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This paper presents results on the fractal and statistical behavior of cosmic ray time series detected in an air shower experiment located at 2000-m altitude above the underground Gran Sasso Laboratory, Italy. We consider single particles (muons), corresponding to primary energies of ≥10 GeV, and air showers, corresponding to primary energies of ≥80 TeV. For all time series the analysis indicates a clear stochastic monofractal, non-Gaussian character; comparing these results with those obtained for underground muons and for neutron monitors, we conclude that these properties likely belong in general to cosmic ray time series, irrespective of the nature of the particles and the energies of their progenitors. In particular, the air shower time series from high-energy primaries have a fractal dimension larger than the single-muon time series originating from low-energy primaries.

The authors investigate the fractal and statistical properties of underground muons recorded at 570 hg/cm{sup 2} and study their response to solar activity variations in the second part of solar cycle 21. A constant feature detected throughout the whole period considered is the self-affine nature of the underground muon fluctuations which display a scaling range extending approximately from a few hours to more than 2 months. An important result of the study is that the scaling and spectral exponents are positively correlated with the sunspot cycle. In addition, the intensity distribution shows a more marked presence of short- and long-term fluctuations near solar maximum. The presence of solar modulation in the muon record suggests dimensions of the heliosphere at least as large as a few scattering mean free paths of the 1.8-TV primaries.

The diurnal variations of underground cosmic ray intensities are analyzed on a day-to-day basis. At the depths of the London and Torino stations an anisotropy in the direction of the interplanetary magnetic field is observed in addition to the corotation effect, which varies in relation to the perturbations produced by the sun. This effect is not recorded in the Hobart data during the same period of observation.

Trains of diurnal waves in the muonic component at 70 MWE have been found during the preliminary phases of some cosmic-ray decreases. A predecrease the day immediately preceding a Forbush decrease has repeatedly been reported from neutron monitor observations. Our analysis indicated that underground data reveal this effect earlier and for a longer period. This is consistent with the interpretation of a Forbush decay as the result of the advance of a shock front.

The vertical negative muon stopping rate at depths 0.35–1000 hg/cm2 of standard rock has been evaluated by means of a Monte Carlo simulation of the muon transport underground. The muon energy losses take into account both continuous (ionization and pair production) and stochastic (bremmstrahlung and nuclear interaction) processes. The dependence of the charge ratio μ+/μ− on the muon momentum is included. The effect of muon multiple scattering has been estimated. Results are given both for high-latitude and equatorial sites, and they are compared to previous calculations and to experimental data.

The existence of the 11-year cycle in solar activity before the Maunder minimum is clearly demonstrated with cosmogenic /sup 10/Be in polar ice during 1180--1500 A.D. For that interval a periodicity of 11.4 +- 0.2 years is found with a high significance level. Indication of a cyclicity that resembles the Hale magnetic cycle is also observed at a lower significance level. A highly variable cyclicity in the band 9.5--11.5 years is also found in the record of historical aurorae which appears to be well correlated with the /sup 10/Be cyclicity for the same time interval. It is concluded that the Schwabe, or 11-year, cycle and the Hale magnetic cycle were present before and after the Maunder minimum, even though it is not possible to understand the variability of the cycle. copyright American Geophysical Union 1988

We study the secular variations observed (1) in the thermoluminescence (TL) profile of a recent sea sedimentary core, (2) in the Δ14C time series from tree rings, and (3) in the mean annual sunspot number Rz. We show that a regular oscillation with a period of approximately 206 years is present in the radiocarbon signal. The comparison between the Δ14C secular oscillation and the 206-year TL modulation produced by the beats of two TL waves with close-by decennial periods is considered. The role of the 206-year radiocarbon wave and its possible relationships with the solar activity (as represented by the annual sunspot number Rz) are finally discussed.

We study a correlation between the solar magnetic dipole moment and the amplitude of the diurnal variation of underground muons from cosmic ray primaries of mean rigidity approx. = 1800 GV. The time series investigated was recorded at Artyomovsk, in the Soviet Union, at a vertical depth of 570 hg/cm/sup 2/. Our results indicate that both diurnal and semidiurnal variations in the muon intensities correlate well with the variations of the solar magnetic dipole. At the time of the maximum amplitude of the heliomagnetic dipole moment (summer 1982) the vector of the diurnal variation shows an increase in amplitude by a factor of /similar to/3.5 relative to the average value for the remaining period, and a phase shift from the direction of /similar to/18 hours toward /similar to/12 hours. These results suggest that during the enhancement of the magnetic dipole field of the Sun the 1800-GV cosmic rays stream preferably along the radially outward direction, and consequently the mechanism of solar convection dominates over that of diffusion. copyright American Geophysical Union 1989

We present results of the spectral analysis of the fluctuations of cosmic rays recorded by different underground muon detectors (h=7--76 meters water equivalent). The experimental power spectra, compared with the predictions of diffusion theory in the nonlinear closure approximation, suggest the persistence of solar modulation up to rigidities of approx.300 GV and the existence of nonlinear interactions between particles and the interplanetary magnetic field.

We study the self-affine properties of intensity fluctuations of underground muons generated by primary cosmic rays of rigidity ≥1600 GV. The muon time series were recorded at a vertical depth of 570 Hg/cm² during the years 1981–1983. This time interval includes a period of intense solar activity in the summer of 1982 which was characterized by the creation of large solar wind shocks and associated production of major interplanetary disturbances. The purpose of our analysis is to obtain from the behavior of the muon intensity some insight into the large-scale behavior of interplanetary magnetic field fluctuations and their effects on the propagation of high-rigidity galactic cosmic rays. The results give good evidence for fractal behavior of large-scale muon fluctuations in the range from a few hours to more than 10 days, with the scaling exponent H varying according to the time interval analyzed. We find that the large time scale muon fluctuations evolve from a preshock condition in late 1981 to early 1982 characterized by a scaling exponent H = 0.28 and power spectrum f−1.6 to a condition with H = 0.07 and an f−1.1 power spectrum during the most intense solar activity in 1982, followed by a slow return in 1983 to the original preshock conditions (H = 0.14, f−1.3).