Using the high-resolution data in the TiO band taken by the 1 m New Vacuum Solar Telescope(NVST)at the Fuxian Lake Solar Observatory(FSO),we statistically investigated the effects of different magnetic field structures within the photosphere on granules via the newly developed algorithms for identifying granules.The data of NVST have much higher contrast(9.6％),therefore which is helpful for identifying smaller granules and performing more detailed analyses and studies than before.It is found that two critical scales of granules,D1 and D2,exist,and that the probability density of the equivalent diameter of granules with scales smaller than D1 follows a power law distribution similar to the Kolmogorov spectrum.We classify granules into three groups of different origins:the granules smaller than D1 are turbulent,those larger than D2 are convective,and those with scales between D1 and D2 result from blending of turbulence and convection,which is an intermediate case of the two formers.Meanwhile,we also noticed that the different magnetic field structures within the photosphere impact the critical scale,D1,of the turbulent granule in an apparent way such that the stronger the nearby magnetic field is,the smaller the value of D1 is.On the other hand,magnetic field imposes almost no effect on the mean radiative intensity of its external granules and the corresponding distribution features.

We conduct 2.5D radiative magnetohydrodynamic simulations to investigate the driving mechanisms of the solar spicules in coronal holes and how the different background magnetic fields affect their formation. The simulation model includes the upper convection zone, photosphere, chromosphere, and lower corona. We run several cases with different background magnetic fields to primarily explore the effects of magnetic field strength and inclination on the characteristics of the formed spicules, such as the maximum height, lifetime, maximum upward velocity, and deceleration. According to the results, we find that a weaker background magnetic field tends to cause solar spicules that exhibit higher heights, longer lifetimes and faster maximum upward velocities. Additionally, when the background magnetic field inclines, the generated spicules incline accordingly; compared with those in a vertical magnetic field, the spicules in the inclined magnetic field are relatively longer, with smaller decelerations, longer lifetimes and lower maximum upward velocities. Meanwhile, by tracking and analyzing the formation processes of the spicules in two cases with different magnetic field strengths, we find that most of the spicules are mainly driven by shock waves induced by convective and turbulent motions around the solar surface, while less than one third of the spicules are primarily driven by high-velocity reconnection outflows. These results provide a more in-depth basis for the theoretical understanding of the driving mechanisms and formation processes of solar spicules.

How the solar atmosphere is heated from a temperature of about 5000 to 6000 K in the lower atmosphere to about 1-2 MK in the corona has challenged the astrophysical community for nearly 80 yr. The same puzzle exists for the stellar coronae heating as well. In this study, we present a series of findings on solar spicules and their subsequent impact on the corona within a coronal hole environment, characterized by locally open magnetic field lines, combining insights from MHD simulations with observations. We find that the convective and turbulent motions around the solar surface cause extensive shocks and small-scale magnetic reconnection in the lower atmosphere. The combined effects of shock compression and reconnection outflows then drive the formation of groups of spicules with a quasiperiod of about 300 s and a width of similar to 200-500 km. The spicule upflows provide an averaged mass flux above 10-9 kg m-2 s-1 in the lower corona to sustain the solar wind in coronal holes, and they continuously trigger further new local slow-mode waves and shocks. These waves supply an energy flux of 10-100 W m-2 in the lower corona, and they are dissipated by heat conduction and compression heating to sustain the corona temperature of about 1 MK. The results also indicate that the upward propagating disturbances observed in extreme ultraviolet passbands are caused by both spicule upflows and slow-mode waves and shocks. Our findings help in understanding the long-standing problem of coronal heating and the origin of solar winds in coronal hole regions.

