Yang Guo

Recurrent solar coronal jets originate from the same source region, providing a useful setting for studying the buildup, redistribution, and release of magnetic energy and helicity. However, how these quantities can characterize magnetic evolution and the onset conditions of the eruptions remains unclear. We perform a full three-dimensional (3D) thermodynamic magnetohydrodynamic simulation of recurrent jets driven by converging motions imposed at the bottom boundary. The simulation naturally produces two successive eruptions. The current-carrying helicity H _J decreases during the first jet and gradually recovers between the two jets. In contrast, the free magnetic energy E _free shows no clear accumulation after its first release. This difference indicates that H _J provides information on magnetic evolution beyond that provided by E _free . Furthermore, the commonly used helicity ratio H _J / H _V reaches different peaks near the onset of the two jets and is sensitive to the integration volume. By comparison, the locally normalized quantity H J / Φ closed 2 reaches similar peaks near the onset of both jets and is relatively insensitive to the choice among the tested integration volumes, where Φ _closed is the single-polarity magnetic flux of the closed-field domain. These results reveal the local nature of the eruptions and suggest that H _J normalized by the square of the closed magnetic flux may be a useful diagnostic of eruptive conditions.

For flares associated with eruptive filaments, the filament normally rises above the postflare loops. Here, we report an unusual event in which the postflare loops instead overlie a filament that remains nonejected throughout the flare. This event was simultaneously captured by the Chinese H α Solar Explorer (CHASE), the Solar Extreme-UltraViolet Imager (SUVI) on board Fengyun-4C, the Hard X-ray Imager (HXI) on board the Advanced Space-based Solar Observatory (ASO-S) and the Solar Dynamics Observatory (SDO). Extreme ultraviolet (EUV) observations provided by FY4C/SUVI and SDO show that two hot loop systems form at the flare onset. The western end of the northern loop system undergoes a southwestward drifting motion with gradually increasing shear, whereas the southern loop system progressively converges toward and eventually overlies the northern one. Meanwhile, three-dimensional magnetic field extrapolations reveal an increase in both the twist of the filament-supporting magnetic structure and its poloidal magnetic field after the flare. Taken together, these observations suggest that the flare is driven by a self-constraining zipper-type magnetic reconnection, in which highly sheared arcades reconnect to form a series of overlying flare arcades and an underlying flux rope. This reconnection continuously strengthens the magnetic confinement of the filament, preventing its outward eruption, while facilitating substantial plasma drainage along the reconnected magnetic field revealed by the CHASE H α spectroscopic observations.

This study investigates the multithermal structure of solar jets by combining extreme ultraviolet and H α observations, addressing whether cool and hot components originate from the same jet, their morphological similarities and differences, and the role of minifilaments. We analyze 70 jet events simultaneously observed by the Atmospheric Imaging Assembly and the Chinese H α Solar Explorer from 2023 May 25 to 2026 January 15. The events are classified into four types based on whether or not there are significant differences between the two wavebands in terms of length and width; nonlinear force-free field extrapolations are applied to examine magnetic fields. We find that the cool and hot components correspond to different temperature parts of a unified jet, showing spatiotemporal coincidence and kinematic synchronization. Morphologically, 30% show no significant difference in length/width, 37% differ in one dimension, and 33% differ in both. About 80% involve minifilament eruptions; jets with filaments more often exhibit morphological differences (filament nonexpansion, hot shell thickness, insufficient kinetic energy, or material rarefaction). In contrast, jets without filaments tend to show consistent morphologies; when discrepancies occur, they are mainly linked to small magnetic field curvature, which reduces magnetic tension and leads to less acceleration of cool material. These results highlight the complex interaction between thermal, dynamic, and magnetic factors in shaping jet morphology.

Accurate photospheric transverse magnetic fields are crucial for solar-activity studies and coronal field modeling but are often limited by lower signal-to-noise ratios and the 180° azimuth ambiguity. We present an observational validation of a dual-perspective stereoscopic approach that reconstructs an improved transverse component in the Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) reference frame using only line-of-sight (LOS) magnetograms from SDO/HMI and the Solar Orbiter Polarimetric and Helioseismic Imager High Resolution Telescope (HRT). Using a coobservation on 2024 October 9 with a separation angle α ≈ 54 . ° 46, we develop a dedicated processing pipeline including solar-rotation compensation, reprojection onto a common grid, resolution homogenization, and tile-based fine coregistration. After applying the 2D stereoscopic relation to the coregistered LOS fields, we obtain the reconstructed transverse component. From weak-field statistics of the analyzed transverse component, the reconstructed field reaches a robust width (median absolute deviation (MAD)) of σ MAD new ≈ 9.5 G, substantially below those of the instrument-provided transverse components, σ MAD HMI ≈ 83.2 G and σ MAD HRT ≈ 62.3 G, bringing the transverse-component uncertainty to the same order as the LOS uncertainty. Direction-consistency tests show 93.5% agreement with the minimum-energy-based (ME0) disambiguation of the HRT transverse field and 99.9% agreement above the ME0 noise threshold. We further demonstrate that the method remains effective when applied to the higher-cadence hmi.M_45s LOS magnetograms, enabling high-cadence, LOS-precision, transverse-field estimates.

