Solar magnetohydrodynamic (MHD) simulation is an indispensable method for studying solar activities. Modern MHD simulations are increasingly realistic and need to be synthesized with multiwavelength radiation to validate observations. We developed radiation synthesis tools (RST), a Cython-optimized Python program to solve the radiative transfer equation, enabling efficient multiwavelength synthesis of optically thick radiation from arbitrary perspectives. By directly calculating the ray traversal distance ds per cell, RST eliminates interpolation. As a result, the computational complexity in Cartesian coordinates is reduced from O(N) (where N = nx & centerdot; ny & centerdot; nz is the total number of voxels in the simulation volume) to O(k & centerdot;n) (where k is the number of ray footpoints and n is the number of sampling steps along each ray), significantly improving efficiency, especially for localized high-resolution synthesis. For spherical coordinates, RST offers two methods. The first interpolates data into Cartesian coordinates for fast O(k & centerdot;n) integration, sacrificing small r resolution. And the second computes ray-plane intersections directly, with O(k & centerdot;n & centerdot;logn) complexity. RST features a user-friendly interface where users simply specify absorption (kappa) and emissivity (j). It includes physical modules for white-light corona, H alpha, EUV, radio, and pseudo-radiation.

The magnetic field in the solar corona cannot be observed routinely at present. Nonlinear force-free field (NLFFF) extrapolation serves as a crucial method for modeling the coronal magnetic configuration. We present a novel physics- reinforced generative adversarial network (PRO-GAN), an integrated deep learning framework designed to efficiently transform solar potential fields into corresponding NLFFFs while enforcing physical constraints to improve the result. This dual-phase framework synthesizes multifaceted integration, including the data-driven mapping relation acquisition, the constraint of physics equations, and supervision by a numerical solver. On the other hand, by incorporating a gradient penalty reinforced by a numerical method during the physics reinforcement training process, this approach resolves the inherent gradient conflicts in physics-informed neural networks from a novel perspective. The validity and efficiency of PRO-GAN have also been verified on the dataset and two analytic models.

Solar jets, collimated plasma ejections driven by magnetic reconnection, play a vital role in energy transport and coronal heating. While rotational motions in jets are often attributed to magnetic field untwisting, alternative explanatory mechanisms remain possible. This study investigates a rotating jet in an active region observed on 2023 August 1 using multiwavelength observations from the Atmospheric Imaging Assembly, Chinese H alpha Solar Explorer, and Interface Region Imaging Spectrograph, combined with a self-consistent time-dependent magnetofrictional model and magnetohydrodynamic simulation. Spectral diagnostics reveal coexisting red and blueshifts along the edges and central axis of the jet, indicating helical plasma motion within a twisted magnetic structure. Numerical simulations demonstrate that the jet's rotation arises from plasma propagating along helical open field lines, formed via reconnection between a pre-existing flux rope and overlying magnetic fields. Contrary to classical untwisting models, both linear and rotational velocities decrease with altitude during the jet propagation. These results highlight that the observed rotation results from plasma spiral motion along twisted fields rather than untwisting dynamics of the magnetic field itself, providing new insights into solar jet energetics and their connection to broader solar phenomena.

Magnetic flux ropes are fundamental magnetic structures in solar eruptions, whose formation is generally attributed to: (1) the emergence of subsurface flux tubes; or (2) flux cancellation driven by photospheric horizontal flows and magnetic reconnection. Both mechanisms can operate simultaneously during active region (AR) evolution, making their relative contributions challenging to quantify. Here, we analyze the formation of a flux rope in a MURaM radiative magnetohydrodynamic simulation, which formed and evolved for approximately 3 hr before an M-class flare. The formation process is quantified by the magnetic helicity flux, which drives the nonpotential evolution of the magnetic field, with its advection and shear terms on the photosphere corresponding to the emergence and photospheric horizontal flows, respectively. Examining the helicity injected into the flux rope through the photosphere, we find both terms increase significantly as the eruption approaches, with the shear term prevailing overall. Height-dependent analysis of the helicity flux, together with the magnetic field and velocity distributions, further reveals a gradual transition from the shear to the advection term with an increasing altitude, which is driven by magnetic reconnection above the photosphere. Our results provide quantitative evidence that flux cancellation governs flux rope formation, arising naturally from magnetic field reorganization during AR evolution: as the flux emergence transports the magnetic flux upward, photospheric shearing motions adjust the magnetic field and inject helicity into the solar atmosphere, and magnetic reconnection ultimately assembles the main body of flux ropes.

