Erupting Flux Rope Research Articles

Formation and Eruption of a Hot Channel Magnetic Flux Rope in a Nested Double Null Magnetic System

The coronal magnetic topology significantly affects the outcome of magnetic flux rope (MFR) eruptions. The recently reported nested double null magnetic system remains unclear as to how it affects MFR eruptions. Using observations from the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we studied the formation and successful eruption of a hot channel MFR from NOAA active region AR 12173 on 2014 September 28. We observed that a hot channel MFR formed and erupted as a coronal mass ejection (CME), and the magnetic field of the source region was a nested double null magnetic system in which an inner magnetic null point system was nested by an outer fan–spine magnetic system. Observational analysis suggests that the origin of the MFR was due to magnetic reconnection at the inner null point, which was triggered by the photospheric swirling motions. The long-term shearing motion in the source region throughout around 26 hr might accumulate enough energy to power the eruption. Since previous studies showed that MFR eruptions from nested double null magnetic systems often result in weak jets and stalled or failed eruptions, it is hard to understand the generation of the large-scale CME in our case. A detailed comparison with previous studies reveals that the birth location of the MFR relative to the inner null point might be the critical physical factor for determining whether an MFR can erupt successfully or not in such a particular nested double null magnetic system.

Non-thermal electrons in an eruptive solar event: Magnetic structure, confinement, and escape into the heliosphere

Filament eruptions and coronal mass ejections (CMEs) reveal large-scale instabilities of magnetic structures in the solar corona. Some of them are accompanied by radio emission, which at decimetric and longer wavelengths is a signature of electron acceleration that may be different from the acceleration in impulsive flares. The radio emission is part of the broadband continua at decimetre and metre wavelengths called type IV bursts. In this article we investigate a particularly well-observed combination of a filament eruption seen in Halpha and at extreme ultraviolet (EUV) wavelengths and a moving type IV burst on 2021 August 24. The aim is to shed light on the relationship between the large-scale erupting magnetic structure and the acceleration and transport of non-thermal electrons. We used imaging observations of a moving radio source and associated burst groups with the refurbished Nan c ay Radioheliograph and whole-Sun radio spectrography from different ground-based and space-borne instruments, in combination with X-ray, radio, and in situ electron observations at tens of keV from Solar Orbiter and EUV imaging by SDO/AIA. The radio sources are located with respect to the erupting magnetic structure traced by the filament (EUV 30.4 nm), and the timing of the electrons detected in situ is compared with the timing of the different radio emissions. We find that the moving radio source is located at the top of the erupting magnetic structure outlined by the filament, which we interpret as a magnetic flux rope. The flux rope erupts in a strongly non-radial direction, guided by the overlying magnetic field of a coronal hole. The electrons detected at Solar Orbiter are found to be released mainly in two episodes, 10 to 40 minutes after the impulsive phase. The releases coincide with two groups of radio bursts, which originate respectively on the flank and near the top of the erupting flux rope. The observation allows an unusually clear association between a moving type IV radio burst, an erupting magnetic flux rope as core structure of a CME, and particle releases into the heliosphere. Non-thermal electrons are confined in the flux rope. Electrons escape to the heliosphere mainly in two distinct episodes, which we relate to magnetic reconnection between the flux rope and ambient open field lines.

Initiation and Eruption of a Two-turn Helical Quiescent Filament on 2013 August 2

We investigate a quiescent filament that erupted on 2013 August 2; the eruption was observed in EUV and Hα by the Solar Dynamics Observatory and GONG. After a B9.7 flare in the nearby active region, the dark filament materials near its eastern footpoint start to move in the direction of eruption, and are followed by a counterclockwise rotation identified as the motion of a combination of dark and bright filament materials. Then the entire filament rises up and keeps rotating in a clockwise direction during the eruption. More interestingly, the filament exhibits an unusual two-helix structure near its western footpoint during the eruption, which indicates the existence of a highly twisted flux rope. This hypothesis is confirmed by magnetic field modeling using the flux rope insertion method. In the best-fit unstable model, the lower limits of the estimated maximum and average twist numbers of the erupting flux rope reach 7.5π and 4π, which suggests that kink instability plays an important role in the eruption. During these magnetically coupled sympathetic eruptions, the highly twisted filament under the western lobe of a pseudo-streamer-like structure becomes unstable and erupts due to the removal of confinement by magnetic reconnection at the overlying hyperbolic flux tube, which is initiated by the B9.7 flare in the nearby active region. The initial filament motion occurs at the more unstable eastern footpoint, where the surrounding fields are weaker and decrease with height more rapidly.

