THE EFFECT OF A DISTORTED INTERPLANETARY MAGNETIC-FIELD CONFIGURATIONON THE DECEMBER 7-8, 1982, GROUND-LEVEL ENHANCEMENT

The cosmic ray ground level enhancement (GLE) of December 7-8, 1982, o ccurred when the interplanetary magnetic field (IMF) direction measure d near Earth indicated significant distortion from the nominal form. W e have modeled the ground level response to this event to derive rigid ity spectra and pitch angle distributions centered on apparent arrival directions. A deficit region associated with a near-Earth magnetic cl oud-like structure has been modeled during the initial phase of the GL E. Using this modified model, we find agreement between the derived pa rticle arrival directions and the measured IMF directions. We find a s ignificant contribution from pitch angles greater than 90 degrees thro ughout the event. This is probably due to scattering in the turbulent region behind the cloud-like structure.