M. Parisi

Hysteresis between solar activity and cosmic rays during cycle 22: the role of drifts, and the modulation region

Abstract Our studies of the neutron monitor observatories data with different cut-off rigidities during solar cycle 22 have made it possible to investigate the hysteresis character of the relationship between the variations in solar activity and in galactic cosmic ray intensity. This effect arises from the delay of interplanetary processes (responsible for cosmic ray modulation) with respect to the initiating solar processes, which correspond to some effective solar wind velocity and shock waves propagation. It gives the possibility to determine the effective dimension of modulation region in depending on the effective energy of galactic cosmic rays. In addition to our previous investigations of cosmic ray—solar activity hysteresis phenomenon made in the frame of convection-diffusion model, we now try to take into account drifts that change sign in periods of solar magnetic field reversal. From comparisons with experimental data on long-term cosmic ray variation in cycle 22, we determine the role of convection-diffusion and drifts in global modulation, and the effective dimension of the modulation region.