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We have numerically demonstrated that simulated cool star coronae naturally form condensations. If the star rotates slowly, with a co-rotation radius greater than the Alfvén radius (i.e. |$R_{\mathrm{K}} \gt R_{\mathrm{A}}$|⁠), these condensations will form below the co-rotation radius |$R_{\mathrm{K}}$| and simply fall back to the stellar surface as coronal rain. If, however, the star is more rapidly rotating, (⁠|$R_{\mathrm{K}} \lt R_{\mathrm{A}}$|⁠), not only rain will form but also 'slingshot prominences'. In this case, condensations collect into a large mass reservoir around the co-rotation radius, from which periodic centrifugal ejections occur. In this case, some 51 per cent of the coronal mass is cold gas, either in rain or prominences. We find that 21  per cent of the mass lost by our simulated fast rotating star is cold gas. Studies of stellar mass-loss from the hot wind do not consider this component of the wind and therefore systematically underestimate mass-loss rates of these stars. Centrifugal ejections happen periodically, between every 7.5–17.5 h with masses clustering around |$10^{16}$|  g, These results agree well with observational statistics. Contrasting the fast and slow rotating magnetospheres, we find that there are two distinct types of solutions, high-lying and low-lying loops. Low-lying loops only produce coronal rain whereas high-lying loops produce both rain and slingshots. [ABSTRACT FROM AUTHOR]

In this paper, we carry out multiwavelength observations of two successive extreme-ultraviolet (EUV) waves originating from active region (AR) NOAA 13575 and a transverse oscillation of a columnar quiescent prominence on 2024 February 9. A hot channel eruption generates an X3.4 class flare and the associated full-halo coronal mass ejection (CME), which drives the first EUV wave front (WF1) at a speed of |$\sim$| 835 km s |$^{-1}$|⁠. WF1 propagates in the south-east direction and interacts with the prominence, causing an eastward displacement of the prominence immediately. Then, a second EUV wave front (WF2) is driven by a coronal jet at a speed of |$\sim$| 831 km s |$^{-1}$|⁠. WF2 follows WF1 and decelerates from |$\sim$| 788 to |$\sim$| 603 km s |$^{-1}$| before arriving at and touching the prominence. After reaching the maximum displacement, the prominence turns back and swings for 1–3 cycles. The transverse oscillation of horizontal polarization is most evident in 304 Å. The initial displacement amplitude, velocity in the plane of the sky, period, and damping time fall in the ranges of 12–34 Mm, 65–143 km s |$^{-1}$|⁠ , 18–27 min, and 33–108 min, respectively. There are strong correlations among the initial amplitude, velocity, period, and height of the prominence. Surprisingly, the oscillation is also detected in 1600 Å, which is totally in phase with that in 304 Å. [ABSTRACT FROM AUTHOR]

The Mg II k resonance line is commonly used for diagnosing the solar chromosphere. We theoretically investigated its intensity and polarization in solar prominences, taking 3D radiative transfer and Hanle and Zeeman effects into account. We used an optically thick 3D model representative of a solar prominence and applied several inversion methods to the synthetic Stokes profiles, clarifying their pros and cons for inferring prominence magnetic fields. We conclude that the self-consistent 3D inversion with radiative transfer is necessary to determine the magnetic field vector, although its geometry cannot be inferred with full fidelity. We also demonstrate that more traditional methods, such as those based on the weak field approximation or the constant-property slab assumption, can offer useful information under certain conditions. [ABSTRACT FROM AUTHOR]

Introduction: The triggering mechanism for filaments located in a weak magnetic field typically leans toward magnetohydrodynamic instabilities due to the weak magnetic strength inherent in filament structures. However, a subset of eruption events associated with significant flares remains. Therefore, we seek to understand the role that reconnection plays in the eruption of filaments with weak magnetic fields. Methods: We reconstruct the coronal magnetic field of an eruptive filament located in a relatively weaker magnetic environment, and analyze the magnetic field properties such as twist number and squashing factor. Results: This filament remains stable until the expansion of the heated bright arcades underneath. This expansion initially activates the filament, prompting its upward movement, leading to a gentle reconnection slightly to its south. The ensuing reconnection continues to propel the filament upward with uniform acceleration. These upward motions cause the drainage of filament mass, likely activating the torus instability of the filament. This torus instability then triggers the final eruption of the filament, successfully generating a coronal mass ejection (CME) and leaving behind a double-ribbon flare. Discussion: We conclude that the torus instability serves as the primary triggering mechanism of this eruption, while pre-eruption reconnection plays a role in pushing the filament upward to meet the instability condition. [ABSTRACT FROM AUTHOR]

We explored the impact that Doppler dimming and brightening effects from bulk motions of solar prominences have on the formation of Ly  |$~\alpha$|⁠ , H  |$~\alpha$|⁠ , and Mg  ii h line profiles. We compared two schemes in which these effects manifest; when the prominence is moving radially away from the solar surface (radial case), and when the prominence is moving parallel to the solar surface (horizontal case). To do this, we analysed 13 332 model profiles generated through the use of the 1D NLTE (i.e. departures from Local Thermodynamic equilibrium) radiative transfer (RT) code promweaver , built on the lightweaver NLTE RT framework to mimic the behaviour and output of the 1D NLTE RT code prom. We found that horizontal velocities are just as, or more important than radial velocities. This demonstrates that horizontal velocities need to be accounted for when attempting to do any sort of forward modelling. [ABSTRACT FROM AUTHOR]

Minifilaments are widespread small-scale structures in the solar atmosphere. To better understand their formation and eruption mechanisms, we investigate the entire life of a sigmoidal minifilament located below a large quiescent filament observed by Big Bear Solar Observatory/Goode Solar Telescope on 2015 August 3. The H α structure initially appears as a group of arched threads, then transforms into two J-shaped arcades, and finally forms a sigmoidal shape. Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly observations in 171 Å show that two coronal jets occur around the southern footpoint of the minifilament before the minifilament eruption. The minifilament eruption starts from the southern footpoint, then interacts with the overlying filament and fails. The aforementioned observational changes correspond to three episodes of flux cancellations observed by SDO/Helioseismic and Magnetic Imager. Unlike previous studies, the flux cancellation occurs between the polarity where the southern footpoint of the minifilament is rooted and an external polarity. We construct two magnetic field models before the eruption using the flux rope insertion method and find a hyperbolic flux tube above the flux cancellation site. The observation and modeling results suggest that the eruption is triggered by the external magnetic reconnection between the core field of the minifilament and the external fields due to flux cancellations. This study reveals a new triggering mechanism for minifilament eruptions and a new relationship between minifilament eruptions and coronal jets. [ABSTRACT FROM AUTHOR]

