Solar and interplanetary disturbances responsible for geomagnetic storms

The geomagnetic storms (GSs) are the large disturbances in the earth's magnetic field. We have selected 142 GSs (Dst ≤-150nT) during the period 1996-2007. Isolated geomagnetic storms typically have a main phase of 3-12 hours and a recovery phase exceeding ∼3 days. Coronal mass ejections (CMEs) associated with radio bursts are major solar events that are responsible to produce large geomagnetic storms (Dst ≤-50nT). Out of 142 events, 77 GSs (-100nT ≤ Dst ≤-50nT), 50 GSs (-200nT ≤ Dst ≤-100nT) and 15 events (Dst ≤ -200nT) of different magnitudes are found during the said period. The percentage of GSs associated with CMEs is ∼ 58%, with type II burst is ∼ 32 % with type IV burst is ∼ 12 % and the percentage of GSs associated with bright flare is ∼ 32 %.