Abstract:
The moderate and intense geomagnetic storms are identified for the first 77 months of solar
cycles 23 and 24. The solar sources responsible for the moderate geomagnetic storms are indentified
during the same epoch for both the cycles. Solar cycle 24 has shown nearly 80% reduction in the occurrence
of intense storms whereas it is only 40% in case of moderate storms when compared to previous cycle. The
solar and interplanetary characteristics of the moderate storms driven by coronal mass ejection (CME) are
compared for solar cycles 23 and 24 in order to see reduction in geoeffectiveness has anything to do with the
occurrence of moderate storm. Though there is reduction in the occurrence of moderate storms, the Dst
distribution does not show much difference. Similarly, the solar source parameters like CME speed, mass, and
width did not show any significant variation in the average values as well as the distribution. The correlation
between VBz and Dst is determined, and it is found to be moderate with value of 0.68 for cycle 23 and 0.61 for
cycle 24. The magnetospheric energy flux parameter epsilon (ε) is estimated during the main phase of all
moderate storms during solar cycles 23 and 24. The energy transfer decreased in solar cycle 24 when
compared to cycle 23. These results are significantly different when all geomagnetic storms are taken into
consideration for both the solar cycles.
