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This is a study designed to analyze the relationship between ground level enhancements (GLEs) and their associated solar active regions during solar cycles 22 and 23. Results show that 90.3% of the GLE events that are investigated are accompanied by X-class flares, and that 77.4% of the GLE events originate from super active regions. It is found that the intensity of a GLE event is strongly associated with the specific position of an active region where the GLE event occurs. As a consequence, the GLE events having a peak increase rate exceeding 50% occur in a longitudinal range from W20° to W100°. Moreover, the largest GLE events occur in a heliographic longitude at roughly W60°. Additionally, an analysis is made to understand the distributional pattern of the Carrington longitude of the active regions that have generated the GLE events.

We examine the solar cycle distribution of major geomagnetic storms (Dst ≤ − 100 nT), including intense storms at the level of −200 nT < Dst ≤ −100 nT, great storms at −300 nT< Dst ≤ −200 nT, and super storms at Dst ≤ −300 nT, which occurred during the period of 1957-2006, based on Dst indices and smoothed monthly sunspot numbers. Statistics show that the majority (82%) of the geomagnetic storms at the level of Dst ≤ −100 nT that occurred in the study period were intense geomagnetic storms, with 12.4% ranked as great storms and 5.6% as super storms. It is interesting to note that about 27% of the geomagnetic storms that occurred at all three intensity levels appeared in the ascending phase of a solar cycle, and about 73% in the descending one. Statistics also show that 76.9% of the intense storms, 79.6% of the great storms and 90.9% of the super storms occurred during the two years before a solar cycle reached its peak, or in the three years after it. The correlation between the size of a solar cycle and the percentage of major storms that occurred, during the period from two years prior to maximum to three years after it, is investigated. Finally, the properties of the multi-peak distribution for major geomagnetic storms in each solar cycle is investigated.

We use wavelet transform to analyze the daily relative sunspot number series over solar cycles 10–23. The characteristics of some of the periods shorter than ~600-day are discussed. The results exhibit not only the variation of some short periods in the 14 solar cycles but also the characteristics and differences around solar peaks and valley years. The short periodic components with larger amplitude such as ~27, ~150 and ~360-day are obvious in some solar cycles, all of them are time-variable, also their lengths and amplitudes are variable and intermittent in time. The variable characteristics of the periods are rather different in different solar cycles.