Forbush decrease of the flux of heavy primary nuclei of cosmic rays on May 12 and July 12, 1959

Abstract

The time variation of the flux of heavy nuclei with Z ≥ 3 of primary cosmic radiation has been measured during seven balloon flights on May 6-12, 1959, and on July 10-12, 1959. Six of these flights were made from Minneapolis and one from Churchill, Canada. During a quiet day on May 6, 1959, the flux of these nuclei at the top of the atmosphere was 21.2 ± 2.3 particles/m².sec.sr. After the orbush decrease on May 12, 1959, the value was 10.0 ۫ 4 particles/m².sec.sr, showing a reduction of 53 ± 9 per cent of the primary heavy nuclei flux. On July 10-11, the flux of Z ≥ 3 nuclei at the top of the atmosphere as measured as 17.5 ± 1.7 particles/m².sec.sr before the Forbush decrease and 10.0 ± 1.8 particles/m².sec.sr after the Forbush decrease on July 12. The reduction was 43 ± 9 per cent during this event. The Deep River neutron monitor showed a reduction of counting rates of 12 and 7.5 per cent respectively during these two Forbush decrease events.