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Studying the interaction between solar flares and sunspot groups (SGs) is crucial for understanding and predicting solar activity. We examined the distribution, correlation, and flaring rates in the northern and southern hemispheres to reveal the relationship between different classes of soft X-ray (SXR) flares and different magnetic classifications of SGs. We discovered a significant north–south asymmetry in SXR flares and SG distribution over Solar Cycles (SC) 21–25. In the rising phase of SC24, the northern hemisphere’s activity is significantly excessive. In the declining phase of SC24, the southern hemisphere’s activity becomes significantly excessive. The total numbers of various SXR flares and SGs vary between the northern and southern hemispheres over the solar cycle. B-class flares are negatively correlated with all SGs at maximum but positively correlated at minimum. C-class flares correlate best with α and β SGs. M-class flares correlate best with β γ δ and β SGs. X-class flares correlate highest with β γ δ SGs. The flaring rate of each flare class is lowest for α SGs and highest for β γ δ SGs. The flaring rates are higher in the southern hemisphere than in the northern hemisphere. Our results demonstrate that solar flares originate from different sources of solar active regions; the high-energy flares tend to be caused by more complex magnetic fields.

Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasiperiodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 yr of observational data, we systematically analyzed the quasiperiodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time–frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 yr, and 3.3–4.3 yr. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2 (±0.01), 3.1 (±0.04), and ≈6.1 (±0.4) months, and 1.2 (±0.1) and 2.4 (±0.4) yr. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1 (±0.2) months and 4.1 (±0.2) yr in the northern hemisphere, 1 (±0.004) and 5.9 (±0.2) months and 1 (±0.1), 1.4 (±0.1), and 2.4 (±0.4) yr in the southern hemisphere, 6.1 (±0.4) months in solar cycle 23, and 6.1 (±0.4) months and 1.2 (±0.1) and 3.7 (±0.2) yr in solar cycle 24. The analysis shows that quasiperiodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.

The hemispheric asymmetry of solar activity is one of the essential physical consequences of the interior dynamo process. However, the hemispheric distribution of halo coronal mass ejection (HCME) source locations has not been investigated in detail. Based on the HCME catalog identified from the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliospheric Observatory, we perform a hemispheric distribution analysis of the HCME source locations from 1996 April to 2022 June. The main results are as follows. (1) The HCME source locations are confined to the active region belt, and there is no “rush to the poles” phenomenon that is unique to large-scale magnetic activity. (2) The HCME source locations exhibit a general hemispheric asymmetry, and autoregressive moving-average model results show that the asymmetry of HCME source locations is significantly different from that of sunspot activity. (3) The hemispheric distribution of cycle 24 is different from that of cycle 23, potentially as a result of the heliospheric dynamic pressure having noticeably decreased after the polarity reversal of cycle 23. Our results contribute to a more comprehensive understanding of the hemispheric asymmetry of energetic magnetic structures and give a new perspective on understanding the geoeffectiveness of HCMEs.

The temporal variations of solar rotation in the photosphere, chromosphere, and corona have been widely investigated, whereas the rotation of the solar transition region is rarely studied. Here, we perform a primary study about the long-term variation of the rotation in the transition region using Lyα irradiance from 1947 February 14 to 2023 February 20. Correlation techniques are used, and the main results are as follows. (1) The sidereal rotation period of the solar transition region varies between 22.24 and 31.49 days, and the mean sidereal rotation period is 25.50 days for the studied time interval 1947–2022. (2) The rotation period of the transition region exhibits a clear downward trend during 1947–2022, which might be caused by the reduced heliospheric pressure and the weaker solar global magnetic fields. (3) Significant periodic signal of the quasi-Schwabe cycle is found in the rotation periods of the transition region. (4) The cross-correlation between the rotation periods of the solar transition region and sunspot activity corroborates a strong correlation with the Schwabe cycle. Possible mechanisms responsible for these results are discussed.

Coronal mass ejections (CMEs) exhibit a wide range of quasiperiodic variations and are crucial for our understanding of the cyclical evolution of large-scale magnetic fields. However, the mid-term periodicities of different types of CMEs associated with different processes at the source location need to be clearly understood. Based on the CDAW catalog released by the Large Angle and Spectroscopic Coronagraph mission on the Solar and Heliospheric Observatory, we investigated the period of CMEs based on the speeds and accelerations using the continuous wavelet transformation method. Our results revealed that the distribution of CMEs over time is quite distinctly different for different speeds, and there are Rieger-type periods and quasi-biennial oscillations of the CMEs. The two types of periodic signals show significant differences in solar cycles 23 and 24. Furthermore, the periodicity patterns for the northern hemisphere differ from those in the southern hemisphere. The potential mechanisms and explanations of the results are also discussed.

Coronal mass ejections (CMEs) are known as the main drivers of the most severe space weather disturbances. Usually, the most severe geomagnetic storms are caused by massive and fast CMEs. The latitudinal dependence of the mass loss of CMEs for different types (regular and specific events) and in different solar cycles is rarely studied. Based on the latest data acquired by the Coordinated Data Analysis Workshop catalog covering solar cycles 23 and 24, we investigated the solar cycle variation of their mass-loss rate in detail. The main results are shown as follows: (1) The temporal distribution of the mass-loss rate is noticeably different from the occurrence rate of CMEs, and this difference might be attributed to the different types. The mass-loss rate of regular CMEs significantly follows the pattern of the solar cycle. (2) The latitudinal evolutions of the mass-loss rate of regular CMEs are indeed different from those of specific CMEs during solar cycles 23 and 24, suggesting that the source region and configuration of regular and specific CMEs differ from each other. (3) Rieger-type periodicity and the quasi-biennial oscillations are found in the long-term evolution of the CME mass-loss rate, but they exhibit different temporal aspects in different subsamples of CMEs. Our results might provide new insight into the solar-cycle dependence of the mass-loss rate of CMEs at different latitudes, and have potential implications for our understanding of the long-term evolution of the mass-loss process on solar-type stars.

