THE OCTOBER 22, 1989, SOLAR COSMIC-RAY ENHANCEMENT - AN ANALYSIS OF THE ANISOTROPY AND SPECTRAL CHARACTERISTICS

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 greater than or equal to 1 GV so lar protons. The results indicate an extended time period during which high-energy particles propagated past Earth with minimal scattering i n the local interplanetary medium. The deduced pitch angle distributio ns of tile particles propagating from the Sun show a relatively slow e volution from a focused particle flux, even though there are dramatic changes in the observed intensity-time profiles. Strong evidence is fo und that reverse scattering of particles beyond Earth resulted in bidi rectional flow along the local interplanetary magnetic field during th e second phase of the event.