Studies on large geomagnetic storm during solar cycle 22-23

The set of 158 intense geomagnetic storms associated with Dst index decreases of more than 100 nT, observed during solar cycle 22 and 23. In the covers whole period of solar cycle 22 and maximum part of solar cycle 23, have been analyzed. The selected storm events have been compiled and their various characteristics features as well as seasonal and solar cycle dependence have been discussed. We find yearly occurrence of intense storm are strongly correlated with 11-year sunspot cycle, but no significant correlation's between the maximum and minimum phases of solar cycle have been found. It is also found that best initial phase duration lies between 0-2 hours. The main and recovery phase duration's lies between 7-12 hours and 2-3 days respectively. The seasonal shows a cyclic variation peaking around April and October months.