Context. Filament eruption is a common phenomenon in solar activity, but the triggering mechanism is not well understood. Aims. We focus our study on a filament eruption located in a complex nest of three active regions close to a coronal hole. Methods. The filament eruption is observed at multiple wavelengths: by the Global Oscillation Network Group (GONG), the Solar Terrestrial Relations Observatory (STEREO), the Solar Upper Transition Region Imager (SUTRI), and the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). Thanks to high-temporal-resolution observations, we were able to analyze the evolution of the fine structure of the filament in detail. The filament changes direction during the eruption, which is followed by a halo coronal mass ejection detected by the Large Angle Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO). A Type III radio burst was also registered at the time of the eruption. To investigate the process of the eruption, we analyzed the magnetic topology of the filament region adopting a nonlinear force-free-field (NLFFF) extrapolation method and the polytropic global magnetohydrodynamic (MHD) modeling. We modeled the filament by embedding a twisted flux rope with the regularized Biot-Savart Laws (RBSL) method in the ambient magnetic field. Results. The extrapolation results show that magnetic reconnection occurs in a fan-spine configuration resulting in a circular flare ribbon. The global modeling of the corona demonstrates that there was an interaction between the filament and open field lines, causing a deflection of the filament in the direction of the observed CME eruption and dimming area. Conclusions. The modeling supports the following scenario: magnetic reconnection not only occurs with the filament itself (the flux rope) but also with the background magnetic field lines and open field lines of the coronal hole located to the east of the flux rope. This multiwavelength analysis indicates that the filament undergoes multiple magnetic reconnections on small and large scales with a drifting of the flux rope. [ABSTRACT FROM AUTHOR]

Context. Spectral inversions are used to analyse spectroscopic observations with the aim of deriving the physical properties of the observed plasma, such as the kinetic temperature, density, pressure, degree of ionisation, or macroscopic velocities. One of the key factors ensuring the high precision of the derived plasma properties is having accurately defined input parameters of the models on which spectral inversions rely. The illumination, which chromospheric and coronal structures receive from the solar surface (and corona), is one of the most crucial input parameters of these models. Aims. We do not perform spectral inversions in this work. Our aim is to study two important factors that contribute to the accurate definition of the incident radiation boundary conditions: the altitude above the solar surface and the dynamics of the illuminated plasma. This investigation takes into account a diverse range of solar structures from the high-rising eruptive prominences to low-lying spicules. Methods. To study the influence of the altitude and dynamics of the observed plasma on the incident radiation boundary conditions, we used geometrical principles valid for any spectral line. However, to demonstrate the strong impact of dynamics, we considered the specific case of narrow spectral lines of Mg II H&K, which are highly sensitive to the presence of velocities. Results. We argue that the altitude of the illuminated plasma strongly influences the way we need to define the incident radiation boundary conditions to achieve the most accurate results. For low-lying structures, generally below 50 000 km, the incident radiation may need to be specified directly from the composition of the portion of the solar disc that illuminates them. For high-altitude structures, generally above 300 000 km, the fraction of the solar disc illuminating the analysed plasma is large enough to be realistically approximated by the composition of the entire disc. We also show that for the narrow spectral lines, such as the Mg II H&K lines, the impact of dynamics on the incident radiation intensity and profile shapes starts from radial velocities of 30 km s−1. Such velocities are even exhibited by the fine structures of quiescent prominences and are easily exceeded in spicules or eruptive prominences. Conclusions. The two aspects of the incident radiation definition studied here are relevant for spectral inversions based on any kind of modelling approach. However, their impact on the precision of the results of spectral inversions is likely less significant than the impact of the choice of the complexity of the model geometry, for example. [ABSTRACT FROM AUTHOR]

We investigate the deflection and rotation behaviour of 49 Earth-directed coronal mass ejections (CMEs) spanning the period from 2010 to 2020 aiming to understand the potential influence of coronal holes (CHs) on their trajectories. Our analysis incorporates data from coronagraphic observations captured from multiple vantage points, as well as extreme ultraviolet (EUV) observations utilised to identify associated coronal signatures such as solar flares and filament eruptions. For each CME, we perform a 3D reconstruction using the Graduated Cylindrical Shell (GCS) model. We perform the GCS reconstruction in multiple time steps, from the time at which the CME enters the field of view (FOV) of the coronagraphs to the time it exits. We analyse the difference in the longitude, latitude, and inclination between the first and last GCS reconstructions as possible signatures of deflection/rotation. Furthermore, we examine the presence of nearby CHs at the time of eruption and employ the Collection of Analysis Tools for Coronal Holes (CATCH) to estimate relevant CH parameters, including magnetic-field strength, centre of mass, and area. To assess the potential influence of CHs on the deflection and rotation of CMEs, we calculate the Coronal Hole Influence Parameter (CHIP) for each event and analyse its relationship with their trajectories. A statistically significant difference is observed between CHIP force and the overall change in a CME's direction in the lower corona. The overall change in a CME's direction accounts cumulatively for the change in latitude, longitude, and rotation. This suggests that the CHIP force in the low corona has a significant influence on the overall change in the direction of Earth-directed CMEs. However, as the CME evolves outward, the CHIP force becomes less effective in causing deflection or rotation at greater distances. Additionally, we observe a negative correlation between the deflection rate of the CMEs and their velocity, suggesting that higher velocities are associated with lower deflection rates. Hence, the velocity of a CME, along with the magnetic field from CHs, appears to play a significant role in the deflection of CMEs. By conducting this comprehensive analysis, we aim to enhance our understanding of the complex interplay between CHs, CME trajectories, and relevant factors such as velocity and magnetic-field strength. [ABSTRACT FROM AUTHOR]

Solar filament eruptions are often characterized by stepwise evolution due to the involvement of multiple mechanisms, such as magnetohydrodynamic instabilities and magnetic reconnection. In this article, we investigated a confined filament eruption with a distinct two-stage evolution by using the imaging and spectroscopic observations from the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory. The eruption originated from a kinked filament thread that separated from an active region filament. In the first stage, the filament thread rose slowly and was obstructed due to flux pile-up in its front. This obstruction brought the filament thread into reconnection with a nearby loop-like structure, which enlarged the flux rope and changed its connectivity through the foot-point migration. The newly formed flux rope became more kink unstable and drove the rapid eruption in the second stage. It ascended into the upper atmosphere and initiated the reconnection with the overlying field. Finally, the flux rope was totally disintegrated, producing several solar jets along the overlying field. These observations demonstrate that the external reconnection between the flux rope and overlying field can destroy the flux rope, thus playing a crucial role in confining the solar eruptions. [ABSTRACT FROM AUTHOR]

Solar filaments are good tracers of space weather and magnetic flux ropes in the corona. Identifying and detecting filaments helps to forecast space weather and explore the solar magnetic field. Many automatic detection methods have been proposed to process the large number of observed images. Current methods face issues of unreliable dataset annotations and poor anti-interference capability. First, to address the issue of unreliable dataset annotations, we built a solar filament dataset using a manual annotation method. Second, we introduced Transformer into Convolutional Neural Networks. Transformer, with the ability to extract more global features, can help counter interference. In addition, there is large disparity in the size of solar filaments. Therefore, a multi-scale residual block is designed to extract features across various scales. Deformable large kernel attention and a res path are used to better integrate encoder and decoder information. Results show that this method outperforms the existing solar filament detection methods (improved U-Net and improved V-Net), achieving an F1 score of 91.19%. In particular, our results show lower interference by sunspots and background noise than existing methods. The ability to counter interference is improved. [ABSTRACT FROM AUTHOR]

