Study of Intense Geomagnetic Storms and associated Cosmic Ray Intensity Variation

Shocks driven by energetic coronal mass ejections (CME's) and other interplanetary (IP) transients are mainly responsible for initiating large and intense geomagnetic storms. Observational results indicate that galactic cosmic rays (GCR) coming from deep surface interact with these abnormal solar and interplanetary conditions and suffer modulation effects. In this paper a systematic study has been performed to analyze the cosmic ray intensity variation during highly geoeffective conditions, referred by geomagnetic storms. These intense geomagnetic storms period have been categorized on the basis of index. Study reveals the signicant decrease in the cosmic ray intensity following the similar pattern as the index depicts. Analysis further indicates that magnitude of all the responses depend upon component of interplanetary magnetic eld (IMF) being well correlated with solar maximum and minimum periods. Transient decrease in cosmic ray intensity with slow recovery is observed during the storm phase duration. 1