Episodic Energy Release during the Main and Post-impulsive Phases of a Solar Flare

When and where the magnetic field energy is released and converted in eruptive solar flares remains an outstanding topic in solar physics. To shed light on this question, here we report multiwavelength observations of a C9.4-class eruptive limb flare that occurred on 2017 August 20. The flare, accompanied by a magnetic flux rope eruption and a white light coronal mass ejection, features three post-impulsive X-ray and microwave bursts immediately following its main impulsive phase. For each burst, both microwave and X-ray imaging suggest that the nonthermal electrons are located in the above-the-loop-top region. Interestingly, contrary to many other flares, the peak flux of the three post-impulsive microwave and X-ray bursts shows an increase for later bursts. Spectral analysis reveals that the sources have a hardening spectral index, suggesting a more efficient electron acceleration into the later post-impulsive bursts. We observe a positive correlation between the acceleration of the magnetic flux rope and the nonthermal energy release during the post-impulsive bursts in the same event. Intriguingly, different from some other eruptive events, this correlation does not hold for the main impulse phase of this event, which we interpret as energy release due to the tether-cutting reconnection before the primary flux rope acceleration occurs. In addition, using footpoint brightenings at conjugate flare ribbons, a weakening reconnection guide field is inferred, which may also contribute to the hardening of the nonthermal electrons during the post-impulsive phase.

A method for determining the locations and configurations of magnetic reconnection within three-dimensional turbulent plasmas

Context. Three-dimensional (3D) reconnection is an important mechanism for efficiently releasing energy during astrophysical eruptive events, which is difficult to be quantitatively analyzed especially within turbulent plasmas. Aims. In this paper, an efficient method for identifying locations and configurations of 3D reconnection from magnetohydrodynamical (MHD) data is developed. Methods. This method analyzes the local nonideal electric field and magnetic structure at an arbitrary position. As only performing algebraical manipulations on the discrete field data and avoiding computationally expensive operations such as field-line tracing and root-finding, this method naturally possesses high efficiency. To validate this method, we apply it to the 3D data from a high-resolution simulation of a Harris-sheet reconnection and a data-driven simulation of a coronal flux rope eruption. Results. It is shown that this method can precisely identify the local structures of discrete magnetic field. Through the information of nonideal electric field and the geometric attributes of magnetic field, the local structures of reconnection sites can be effectively and comprehensively determined. For fine turbulent processes, both qualitative pictures and quantitative statistical properties of small-scale reconnection structures can be obtained. For large-scale solar simulations, macro-scale magnetic structures such as flux ropes and eruption current sheets can also be recognized. Conclusions. We develop a powerful method to analyze multi-scale structures of 3D reconnection. It can be applied not only in MHD simulations but also in kinetic simulations, plasma experiments, and in situ observations.

How Small-scale Jetlike Solar Events from Miniature Flux Rope Eruptions Might Produce the Solar Wind

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.

A model of solar magnetic flux rope eruption initiated primarily by magnetic reconnection

ABSTRACT There is a heated debate regarding the specific roles played by ideal magnetohydrodynamic (MHD) instability and magnetic reconnection in triggering solar eruptions. In the context of a pre-existing magnetic flux rope (MFR) before an eruption, it is widely believed that an ideal MHD instability, in particular, the torus instability, is responsible for triggering and driving the eruption, while reconnection, as invoked in the wake of the erupting MFR, plays a secondary role. Here, we present a new numerical MHD model in which the eruption of a pre-existing MFR is primarily triggered and driven by reconnection. In this model, a stable MFR embedded in a strapping field is set as the initial condition. A surface converging flow is then applied at the lower boundary, pushing magnetic flux towards the main polarity inversion line. It drives a quasi-static evolution of the system, during which a current layer is built up below the MFR with decreasing thickness. Once reconnection starts in the current sheet, the eruption commences, which indicates that the reconnection plays a determining role in triggering the eruption. By further analysing the works done by the magnetic flux of the pre-existing MFR and the newly reconnected flux during the acceleration stage of the eruption, we find that the latter plays a major role in driving the eruption. Such a model may explain observed eruptions in which the pre-eruption MFR has not reached the conditions for ideal instability.