Understanding the origin of coherent solar radio bursts requires linking macroscopic coronal structures with the kinetic processes responsible for wave generation. We investigate emissions from slowly positively drifting bursts (SPDBs), a specific type of solar radio emission. SPDBs provide observational constraints for modeling beam-plasma interactions in coronal loops, serving as a basis for a multiscale description. We employ a three–stage numerical framework that combines nonlinear force–free field (NLFFF) magnetic extrapolation, guiding–center simulations, and fully kinetic particle–in–cell (PIC) modeling. The background plasma density is described using a hydrostatic model consistent with active–region conditions, producing a plasma–frequency gradient comparable to that inferred from the observed SPDBs spectrum. Energetic electrons injected near the loop top evolve through magnetic mirroring, pitch–angle scattering, turbulence development, and partial precipitation. Evolved velocity distribution functions (EVDFs) are sampled after approximately one bounce period and used in PIC simulations to evaluate emission properties. The results show that the evolved beam distribution of energetic electrons predominantly excites beam–Langmuir waves and fundamental plasma emission along the loop, with the emission intensity gradually decreasing from the loop top toward the footpoint. The modest initial beam velocity of energetic electrons explains the inefficient generation of harmonic plasma emission. The temporal evolution of the modeled emission reproduces key SPDB characteristics, including the 4s duration and frequency drift behavior. These results suggest plasma emission explains the mechanisms behind SPDB generation and demonstrate the feasibility of a unified model connecting coronal magnetic topology, particle transport, and radio emission.

Magnetic reconnection in twisted loops has long been invoked as an engine powering energetic transients from black hole accretion to neutron star mergers, yet never directly observed. Here we report the first direct observation of the complete reconnection of this type in a solar flare. We find a magnetic loop twisted to about 540 degrees, far exceeding the 180 degrees twist assumed in existing simulations. This extreme twist inherently enables efficient multiple X-line reconnection, akin to the role of turbulence in contemporary theory. Remarkably, the intertwined end breaks unilaterally after reconnection (unlike symmetric breaking in simulations), forming open field lines that release hot plasma – providing a promising mechanism for coronal generation or heating. We first detect hard X-ray emission from the current sheet, directly proving it as a particle accelerator. Moreover, we discover a power-law relationship between quasi-periodic oscillation frequency and magnetic field strength across solar flares, black hole binaries, active galactic nuclei, magnetars, and gamma-ray bursts. This relation identifies twisted-pair unilateral reconnection as a common burst mechanism and provides a natural ruler for cosmic magnetic fields. These findings establish an observational foundation for future reconnection theory and simulations, offering a unified framework for magnetically powered bursts.

Solar flares are the largest energy releasing events in the solar system, where the open magnetic field lines reconnect and form the closed flare loops. During this process, rapid magnetic reconnection, the associated shock waves, and chromospheric evaporation are expected but not yet well understood. These processes are crucial for understanding similar features in stellar flares and other astrophysical jets. Here, we report the characteristics of propagating slow-mode shocks in the flare loop system, by combining a 3D high-resolution magnetohydrodynamics modeling and spectral analysis of Extreme Ultra-Violet observations. It is found that normal slow shocks are recurrently formed after the collision between the post-reconnection downflows and evaporation flows in the flare loops, which subsequently propagate toward the chromosphere at speeds comparable to the evaporation flows. In particular, the Doppler analysis of the Fe XXI 1354 Å line normally shows a sharp change in blueshifted velocity and an asymmetrical line broadening once the line-of-sight passes through the shock front. This study highlights that propagation of slow shocks can facilitate energy release in flares and affect energy transport, suggesting an advancement in the standard flare model framework.

The Solar Close Observation and Proximity Experiment (SCOPE) mission, targeting a perihelion of 5 R, faces an extreme unsteady thermal environment, in which the sun-facing side must withstand a solar radiation heat flux as high as 2.52MW/m2 and temperatures approaching 2400℃. Under such conditions, conventional thermal protection systems (TPS) based on microscopic porous media are challenged by excessive mass and a risk of thermal-stress-induced failure. In this study, two TPS schemes for the SCOPE mission, namely traditional carbon foam and carbon nanotube (CNT)-based insulation, are systematically compared. The simulation model is benchmarked against in-orbit flight data from the Parker Solar Probe (PSP) to validate numerical reliability. A three-dimensional finite-element model was established. The model includes a multilayer coating, an insulation layer, and a rear radiation structure. A fourth-order Runge-Kutta algorithm is used to simulate the transient temperature field and the resulting mechanical response near perihelion, while the influence of microstructure on macroscopic thermal insulation performance is analyzed based on multiscale heat transfer theory. The numerical results indicate that, owing to nanoscale interfacial thermal resistance and phonon boundary scattering, the CNT scheme can mitigate the back-surface temperature to 400℃ with an insulation layer thickness of only 5mm, compared with 140mm for the carbon foam scheme, and the total system mass is reduced by about 49% . Thermo-mechanical coupling analysis further confirms that the maximum thermal stress remains well below the material strength limit, and Monte Carlo sensitivity analysis verifies the robustness of the design against manufacturing tolerances.

