Wenhua Wang

The angular width of coronal mass ejections (CMEs) reflects their eruption scale, dynamics, and potential geoeffectiveness. To deepen our understanding of the hemispheric distribution characteristics of CME activities, we systematically investigate the north–south asymmetry of CMEs with different angular widths. Based on the white-light CME catalog from the Coordinated Data Analysis Workshop during solar cycles 23–25, our main results are as follows: (1) the temporal evolution of CME activity across solar cycles is primarily governed by normal and partial-halo CMEs, while narrow CMEs contribute relatively little to the overall variation; (2) CME activity in cycles 23 and 25 exhibits similar hemispheric patterns, with both cycles showing southern hemisphere dominance, in contrast to the northern dominance observed in cycle 24 (this difference may be attributed to the weaker heliospheric pressure during cycle 24); (3) the phase lag between CME activities in the two hemispheres is generally within five months. These findings reveal the solar activity cycle evolution of CME angular width distributions and hemispheric asymmetries, providing new physical constraints for understanding interhemispheric coupling in solar dynamo processes and improving space weather forecasting models.

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.

The hemispheric asymmetry of solar activity provides important diagnostics of solar dynamo processes. In this study, we present a phase-resolved statistical analysis of hemispheric sunspot number asymmetry over solar cycles 17–25 (1939–2024), using monthly mean data from the National Astronomical Observatory of Japan. By combining normalized asymmetry indices, cumulative deviation tracking, and year-by-year significance testing, we identify four key results: (1) the northern hemisphere consistently dominates during the ascending phases of most cycles, suggesting a preferential emergence of magnetic flux at the northern hemisphere; (2) the hemispheric asymmetry significantly diminishes during polarity reversal periods, indicating a balancing effect of global magnetic reconfiguration; (3) solar cycles 23 and 25 exhibit remarkably similar asymmetry patterns, implying solar cycle 25 is likely to be similar to solar cycle 23; and (4) the strength of hemispheric dominance correlates with the overall solar activity level, with stronger asymmetries observed during high-activity phases and weaker signals near solar minima. These findings offer new observational constraints for modeling hemispheric solar dynamics and establish a reproducible, scalable framework for future investigations of long-term solar magnetic asymmetries.

Solar flares, the significant indicators of solar activity, have an impact on Earth's satellites and communication systems. Accurate prediction of solar flare events is crucial for mitigating these effects. In this work, we use multiple data sources, including Geostationary Operational Environmental Satellites soft X‐ray flare flux and the solar flare index, to forecast solar flare activity during Solar Cycle 25 (SC25). Our results show that: (a) The north‐south asymmetry of solar flare activity during SC25 is well revealed, and the southern hemisphere is greater than the northern one. (b) The Gnevyshev peaks of chromospheric flare activity are clearly identified and they are deeper than other atmospheric activity indicators. The different timescales of solar flare responses to the geomagnetic and interplanetary magnetic fields may be the cause of the Gnevyshev peaks. (c) Chromospheric flare activity lags behind photospheric sunspot activity, indicating that changes in sunspot activity precede flare events. (d) The activity level of SC25 is influenced by the modulating effect of the Gleissberg Cycle, as supported by geomagnetic precursor indices. These results offer valuable insights into the temporal and spatial distribution of solar flare activity during SC25.

Coronal mass ejections (CMEs), the large-scale eruptions of plasma and magnetic fields from the solar corona, play a critical role in space weather and solar–terrestrial interactions. Understanding the periodicities of CMEs is essential for predicting their occurrences and impacts, but their quasiperiodic variations in different cycles, at different latitudes, and for different angular widths, are still unclear. In the present work, we classify CMEs based on their angular widths and latitudinal distribution, using data from the version 2.0 of the Coordinated Data Analysis Workshop catalog (1996 January–2024 March). Employing Fourier and wavelet transforms, we systematically analyze the quasiperiodic variations in the occurrence rates of CMEs. The main results show the following: (1) A lesser number of periodicities is found in high-latitude CMEs while the low-latitude CMEs show a greater number of periodicities; (2) for the periodic variations, significant differences exist between different types of CMEs across latitudes. Narrow and normal CMEs exhibit similar periodicities, whereas halo CMEs show a different periodic pattern. (3) Additional periodicities were identified for all CMEs, which occur exclusively at low latitudes or during specific cycles, potentially as a result of the noticeable heliospheric dynamic pressure after the maximum time of cycle 23. (4) The identified dominant periodicities may be associated with magneto-Rossby waves at the tachocline. This mechanism can effectively explain the periodic behavior of the observed CMEs. Our analysis results might be useful for better understanding the long-term variations of CMEs during different cycles and at different latitudes, and could also have implications for the geoeffectiveness predictions of CMEs.