The cosmic-ray 1.68-year variation: A clue to understand the nature of the solar cycle?

Abstract

Using the maximum entropy method (MEM), the cosmic-ray power spectral density in the frequency range 3 x 10-9-2 • 10-Hz has been estimated for the period 1947-1990. Cosmic-ray intensity data were integrated from the ion chamber at Huancayo and the neutron monitor at Deep River, following the method of Nagashima and Morishita (1980). The estimated spectrum shows power-law dependence (f-1.62), with several peaks superimposed. Periodicities of the different peaks are identified and related to solar activity phenomena; most of them were reported in the past. Once the ll-yr variation is eliminated, the most prominent feature in the spectrum is a variation, not reported before, with a period of L68 yr (604.8 d). This peak is correlated with fluctuations of similar periodicities found in the southern coronal hole area and in large active regions. The importance that this variation may have to elucidate the solar magnetic flux emergence and the activity cycle is discussed.

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

“…The last ones are consistent with the fact that the short time periods have a different probability of occurrence in different epochs (Xanthakis et al, 1989). Valdes-Galicia, Perez-Enriquez and Otaola (1996) and Valdes-Galicia and Mendoza (1998) have reported on a short-time variation of 1.68 year in the cosmicray intensity observed at the Earth at neutron monitor energies (several GeV). They proposed that this cosmic-ray variation might appear as a consequence of phenomena rooted in the solar interior and could help in understanding the origin of the solar magnetic cycle.…”

“…The peak of 5.1 months is present in all cycles with a strong appearance in cycle 21. Valdes-Galicia et al (1996) and Mavromichalaki et al (2002) have already reported that the cosmic ray fluctuation of 5.1 m has appeared in cosmic-ray intensity at the maximum phase only of cycle 21 and not of cycle 20, while for earlier (and later) cycles and periods the evidence is contradictory. The evidence for this periodicity (154 days) in flare-related data is convincing for the interval 1978-1983 of the cycle 21.…”

“…1. This method is better than other spectral techniques to resolve different frequency peaks (Ulryich and Bishop, 1975;Kudela et al, 1991;Valdes-Galicia et al, 1996). Algorithms for performing the MEM analysis were based on the algorithm developed by Burg (1967).…”

Oscillations in the open solar magnetic flux with a period of 1.68 years: imprint on galactic cosmic rays and implications for heliospheric shielding

“…A strong oscillation in GCR fluxes of period T =1.68 yr (frequency, f =0.595 yr −1 =9 nHz) has been reported recently and related to similar oscillations in solar surface features (Valdés-Galicia et al, 1996;Valdés-Galicia and Mendoza, 1998). This periodicity has also been found in the coronal hole area (McIntosh et al, 1992;Maravilla et al, 2001).…”

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.…”