The optical system of the balloon-borne coronagraph typically adopts a small focal ratio design, leading to a slender tube structure that is highly sensitive to fluctuations in ambient temperature. To ensure stable operation under the low-temperature and low-pressure conditions of near-space, this study developed a high-precision thermal control system. The system comprises 12 sets of independently regulated temperature control units, utilizing thermistors as sensors, along with thin-film heaters and a PID (Proportional-Integral-Derivative) control algorithm, to accurately maintain the mirror tube temperature within (−5±3) ∘C. By exploiting the differential thermal contraction properties between aluminum alloy and optical materials, the system effectively eliminates structural gaps and mitigates thermal deformation, while an active focusing mechanism compensates for focal shift caused by temperature variations. Through systematic analysis of the structural characteristics of the coronagraph and its operating environment, a heat transfer model specific to near-space conditions was established, identifying the key factors influencing the system temperature, and then a thermal control scheme combining multi-layer insulation and active heating was proposed. On 4 October 2022, a successful flight experiment was conducted in Da Qaidam, Qinghai Province, where the system operated at an altitude of 30 km, acquiring valuable observational data. The recovered data indicates that the temperature control system operates stably, with the temperature fluctuation of the coronagraph tube controlled within the design range. This effectively ensures the normal of the coronagraph in extreme environments, and provides an important technical reference for future similar missions.

We performed numerical simulations of magnetic reconnection with different strengths of magnetic fields from the solar photosphere to the upper chromosphere. The main emphasis is to identify dominant mechanisms for heating plasmas in the reconnection region under different plasma- β conditions in the partially ionized low solar atmosphere. The numerical results show that more plasmoids are generated in a lower β reconnection event. The frequent coalescence of these plasmoids leads to a significant enhancement of turbulence and compression heating, which becomes the dominant mechanism for heating plasma in a lower plasma- β reconnection process. The average power density of the compression heating ( Q comp ) decreases with increasing initial plasma- β as a power function: Q comp ∼ β 0 − a , where the value a is 1.9 in the photosphere and decreases to about 1.29 in the upper chromosphere. In the photosphere and lower chromosphere, the Joule heating contributed by electron-neutral collisions Q en = η en J 2 eventually dominates over the compression heating when the initial plasma- β is larger than the critical value β 0−critical = 8. In the upper chromosphere, the ambipolar diffusion heating and the viscous heating will become equally important as the compression heating when the initial plasma- β is larger than the critical value β 0−critical = 0.5. These results indicate that the compression heating caused by turbulent reconnection mediated with plasmoids is likely the major heating mechanism for the small-scale reconnection events with stronger magnetic fields, such as active region Ellerman bombs (EBs) and UV bursts. However, the heating caused by the partial ionization effects can not be ignored for those reconnection events with weaker magnetic fields, such as quiet Sun EBs and cold surges.

The Solar Close Observations and Proximity Experiments(SCOPE)mission will send a spacecraft into the solar atmosphere at a low altitude of just 5 R☉ from the solar center.It aims to elucidate the mechanisms behind solar eruptions and coronal heating,and to directly measure the coronal magnetic field.The mission will perform in situ measurements of the current sheet between coronal mass ejections and their associated solar flares,and energetic particles produced by either reconnection or fast-mode shocks driven by coronal mass ejections.This will help to resolve the nature of reconnections in current sheets,and energetic particle acceleration regions.To investigate coronal heating,the mission will observe nano-flares on scales smaller than 70 km in the solar corona and regions smaller than 40 km in the photosphere,where magnetohydrodynamic waves originate.To study solar wind acceleration mechanisms,the mission will also track the process of ion charge-state freezing in the solar wind.A key achievement will be the observation of the coronal magnetic field at unprecedented proximity to the solar photosphere.The polar regions will also be observed at close range,and the inner edge of the solar system dust disk may be identified for the first time.This work presents the detailed background,science,and mission concept of SCOPE and discusses how we aim to address the questions mentioned above.

