The low‐frequency spectral behavior of cosmic ray intensity

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 3×10−9 Hz to 6×10−6 Hz (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 > 2×10−6 Hz 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.

Low- and high-frequency spectral behavior of cosmic-ray intensity for the period 1953–1996

“…A network of periodicities rang-ing from 130 to 65 months with a significance level >99.5% has appeared in which the periodicities of 130 and 86.7 m are more distinguished, while the peak of 65 m is not easily well-recognized. It is noticeable that there is a change in the spectrum slope below the period of 20 months, which is also reported by Kudela et al (1991).…”

“…Long-and short-term quasi-periodicities shown in the lower panel of Fig. 1 are separated by a limit of about 1.7 years (Xanthakis et al, 1989;Kudela et al, 1991). It is clear that the long-term periodicities have appeared with higher amplitude than that of the short-term ones (see middle panel of Fig.…”

“…The power spectral density (PSD) analysis of the cosmic-ray intensity recorded at ground level by polar and non-polar stations has indicated in the frequency range 10 −6 − 10 −4 Hz (1 cycle/4 months -1 cycle/3 hours) a predominant component of the type f 2 , with indications of a change below 5 × 10 −7 Hz. Kudela et al (1991) noted that there are two distinct regions of cosmic-ray periods with respect to the underlying physical mechanisms, and that the barrier between them is located around 20 months. The large-scale variations are caused by the solar dynamics, whereas transient effects in the interplanetary space cause the short-scale variations.…”

Variability of Low Energy Cosmic Rays Near Earth

“…It was eported first by (Valdés-Galicia et al, 1996), analyzed by wavelet technique by (Kudela et al, 2002), found also in the outer heliosphere in Voyager data (Kato et al, 2003). Earlier, using NM data Calgary and Deep River, (Kudela et al, 1991) indicated that around ~20 month the change of the shape of PSD occurs. Recently Okhlopkov (2011) reports that length of the quasi-2 year periodicity in even and odd numbered cycles differs by ~2 months.…”

Power Spectral Analysis of Cosmic Ray Time Series Data over a Wide Rigidity Range.

“…Bergamasco et al (1990Bergamasco et al ( ,1992 examined ration time series from the Artyomovsk station at a depth of 570 m.w.e. Kudela et al (1991 and Kudela and Venkatesan (1993) studied data from several neutron monitor stations. Yasue and Mori (1990) and Yasue et al (1993) used time series from several underground stations including Matsushiro (220 m.w.e) and Sakashita (80 m.w.e).…”