Neutron monitor latitude survey of cosmic ray intensity during the 1986/1987 solar minimum

A latitude survey of the cosmic ray intensity at sea level was conducted during the 1986/1987 solar minimum period on commercial vessels of the South African Marine Corporation (SAFMARINE). The results show that the differential response function for the 1986/1987 solar minimum agrees well with that measured in 1965. Both these response functions are significantly lower than those for 1976 and 1954. This result supports the 22‐year modulation cycle as predicted, for example, by models including drift effects of the charged cosmic ray particles in the large‐scale interplanetary magnetic field. A cross‐over of the spectra at rigidities of about 7 GV was also observed. Such a crossover is necessary to explain both the stationary neutron monitor counting rates and the lower‐energy balloon and space observations in consecutive solar cycles.

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