Solar coronal rotation exhibits significant complexity, and its relationship with the 11 yr solar cycle remains poorly understood. Using 597 McIntosh synoptic maps (CR1601–CR2197), we construct the temporal evolution of coronal rotation by performing cross-correlation analysis of coronal hole areas between consecutive Carrington rotations. Results show coronal rotation rate decreases from the equator to mid-latitudes (45°–60°), then increases at high latitudes (>60°). Comparison across solar cycles 21–24 reveals that cycle 23 displays the highest equatorial rotation rate and the strongest differential rotation. Equatorial rotation rates in odd-numbered cycles are generally higher than in preceding even-numbered ones. The latitudinally averaged rotation rate reaches a minimum near solar maximum and recovers during the declining phase, likely due to the latitudinal migration of coronal holes. Hemispheric asymmetry analysis shows no significant north–south difference in rotation rates, contrasting sharply with the strong asymmetry in sunspot distributions. Time series analysis of rotational parameters A, B, and C reveals a significant negative correlation between A and B, and a positive correlation between A and C. Singular spectrum analysis identifies prominent 5.6 and 6.9 yr periods in all three, with only C showing a strong 10 yr period.

Rotation is one of the fundamental characteristics of the Sun, and it plays a crucial role in understanding the magnetic activities and dynamo processes. To reveal the variability patterns of the global rotation of the solar chromosphere, the Bremen composite Mg II index covering more than four solar cycles during the time interval from 1979 to 2024 is utilized in the present work. Our main findings are as follows: (1) The sidereal rotation period of the solar chromosphere varies between 22.63 and 27.10 days, with an average value of 25.13 days during the studied time interval. (2) From a global point of view, the period lengths of chromospheric rotation exhibit an obvious decreasing trend, which may be associated with the structural changes in magnetic fields and solar atmosphere in the declining phase of the most recent Gleissberg cycle. (3) The time-varying period lengths of chromospheric rotation display significant quasiperiodicities of 8.38 and 19.84 yr, indicating that chromospheric rotation might be related to the Schwabe cycle and Hale cycle. (4) There exists a moderate positive correlation between chromospheric rotation period and sunspot number. Chromospheric rotation is modulated by the solar activity cycle, further supporting its association with the Schwabe cycle. The possible physical mechanisms underlying the analysis results are discussed.

Forecasting the amplitude and timing of the sunspot cycle is highly important for solar physics and space weather applications, but high-precision prediction of solar magnetic activity has remained an outstanding challenge. The Informer model, as the most advanced deep learning technique, is an ideal approach for predicting solar activity cycle. Using the whole-disk sunspot numbers (SSNs) between 1749 and 2023 and the hemispheric SSNs between 1992 and 2023, the amplitudes and timings of Solar Cycles 25 and 26 are predicted by the Informer model. The main results are the following: (1) the activity levels of Solar Cycles 25 and 26 continue being weak-moderate cycles with their strengths stronger than Solar Cycle 24, implying that the long-term solar variability is significantly modulated in length and magnitude by the Gleissberg century cycle; (2) the Gnevyshev peaks of Solar Cycles 25 and 26 are clearly observed with a higher value in the second peak, suggesting that the numbers of the large sunspot groups are greater compared to the small sunspot groups in these two cycles; and (3) during Solar Cycle 25, the activity level in the southern hemisphere is predicted to be stronger than that in the northern one, revealing significant asymmetry and asynchronization between the two hemispheres. Our analysis results show that solar cycle predictions can be made more accurate if performed separately for each hemisphere. Furthermore, Solar Cycles 25 and 26 are likely to be weak-moderate cycles, in agreement with the precursor-based and model-based prediction methods.

Coronal mass ejection (CME) is a powerful solar phenomenon that can lead to severe space weather events. Forecasting whether and when the corresponding interplanetary coronal mass ejection (ICME) will reach the Earth is very important in space weather study and forecast. At present, many different kinds of models use the near-Sun CME observations as model inputs to predict its propagation with similar prediction accuracies for large sample events. Among a series of physics-based models, the best-performing version of the shock propagation model (SPM) for large sample events, i.e., SPM3, had achieved a good forecast effect for the 23rd Solar Cycle events (1997.02–2006.12). To further evaluate SPM3, we collected CME events from 2013 January to 2023 July from the Community Coordinated Modeling Center (CCMC) CME scoreboard as a new data set. SPM3 achieved a total prediction success rate of 57% for these new events with a mean absolute error of 8.93 hr and a rms error of 10.86 hr for the shock's arrival time. Interestingly, SPM3 provided better predictions for the CME/shock events during high solar activity years than low solar activity years. We also analyzed the influence of input parameters on CME propagation and found that the larger the angular width of the CME event, the higher the probability of the corresponding IP shock's reaching the Earth. Source latitude had little effect on the arrival probability of the corresponding shock, while source longitude did. The CMEs originating from around W15° had the largest probability of hitting the Earth.