Study of Forbush Decrease Event and Associated Geomag- netic Field Variation During Space Radiation Storm

Transient decrease in cosmic ray intensity followed by a slow recovery typically lasting for several days is identified as Forbush decrease (Fd) event. Such Fd has been recorded by the world grid of neutron monitoring stations. The event was the result of a powerful explosion from sunspot region 9077, which sparked an X-5 class, one of the most powerful solar flare of the ascending phase of solar cycle 23. As a result the geomagentic index Dst decreased upto-300 nT, indicating a large geomagnetic storm and the % Fd decrease has gone to 16 % giving rise a cosmic ray storm. Both events coincided with interplanetary conditions. Therefore, a systematic study has been performed to investigate the variation of cosmic ray intensity alongwith the interplanetary and geomagnetic disturbances. Results indicate a strong relationship between geomagnetic activity and Forbush decrease on short- term basis. 2