Solar cosmic ray ‘square wave’ of August 1972

Three Rice University suprathermal ion detector experiments (Sides) were deployed on the lunar surface during the Apollo 12, 14, and 15 missions. During the exceptional period of solar activity in August 1972, penetrating particles were observed by all Side detectors on the night side of the moon. The penetrating particles are tentatively identified as solar protons with energies (∼25 MeV or greater) that were able to penetrate the shielding of all detectors. Of particular interest is the occurrence on August 5 of a ‘square wave’ flux enhancement of 2‐hour duration. Data from a variety of ground‐based and space experiments are examined in relation to the square wave. Based on the results of this investigation a model relating the square wave to the flare plasma propagation is proposed. This model hypothesizes transport of energetic particles along a ‘corridor’ formed by the tangential discontinuity produced by the driver gas of a flare‐induced shock wave. This model could explain other frequently observed delayed particle events.