Variations in the cosmic radiation, 1890–1986, and the solar and terrestrial implications Original Research Article

Comparison of cosmogenic 10Be data and the records from several independent cosmic ray instruments for the period 1933–1977 demonstrates that the 10Be data provide a reliable measure of the ∼2 GeV/nucleon cosmic ray intensity at Earth, over short (∼5 years) and long (>20 years) time scales. The 10Be data show that the cosmic ray flux at sunspot minimum was anticorrelated with Zmin, the sunspot number at solar minimum over the interval 1901–1986. There was a 26% enhancement in the 10Be data in the interval 1951–1954, and the data from two independent cosmic ray instruments verify that this was due an influx of low energy (<3 GeV/nucleon) cosmic radiation. It is suggested that this enhancement was associated with the very low sunspot number in 1954 (one of the lowest outside the Maunder and Dalton Minima), and with an anomalous cosmic ray diurnal variation in 1954. It is proposed that these several observations are the consequence of cosmic ray drift effects, and that the heliomagnetic field was relatively ordered in 1954. It is shown that the enhancement of 1954 is not consistent with the several models of the open solar magnetic field, unless factors other than the magnetic field strength are taken into account. Using the instrumental and 10Be data, the cosmic ray spectra are estimated for 1965, 1954, 1890–1895, 1810–1820, and 1680–1720. From these, the ionization in the Earthʹs polar atmosphere is estimated for each of these periods.