Loop-aligned hydrodynamic modelings help better understand the thermodynamic evolution of flaring plasma confined in solar flare loops. Conventional loop modelings typically assume a uniform loop cross section. With a variation of the cross section taken into account, in this work we carry out both analytical and numerical modelings of the radiative cooling in a solar flare loop. It is found that a cross-sectional expansion with height can efficiently suppress the draining of loop material from the corona while not significantly affecting the decrease of loop temperature. Reflected in the loop energetics, the coronal part of the loop cools more dominantly by radiation, and more importantly, the loop radiative outputs are shifted toward lower temperatures. These findings pose important physical implications for extreme-ultraviolet (EUV) late-phase emissions discovered in some solar flares. The late-phase loops in these flares are believed to bear a more notable cross-sectional expansion owing to their longer lengths. Compared with the main-phase loops, the late-phase loops would emit more effectively at middle temperatures, which could, to a certain degree, mitigate the severe heating requirement for the production of a prominent warm coronal late-phase peak. In addition, the cross-sectional expansion also affects the shape of the emission light curves, causing a sharper decay after the emission peak. Such an emission pattern has been validated with the observations of an EUV late-phase flare, and could serve as a potential diagnostic tool to judge the degree of loop cross-sectional expansion in an extended flare dataset.

Total solar eclipses (TSEs) provide a unique opportunity to observe the large-scale solar corona. The solar wind plays an important role in forming the large-scale coronal structure and magnetohydrodynamic (MHD) simulations are used to reproduce it for further studying coronal mass ejections (CMEs). We conduct a data-constrained MHD simulation of the global solar corona including solar wind effects of the 2024 April 8 TSE with observed magnetograms using the Message Passing Interface Adaptive Mesh Refinement Versatile Advection Code (MPI-AMRVAC) within 2.5 R_⊙. This TSE happened within the solar maximum, hence the global corona was highly structured. Our MHD simulation includes the energy equation with a reduced polytropic index γ=1.05. We compare the global magnetic field for multiple magnetograms and use synchronic frames from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager to initialize the magnetic field configuration from a magneto-frictionally equilibrium solution, called the Outflow field. We detail the initial and boundary conditions employed to time-advance the full set of ideal MHD equations such that the global corona is relaxed to a steady state. The magnetic field, the velocity field, and distributions of the density and thermal pressure are successfully reproduced. We demonstrate direct comparisons with TSE images in white-light and Fe XIV emission augmented with quasi-separatrix layers, the integrated current density, and the synthetic white-light radiation, and find a good agreement between simulations and observations. This provides a fundamental background for future simulations to study the triggering and acceleration mechanisms of CMEs under solar wind effects.

Accurately estimating the bolometric energy of solar and stellar white-light flares (WLFs) is crucial for understanding their physical nature and impact on surrounding planets. However, the lack of spatial resolution in stellar observations forced pioneering stellar WLF studies to adopt simplified energy estimation methods, typically assuming either a constant flare temperature or a fixed radiating area. To assess the physical plausibility of these assumptions, we utilize high-spatiotemporal-resolution solar observations to analyze the true evolution of the source region’s radiating area and temperature of 70 solar WLFs. It is revealed that both area and temperature of most solar WLFs undergo significant temporal evolution, and the flare area strongly correlates with the flare’s peak optical continuum flux. Therefore, we propose a new energy estimation method that permits both flare area and temperature to evolve. Compared with existing methods, our dynamic approach yields systematically lower flare energies, which then prompts us to revisit classical macroscopic scaling laws related to the flare energy. It is further revealed that different energy estimation approaches can systematically alter these scaling relations, calling for a re-examination of these established statistical results and their targeted testing or revision in future work.