Similar to the cases of anemone jets, two-sided loop solar jets can also be produced by either flux emergence from the solar interior or small-scale filament eruptions. Using high-quality data from the Solar Dynamics Observatory, we have analyzed a two-sided loop solar jet triggered by the eruption of a small filament. The jet occurred in a pre-existing big filament channel. The detailed processes involved in the eruption of the small filament, the interaction between the erupted filament and the big filament channel, and the launch of the two-sided loop jet are presented. The observations further revealed notable asymmetry between the two branches of the jet spire: the northeastern branch is narrow and short, while the southern branch is wide and long and accompanied by discernible untwisting motions. We explored the unique appearance of the jet by employing the method of local potential field extrapolation to calculate the coronal magnetic field configuration around the jet. The photospheric magnetic flux below the small filament underwent cancellation for approximately 7 hr before the filament eruption, and the negative flux near the southern footpoint of the filament decreased by about 56% during this interval. Therefore, we propose that the primary photospheric driver of the filament eruption and the associated two-sided loop jet in this event is flux cancellation rather than flux emergence. [ABSTRACT FROM AUTHOR]

We consider small-scale jetlike events that might make the solar wind, as has been suggested in recent studies. We show that the events referred to as "coronal jets" and as "jetlets" both fall on a power-law distribution that also includes large-scale eruptions and spicule-sized features; all of the jetlike events could contribute to the solar wind. Based on imaging and magnetic field data, it is plausible that many or most of these events might form by the same mechanism: Magnetic flux cancelation produces small-scale flux ropes, often containing a cool-material minifilament. This minifilament/flux rope erupts and reconnects with adjacent open coronal field, along which "plasma jets" flow and contribute to the solar wind. The erupting flux ropes can contain twist that is transferred to the open field, and these become Alfvénic pulses that form magnetic switchbacks, providing an intrinsic connection between switchbacks and the production of the solar wind. [ABSTRACT FROM AUTHOR]

We perform a data-constrained simulation with the zero- β assumption to study the mechanisms of strong rotation and failed eruption of a filament in active region 11474 on 2012 May 5 observed by Solar Dynamics Observatory and Solar Terrestrial Relations Observatory. The initial magnetic field is provided by nonlinear force-free field extrapolation, which is reconstructed by the regularized Biot–Savart laws and magnetofrictional method. Our simulation reproduces most observational features very well, e.g., the filament large-angle rotation of about 130°, the confined eruption, and the flare ribbons, allowing us to analyze the underlying physical processes behind observations. We discover two flux ropes in the sigmoid system, an upper flux rope (MFR1) and a lower flux rope (MFR2), which correspond to the filament and hot channel in observations, respectively. Both flux ropes undergo confined eruptions. MFR2 grows by tether-cutting reconnection during the eruption. The rotation of MFR1 is related to the shear-field component along the axis. The toroidal field tension force and the nonaxisymmetry forces confine the eruption of MFR1. We also suggest that the mutual interaction between MFR1 and MFR2 contributes to the large-angle rotation and the eruption failure. In addition, we calculate the temporal evolution of the twist and writhe of MFR1, which is a hint of probable reversal rotation. [ABSTRACT FROM AUTHOR]

Partial eruptions of solar filaments are the typical representatives of solar eruptive behavior diversity. Here we investigate a typical filament partial eruption event and present integrated evidence for the configuration of the pre-eruption filament and its formation. The Chinese H α Solar Explorer H α observations reveal a structured Doppler velocity distribution within the pre-eruption filament, where distinct redshift only appeared in the eastern narrow part of the southern filament region and then disappeared after the partial eruption, while the northern part dominated by blueshift remained. Combining the Solar Dynamics Observatory and Advanced Space-based Solar Observatory observations, together with nonlinear-force-free-field modeling results, we verify that there were two independent material flow systems within the preflare filament, whose magnetic topology is a special double-decker configuration consisting of two magnetic flux ropes (MFRs) with opposite magnetic twist. During the formation of this filament system, continuous magnetic flux cancellation and footpoint motion were observed around its northern end. Therefore, we propose a new double-decker formation scenario: that the two MFRs composing such a double-decker configuration originated from two magnetic systems with different initial connections and opposite magnetic twist. Subsequent magnetic reconnection with the surrounding newly emerging fields resulted in the motion of the footpoint of the upper MFR to the region around the footpoint of the lower MFR, thus leading to the eventual formation of the double-decker configuration consisting of two MFRs with similar footpoints but opposite signs of magnetic twist. These results provide a potential way to determine unambiguously the progenitor configuration of a partially eruptive filament and reveal a special type of double-decker MFR configuration and a new double-decker formation scenario. [ABSTRACT FROM AUTHOR]

In this paper, we present the imaging and spectroscopic observations of the simultaneous horizontal and vertical large-amplitude oscillation of a quiescent filament triggered by an extreme-ultraviolet (EUV) wave on 2022 October 2. Particularly, the filament oscillation involved winking phenomenon in H α images and horizontal motions in EUV images. Originally, a filament and its overlying loops across AR 13110 and 13113 erupted with a highly inclined direction, resulting in an X1.0 flare and a non-radial coronal mass ejection. The fast lateral expansion of loops excited an EUV wave and the corresponding Moreton wave propagating northward. Once the EUV wave front arrived at the quiescent filament, the filament began to oscillate coherently along the horizontal direction, and the "winking filament" appeared concurrently in H α images. The horizontal oscillation involved an initial amplitude of ∼10.2 Mm and a velocity amplitude of ∼46.5 km s−1, lasting for ∼3 cycles with a period of ∼18.2 minutes and a damping time of ∼31.1 minutes. The maximum Doppler velocities of the oscillating filament are 18 km s−1 (redshift) and −24 km s−1 (blueshift), which were derived from the spectroscopic data provided by the Chinese H α Solar Explorer/H α Imaging Spectrograph. The three-dimensional velocity of the oscillation is determined to be ∼50 km s−1 at an angle of ∼50° to the local photosphere plane. Based on the wave–filament interaction, the minimum energy of the EUV wave is estimated to be 2.7 × 1020 J. Furthermore, this event provides evidence that Moreton waves should be excited by the highly inclined eruptions. [ABSTRACT FROM AUTHOR]