Identifying footpoints of pre-eruptive and coronal mass ejection flux ropes with sunspot scars

Context. The properties of pre-eruptive structures and coronal mass ejections (CMEs) are characterized by those of their footpoints, the latter of which attract a great deal of interest. However, the matter of how to identify the footpoints of pre-eruptive structures and how to do so with the use of ground-based instruments still remains elusive. Aims. In this work, we study an arc-shaped structure intruding in the sunspot umbra. It is located close to the (pre-)eruptive flux rope footpoint and it is expected to help identify the footpoint. Methods. We analyzed this arc-shaped structure, which we call a “sunspot scar”, in a CME event on July 12, 2012, and in two CME events from observationally inspired magnetohydrodynamic simulations performed by OHM and MPI-AMRVAC. Results. The sunspot scar displays a more inclined magnetic field with a weaker vertical component and a stronger horizontal component relative to that in the surrounding umbra and is manifested as a light bridge in the white light passband. The hot field lines anchored in the sunspot scar are spatially at the transition between the flux rope and the background coronal loops and temporally in the process of the slipping reconnection which builds up the flux rope. Conclusions. The sunspot scar and its related light bridge mark the edge of the CME flux rope footpoint and particularly indicate the edge of the pre-eruptive flux rope footpoint in the framework of “pre-eruptive structures being flux ropes”. Therefore, they provide a new perspective for the identification of pre-eruptive and CME flux rope footpoints, as well as new methods for studying the properties and evolution of pre-eruptive structures and CMEs with photospheric observations only.

Observations of a Failed Solar Filament Eruption Involving External Reconnection

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.

Numerical Simulation on the Leading Edge of Coronal Mass Ejection in the Near-Sun Region

The coronal mass ejections (CMEs) observed by white-light coronagraphs, such as the Large Angle and Spectrometric Coronagraph (LASCO) C2/C3, commonly exhibit the three-part structure, with the bright leading edge as the outermost part. In this work, we extend previous work on the leading edge by performing a large-scale 3D magnetohydrodynamic numerical simulation on the evolution of an eruptive magnetic flux rope (MFR) in a near-Sun region based on a radially stretched calculation grid in spherical coordination and the incorporation of solar wind. In the early stage, the new simulation almost repeats the previous results, i.e., the expanding eruptive MFR and associated CME bubble interact with the ambient magnetic field, which leads to the appearance of the helical current ribbon/boundary (HCB) wrapping around the MFR. The HCB can be interpreted as a possible mechanism of the CME leading edge. Later, the CME bubble propagates self-consistently to a larger region beyond a few solar radii from the solar center, similar to the early stage of evolution. The continuous growth and propagation of the CME bubbles leading to the HCB can be traced across the entire near-Sun region. Furthermore, we can observe the HCB in the white-light synthetic images as a bright front feature in the large field of view of LASCO C2 and C3.

Radiative Magnetohydrodynamic Simulation of the Confined Eruption of a Magnetic Flux Rope: Unveiling the Driving and Constraining Forces

We analyze the forces that control the dynamic evolution of a flux rope eruption in a three-dimensional radiative magnetohydrodynamic simulation. The confined eruption of the flux rope gives rise to a C8.5 flare. The flux rope rises slowly with an almost constant velocity of a few kilometers per second in the early stage when the gravity and Lorentz force are nearly counterbalanced. After the flux rope rises to the height at which the decay index of the external poloidal field satisfies the torus instability criterion, the significantly enhanced Lorentz force breaks the force balance and drives the rapid acceleration of the flux rope. Fast magnetic reconnection is immediately induced within the current sheet under the erupting flux rope, which provides strong positive feedback to the eruption. The eruption is eventually confined due to the tension force from the strong external toroidal field. Our results suggest that the gravity of plasma plays an important role in sustaining the quasi-static evolution of the preeruptive flux rope. The Lorentz force, which is contributed from both the ideal magnetohydrodynamic instability and magnetic reconnection, dominates the dynamic evolution during the eruption process.