The evolution of magnetic fields in the tenuous solar corona is predominantly governed by the motions of the underlying dense photosphere. Despite this, coronal magnetic restructuring driven by magnetic reconnection between interacting coronal fields can sometimes react backward to change photospheric magnetic fields. However, the mechanism of reactions remains undetermined. Here, we report the discovery of a back-reaction phenomenon: The untwisting of coronal loops that become twisted during reconnection in an eruption results in enhanced currents at the boundary of their footpoint away from the eruption, manifesting as the growth of a sunspot scar. It is revealed to arise from the Alfvénic reverse transfer of magnetic twist from the corona to the lower atmosphere, through joint space observations and a magnetohydrodynamic simulation. These findings provide a viable and quantitative interpretation for the majority of puzzling photospheric changes associated with coronal mass ejections and/or flares and warn for unexpected magnetic field evolutions in sunspots and starspots.

Solar flares are a major driver of hazardous space weather, whose intense electromagnetic emissions and energetic particles can significantly disturb the near-Earth space environment. Therefore, understanding the physical processes during a solar flare and predicting its radiation profiles are of great importance. In this study, we analyze and model an M1.4 two-ribbon long-duration flare, whose multiple extreme-ultraviolet (EUV) emission peaks are found to correspond to different three-dimensional (3D) magnetic reconnections driven by the continuous evolution of a flux rope. In particular, the second and third peaks in the 335 & Aring; EUV channel originate from longer and higher flare loops with extended cooling times, formed by reconnection between flux-rope field lines and ambient sheared-arcade field lines (ar-rf) and between flux-rope field lines themselves (rr-rf). These results are supported by the drifting of the flux-rope footpoint (and flare ribbon) and the decrease in toroidal flux of the flux rope, as well as by the connectivity transfer of representative field lines in the magnetohydrodynamic simulation. This work points out, for the first time, new manifestations of the 3D flare scenario in EUV light curves. In addition to providing an explanation for two-ribbon late-phase flares, the results presented help bridge the gap between imaging observations, EUV light-curve diagnostics, and the magnetic structures of the associated coronal mass ejections.

Context. On 2024 May 6, Active Region 13663 produced an X4.5-class flare associated with a filament eruption that exhibited remarkable rotation and deflection dynamics. Aims. We investigated two key aspects of this event: the formation mechanisms of the complex flare ribbon structures and the physical drivers behind the observed filament deflection. Methods. We conducted a data-constrained magnetohydrodynamic simulation using the zero-beta approximation to reconstruct the filament’s evolution. Through detailed analysis of quasi-separatrix layers (QSLs) and their comparison with observed flare ribbons, we established crucial connections between magnetic topology and flare morphology. Results. Our simulation successfully reproduces key observational features of the eruption. We also connect the flare ribbon morphology with calculated QSLs. Finally, we find filament deflection resulting from localized reconnection at the X-point, as evidenced by Lorentz force decomposition. Conclusions. We demonstrate that reconnection above two current channels of opposite helicity governs the eruption dynamics, with magnetic pressure gradients driving flux rope deflection and a magnetic tension force simultaneously restraining arcade ascent. The event features a “sandwich” magnetic configuration that includes double parallel polarity inversion lines with a strong shear component. We suggest that this particular configuration could serve as a plausible formation mechanism for the observed parallel three-ribbon structure. In addition, the evolution of QSLs and flare ribbons provides clear evidence of reconnection between two flux ropes.

