Rigidity Dependence of the Long-Term Variations of Galactic Cosmic-Ray Intensity in Relation to the Interplanetary Magnetic-Field Turbulence: 1968 – 2002

We studied the relationship between the power-law exponent γ on the rigidity R of the spectrum of galactic cosmic-ray (GCR) intensity variation (δD(R)/D(R)∝R−γ) and the exponents νy and νz of the power spectral density (PSD) of the By and Bz components of the interplanetary magnetic field (IMF) turbulence (PSD∼f−ν, where f is the frequency). We used the data from neutron monitors and IMF for the period of 1968 – 2002. The exponents νy and νz were calculated in the frequency interval Δf=f2−f1=3×10−6 Hz of the resonant frequencies (f1=1×10−6 Hz, f2=4×10−6 Hz) that are responsible for the scattering of GCR particles with the rigidity range detected by neutron monitors. We found clear inverse correlations between γ and νy or νz when the time variations of the resonant frequencies were derived from in situ measurements of the solar wind velocity Usw and IMF strength B during 1968 – 2002. We argue that these inverse relations are a fundamental feature in the GCR modulation that is not restricted to the analyzed years of 1968 – 2002.