the interplanetary scattering mean free path, [Formula: see text]. By fitting the well-known diffusion model to worldwide neutron monitor and muon telescope data, we calculate the value of [Formula: see text] observed by each station. A plot of [Formula: see text] observed by each station versus the mean rigidity of solar flare particles observed by each station (which ranges from 3–16 GV) clearly indicates that [Formula: see text] is rigidity dependent. If we assume that [Formula: see text] for P > 3 GV, where the power-law index q is a measure of the deviation from isotropic scattering (q = 1), then we find that q = 0.86 ± 0.03 at the time of this ground-level enhancement.

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