Kinematics of solar eruptive filaments is one of the important diagnostic parameters for predicting whether solar eruptions would induce geomagnetic storms. Particularly, some geomagnetic storms might be induced by solar filament eruptions originating from unexpected surface source regions because of nonradial ejection. The nonradial ejection of filaments has received widespread attention but remains inconclusive. We select two eruptive filaments, both of which are supported by flux ropes, as indicated by the hot channel structures seen in the 94 Å images and the hook-shaped brightenings where the filament material falls back. We measure the three-dimensional ejection trajectory of the eruptive filaments by integrating the simultaneous observations from the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations Observatory (STEREO). Furthermore, we calculate the distribution of the poloidal field along the ejection path and compare it to the ejection acceleration. It is revealed that the reinforcement of the poloidal magnetic field may lead to the suppression of the acceleration, with the acceleration resuming its increase only when the poloidal field diminishes to a certain level. Additionally, we compute the spatial distribution of the poloidal field in various directions and find that the poloidal magnetic field above the filaments is asymmetric. For both investigated events, the filaments appear to eject toward the side where the poloidal magnetic field is weaker, indicating that the eruptive filaments tend to propagate along the side with weaker strapping force. This may provide a new explanation for the inclined ejection of filaments.

Magnetic reconnection is a fundamental mechanism of driving eruptive phenomena of different scales and may be coupled with turbulence as suggested by recent remote-sensing and in situ observations. However, the specific physics behind the complex three-dimensional (3D) turbulent reconnection remains mysterious. Here, we develop a novel methodology to identify and analyze multitudes of multiscale reconnection fragments within a strongly turbulent current sheet (CS) and apply it to a state-of-the-art numerical simulation of turbulent reconnection for solar flares. It is determined that the reconnection fragments tend to appear as quasi-2D sheets forming along local magnetic flux surfaces, and, due to strong turbulence, their reconnection flow velocities and reconnection rates are significantly broadened statistically but are scale independent. Each reconnection fragment is found to be surrounded by strongly fluctuated in/outflows and has a widely distributed reconnection rate, mainly in the range of 0.01-0.1. The results, for the first time, provide quantitative measurements of 3D magnetic reconnection in strongly turbulent flare CSs, offering insights into the cascading laws of 3D reconnection in other turbulent plasmas.

A thorough understanding of the initiation of coronal mass ejections (CMEs), which is manifested as a slow rise of pre-eruptive structures before the impulsive ejection in kinematics, is key for forecasting solar eruptions. In our previous work, we showed that the slow rise of a hot flux rope with coronal mass density is caused by the moderate magnetic reconnection occurring in the hyperbolic flux tube (HFT) combined with the torus instability. However, it remains unclear how the initiation process varies when a filament is present in the pre-eruptive flux rope. In this work, we reveal the complete initiation route of a CME containing filament mass with a state-of-the-art full-magnetohydrodynamics simulation. The comprehensive analyses show that the filament mass has an important impact on the CME initiation through triggering and driving the slow rise of flux rope with its drainage, besides the contributions of HFT reconnection and torus instability. Finally, in combination with our previous work, we propose that the enhanced drainage of filament mass and various features related to the HFT reconnection, such as the split of pre-eruptive structure and the preflare loops and X-ray emissions, can serve as precursors of CME initiation in observations.