The Eruption of a Magnetic Flux Rope Observed by Solar Orbiter and Parker Solar Probe

Magnetic flux ropes are a key component of coronal mass ejections, forming the core of these eruptive phenomena. However, determining whether a flux rope is present prior to eruption onset and, if so, the rope’s handedness and the number of turns that any helical field lines make is difficult without magnetic field modeling or in situ detection of the flux rope. We present two distinct observations of plasma flows along a filament channel on 2022 September 4 and 5 made using the Solar Orbiter spacecraft. Each plasma flow exhibited helical motions in a right-handed sense as the plasma moved from the source active region across the solar disk to the quiet Sun, suggesting that the magnetic configuration of the filament channel contains a flux rope with positive chirality and at least one turn. The length and velocity of the plasma flow increased from the first to the second observation, suggesting evolution of the flux rope, with the flux rope subsequently erupting within ∼5 hr of the second plasma flow. The erupting flux rope then passed over the Parker Solar Probe spacecraft during its encounter (13), enabling in situ diagnostics of the structure. Although complex and consistent with the flux rope erupting from underneath the heliospheric current sheet, the in situ measurements support the inference of a right-handed flux rope from remote-sensing observations. These observations provide a unique insight into the eruption and evolution of a magnetic flux rope near the Sun.

A multiple spacecraft detection of the 2 April 2022 M-class flare and filament eruption during the first close Solar Orbiter perihelion

Context. The Solar Orbiter mission completed its first remote-sensing observation windows in the spring of 2022. On 2 April 2022, an M-class flare followed by a filament eruption was seen both by the instruments on board the mission and from several observatories in Earth’s orbit, providing an unprecedented view of a flaring region with a large range of observations. Aims. We aim to understand the nature of the flaring and filament eruption events via the analysis of the available dataset. The complexity of the observed features is compared with the predictions given by the standard flare model in 3D. Methods. In this paper, we use the observations from a multi-view dataset, which includes extreme ultraviolet (EUV) imaging to spectroscopy and magnetic field measurements. These data come from the Interface Region Imaging Spectrograph, the Solar Dynamics Observatory, Hinode, as well as several instruments on Solar Orbiter. Results. The large temporal coverage of the region allows us to analyse the whole sequence of the filament eruption starting with its pre-eruptive state. Information given by spectropolarimetry from SDO/HMI and Solar Orbiter PHI/HRT shows that a parasitic polarity emerging underneath the filament is responsible for bringing the flux rope to an unstable state. As the flux rope erupts, Hinode EIS captures blue-shifted emission in the transition region and coronal lines in the northern leg of the flux rope prior to the flare peak. This may be revealing the unwinding of one of the flux rope legs. At the same time, Solar Orbiter SPICE captures the whole region, complementing the Doppler diagnostics of the filament eruption. Analyses of the formation and evolution of a complex set of flare ribbons and loops, of the hard and soft X-ray emissions with STIX, show that the parasitic emerging bipole plays an important role in the evolution of the flaring region. Conclusions. The extensive dataset covering this M-class flare event demonstrates how important multiple viewpoints and varied observations are in order to understand the complexity of flaring regions. While the analysed data are overall consistent with the standard flare model, the present particular magnetic configuration shows that surrounding magnetic activity such as nearby emergence needs to be taken into account to fully understand the processes at work. This filament eruption is the first to be covered from different angles by spectroscopic instruments, and provides an unprecedented diagnostic of the multi-thermal structures present before and during the flare. This complete dataset of an eruptive event showcases the capabilities of coordinated observations with the Solar Orbiter mission.

