Quasiperiodic Variations of the GOES Soft X-Ray Flares during Solar Cycles 21–25

The long-term variations of quasiperiodic solar flares are of great importance for a better understanding and accurate prediction of solar flare activity. To explore the quasiperiodic characteristics of different classes of solar flares and the hemispheric difference, we comprehensively analyzed the quasiperiodic variations of different classes of solar flares, including the whole solar disk and hemispheres during solar cycles (SC) 21–25. The main results show that: (1) Certain periods are observed only in one hemisphere or some specific solar cycles. For example, over the entire time interval, the period of 3.49 yr was detected exclusively in C-class, M-class, and X-class flares in the northern hemisphere. (2) The quasi-biennial oscillation periodicities were observed for B-class, C-class, M-class, and X-class flares during SC22, SC24, and SC25. Moreover, the quasi-biennial oscillation periodicities were more pronounced in C-class and X-class flares in SC21 and in B-class and M-class flares in SC23. (3) The occurrence of different classes of solar flares displayed statistically significant short- and medium-range oscillations in both hemispheres, with distinct periodic variations and asymmetric evolutionary features. Identifying features such as the 3.49 yr period and quasi-biennial oscillation periodicities may help predict the activity patterns of different classes of solar flares across hemispheres and solar cycles, potentially improving forecasts of solar flare impacts on Earth’s technological infrastructure and space weather systems.