We investigate the acceleration and transport of electrons in the highly fine-structured current sheet that develops during magnetic flux rope (MFR) eruptions. Our work combines ultraresolved magnetohydrodynamic (MHD) simulations of MFR eruption, with test-particle studies performed using the guiding center approximation. Our grid-adaptive, fully 3D, high-resolution MHD simulations model MFR eruptions that form complex current-sheet topologies, serving as background electromagnetic fields for particle acceleration. Within the current sheet, tearing-mode instabilities give rise to mini flux ropes. Electrons become temporarily trapped within these elongated structures, undergoing acceleration and transport processes that significantly differ from those observed in 2D or 2.5D simulations. Our findings reveal that these fine-scale structures act as efficient particle accelerators, surpassing the acceleration efficiency of single X-line reconnection events, and are capable of energizing electrons to energies exceeding 100 keV. High-energy electrons accelerated in different mini flux ropes follow distinct trajectories, due to spatially varying magnetic field connectivity, ultimately precipitating onto opposite sides of flare ribbons. Remarkably, double electron sources at the flare ribbons originate from different small-flux-rope acceleration regions, rather than from the same reconnecting field line, as previously suggested. Distinct small flux ropes possess opposite magnetic helicity, to accelerate electrons to source regions with different magnetic polarities, establishing a novel conjugate double-source configuration. Furthermore, electrons escaping from the lower regions exhibit a broken-power-law energy spectrum. This spectral break arises from electrons accelerated in disparate mini flux ropes, each exhibiting magnetic reconnection rates and acceleration efficiencies, which reflect the varying local reconnection conditions.

The elongated bright structures above solar flare loops are suggested to be current sheets, where magnetic reconnection takes place. Observations have revealed various characteristics of the current sheet; however, their physical origin remains to be ascertained. In this study we aim to reveal the relations of observational characteristics of current sheets with the fundamental processes of magnetic reconnection. Using high-resolution 3D magnetohydrodynamic simulations of turbulent magnetic reconnection within a solar flare current sheet, we synthesized the remote-sensing observations of the current sheet and determined their physical properties. Turbulent magnetic reconnection can significantly broaden the apparent width of the current sheet, which is much larger than the realistic physical width because of the superposition effect. The differential emission measures of the current sheet have two peaks; the high-temperature component is spatially related to confirmed small-scale reconnection sites, showing that the current sheet is directly heated by reconnection. Moreover, we demonstrate that strong turbulence can cause the nonthermal broadening of spectral lines at both the current sheet and flare loop-top regions. A strong correlation between them in time is also observed. Our 3D turbulent magnetic reconnection flare model can be used to interpret primary observational characteristics of the elongated bright current sheets of solar flares.

Image denoising based on deep learning has witnessed significant advancements in recent years. However, existing deep learning methods lack quantitative control of the deviation or error on denoised images. The neural networks Self2Self is designed for denoising single-image, training on it and denoising itself, during which training is costly. In this work we explore training Self2Self on an astronomical image and denoising other images of the same kind, which is suitable for quickly denoising massive images in astronomy. To address the deviation issue, the abnormal pixels whose deviation exceeds a predefined threshold are restored to their initial values. The noise reduction includes training, denoising, restoring and named TDR-method, by which the noise level of the solar magnetograms is improved from about 8 G to 2 G. Furthermore, the TDR-method is applied to galaxy images from the Hubble Space Telescope and makes weak galaxy structures become much clearer. This capability of enhancing weak signals makes the TDR-method applicable in various disciplines.

Solar filaments are believed to be a clump of cold plasma accumulated in the magnetic dips. However, the magnetic configuration of filaments and the key factors for their formation remains elusive. In this Letter, we present a detailed study of the formation and eruption of a multifilament system with observations and simulations. Before the filament appeared visible, the chromospheric fibrils gradually gathered together, evolving from a diffuse distribution into threadlike structures that were nearly parallel to the polarity inversion lines. On 2022 March 20, an arch filament first appeared showing high dynamics, and subsequently two reserved S-shaped filaments were visibly observed. These two filament segments further reconnected, forming a long coherent filament and resulting in a double-decker configuration. In addition, continuous converging motion and magnetic flux cancellation were found in the photosphere during the evolution. Simultaneously, more bald patch structures appeared at the polarities' collision position. Through a data-driven numerical simulation, we further reconstructed the coronal magnetic field, which is composed of two twisted magnetic flux ropes (MFRs) with their bottom touching the photosphere, along with a group of sheared arcades forming an X-shaped configuration. These findings suggest that the magnetic configuration of the filament is in a highly dynamic state, evolving from a hybrid to a coherent MFR. Moreover, we propose that the formation and eruption of the multifilament system are closely related to magnetic reconnection taking place on the photosphere and in the lower corona, respectively, both mainly driven by the photospheric converging motion.