Formation of an observed eruptive flux rope above the torus instability threshold through tether-cutting magnetic reconnection

Context. Erupting magnetic flux ropes (MFRs) are believed to play a crucial role in producing solar flares. However, the formation of erupting MFRs in complex coronal magnetic configurations and the role of their subsequent evolution in the flaring events are not fully understood. Aims. We perform a magnetohydrodynamic (MHD) simulation of active region NOAA 12241 to understand the formation of a rising magnetic flux rope during the onset of an M6.9 flare on 2014 December 18 around 21:41 UT (SOL2014-12- 18T21:41M6.9), which was followed by the appearance of parallel flare ribbons. Methods. The MHD simulation was initialised with an extrapolated non-force-free magnetic field generated from the photospheric vector magnetogram of the active region taken a few minutes before the flare. Results. The initial magnetic field topology displays a pre-existing sheared arcade enveloping the polarity inversion line. The simulated dynamics exhibit the movement of the oppositely directed legs of the sheared arcade field lines towards each other due to the converging Lorentz force, resulting in the onset of tether-cutting magnetic reconnection that produces an underlying flare arcade and flare ribbons. Concurrently, a magnetic flux rope above the flare arcade develops inside the sheared arcade and shows a rising motion. The flux rope is found to be formed in a torus-unstable region, thereby explaining its eruptive nature. Interestingly, the location and rise of the rope are in good agreement with the corresponding observations seen in extreme-ultraviolet channels of the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO). Furthermore, the foot points of the simulation’s flare arcade match well with the location of the observed parallel ribbons of the flare. Conclusions. The presented simulation supports the development of the MFR by the tether-cutting magnetic reconnection inside the sheared coronal arcade during flare onset. The MFR is then found to extend along the polarity inversion line (PIL) through slip-running reconnection. The MFR’s eruptive nature is ascribed both to its formation in the torus-unstable region and also to the runaway tether-cutting reconnection.

Sequential Remote Brightenings and Co-spatial Fast Downflows during Two Successive Flares

Remote brightenings often appear at the outskirts of the active regions of solar eruptive events. Nevertheless, their origin remains to be ascertained. In this study, we report imaging and spectroscopic observations of sequential remote brightenings with a combination of observations from the Hα Imaging Spectrograph on board the Chinese Hα Solar Explorer, which is the first space-based solar telescope of China, and from the Solar Dynamics Observatory. It is found that during two successive M-class flares occurring on 2022 August 17 multiple ribbon-like brightenings appeared in sequence away from the flaring active region. Meanwhile, abundant cool filament materials moved downward to the sequential remote brightenings, which were visible at the Hα red wing with a line-of-sight speed of up to 70 km s−1. The extrapolated three-dimensional magnetic field configuration shows that the sequential remote brightenings correspond to the footpoints of closed ambient field lines whose conjugate footpoints are rooted in the main flare site. We suggest that the sequential remote brightenings are most likely to be caused by the heating of the interchange reconnection between the erupting flux rope and the closed ambient field, during which the rope-hosting filament materials are transferred to the periphery of the flaring active region along the closed ambient field rather than to the interplanetary space, such as in the scenario of slow solar wind formation.

High-Cadence Observations of Magnetic Field Dynamics and Photospheric Emission Sources in the Eruptive Near-the-Limb X4.9 Solar Flare on 25 February, 2014: Evidences for Two-Stage Magnetic Reconnection during the Impulsive Phase

—We present an analysis of the pre-limb eruptive X4.9 solar flare on February 25, 2014, by means of which we confirm a hypothesis of the two-stage energy release corresponding to two magnetic reconnection regimes in the flare impulsive phase. This flare is selected, firstly, because of its morphological peculiarities suggesting the presence of the two energy release stages. Secondly, the flare was very suitably located near the solar limb and it was well-observed by many instruments. We performed an analysis of multiwavelength observational data of this flare region to find a connection between changes of the photospheric magnetic field, morphology of hard and soft X-ray sources, dynamics of the photospheric optical emission sources, metric radio bursts, and kinematics of an eruptive structure. The simultaneous usage of the line-of-sight and vector Helioseismic Magnetic Imager (HMI) magnetograms allowed us to trace magnetic field changes during the flare impulsive phase with high temporal resolution. HMI filtergrams allowed to trace displacement of the photospheric emission sources, associated with the magnetic reconnection, with very high temporal resolution up to 2 s. Using all observational results, we argue that the found flare stages are characterized by the following magnetic reconnection regimes. The first stage is predominantly characterized by the three-dimensional zipping reconnection in the strong sheared magnetic field assuming the tether-cutting geometry. The second stage corresponds to the so-called “standard” model of eruptive flares with the quasi-two-dimensional reconnection below the eruptive flux-rope. All observational peculiarities of these two stages are discussed in details.

