Hysteresis Phenomena in the Relationship between the Cosmic Ray Cutoff Rigidity and Parameters of the Magnetosphere during a Storm on May 15, 2005

Abstract

Variations in the cutoff rigidities of cosmic rays (ΔR) depending on the parameters of the solarwind, the interplanetary magnetic field (IMF), and geomagnetic activity were studied at different phases ofthe strong magnetic storm on May 15, 2005. We found that the trajectories ΔR, i.e., the successive values thatΔR takes depending on the parameters under study during the main phase of the storm did not coincide withthe trajectories in the recovery phase, which led to the formation of hysteresis loops. The clearest hysteresisloops are formed for the relationship between ΔR and the Bz component of the IMF, the density and pressureof the solar wind, and the Dst index of geomagnetic activity. The area of the hysteresis loops increases withthe latitude of the cosmic ray observation station.