A model of the long period Galactic Cosmic Ray variations

Abstract

We develop a two-dimensional (2-D) time dependent model of the long period variation of Galactic Cosmic Ray (GCR) intensity. Besides the well-known fundamental processes responsible for the modulation of GCR intensity, we implement the following in the model: the parameters characterizing temporal changes in the exponent ν of the Power Spectral Density (PSD) of the Interplanetary Magnetic Field (IMF) turbulence, the modulus B of the IMF, the tilt angle δ of the Heliospheric Neutral Sheet (HNS), and changes in the drift effect of the GCR particles upon solar activity. We assume that the drift effect of the GCR particles has the maximal value in the minimum epoch of solar activity, when drift dominates, and that it has the minimal value in the maximum epoch, when diffusion dominates. We show that an acceptable compatibility is maintained for the period between 1976 and 1987 (solar cycle #21), when the expected temporal changes in the GCR particle density are shifted, as regards the temporal changes of the smoothed experimental data on the GCR intensity, for 18 months. We consider a delay time ∼18 months as an effective delay time caused by the combined influence of all parameters implemented in the 2-D model. We also conclude that one of the important indicators of the compatibility of the experimental data (1976–1987) and 2-D time dependent modeling of the long period variations of the GCR intensity is the high correlation between the temporal changes of the rigidity spectrum exponents γ calculated from theoretical model and the experimental data.