The Lobster Eye Imager for Astronomy (LEIA) detected a new X-ray transient on 2022 November 7, identified as a superflare event occurring on a nearby K-type giant star HD 251108. The flux increase was also detected in follow-up observations at X-ray, UV, and optical wavelengths. The flare lasted for about 40 days in soft X-ray observations, reaching a peak luminosity of ∼1.1 × 10 ^34 erg s ^−1 in 0.5–4.0 keV, which is roughly 60 times the quiescent luminosity. Optical brightening was observed for only one night. The X-ray light curve is well described by a double fast rise and exponential decay model, attributed to the cooling process of a loop arcade structure formed subsequent to the initial large loop with a half-length of ∼1.9 × 10 ^12 cm. Time-resolved X-ray spectra were fitted by a four-temperature apec model (with three components being the quiescent background), showing significant evolution of plasma temperature and emission measure over time. The estimated energy released in the LEIA band is ∼3 × 10 ^39 erg, suggesting that this is likely the most energetic X-ray stellar flare with the longest duration detected to date.

Context. Flux emergence is ubiquitous in the Sun's lower atmosphere. The emerging flux can reconnect with the pre-existing magnetic field. Aims. We aim to investigate plasmoid formation and the resulting multithermal emissions during the three-dimensional reconnection process in the lower solar atmosphere. Methods. We conducted 3D radiation magnetohydrodynamic (RMHD) simulations using the MURaM code, which incorporates solar convection and radiation. We simulated the emergence of a flat magnetic flux sheet that was introduced into the convection zone. For comparison with results previously reported from observations, we employed the RH1.5D code to synthesize H alpha and Si IV spectral line profiles and we synthesized the ultraviolet images using the optical thin methods. Results. Flux emergence took place as part of the imposed flux tube crossed the photosphere. In the lower solar atmosphere, magnetic reconnection occurred and formed thin, elongated current sheets. Plasmoid-like features appear as part of the reconnection process; this results in many small twisted magnetic flux ropes, which are expelled toward the two ends of the reconnection region. Consequently, hot plasma with a temperature exceeding 20 000 K and much cooler plasmas with a temperature below 10 000 K can coexist in the reconnection region. Synthesized images and spectral line profiles through the reconnection region display typical characteristics of reconnection occuring in the lower solar atmosphere, such as Ellerman bombs (EBs) and UV bursts. The cooler plasmas that show characteristics of EBs can be found above hot plasma and reach altitudes more than 2 Mm above the solar surface. Meanwhile, some hot plasma that features characteristics of UV bursts can extend downward to the lower chromosphere, approximately 0.7 Mm above the solar surface. Conclusions. Our simulation results indicate that the turbulent reconnection mediated with plasmoid instability can occur in small-scale reconnection events such as EBs and UV bursts. The coexistence of hot and much cooler plasmas in such a turbulent reconnection process can well explain the temporal and spatical connection of UV bursts with EBs.

The Solar flare is one of the most violent eruptive phenomena in the Solar system, which releases energy up to 1025 J in tens of minutes. With the development of observational techniques, similar flare events have been observed on stars, with typical energy of 10 to 104 times that of Solar flares, which is known as the superflare. Studies of stellar superflares and their mechanisms are not only important for understanding the internal structure, evolution, and magnetic activities of stars, but also for exploring the habitability and extraterrestrial life on exoplanets. A brief introduction is first given on Solar flares and the associated phenomena of magnetic activities, stellar magnetic field, and superflares of stars. Then, current detection methods and research results of stellar superflares are reviewed in terms of selection, energy evaluation, starspots, and the statistical relationships between the flare parameters and stellar parameters. Meanwhile, a comparison is made with the theories of Solar flares and the related physical processes to explore their similarities and connections. Finally, a summary is made and the related further work is also discussed.

A 50 mm balloon-borne white-light coronagraph (BBWLC) to observe white-light solar corona over the altitude range from 1.08 R-circle dot to 1.50 R-circle dot has recently been indigenously developed by Yunnan Observatories in collaboration with Shandong University (in Weihai) and Changchun Institute of Optics, Fine Mechanics and Physics, which will significantly improve the ability of China to detect and measure the inner corona. On 2022 October 4, its first scientific flight took place at the Dachaidan area in Qinghai province of China. We briefly describe the BBWLC mission including its optical design, mechanical structure, pointing system, the first flight and results associated with the data processing approach. Preliminary analysis of the data shows that BBWLC imaged the K-corona with three streamer structures on the west limb of the Sun. To further confirm the coronal signals obtained by BBWLC, comparisons were made with observations of the K-coronagraph of the High Altitude Observatory and the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We conclude that BBWLC eventually observed the white-light corona in its first scientific flight.