We report a failed solar filament eruption that involves external magnetic reconnection in a quadrupolar magnetic configuration. The evolution exhibits three phases of kinematic evolution: a slow rise, an acceleration, and a deceleration. In the early slow rise, extreme-ultraviolet brightenings appear at the expected null point above the filament and are connected to the outer polarities by the hot loops, indicating the occurrence of a breakout reconnection. Subsequently, the filament is accelerated outward, accompanied by the formation of low-lying high-temperature post-flare loops (>15 MK), complying with the standard flare model. However, after 2–3 minutes, the erupting filament starts to decelerate and is finally confined in the corona. The important finding is that the confinement is closely related to an external reconnection as evidenced by the formation of high-lying large-scale hot loops (>10 MK) with their brightened footpoints at the outer polarities, the fragmentation and subsequent falling of the filament along the newly formed large-scale loops, as well as a hard X-ray source close to one of the outer footpoint brightenings. We propose that, even though the initial breakout reconnection and subsequent flare reconnection commence and accelerate the filament eruption, the following external reconnection between the erupting flux rope and overlying field, as driven by the upward filament eruption, causes the eruption to finally fail, as validated by the numerical simulation of a failed flux rope eruption. [ABSTRACT FROM AUTHOR]

Filaments are one of the most common features in the solar atmosphere and are of significance in solar, stellar, and laboratory plasma physics. Using data from the Chinese H α Solar Explorer, the Solar Upper Transition Region Imager, and the Solar Dynamics Observatory, we report on multiwavelength imaging and spectral observations of the activation of a small filament. The filament activation produces several localized dynamic brightenings, which are probably produced by internal reconnections of the braided magnetic fields in the filament. The filament expands during the activation, and its threads reconnect with the ambient magnetic fields, which leads to the formation of hot arcades or loops overlying the filament. The thermal energy of each of these localized brightenings is estimated in the order of 1025–1027 erg, and the total energy is estimated to be ∼1.77 × 1028 erg. Our observations demonstrate that the internal magnetic reconnections in the filament can lead to localized heating in the filament threads and prompt external reconnections with ambient corona structures and thus could contribute to the energy and mass transferring into the corona. [ABSTRACT FROM AUTHOR]

We present an observational study of the formation and disappearance of a funnel prominence. Before the funnel prominence formed, cool materials from the top of a preexisting polar crown prominence flowed along saddle-shaped coronal loops to their base, forming a smaller prominence. Meanwhile, the saddle-shaped coronal loops gradually rose, and U-shaped coronal loops, termed prominence horns, began to appear along with a coronal cavity. Afterward, a cool column emerged from the chromosphere, rose vertically into the corona, and then moved laterally to be transported into the U-shaped coronal loops. The formed prominence slid into the chromosphere, while the U-shaped coronal loops and the coronal cavity became more pronounced. As cool materials accumulated at the base of the U-shaped coronal loops, these loops underwent a significant descent and a V-shaped structure appeared at the base of the cool materials, indicating that the U-shaped coronal loops may be dragged down to sag. Subsequently, cool materials from the V-shaped structure continued to flow almost vertically toward the chromosphere, forming the funnel prominence. The vertical downflows might be produced by magnetic reconnection within or between the sagging field lines. Due to persistent vertical downflows, the U-shaped coronal loops were lifted up and prominence materials followed along inclined coronal loops toward the chromosphere, causing the funnel prominence to disappear. Our observations suggest that chromospheric plasma transported into a coronal cavity and then drained out via vertical downflows can form a funnel prominence.

Active regions are the brightest structures seen in the solar corona, so their physical properties hold important clues to the physical mechanisms underlying coronal heating. In this work, we present a comprehensive study for a filament-embedding active region as determined from observations from multiple facilities including the Chinese H α Solar Explorer. We find three types of dynamic features that correspond to different thermal and magnetic properties, i.e., the overlying loops—1 MK cool loops, the moss region—2–3 MK hot loops’ footprints, and the sigmoidal filament. The overlying cool loops, which have a potential field, always show Doppler blueshifts at the east footprint and Doppler redshifts at the west, indicating a pattern of “siphon flow.” The moss-brightening regions, which sustain the hot loops that have a moderate sheared field, always show downward Doppler redshifts at the chromosphere, which could be a signature of plasma condensing into the inner region adjacent to the filament. The sigmoidal filament, which has strongly sheared field lines along the polarity inversion line, however, shows a different Doppler velocity pattern in its middle part, i.e., an upward Doppler blueshift at the double- J -shaped stage indicating tether-cutting reconnection during the filament channel formation and then a downward redshift showing the plasma condensation for the sigmoidal filament formation. The present work shows overall properties of the filament-embedding active region, constraining the heating mechanisms of different parts of the active region and providing hints regarding the mass loading of the embedded filament.

Solar prominences observed close to the limb commonly include a bright feature that, from the perspective of the observer, runs along the interface between itself and the underlying chromosphere. Despite several idealized models being proposed to explain the underlying physics, a more general approach remains outstanding. In this manuscript we demonstrate as a proof of concept the first steps in applying the Lightweaver radiative transfer framework’s 2.5D extension to a “toy” model prominence + VAL3C chromosphere, inspired by recent 1.5D experiments that demonstrated a significant radiative chromosphere–prominence interaction. We find the radiative connection to be significant enough to enhance both the electron number density within the chromosphere, as well as its emergent intensity across a range of spectral lines in the vicinity of the filament absorption signature. Inclining the viewing angle from the vertical, we find these enhancements to become increasingly asymmetric and merge with a larger secondary enhancement sourced directly from the prominence underside. In wavelength, the enhancements are then found to be the largest in both magnitude and horizontal extent for the spectral line cores, decreasing into the line wings. Similar behavior is found within new Chinese H α Solar Explorer/H α Imaging Spectrograph observations, opening the door for subsequent statistical confirmations of the theoretical basis we develop here.

Fan-spine magnetic structure, as a fundamental three-dimensional topology in magnetic reconnection theory, plays a crucial role in producing solar jets. However, how fan-spine configurations form in the solar atmosphere remains elusive. Using the Chinese H α Solar Explorer (CHASE) and the Solar Dynamics Observatory, we present a case study on the complete buildup of fan-spine topology driven by flux emergence and the subsequent jet production. Two fan-spine structures and the two associated null points are present. Variations in null-point heights and locations were tracked over time during flux emergence. The north fan-spine structure is found to be created through magnetic reconnection between the newly emerged flux and the background field. Gentle reconnection persistently occurs after formation of the north fan-spine structure, resulting in weak plasma outflows. Subsequently, as flux emergence and magnetic helicity injection continue, the formation and eruption of minifilaments after reconnection at the quasi-separatrix layer between the two nulls trigger three homologous jets. The CHASE observations reveal that the circular flare ribbon, inner bright patch, and remote brightening all exhibit redshifted signatures during these jet ejections. This work unveils the key role of flux emergence in the formation of fan-spine topology, and highlights the importance of minifilaments for subsequent jet production.

