AN EXTENDED ANALYSIS OF THE SEPTEMBER 1989 COSMIC-RAY GROUND-LEVEL ENHANCEMENT

The September 29, 1989, cosmic ray ground level enhancement had a comp lex intensity-time profile with two distinct peaks observed at some ne utron monitors, The event was detected by surface and some underground muon telescopes indicating the presence of particles up to similar to 30 GV. We have modeled the response of neutron monitors and surface m uon telescopes at the times of both intensity peaks and during the dec ay phase, We have determined particle rigidity spectra and pitch angle distributions centered on apparent arrival directions. Some evidence of bidirectional flow is present during the second peak, This may be d ue to backscattering of particles from beyond Earth. There was a high degree of scattering from all directions resulting in a significant is otropic component. Spectra derived from ground level responses are con sistent with satellite observations, The spectrum between a few MeV an d a few tens of GeV is consistent with shock acceleration.