Mapping of Geomagnetic Cutoff Rigidity of Cosmic Rays during the Main Phase of the Magnetic Storm of November 20, 2003

Abstract

In this work, geomagnetic cutoff rigidities are calculated in a model magnetosphere field on the world latitude–longitude 5° × 15° grid during the main phase of the magnetic storm of November 20, 2003. A decrease in geomagnetic thresholds (ΔR) by up to 1.8 GV as compared to thresholds in the main field is observed in the maximum of the geomagnetic storm at 2000 UT at middle and low latitudes. In the equatorial part, ΔR amounts to 0.5–0.6 GV. It has been found that the global distribution of drops in the cutoff rigidities exhibits a North–South asymmetry, as well as day–night asymmetry. This is expressed by the fact that the ΔR maximum in the daytime sector is observed at a latitude of ~40° N in the Northern Hemisphere and ~60° S in the Southern Hemisphere. Conversely, the ΔR maximum is observed in the nighttime sector at a latitude of ~55° N in the Northern Hemisphere and ~45° S in the Southern Hemisphere. Moreover, the maximum ΔR values in the Northern Hemisphere in the daytime sector are higher than in the nighttime sector; in the Southern Hemisphere, the maximum ΔR values in the daytime sector are lower than in the nighttime sector. The observed magnetospheric effects in the global distribution of ΔR seem to be caused by the dominant impact of the partial ring current that develops in the main storm phase.