The eruption of solar filaments, also known as prominences appearing off limb, is a common phenomenon in the solar atmosphere. It ejects massive plasma and high-energy particles into interplanetary space, disturbing the solar-terrestrial environment. It is vital to obtain the three-dimensional velocity fields of erupting filaments for space-weather predictions. We derive the three-dimensional kinematics of an off-limb prominence and an on-disk filament, respectively, using the full-disk spectral and imaging data detected by the Chinese H α Solar Explorer (CHASE). It is found that both the prominence and the filament experience a fast semicircle-shaped expansion at first. The prominence keeps propagating outward with an increasing velocity until escaping successfully, with the south leg of the prominence finally moving back to the Sun in a swirling manner. For the filament, the internal plasma falls back to the Sun in a counterclockwise rotation in the late ejection, matching the failed eruption without a coronal mass ejection. During the eruptions, both the prominence and the filament show material splitting along the line-of-sight direction, revealed by the bimodal H α spectral profiles. For the prominence, the splitting begins at the top and gradually spreads to almost the whole prominence with a fast blueshift component and a slow redshift component. The material splitting in the filament is more fragmental. As shown by the present results, the CHASE full-disk spectroscopic observations make it possible to systematically study the three-dimensional kinematics of solar filament eruptions.

Solar eruptive activities could occur in weak magnetic field environments and over large spatial scales, which are especially relevant to eruptions involving intermediate or quiescent solar filaments. To handle the large scales, we implement and apply a flux rope embedding method using regularized Biot–Savart laws in the spherical coordinate system. Combined with a potential field source surface model and a magneto-frictional method, a nonlinear force-free field comprising a flux rope embedded in a potential field is constructed. Using the combined nonlinear force-free field as the initial condition, we then perform a zero- β data-constrained magnetohydrodynamic (MHD) simulation for an M8.7 flare at 03:38 UT on 2012 January 23. The MHD model reproduces the eruption process, flare ribbon evolution (represented by the quasi-separatrix layer evolution), and kinematics of the flux rope. This approach could potentially model global-scale eruptions from weak field regions. [ABSTRACT FROM AUTHOR]

The eruption of magnetic flux ropes (MFRs), often taking filaments together, leads to coronal mass ejections (CMEs). Theoretical studies propose that both the resistive magnetic reconnection and the ideal instability of an MFR system can release magnetic-free energy and accelerate CMEs (i.e., MFRs or filaments) during eruptions. Observations find that the full kinematic evolution of CMEs usually undergoes three phases: the initiation phase, impulsive acceleration phase, and propagation phase. The impulsive acceleration phase often starts and ceases simultaneously with the flare onset time and peak time, respectively. This synchronization can be explained by the positive feedback relationship between the acceleration of CMEs and flare magnetic reconnection, and suggests that the reconnection has the dominant contribution to the acceleration of CMEs. It is rare to see strong evidence that supports the dominant contribution of ideal instability to the acceleration. In this paper, we report an intriguing filament eruption that occurred on 2011 May 11. Its complete acceleration is well recorded by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The kinematic analysis shows that the impulsive acceleration phase starts and ceases obviously earlier than the flare onset time and peak time, respectively, which means a complete asynchronization between the impulsive acceleration phase and flare rise phase, and strongly supports that the ideal instability plays a dominant role in this impulsive acceleration. Furthermore, the accompanied flare is a B-class one, also implying that the contribution of reconnection is negligible in the energy release process. [ABSTRACT FROM AUTHOR]

Although the magnetic field structures of solar filaments have been studied for several decades, the detailed evolution of the structure around a filament prior to its eruption is rarely observed. On 2021 October 28 in AR 12887, a major solar flare (X1.0 class) occurred at 15:35 UT. Based on the Solar Dynamics Observatory high-spatial-resolution observations, we find this flare is associated with the eruption of two filaments, namely F1 and F2. The two filaments are initially independent. The western leg (WLEG) of F1 approaches the northern leg of F2, due to the continuous movement and rotation of the magnetic field in which the WLEG roots in. We find first that there are some threads wrapping the WLEG. Brightening and bidirectionally plasmoid flows that originate from a brightening are detected in these threads, then the threads disappear, and the two filaments connect. NLFFF extrapolation reveals that there is a toroidal magnetic structure enveloping the WLEG and corresponding spatially to the threads. It is expected that a filament is enveloped by toroidal magnetic fields. According to the observations and extrapolation, we suggest that these threads represent the toroidal magnetic fields wrapping the WLEG. This paper provides new details about the dynamics of the toroidal magnetic fields. Magnetic reconnection takes place in the toroidal fields and thus destroys the fields, then F1 and F2 connect, and subsequently, the two filaments erupt and the flare occurs. [ABSTRACT FROM AUTHOR]

Solar filaments are good tracers of space weather and magnetic flux ropes in the corona. Identifying and detecting filaments helps to forecast space weather and explore the solar magnetic field. Many automatic detection methods have been proposed to process the large number of observed images. Current methods face issues of unreliable dataset annotations and poor anti-interference capability. First, to address the issue of unreliable dataset annotations, we built a solar filament dataset using a manual annotation method. Second, we introduced Transformer into Convolutional Neural Networks. Transformer, with the ability to extract more global features, can help counter interference. In addition, there is large disparity in the size of solar filaments. Therefore, a multi-scale residual block is designed to extract features across various scales. Deformable large kernel attention and a res path are used to better integrate encoder and decoder information. Results show that this method outperforms the existing solar filament detection methods (improved U-Net and improved V-Net), achieving an F1 score of 91.19%. In particular, our results show lower interference by sunspots and background noise than existing methods. The ability to counter interference is improved.

Although magnetic reconnection plays a key role in the formation of a solar filament, the detailed formation process is still ambiguous. Combining the observational data from the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we analyzed the formation of a U -shaped filament via successive magnetic reconnection in the AR NOAA 11598 on 2012 October 25. The successive reconnection occurred between a filament (F) and its nearby chromospheric fibrils (CF). The associated brightening and magnetic cancellation were observed. The changes in appearance of the CF at the reconnection site were accompanied by the formation and accumulation of some new magnetic loops, as well as plasmas propagated along the formed magnetic loops from the reconnection site, indicating the changes in the topology of the F and CF. These can provide comprehensive observational evidence for successive reconnection. After the reconnection, a longer U -shaped filament was formed. During the formation of the U -shaped filament, two major magnetic energy releases took place. While in the two energy release processes, the injected plasma from the reconnection site can provide part of the material for the formation of the U -shaped filament. Therefore, we conclude that the successive reconnection results in both the dynamical evolution and the subsequent formation associated with the U -shaped filament. And the results of nonlinear force-free field extrapolation demonstrated that the magnetic topology of the F was changed significantly; this is consistent with the observational results and further confirms the formation of the U -shaped filament. [ABSTRACT FROM AUTHOR]

