Solar cycle effect on geomagnetic storms caused by interplanetary magnetic clouds
Wu, C.-C, R.P. Lepping
We investigated geomagnetic activity which was induced by interplanetary magnetic clouds during the past four solar cycles, 1965-1998. We have found that the intensity of such geomagnetic storms is more severe in solar maximum than in solar minimum. In addition, we affirm that the averaged solar wind speed of magnetic clouds is faster in solar maximum than in solar minimum. In this study, we find that solar activity level plays a major role on the intensity of geomagnetic storms. In particular, some new statistical results are found and listed as follows. (1) The intensity of a geomagnetic storm in a solar active period is stronger in than in solar quiet period. (2) The magnitude of negative Bz_min is larger in a solar active period than in a quiet period. (3) Solar wind speed in an active period is faster than in a quiet period. (4) VBs_max in an active period is much larger than in a quiet period. (5) Solar wind parameters, Bz_min, V_max and VBs_max are correlated well with geomagnetic storm intensity, Dst_min duringa a solar active period. (6) Solar wind parameters, Bz_min, and VBs_max are not correlated well (very poorly for V_max) with geomagnetic storm intensity during a solar quiet period. (7) The speed of the solar wind plays a key role in the correlation of solar wind parameters vs. the intensity of a geomagnetic storm. (8) More severe storms with Dst_min <= -100 nT caused by MCs occurred in the solar active period than in the solar quiet period.
Annales Geophysicae, submitted, 2006.