Effects of the Sector Structure of the Interplanetary Magnetic Field on Galactic Cosmic Ray Anisotropy

We study the effects of the sector structure of the interplanetary magnetic field (IMF) on the Galactic cosmic ray (GCR) anisotropy at solar minimum by using Global Network neutron monitor data. The hourly neutron monitor data for 1976 were averaged for the positive (+) and negative (–) IMF sectors (+ and – correspond to the antisolar and solar directions of magnetic field lines, respectively) and then processed by the global survey method. We found that the magnitude of the GCR anisotropy vector is larger in the positive IMF sector and that the phase shifts toward early hours. The derived GCR components Ar, Aθ, and Aϕ for the different + and – sectors are then used to calculate the angle ψ (≈ 46°) between the IMF lines and the Sun–Earth line, the solar wind velocity U (≈ 420 km/s), the ratio of the perpendicular (K⊥) and parallel (K||) diffusion coefficients K⊥/K|| = α (≈ 0.33), and other parameters that characterize the GCR modulation in interplanetary space.