Solar filaments are dense, cool plasma clouds in the solar corona. They are supposed to be supported in a dip of the coronal magnetic field. However, the models still disagree between two types of field configuration; one is the normal polarity model proposed by Kippenhahn and Schlueter (1957, Z. Astrophys., 43, 36), and the other is the reverse polarity model proposed by Kuperus and Raadu (1974, A&A, 31, 189). To understand the mechanism that makes the filaments become unstable before eruption, it is critical to know the magnetic structure of solar filaments. We performed spectropolarimetric observation in the He  i (10830 Å) line to investigate the magnetic field configuration of dark filaments. The observation was carried out with the Domeless Solar Telescope at Hida Observatory with a polarization sensitivity of 3.0 × 10−4. We obtained eight samples of filaments in a quiet region. As a result of the analysis of full Stokes profiles of filaments, we found that the field strengths were estimated as 8–35 G. By comparing the direction of the magnetic field in filaments and the global distribution of the photospheric magnetic field, we determined the magnetic field configuration of the filaments, and we concluded that one out of the eight samples has normal polarity configuration, and seven out of the eight have reverse polarity configuration. [ABSTRACT FROM AUTHOR]

Prominences are cold and dense chromospheric material suspended in the solar atmosphere with the support of coronal magnetic fields. Oscillatory behavior of a limb core prominence is studied in the AIA 171, 193, 211, 335, and 94 Å passbands of AIA aboard SDO. Vertical oscillations with periods of 34.8, and 40.0 minutes with velocity amplitudes of 4.6, and 5.2 km/s are obtained over the prominence core structure in the all studied channels. These long period oscillation started 54 minutes before an external flare eruption starts to develop over the north side of the studied core prominence, and continued for about two hours. Wave fronts from the Flare Eruption (FE) might be the exciter of these long period oscillation over the entire core prominence. Propagating upward and Downward slow magneto-acoustic waves with velocities in the range of 11.3 to 24.2 km/s are observed over the upper and lower boundaries of the prominence. The multiple rapidly heating and cooling effects, with the time scales less than one minutes, are observed over the propagating peak intensities, which might be the response of the plasma before reaching to a thermal balance between the injected heating flux (through the wave fronts of the FE) and heating loss flux through conduction, radiation, and viscosity. [ABSTRACT FROM AUTHOR]

We present observations and interpretation of a nonerupting filament in NOAA active region (AR) 12827 that undergoes splitting and restructuring on 2021 June 4, using the high-resolution data obtained by the New Vacuum Solar Telescope, the Solar Dynamics Observatory, and the Interface Region Imaging Spectrograph. At the beginning, the right footpoint of the filament is rooted in the AR positive polarity, and its right leg has a spread-out structure, which is confirmed by the extrapolated 3D magnetic structure. Many small positive and negative magnetic polarities connected by EUV-emitting loops gradually appear between two extensions of the right footpoint polarity as the extensions separate. The right leg of the filament is then observed to split into two parts, which continue to separate, while the left part of the filament still maintains a whole structure. As the newly emerged magnetic loops rise between the two parts of the right leg, magnetic reconnection occurs between the newly emerged magnetic loops and the magnetic fields supporting the southeastern splitting part. The longer magnetic loops resulting from this reconnection merge with the magnetic fields of the other part of the split filament leg, thus reforming an entire filament with a displaced right footpoint. We conclude that magnetic emergence is responsible for the splitting of the filament leg, while magnetic reconnection leads to the reconstruction of the filament. [ABSTRACT FROM AUTHOR]

We present observations and analysis of an eruptive M1.5 flare (SOL2014-08-01T18:13) in NOAA active region (AR) 12127, characterized by three flare ribbons, a confined filament between ribbons, and rotating sunspot motions as observed by the Solar Dynamics Observatory. The potential field extrapolation model shows a magnetic topology involving two intersecting quasi-separatrix layers (QSLs) forming a hyperbolic flux tube (HFT), which constitutes the fishbone structure for the three-ribbon flare. Two of the three ribbons show separation from each other, and the third ribbon is rather stationary at the QSL footpoints. The nonlinear force-free field extrapolation model implies the presence of a magnetic flux rope (MFR) structure between the two separating ribbons, which was unclear in the observation. This suggests that the standard reconnection scenario for eruptive flares applies to the two ribbons, and the QSL reconnection for the third ribbon. We find rotational flows around the sunspot, which may have caused the eruption by weakening the downward magnetic tension of the MFR. The confined filament is located in the region of relatively strong strapping field. The HFT topology and the accumulation of reconnected magnetic flux in the HFT may play a role in holding it from eruption. This eruption scenario differs from the one typically known for circular ribbon flares, which is mainly driven by a successful inside-out eruption of filaments. Our results demonstrate the diversity of solar magnetic eruption paths that arises from the complexity of the magnetic configuration.

To gain a deeper understanding of the intricate process of filament eruption, we present a case study of a filament splitting and erupting by using multiwavelength data of the Solar Dynamics Observatory. It is found that the magnetic reconnection between the filament and the surrounding magnetic loops resulted in the formation of two new filaments, which erupted successively. The observational evidence of magnetic reconnection, such as the obvious brightening at the junction of two different magnetic structures, the appearance of a bidirectional jet, and subsequent filament splitting, were clearly observed. Even though the two newly formed filaments experienced failed eruptions, three obvious dimmings were observed at the footpoints of the filaments during their eruptions. Based on these observations, it is suggested that magnetic reconnection is the trigger mechanism for the splitting of the original filament and the subsequent eruption of the newly formed filaments. Furthermore, the process of filament splitting dominated by magnetic reconnection can shed light on the explanation of double-decker filament formation.

The mass cycle of solar prominences or filaments is still not completely understood. Researchers agree that these dense structures form by coronal in situ condensations and plasma siphoning from the underlying chromosphere. In the evaporation–condensation model siphoning arises due to evaporation of chromospheric plasma from localized footpoint heating, but this is challenging to justify observationally. Here, we simulate the reconnection–condensation model at extreme resolutions down to 20.8 km within a three-dimensional (3D) magnetohydrodynamic coronal volume. We form a draining, quiescent prominence and associated coronal rain simultaneously. We show that thermal instability—acting as a trigger for local condensation formation—by itself drives siphoning flows from the low corona without the need of any localized heating. In addition, for the first time, we demonstrate through a statistical analysis along more than 1000 magnetic field lines that cold condensations give rise to siphoning flows within magnetic threads. This siphoning arises from the strong pressure gradient along field lines induced by thermal instability. No correlation is found between siphoning flows and the prominence mass, making thermal instability the main in situ mass-collection mechanism. Our simulated prominence drains by gliding along strongly sheared, asymmetric, dipped magnetic arcades, and develops natural vertical fine structure in an otherwise horizontal magnetic field due to the magnetic Rayleigh–Taylor instability. By synthesising our data, our model shows remarkable agreement with observations of quiescent prominences such as its dark coronal cavity in extreme-ultraviolet emission channels, fine-scale vertical structure, and reconnection outflows, which, for the first time, have been self-consistently obtained as the prominence evolves.

