The effect of a distorted interplanetary magnetic field configuration on the December 7-8, 1982, ground level enhancement

The cosmic ray ground level enhancement (GLE) of December 7-8, 1982, occurred when the interplanetary magnetic field (IMF) direction measured near Earth indicated significant distortion from the nominal form. We have modeled the ground level response to this event to derive rigidity spectra and pitch angle distributions centered on apparent arrival directions. A deficit region associated with a near-Earth magnetic cloud-like structure has been modeled during the initial phase of the GLE. Using this modified model, we find agreement between the derived particle arrival directions and the measured IMF directions. We find a significant contribution from pitch angles greater than 90° throughout the event. This is probably due to scattering in the turbulent region behind the cloud-like structure. Copyright 1997 by the American Geophysical Union.