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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.

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.

Since fast head-on coronal mass ejections and their associated shocks represent potential hazards to the space environment of the Earth and even other planets, forecasting the arrival time of the corresponding interplanetary shock is a priority in space weather research and prediction. Based on the radio spectrum observations of the 16-element array of the Daocheng Solar Radio Telescope (DSRT), the flagship instrument of the Meridian Project of China, during its construction, this study determines the initial shock speed of a type II solar radio burst on 2022 April 17 from its drifting speed in the spectrum. Assuming that the shock travels at a steady speed during the piston-driven phase (determined from the X-ray flux of the associated flare) and then propagates through interplanetary space as a blast wave, we estimate the propagation and arrival time of the corresponding shock at the orbit of the Solar Terrestrial Relations Observatory-A (STEREO-A). The prediction shows that the shock will reach STEREO-A at 14:31:57 UT on 2022 April 19. The STEREO-A satellite detected an interplanetary shock at 13:52:12 UT on the same day. The discrepancy between the predicted and observed arrival time of the shock is only 0.66 hr. The purpose of this paper is to establish a general method for predicting the shock’s propagation and arrival time from this example, which will be utilized to predict more events in the future based on the observations of ground-based solar radio spectrometers or telescopes like DSRT.

Coronal mass ejections (CMEs) and their associated shock waves have severe space weather effects in the near-Earth space. Therefore, predicting the propagation and arrival time of the CME/shock is an important component of the space weather forecast. In this work, the analytical solutions for the propagation of blast waves are reorganized and derived, and a novel solution is obtained to describe their propagation in the background flow field moving at a constant speed. This novel solution can be used to predict the propagation and arrival time of the CME-associated shock waves in both the coronal and interplanetary medium. The input parameters of this novel solution are the shock wave’s initial velocity, the piston-driving time in an analog of the initial blast process, and the background solar wind velocity. Based on the same initial conditions, we compare quantitatively the propagation processes of shock waves predicted by this novel solution and those predicted by other already existing models of the blast wave theory. The obtained results demonstrate the feasibility of this novel solution in predicting the arrival time of the interplanetary shock in the future.

Coronal mass ejections (CMEs), as one of the most destructive solar activity phenomena, are the primary driver of extreme space weather events. Accurately predicting the probability and arrival time of the corresponding interplanetary CMEs and their associated shocks is crucial in space weather forecasting. Currently, the primary shock propagation prediction models mainly input the initial kinematic parameters of CMEs near the Sun. The physics-based Shock Propagation Model Version 3 (SPM3) has demonstrated a good forecasting performance for the CME/shock events from 2013 January to 2023 July. To further improve the prediction accuracy, this study incorporates the flux of solar energetic particles (SEPs). A composite index (I), constructed using principal component analysis, quantifies the combined influence of SEP and CME’s source longitude. The analysis reveals that SPM3 systematically underestimates the shock’s transit times when the I < 0.2 and VCME < 650 km s−1. For the events identified by these criteria, an empirical velocity-based bias correction is applied. Notably, the SEP flux data are specifically used to flag events where the correction is applied, rather than entering as a continuous predictor. The revised version SPM3v2 achieves a total prediction success rate of 61%, with mean absolute error and root mean square error reduced to 8.27 and 10.65 hr, outperforming the original SPM3.

Solar active regions are believed to provide significant information on the mutual conversion of the poloidal and toroidal components of the global magnetic field. However, the multiscale periodic variations, in particular the quasi-biennial oscillations (QBOs), of solar active regions are not fully understood. In the present study, the flux, area, and number of solar active regions, as well as the sunspot number data in the period from 1996 May to 2023 November, are studied in detail. The multiscale periodic components in the above four data sets are investigated by the techniques of ensemble empirical mode decomposition and cross-correlation analysis. The main results are as follows. (1) The four data sets exhibit similar periodic components, including the 11 yr Schwabe cycle, the QBOs, and a Rieger-type period. (2) The multiscale periodicity of solar active regions shows different physical characteristics. Under different periodic scales, the highest correlation is between active region flux and area, indicating that active region flux and area better reflect the evolution of active regions. (3) By superimposing the QBOs on the 11 yr Schwabe cycle, the Gnevyshev gap phenomenon was clearly observed, implying that the Gnevyshev gap may be caused by the modulation of the 11 yr Schwabe cycle. (4) The active region flux in both hemispheres shows similar periodic components to the full disk, but the periodic variations are uneven between the northern and southern hemispheres. The results of our analysis could be beneficial for the understanding of the spatiotemporal distribution of solar active regions, and could also provide statistical constraints on solar dynamo theories.