In this work, we analyze a successful eruption, accompanied by an X5.4-class flare in active region 11429. The eruptive structure is an elongated hot structure, with two curved brightenings below it. Additionally, we find that snail-shell-shaped flare loops are formed at the end of the flare, with a filament channel beneath the loops that implies a magnetic flux rope structure. The flare ribbons indicate a highly complex eruption process. During the eruption, using Global Oscillation Network Group data, we find a small filament that exists before and after the eruption. We reproduce the eruption using a full thermodynamic magnetohydrodynamic simulation, with the purpose to illustrate the mechanisms of the eruption. The small magnetic flux rope continuously rises due to arcade–arcade to rope–flare loop reconnection below, compressing the sheared magnetic arcades above. Slipping reconnection between the upper sheared magnetic arcades leads to the formation of new sheared magnetic arcades, resulting in a successful eruption. Simultaneously, the newly formed snail-shell-shaped flare loops constrain the elevation of the original magnetic flux rope below, implying that the original magnetic flux rope is not the eruptive structure of this successful eruption. Instead, the sheared magnetic arcades produced by the upper slipping reconnection above the original flux rope is the eruptive structure involved.

Line-of-sight oriented flows with several red and blue Doppler-shifted rings in coronal cavities have been observed by the Coronal Multi-channel Polarimeter (CoMP) but rarely explained. In this paper, we perform pseudo-3D simulations with a Titov–Démoulin-modified magnetic flux rope (MFR) to study the corresponding flows in coronal cavities by forward modeling. Two types of field-aligned flows are found. The first type is converging flows, which are located in the magnetic field lines near the MFR axis, converging toward the magnetic dips and driven by the filament condensation, corresponding to the inner flows. The second type is unidirectional flows, which are located in the magnetic field lines near the MFR boundary, flowing from one footpoint to the other, and are driven by the asymmetric heating, corresponding to the outer flows. These inner and outer flows naturally form a nested structure with a velocity of several km s ^−1 , leading to the formation of multiple rings observed in the cavity view. Synthetic Doppler images indicate two to four rings in our simulations, which is consistent with most of the observational situations by CoMP.

Context. Circular ribbon flares, a typical kind of multi-ribbon flare, have been the focus of many studies. Along with the flares themselves, many other related phenomena also merit investigation, such as jets, chromosphere condensation, and magnetohydrodynamic (MHD) waves. Aims. We analyzed a circular ribbon flare accompanied by a rotating jet that occurred on 2023 May 25, and we find observational evidence of chromosphere condensation in the flare ribbon and an Alfv & eacute;n wave along the jet. Methods. We derived the plane-of-sky velocity of the cool component of the jet using the Fourier local correlation tracking method, and we obtained the Doppler velocity of the flare and the cool component of jet by analyzing the spectrum observed by the Chinese H alpha Solar Explorer (CHASE). To obtain the magnetic topology of the circular ribbon flare, we performed a nonlinear force-free field extrapolation using the photosphere vector magnetogram observed by the Helioseismic and Magnetic Imager (HMI). We additionally fit the hard X-Ray (HXR) energy spectrum obtained by the Hard X-ray Imager (HXI) aboard the Advanced Space-based Solar Observatory (ASO-S), and made a comparison between the Doppler velocity and the HXR sources. Results. We derive the velocity field of the cool component of jet, illustrate the spine-fan magnetic structure of the circular ribbon flare, and by comparing the vector magnetic field and the vector velocity field, we find a strong correlation between their inclination and azimuth angles, indicating that the jet mostly moves along the magnetic field. Through the Doppler velocity of the flare ribbon derived by CHASE observations, the redshift in the H alpha waveband indicates the existence of chromosphere condensation. The HXI HXR spectra and images demonstrate that nonthermal electrons are the primary source of the chromosphere condensation.