Statistical Analysis on Four Kinds of Space Weather Events during Solar Cycles 21~24

Based on the statistics of different intensity levels of solar X-ray flares, solar proton events, geomagnetic storms and relativistic electron flux enhancement of Solar Cycle 21~24, the following conclusions can be drawn. Firstly, the total number of X-ray flares in solar cycle is directly proportional to the number of sunspot maximum, and the correlation coefficients of the total number of flares, X-class flares and sunspot maximum are 0.974 and 0.997, respectively. Secondly, the solar proton events mainly occurred in the first two years before and after the peak year, accounting for 80% of the total number of events. 83% solar proton events with peak flux over 10 pfu (1 pfu=1 cm^-2·sr^-1·s^-1) were mainly accompanied by X-class and M-class flares, but also with a small number of M-class flares. For the solar proton events with the peak flux over 1000 pfu, about 98% of them were accompanied by C-class flares. Thirdly, the most frequent time of geomagnetic storms occurred during Cycle 21, 22, 23 and 24 was in 1982, 1991, 2003 and 2015, respectively, which lagged behind the peak time of sunspot maximum by three years, two years, two years and one year, respectively. Finally, 72% of the relativistic electron flux enhancement occurred in the declining phase of solar cycle, and 24% of them occurred in the rising phase.