The October 22, 1989, solar cosmic ray enhancement: An analysis of the anisotropy and spectral characteristics

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Abstract
A solar cosmic ray ground‐level enhancement was observed at Earth on October 22, 1989, with an extremely anisotropic onset. On the basis of neutron monitor data we have derived the arrival directions, spectra, and pitch angle distributions of the ≥1 GV solar protons. The results indicate an extended time period during which high‐energy particles propagated past Earth with minimal scattering in the local interplanetary medium. The deduced pitch angle distributions of the particles propagating from the Sun show a relatively slow evolution from a focused particle flux, even though there are dramatic changes in the observed intensity‐time profiles. Strong evidence is found that reverse scattering of particles beyond Earth resulted in bidirectional flow along the local interplanetary magnetic field during the second phase of the event.