Minifilaments are widespread small-scale structures in the solar atmosphere. To better understand their formation and eruption mechanisms, we investigate the entire life of a sigmoidal minifilament located below a large quiescent filament observed by Big Bear Solar Observatory/Goode Solar Telescope on 2015 August 3. The H α structure initially appears as a group of arched threads, then transforms into two J-shaped arcades, and finally forms a sigmoidal shape. Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly observations in 171 Å show that two coronal jets occur around the southern footpoint of the minifilament before the minifilament eruption. The minifilament eruption starts from the southern footpoint, then interacts with the overlying filament and fails. The aforementioned observational changes correspond to three episodes of flux cancellations observed by SDO/Helioseismic and Magnetic Imager. Unlike previous studies, the flux cancellation occurs between the polarity where the southern footpoint of the minifilament is rooted and an external polarity. We construct two magnetic field models before the eruption using the flux rope insertion method and find a hyperbolic flux tube above the flux cancellation site. The observation and modeling results suggest that the eruption is triggered by the external magnetic reconnection between the core field of the minifilament and the external fields due to flux cancellations. This study reveals a new triggering mechanism for minifilament eruptions and a new relationship between minifilament eruptions and coronal jets.

Sigmoids produce strong eruptive events. Earlier studies have shown that the ICME axial magnetic field Bz can be predicted with some credibility by observing the corresponding filament or the polarity inversion line in the region of eruption and deriving the magnetic field direction from that. Sigmoids are coronal structures often associated with filaments in the sigmoidal region. In this study, we compare filament chirality with sigmoid handedness to observe their correlation. Second, we perform nonlinear force-free approximations of the coronal magnetic connectivity using photospheric vector magnetograms underneath sigmoids to obtain a weighted-average value of the force-free parameter and to correlate it with filament chirality and the observed coronal sigmoid handedness. Importantly, we find that the sigmoids and their filament counterparts do not always have the same helicity signs. Production of eruptive events by regions that do not have the same signs of helicities is ∼3.5 times higher than when they do. A case study of magnetic energy/ helicity evolution in NOAA AR 12473 is also presented.

Solar magnetic flux rope (MFR) plays a central role in the physics of coronal mass ejections (CMEs). It mainly includes a cold filament at typical chromospheric temperatures (∼10,000 K) and a hot channel at high coronal temperatures (∼10 MK). The warm MFR at quiescent coronal temperatures of a million Kelvin is, however, rarely reported. In this study, using multiwavelength images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory and Extreme Ultraviolet Imager (EUVI) on board the Solar Terrestrial Relations Observatory-A, we present an eruption of a warm channel that represents an MFR with quiescent coronal temperatures (∼0.6–2.5 MK). On 2022 May 8, we observed the failed eruption of a hot channel, with the average temperature and emission measure (EM) of 10 MK and 1.1 × 10 ^28 cm ^−5 , using AIA high-temperature images in the active region (AR) 13007. This failed eruption was associated with a C8.2 flare, with no CME. Subsequently, we observed a warm channel that appeared in AIA and EUVI low-temperature images rather than in AIA high-temperature images. It then erupted and transformed into a semicircular shape. An associated C2.1 flare, along with the signatures of magnetic reconnection in AIA high-temperature images, were identified. Additionally, we observed a CME associated with this event. Compared with the hot channel, the warm channel is cooler and rarer with the average temperature and EM of 1.7 (1.6) MK and 2.0 × 10 ^26 (2.3 × 10 ^26 ) cm ^−5 . All the results suggest an unambiguous observation of the million-Kelvin warm MFR that erupted as a CME and fill a gap in the temperature domain of coronal MFRs.

Studies on the dynamics of solar filaments have significant implications for understanding their formation, evolution, and eruption, which are of great importance for space weather warning and forecasting. The H α Imaging Spectrograph (HIS) on board the recently launched Chinese H α Solar Explorer (CHASE) can provide full-disk solar H α spectroscopic observations, which bring us an opportunity to systematically explore and analyze the plasma dynamics of filaments. The dramatically increased observation data require automated processing and analysis, which are impossible if dealt with manually. In this paper, we utilize the U-Net model to identify filaments and implement the Channel and Spatial Reliability Tracking algorithm for automated filament tracking. In addition, we use the cloud model to invert the line-of-sight velocity of filaments and employ the graph theory algorithm to extract the filament spine, which can advance our understanding of the dynamics of filaments. The favorable test performance confirms the validity of our method, which will be implemented in the following statistical analyses of filament features and dynamics of CHASE/HIS observations.

Double-decker filaments and their eruptions have been widely observed in recent years, but their physical formation mechanism is still unclear. Using high spatiotemporal resolution, multi-wavelength observations taken by the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we show the formation of a double-decker pair of flux rope system by two successive tether-cutting eruptions in a bipolar active region. Due to the combined effect of photospheric shearing and convergence motions around the active region’s polarity inversion line (PIL), the arms of two overlapping inverse-S-shaped short filaments reconnected at their intersection, which created a simultaneous upward-moving magnetic flux rope (MFR) and a downward-moving post-flare-loop (PFL) system striding the PIL. Meanwhile, four bright flare ribbons appeared at the footpoints of the newly formed MFR and the PFL. As the MFR rose, two elongated flare ribbons connected by a relatively larger PFL appeared on either side of the PIL. After a few minutes, another MFR formed in the same way at the same location and then erupted in the same direction as the first one. Detailed observational results suggest that the eruption of the first MFR might experienced a short pause before its successful eruption, while the second MFR was a failed eruption. This implies that the two newly formed MFRs might reach a new equilibrium at relatively higher heights for a while, which can be regarded as a transient double-decker flux rope system. The observations can well be explained by the tether-cutting model, and we propose that two successive confined tether-cutting eruptions can naturally produce a double-decker flux rope system, especially when the background coronal magnetic field has a saddle-like distribution of magnetic decay index profile in height.

We present imaging and spectroscopic diagnostics of a long filament during its formation with the observations from the Chinese H α Solar Explorer and Solar Dynamics Observatory. The seed filament first appeared at about 05:00 UT on 2022 September 13. Afterward, it grew gradually and connected to another filament segment nearby, building up a long filament at about 20:00 UT on the same day. The CHASE H α spectra show an obvious centroid absorption with mild broadening at the main spine of the long filament, which is interpreted as evidence of filament material accumulation. More interestingly, near the footpoints of the filament, persistent redshifts have been detected in the H α spectra during the filament formation, indicating continuous drainage of filament materials. Furthermore, through inspecting the extreme-ultraviolet (EUV) images and magnetograms, it was found that EUV jets and brightenings appeared repeatedly at the junction of the two filament segments, where opposite magnetic polarities converged and canceled each other continuously. These results suggest the occurrence of intermittent magnetic reconnection that not only connects magnetic structures of the two filament segments but also supplies cold materials for the filament channel likely by the condensation of injected hot plasma, even though a part of the cold materials falls down to the filament footpoints at the same time.

Small-scale eruptions could play an important role in coronal heating, generation of solar energetic particles (SEPs), and mass source of the solar wind. However, they are poorly observed, and their characteristics, distributions, and origins remain unclear. Here a mini coronal dimming was captured by the recently launched Solar Orbiter spacecraft. The observations indicate that a minifilament eruption results in the dimming and takes away approximately (1.65 ± 0.54) × 10 ^13 g of mass, which also exhibits similar features as the sources of SEP events. The released magnetic free energy is of the order of ∼10 ^27 erg. Our results suggest that weak constraining force makes the flux rope associated with the minifilament easily enter a torus-unstable domain. We discuss that weak magnetic constraints from low-altitude background fields may be a general condition for the quiet-Sun eruptions, which provide a possible mechanism for the transport of coronal material and energy from the lower to the middle or even higher corona.