Newly emerging flux (NEF) has been widely studied as a trigger of solar filament eruptions, but its influence on the subsequent dynamics remains poorly explored. Because NEF typically emerges adjacent to filaments, it imposes magnetic asymmetry that can drive nonradial eruptions and complicate space-weather forecasting. We bridge analytic catastrophe theory with 2D resistive MHD simulations: analytic solutions provide magnetic configurations containing a flux rope at the loss-of-equilibrium point, which are then used as initial conditions for simulations to examine the following dynamics. We find that NEF governs the kinematics of filament eruptions in two ways. First, by reshaping coronal stability, NEF can create or eliminate a higher equilibrium in the corona, thereby producing failed eruptions or coronal mass ejections (CMEs). In the transitional situation where a metastable equilibrium appears, the rising filament decelerates and stalls before reaccelerating into a CME, consistent with observed two-step eruptions. Second, by breaking symmetry, NEF deflects eruptions away from the radial direction: depending on its polarity, it acts as a repulsor or an attractor on eruptive filaments, and the deflection magnitude increases with the degree of asymmetry. Our theory yields two characteristic angles that predict the deflection directions of CMEs and failed eruptions, and simulations closely align with these predictors. These results highlight the NEF not only as a trigger but also as a key factor that governs both the acceleration and deflection of eruptions during their propagation in the low corona.

Three modes of magnetic reconnection, flux pile-up, Sonnerup, and hybrid, are examined in the context of driven magnetic reconnection via 2D and 2.5D magnetohydrodynamic (MHD) numerical simulations. They result from variances in gas pressure and magnetic field strength in the reconnection inflow region. The simulation demonstrates that the Spitzer diffusion region of magnetic reconnection is not just an X-point; instead, it appears as a slim and elongated current sheet that creates two pairs of the slow-mode shock (SS) on either end. These shocks contribute to forming four boundaries that separate the inflow from the outflow. In the regions far from the Spitzer diffusion region, two sets of rotational discontinuity (RD) stand inside the SSs and form the combination of SS and RD structures. The RDs reverse the magnetic field inside the reconnection outflow region, and create a W-shaped magnetic field in that region. The scenario that the rotation of the magnetic field is not caused by an intermediate wave, and the SS is located outside the RD, is consistent with the inference of Priest (Mon. Not. R. Astron. Soc. 159, 389 (1972)), and is contrary to that of Petschek and Thorne (Astrophys. J. 147, 1157 (1967)) and Vasyliunas (Rev. Geophys. Space Phys. 13, 303 (1975)).

Magnetic reconnection is a fundamental process in astrophysics and plasma physics that involves a change in the topological structure of magnetic fields. The long ray-like current sheet (CS) trailing behind a solar coronal mass ejection (CME) serves as a unique reconnection site, extending in length from several to over twenty solar radii. However, the three-dimensional (3D) geometry, internal reconnection process and the resultant topological changes in the magnetic field remain elusive. Here, in a 3D isothermal magnetohydrodynamic simulation that covers the entire solar-terrestrial region to follow a CME evolution through the solar wind from Sun to Earth, we reproduce all major observational features of CS and recover observationally inferred plasma blobs inside the CS. Furthermore, we find that magnetic reconnection within the long CS results in a knotting of magnetic field lines and the formation of a M\"obius band. When the CME propagates in the Sun-earth space, these knotted magnetic fields persist and continue moving earth-ward. Our findings open a new window to understanding complex topological magnetic structures.

We propose a mechanism for the excitation of large-scale quasiperiodic fast-propagating magnetoacoustic (QFP) waves observed on both sides of the coronal mass ejection. Through a series of numerical experiments, we successfully simulated the quasi-static evolution of the equilibrium locations of the magnetic flux rope in response to the change of the background magnetic field, as well as the consequent loss of the equilibrium that eventually gives rise to the eruption. During the eruption, we identified QFP waves propagating radially outward of the flux rope, and tracing their origin reveals that they result from the disturbance within the flux rope. Acting as an imperfect waveguide, the flux rope allows the internal disturbance to escape to the outside successively via its surface, invoking the observed QFP waves. Furthermore, we synthesized the images of QFP waves on the basis of the data given by our simulations and found consistency with observations. This indicates that the leakage of the disturbance outside the flux rope could be a reasonable mechanism for QFP waves.