The low‐frequency spectral behavior of cosmic ray intensity

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Abstract
Power spectral analysis of cosmic ray intensity recorded by neutron monitors at Calgary and Deep River, Alberta, was carried out over a wide range of frequencies from 3×10−9Hz to 6×10−6Hz (periodicities from 2 days to 11 years) during the epoch 1965–1989 and revealed different behavior of the power spectral density for the three ranges of frequency domains. At low frequencies corresponding to the periodicity T ≈ 20 months the power spectrum shows an abrupt change in the level and profile of power spectral density (PSD). This indicates that the processes responsible for the long‐period variations are different from the one which causes short‐period variations. At middle frequencies corresponding to periodicities between 6 and 18 months, the PSD indicates that the periodicities are not stable and show a transient character over the entire epoch of analysis. The PSD for periods T ≈ 27 days indicates an 11 year recurring tendency related to solar activity. The PSD for periods T > 27 days indicates a depression during the minimum of solar activity showing a 22 year recurring tendency and suggests that it is controlled by drift effects which are correlated to the solar polar field reversal. For higher frequencies f > 2×10−6Hz corresponding to periods T < 6 days, the slope of the PSD is found to be similar to that of the interplanetary magnetic field inhomogeneties measured at different radial distances between 1 and 30 AU.