Coronal Mass Ejection, Magnetic Cloud and their Geoeffectiveness During 1996-2009

A detailed investigation on geoeffectiveness of Coronal Mass Ejections [ CMEs] associated with Magnetic Clouds [ MCs] observed during 1996-2009 have been studied. The collected sample events are divided into two groups based on their association with CMEs related to geomagnetic storms Dst -50 nT eg.1. geoeffective events and 2. For nongeoeffective events Dst -50nT. Furthermore, most of the CMEs are of halo type occurred mostly in western hemisphere. Halo and partial halo CMEs are likely to be the major cause for Geomagnetic storms [GMSs] of high intensity. There exists a weak anti-correlationship ( R = - 0.36) for geoeffective events between CME speed [ VCME] and Dst index and relatively better correlation 1. between VCME and solar wind speed [ VSW] ( R= 0.54) and 2. Dst index and solar wind speed ( R=0.64), whereas, the correlation ( R=0.16) between Dst index and southward magnetic field component [ BZ] is very poor. From our findings, we have observed that the intense and long duration, southward magnetic field component [ BZ] and fast solar wind speed are responsible for geomagnetic storms, and geomagnetic storms weakly depend on CME velocity.