Quasi-periodic transverse oscillations of a quiescent solar filament based on the H α and the 304 Å EUV intensity maps have been studied. Time-distance diagrams of filament intensity variations were produced. The method of the identification of local peaks on the time-distance diagrams allowed us to reveal non-linear transverse oscillations, which were interpreted as a transverse wave propagating along the filament with a characteristic period of about 13 min. The relatively small average wave amplitude and well pronounced period are in favour of the quasi-linear kink mode excited in the filament threads, which is modelled as the thin independent magnetic flux tubes. In terms of the phase difference for the propagating wave in two different points of the filament and the dispersion equation for kink modes, the Alfvén velocity (≈ 60 km s - 1 ) and the magnetic field (7 - 30 G) in the filament threads have been estimated. The nonlinear effects are discussed. [ABSTRACT FROM AUTHOR]

The fine magnetic structure is vitally important to understanding the formation, stabilization, and eruption of solar filaments, but so far, it is still an open question yet to be resolved. Using stereoscopic observations taken by the Solar Dynamics Observatory and Solar TErrestrial RElations Obsevatory , we studied the generation mechanism of a two-sided-loop jet (TJ) and the ejection process of the jet plasma into the overlying filament-cavity system. We find that the generation of the two-sided-loop jet was due to the magnetic reconnection between an emerging flux loop and the overlying filament. The jet's two arms ejected along the filament axis during the initial stage. Then, the north arm bifurcated into two parts at about 50 Mm from the reconnection site. After the bifurcation, the two bifurcated parts were along the filament axis and the cavity which hosted the filament, respectively. By tracing the ejecting plasma flows of the TJ inside the filament, we not only measured that the magnetic twist stored in the filament was at least 5π but also found that the fine magnetic structure of the filament-cavity flux rope system is in well agreement with the theoretical results of Magnetic flux rope models. [ABSTRACT FROM AUTHOR]

The solar filaments obtained from the daily Ca ii K3 observations at the Coimbra Astronomical Observatory, which is now called the Geophysical and Astronomical Observatory of the University of Coimbra (OGAUC), for the period 1929 – 1941 have been digitized and validated, and they are confirmed to be reliable for solar activity studies. We use these filament data to investigate the rotation and differential degree of the solar high chromosphere. The main results are as follows: (1) the rotation profile of filaments is somewhat steeper than the rotation profile for long-lived Hα filaments; (2) the high chromosphere filaments rotate faster than sunspots, the photosphere, and the medium-low chromosphere at middle-low latitudes; (3) solar filaments rotate at a higher rotation rate in the descending phase of the solar cycle than in the ascending phase, and their rotation velocities are relatively faster around the year of solar maximum. The possible explanation for the above results is given. [ABSTRACT FROM AUTHOR]

Solar filaments are distinct strip-like structures observed in chromospheric H α images. Filament eruptions, flares, and coronal mass ejections (CMEs) can be regarded as the same physical process of releasing magnetic energy at different times and solar atmosphere heights. It is very important to detect filaments for forecasting flares and CMEs. This article proposes a new solar-filament detection and classification method based on CondInst; a deep-learning model. A data set of solar filaments is built, including ten thousand filaments. To distinguish filaments that consist of only a single connected dark region and filaments that are broken into several fragments, the filaments are classified into isolated filaments and non-isolated filaments. The mean precision, recall, A P , and F1 obtained using the proposed method are 90.83 % , 83.88 % , 82.86 % , and 87.22 % , respectively. The results show that the method performs well in detecting and classifying isolated and non-isolated filaments, especially in solving the fragments problem of how to detect a filament that is broken into several fragments. The method also has good performance in handling various images, even with existing uneven brightness or low contrast. The precision of filament masks still needs to be improved in the future. [ABSTRACT FROM AUTHOR]

Both observations and simulations suggest that the solar filament eruption is closely related to magnetic flux emergence. It is thought that the eruption is triggered by magnetic reconnection between the filament and the emerging flux. However, the details of such a reconnection are rarely presented. In this study, we report the detailed reconnection between a filament and its nearby emerging fields, which led to the reconfiguration and subsequent partial eruption of the filament located over the polarity inversion line of active region 12816. Before the reconnection, we observed repeated brightenings in the filament at a location that overlies a site of magnetic flux cancellation. Plasmoids form at this brightening region, and propagate bidirectionally along the filament. These indicate the tether-cutting reconnection that results in the formation and eruption of a flux rope. To the northwest of the filament, magnetic fields emerge, and reconnect with the context ones, resulting in repeated jets. Afterwards, other magnetic fields emerge near the northwestern filament endpoints, and reconnect with the filament, forming the newly reconnected filament and loops. A current sheet repeatedly occurs at the interface, with the mean temperature and emission measure of 1.7 MK and 1.1Ă—1028 cmâˆ'5. Plasmoids form in the current sheet, and propagate along it and further along the newly reconnected filament and loops. The newly reconnected filament then erupts, while the unreconnected filament remains stable. We propose that besides the orientation of emerging fields, some other parameters, such as the position, distance, strength, and area, are also crucial for triggering the filament eruption. [ABSTRACT FROM AUTHOR]

We analyze 152 large confined flares (GOES class ≥ M1.0 and ≤ 45° from disk center) during 2010âˆ'2019, and classify them into two types according to the criterion taken from the work of Li et al. “Type I” flares are characterized by slipping motions of flare loops and ribbons and a stable filament underlying the flare loops. “Type II” flares are associated with the failed eruptions of the filaments, which can be explained by the classical 2D flare model. A total of 59 flares are “Type I” flares (about 40%) and 93 events are “Type II” flares (about 60%). There are significant differences in distributions of the total unsigned magnetic flux (ΦAR) of active regions (ARs) producing the two types of confined flares, with “Type I” confined flares from ARs with a larger ΦAR than “Type II.” We calculate the mean shear angle ΨHFED within the core of an AR prior to the flare onset, and find that it is slightly smaller for “Type I” flares than that for “Type II” events. The relative nonpotentiality parameter ΨHFED/ΦAR has the best performance in distinguishing the two types of flares. About 73% of “Type I” confined flares have ΨHFED/ΦAR<1.0 Ă— 10âˆ'21 degree Mxâˆ'1, and about 66% of “Type II” confined events have ΨHFED/ΦAR ≥ 1.0 Ă— 10âˆ'21 degree Mxâˆ'1. We suggest that “Type I” confined flares cannot be explained by the standard flare model in 2D/3D, and the occurrence of multiple slipping magnetic reconnections within the complex magnetic systems probably leads to the observed flare. [ABSTRACT FROM AUTHOR]