Context. Observations show that many solar eruptions remain confined in the magnetic configuration of strong overlying magnetic fields, which is commonly referred to as the magnetic cage. Aims. Confined eruptions under strong, poloidal overlying fields have been widely studied. In contrast, the confined eruption scenario under strong external toroidal fields remains unknown. Methods. We used three-dimensional magnetohydrodynamic simulations to systematically study confined eruptions in a toroidal magnetic cage, focusing on the roles of the Lorentz force and magnetic reconnection, as well as their observational manifestations, such as flare ribbons and loops. We further applied the test-particle method with the guiding-centre approximation to synthesize hard X-ray sources, enabling comparison between thermal and nonthermal responses. Results. Our results show that overlying toroidal magnetic fields are crucial in confining eruptions. They generate strong return currents that produce a significant downward Lorentz force, suppressing the rise of the flux rope. Simultaneously, they drive the large-angle rotation of the rope, triggering reconnection with the overlying fields and ultimately causing its breakup. The synthesized EUV images display multi-ribbon flare structures with highly sheared loops with a global “cowboy-hat-like” shape. Additionally, comparisons with hard X-ray sources reveal that thermal and nonthermal responses are not co-spatial, in which return current is a major accelerator to energetic electrons. Conclusions. The simulations clarify how the magnetic cage constrains solar eruptions. First, the downward Lorentz force related to return current effectively suppresses eruptions, explaining why confined flares tend to occur in electric-current neutralized active regions. Second, we demonstrate that toroidal-field-induced force is the key driver for rotation and confinement of the flux rope. This explains why many filament eruptions with rotation fail despite being torus-unstable. Finally, we suggest that the global morphology of flare loops (cowboy-hat–like or “saddle-like”) and the shearing degree of flare loops can serve as useful diagnostics to distinguish confined from eruptive flares.

Context . Spectropolarimetric inversions are usually employed to obtain the physical parameters (e.g., magnetic field, velocity, temperature) of the solar atmosphere that contribute to the observed Stokes spectra. However, this process involves optimization in a multi-dimensional parameter space, which not only demands substantial computational time, but also frequently encounters local minima during the search. Aims . Our aim is to develop a spectropolarimetric inversion code leveraging the physics-informed neural networks (PINNs) and a novel gradient-bias annealing (GBA) algorithm with global minimum search capabilities to enable computationally efficient convergence toward near-optimal solutions. Methods . Inversions were trained on synthetic data generated by a forward model. The training process incorporated both data regression and cyclic physics-informed constraints to ensure physical consistency. Additionally, we developed a GBA algorithm to enable preferential annealing during optimization. The entire framework was implemented with CUDA for parallel acceleration. Results . We evaluated the effectiveness of the GBA algorithm, PINN, and their combined approach using the Helioseismic and Magnetic Imager (HMI) Stokes spectrum observations. When employed independently, the PINN achieved inversion results comparable to HMI’s quick products, via Very Fast Inversion of the Stokes Vector (VFISV), within significantly shorter timescales. The GBA algorithm alone demonstrated superior spectral recovery, despite requiring several hours to process millions of pixels in a single field of view. By initializing the annealing process with the PINN results, we obtained quality-enhanced results on minute-level timescales.

Solar active regions (ARs) are the primary source of solar eruptions and space weather. Accurate detection and tracking of ARs is crucial for understanding their evolution and predicting solar activities. In the previous work, based on the density-based spatial clustering of applications with noise (DBSCAN) approach, we proposed the DBSCAN-based solar active region detection (DSARD) framework. To mitigate its limitations, in this paper we applied the hierarchical density-based spatial clustering of applications with noise (HDBSCAN) approach to the detection of solar active regions, which is called the HDBSCAN-based solar active region detection and tracking (HARDAT) method. This enables the algorithm to handle multidensity magnetic structures dynamically, eliminating the need for fixed thresholds. Consequently, the algorithm can detect diffuse and small ARs more effectively while preserving morphological integrity. We have also developed a solar differential rotation-based tracking algorithm that integrates physical motion models and Hamming distance similarity metrics to achieve robust multiobject tracking. Additionally, we propose a novel polarity inversion line extraction method that uses support vector classification, which offers superior generalization for complex AR boundaries. Processing line-of-sight magnetograms from Solar and Heliospheric Observatory/Michelson Doppler Imager (1996–2011) and Solar Dynamics Observatory/Helioseismic and Magnetic Imager (2010–2024) and evaluating them against the National Oceanic and Atmospheric Administration and DSARD catalogs demonstrates that HARDAT is superior in terms of sensitivity, accuracy, and stability of detection and tracking. This is particularly evident when resolving clustered ARs and maintaining identity continuity. HARDAT therefore offers a comprehensive solution for the long-term analysis of AR evolution and space weather prediction.

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 = n _x · n _y · n _z is the total number of voxels in the simulation volume) to O ( k · 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 · n ) integration, sacrificing small r resolution. And the second computes ray-plane intersections directly, with O ( k · n · log n ) complexity. RST features a user-friendly interface where users simply specify absorption ( κ ) and emissivity ( j ). It includes physical modules for white-light corona, H α , EUV, radio, and pseudo-radiation.

The solar magnetic field is central to understanding solar activity, making high-precision spectropolarimetric observations of great importance. Xihe-2, positioned at the Sun--Earth L5 point, is designed to observe the solar polarized spectrum. Its onboard Spectral Magnetic Telescope (SMT) is expected to employ a three-retarder stepwise modulation scheme to retrieve solar magnetic field information. However, this scheme has not yet been sufficiently studied in terms of contingency operation and accuracy control. In this work, we present a systematic analysis and improvement of the scheme from both perspectives. In the event that one retarder becomes inoperative owing to stepper motor failure, the remaining two retarders must be adjusted so that all four Stokes parameters can still be measured. We examine the feasibility of such backup modulation schemes for different retarder-failure cases and derive the corresponding conclusions. We further analyze the three major error sources in the ideal three-retarder stepwise modulation scheme, determine their acceptable ranges, and perform comprehensive validation and optimization through Monte Carlo simulations. The results show that the measurement accuracy of the retrieved Stokes parameters can reach the order of ten raised to the power of minus three.

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.