Forbush decreases and geomagnetic storms

Forbush decreases in galactic cosmic rays (according to data from a network of neutron monitors) and accompanying geomagnetic disturbances over a long period from 1957 to 2022 have been identified and studied. Statistical relationships between various parameters of cosmic ray flux and geomagnetic activity indices are analyzed. It has been established that the magnitude of Forbush decreases depends nonlinearly on the class of geomagnetic storm. A moderate correlation is found between the extreme values of various geomagnetic activity indices (Ap, Kp, Dst) and the characteristics of cosmic rays. It is also shown that the simultaneous registration of extreme values of cosmic rays and geomagnetic activity parameters does not always occur but depends on the sign of the Bz-component of the interplanetary magnetic field in a particular event.