Unique series of increases in cosmic-ray intensity due to solar flares

Abstract

THE second half of 1989 was the most prolific period of relativistic particle production by the Sun since continuous monitoring of cosmic-ray activity by neutron detectors was begun in 1957. Some of last year's events were among the largest bursts of particles observed throughout the last three solar cycles. Only when the particles released by the Sun during flares have energies greater than 0.5 gigaelectronvolt (GeV) are the secondary particles generated through interactions in the upper atmosphere able to reach ground level. Six different ground-level events were detected by the super neutron monitor in Calgary (geomagnetic latitude and longitude 51.08° N 245.91°, altitude 1,128 m, cut-off 1.07 GV) in the period July to October 1989. The intensity of energetic particle fluxes during these ground-level events is high enough to be a potential hazard, especially for passengers in aircraft at altitudes of 10 to 15 km.