Prompt injection of relativistic protons from the September 1, 1971 solar flare

The September 1, 1971 flare in McMath region 11482 was projected to have occurred 30° behind the west limb. An anisotropic Ground Level Effect (GLE) began <30 min after the inferred explosive phase of the flare. We attribute the rapid injection of relativistic protons onto the earth spiral field line to a shock wave associated with an observed type II burst.