Change of the main characteristics of cosmic-ray variations and interplanetary space with the cycle of solar activity

Abstract

Changes of the characteristics of the solar-diurnal variation and Forbush decreases of cosmic rays with the solar activity cycle are analyzed. It is shown that the energy spectrum of the solar-diurnal variation is well described by the Krymsky diffusion mechanism spectrum with b parameters of 59, 40, and 30 BeV for high, middle, and low solar activity levels, respectively. The Forbush-decrease spectrum is described by a power law with exponents −0.8 and −0.6 during high and low solar activity. These changes are interpreted to be the result of a decrease of solar wind velocity and a decrease of the mean strength of the interplanetary magnetic field with a decrease in solar activity.