The high-energy cosmic-ray flare of May 4, 1960: 1. High-altitude ionization and counter measurements

Total ionization and counting rate measurements were made at 6 g/cm2 depth at Minneapolis in the period from 7 to 16 hours following the cosmic-ray flare of May 4, 1960. The excess energy influx 7 hours after the flare was 340 Mev/cm2·sec in an atmospheric column. The omnidirectional ionization and counting rates were about 25 per cent above normal and the ionization ratio per particle was 1.2 times normal galactic cosmic rays at the same altitude. This is consistent with the high-energy nature of the event and contrasts greatly with the steep low-energy spectrum frequently observed during geomagnetic disturbances at Minneapolis. There is evidence for a displaced impact zone effect in the period 7 to 15 hours after the flare.