Variations in geomagnetic cutoff rigidity of cosmic rays in some regions of Asia during the 2003 extreme events

Variations of geomagnetic cutoff rigidity in Irkutsk, Alma-Ata and Beijing in October-November 2003 were calculated with data from ground-based observations of cosmic ray intensity at the world-wide network of stations and GOES spacecrafts. The calculated variations in geomagnetic cutoff rigidity are presented together with Dst-variations of the geomagnetic field. The obtained results are compared with calculation results from the Tsyganenko model of the magnetosphere.