Chang Zhou

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.

Coronal mass ejections (CMEs) are the primary drivers of adverse space-weather events, yet their initiation and onset prediction remain insufficiently understood due to the complexity of the magnetic topology and physical processes in real solar source regions. Using a fully observational-data-driven magnetohydrodynamic simulation, we successfully reproduced the initiation of a CME originating from the super active region 13663, with only a one-minute time lag between the flare peak in observations and the velocity peak of the rising flux rope in the simulation. Moreover, the eruptive structure exhibits a multi-stage kinematic evolution: an initial slow acceleration, a plateau at a nearly stationary height, and a subsequent impulsive acceleration. These stages correspond to torus instability, the downward tension force exerted by the overlying toroidal field, and fast magnetic reconnection, respectively. Our results highlight the inherently multistage nature of CME initiation in real events. In configurations with strong overlying toroidal fields, the downward toroidal-field-induced tension force can suppress the rise of the flux rope and produce a plateau phase at a nearly stable height, even when torus instability occurs. In contrast, the subsequent fast magnetic reconnection beneath the flux rope can drive the impulsive eruption more effectively. The close agreement between the observed and simulated peak times over one minute demonstrates the strong potential of our data-driven model for predicting CME onset.

Understanding the filament rising process is crucial for unveiling the triggering mechanisms of coronal mass ejections and forecasting space weather. In this paper, we present a detailed study of the filament initial eruption under a fan–spine structure. It was found that the filament underwent two distinct acceleration stages corresponding to class M1.0 and M4.6 flare events. The first acceleration stage commenced with the filament splitting, after which the upper portion was subsequently heated, being a hot channel, and slowly rose at an average speed of 22 km s ⁻¹ . A set of hot reverse C-shaped loops appeared repeatedly during the filament splitting, and a hook structure was recognized at this phase, suggesting ongoing growth of the magnetic flux rope (MFR). When it reached a certain altitude, the hot channel appeared to get into a quasi-static phase with its upper edge seriously decelerated and its lower edge expanding downward. Approximately 30 minutes later, as a distinct annular ribbon appeared outside the hook structure, the hot channel rose again at a velocity of over 50 km s ⁻¹ accompanied by rapidly drifting footpoints and experienced a second acceleration stage with its axial flux increased to 1.1 × 10 ²¹ Mx. It is deduced that the filament initial eruption under a magnetic dome possesses multiple kinetic processes. We suggest that the magnetic reconnection taking place within and beneath the filament continues to trigger the growth of preeruptive MFR and the first acceleration, when the magnetic reconnection above the filament plays a key role in the second acceleration.

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 Alfvén 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 α 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 α 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.

We observed three recurrent blowout jets in an active regio with Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO). Using Helioseismic Magnetic Imager (HMI) data. We found that the magnetic flux of an emerging negative pole increases steadily before declining just as the jets erupt. Certain physical quantities, like the total unsigned vertical current, align with the periodicity of the jets. The differential affine velocity of the vector magnetograms reveals strong shear around the negative pole. The Doppler velocity map, calculated from the H$α$ spectra observed by the Chinese H$α$ Solar Explorer (CHASE), shows upflows with large initial velocity before it can be observed by AIA. The magnetic field derived from the nonlinear force-free field (NLFFF) model suggests a topology akin to fan-spine structure, consistent with AIA images. We calculated the evolution of volumetric helicity ratio using the NLFFF model and found its phase aligns with the jet flux in AIA 171 Å. These results suggest that recurrent jets may be triggered by the accumulation and release of energy and helicity, driven by emergence, shearing and cancellation of photospheric magnetic field.

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.

We observed three recurrent blowout jets in an active region with the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. Using Helioseismic Magnetic Imager data we found that the magnetic flux of an emerging negative pole increases steadily before declining just as the jets erupt. Certain physical quantities, such as the total unsigned vertical current, align with the periodicity of the jets. The differential affine velocity of vector magnetograms reveals strong shear around the negative pole. The Doppler velocity map, calculated from the Hα spectra observed by the Chinese Hα Solar Explorer, shows upflows with large initial velocity before they can be observed by AIA. The magnetic field derived from the nonlinear force-free field (NLFFF) model suggests a topology akin to a fan–spine structure, consistent with AIA images. We calculated the evolution of the volumetric helicity ratio using the NLFFF model and found its phase aligns with the jet flux in AIA 171 Å. These results suggest that recurrent jets may be triggered by the accumulation and release of energy and helicity, driven by emergence, shearing, and cancellation of photospheric magnetic field.