Solar active regions (ARs) are crucial for understanding the long-term evolution of solar activities and predicting eruptive phenomena, including solar flares and coronal mass ejections. However, the cycle-dependent properties in the north–south asymmetry of ARs are not fully understood. In this study, we investigate the hemispheric distribution of ARs from Carrington rotations 1909–2278 (between 1996 May and 2023 November) by using three parameters that describe the magnetic field distribution of ARs: number, area, and flux. The main findings are as follows: (1) The three AR parameters show significant hemispheric asymmetry in cycles 23–25. The strong correlation between the AR area and flux indicates that they can better reflect the intrinsic properties of the solar magnetic field. (2) The correlation between sunspot activity and AR parameters varies in the two hemispheres across the different cycles. The AR parameters provide additional information for the variations in sunspot activity, which can better predict the intensity and cyclical changes of solar activity. (3) The variation in the fitting slope sign of the asymmetry index for AR parameters reflects periodic changes in hemispheric ARs, providing valuable insights into the activity of other stars. (4) Both the dominant hemisphere and the cumulative trend of AR parameters display a cycle-dependent behavior. Moreover, the trend variations in the AR area and flux are similar, reflecting the long-term evolutionary characteristics of the solar magnetic field. Our analysis results are relevant for understanding the hemispheric coupling of solar magnetic activity and its cyclic evolutionary patterns.

Solar active regions (ARs) provide the required magnetic energy and the topology configuration for flares. Apart from conventional static magnetic parameters, the evolution of AR magnetic flux systems should have nonnegligible effects on magnetic energy store and the trigger mechanism of eruptions, which would promote the prediction for the flare using photospheric observations conveniently. Here we investigate 322 large (M- and X-class) flares from 2010 to 2019, almost the whole solar cycle 24. The flare occurrence rate is obviously higher in the developing phase, which should be due to the stronger shearing and complex configurations caused by affluent magnetic emergences. However, the probability of flare eruptions in decaying phases of ARs is obviously higher than that in the developing phase. The confined flares were in nearly equal counts to eruptive flares in developing phases, whereas the eruptive flares were half over confined flares in decaying phases. Yearly looking at flare eruption rates demonstrates the same conclusion. The relationship between sunspot group areas and confined/erupted flares also suggested that the strong field make constraints on the mass ejection, though it can contribute to flare productions. The flare indexes also show a similar trend. It is worth mentioning that all the X-class flares in the decaying phase were erupted, without the strong field constraint. The decaying of magnetic flux systems had facilitation effects on flare eruptions, which may be consequent on the splitting of magnetic flux systems.

The formation mechanism of light bridges (LBs) is strongly related to the dynamic evolution of solar active regions (ARs). To study the relationship between LB formation and AR evolution phases, we employ 109 LB samples from 69 ARs in 2014 using observational data from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. LBs are well matched with the weak field lanes (WFLs), except those aligned on the polarity inversion line of δ sunspots. For penumbral intrusion (type-A) and umbral-dot emergence (type-C) LBs, the WFLs represent the splitting of magnetic flux systems. The sunspots tend to decay and split into several parts after type-A and type-C LBs are formed. For sunspot/umbra-merging (type-B) LBs, the declining WFLs are caused by collisions of flux systems. The sunspots merged and remained stable after type-B LBs formed. We conclude that type-B LBs are formed by collisions of flux systems, while type-A and type-C LBs are generated by splits. The time differences (δ T) between LBs appearing and ARs peaking have an average value of 1.06, −1.60, and 1.82 days for type-A, B, and C LBs, with the standard deviations of 3.27, 2.17, and 1.89, respectively. A positive value of δ T means that the LB appears after the AR peaks, whereas a negative δ T means it appears before the peak. Type-A LBs tend to form in the decaying phase or around the peak time. Type-B LBs are more likely to be formed in the developing phase. Type-C LBs mostly take shape in the decaying phase of ARs.

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.