Sunspots and geomagnetic storms during solar cycle-23

Geo-magnetic storms generally occur due to abnormal conditions in the interplanetary magnetic field (IMF) and solar wind plasma emissions caused by various solar activities. The Disturbance storm time (Dst) index is used to identify more than 220 storms which occurred in time interval 1996–2007, the span of solar cycle-23. Using the minimum Dst value as an indicator, we classify the storms as moderate (138), strong (67), severe (11), and great (4). We have analyzed and studied them statistically. We have found that yearly occurrences of geomagnetic storm are strongly correlated with 11 year sunspot cycle, but no significant correlation between the maximum and minimum phase of solar cycle-23 has been found. It is also found that solar cycle-23 is remarkable for occurrence of intense geomagnetic storms during its declining phase. It is also observed that Halo CME is the main cause to produce geomagnetic storms. The results are discussed in the present paper.