A Model for Confined Solar Eruptions Including External Reconnection

The violent disruption of the coronal magnetic field is often observed to be restricted to the low corona, appearing as a confined eruption. The possible causes of the confinement remain elusive. Here, we model the eruption of a magnetic flux rope in a quadrupolar active region, with the parameters set such that magnetic X-lines exist both below and above the rope. This facilitates the onset of magnetic reconnection in either place but with partly opposing effects on the eruption. The lower reconnection initially adds poloidal flux to the rope, increasing the upward hoop force and supporting the rise of the rope. However, when the flux of the magnetic side lobes enters the lower reconnection, the flux rope is found to separate from the reconnection site and the flux accumulation ceases. At the same time, the upper reconnection begins to reduce the poloidal flux of the rope, decreasing its hoop force; eventually this cuts the rope completely. The relative weight of the two reconnection processes is varied in the model, and it is found that their combined effect and the tension force of the overlying field confine the eruption if the flux ratio of the outer to the inner polarities exceeds a threshold, which is ∼1.3 for our Cartesian box and chosen parameters. We hence propose that external reconnection between an erupting flux rope and overlying flux can play a vital role in confining eruptions.

Effects of optimisation parameters on data-driven magnetofrictional modelling of active regions

Context. The solar magnetic field plays an essential role in the formation, evolution, and dynamics of large-scale eruptive structures in the corona. The estimation of the coronal magnetic field, the ultimate driver of space weather, particularly in the ‘low’ and ‘middle’ corona, is presently limited due to practical difficulties. Data-driven time-dependent magnetofrictional modelling (TMFM) of active region magnetic fields has been proven to be a useful tool to study the corona. The input to the model is the photospheric electric field that is inverted from a time series of the photospheric magnetic field. Constraining the complete electric field, that is, including the non-inductive component, is critical for capturing the eruption dynamics. We present a detailed study of the effects of optimisation of the non-inductive electric field on the TMFM of AR 12473. Aims. We aim to study the effects of varying the non-inductive electric field on the data-driven coronal simulations, for two alternative parametrisations. By varying parameters controlling the strength of the non-inductive electric field, we wish to explore the changes in flux rope formation and their early evolution and other parameters, for instance, axial flux and magnetic field magnitude. Methods. We used the high temporal and spatial resolution cadence vector magnetograms from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The non-inductive electric field component in the photosphere is critical for energising and introducing twist to the coronal magnetic field, thereby allowing unstable configurations to be formed. We estimated this component using an approach based on optimising the injection of magnetic energy. Results. Our data show that flux ropes are formed in all of the simulations except for those with the lower values of these optimised parameters. However, the flux rope formation, evolution and eruption time varies depending on the values of the optimisation parameters. The flux rope is formed and has overall similar evolution and properties with a large range of non-inductive electric fields needed to determine the non-inductive electric field component that is critical for energising and introducing twist to the coronal magnetic field. Conclusions. This study shows that irrespective of non-inductive electric field values, flux ropes are formed and erupted, which indicates that data-driven TMFM can be used to estimate flux rope properties early in their evolution without needing to employ a lengthy optimisation process.

Energy-releasing Process for the 2013 May 13 X1.7 Limb Flare: A Continued Study

In this paper, we reanalyze the X1.7 class limb flare that occurred on 2013 May 13 (SOL2013-05-13T01:56 UT), concentrating on the energy-releasing process using microwave observations mainly made by Nobeyama and X-ray observations made by RHESSI. The analysis was carried out in the context of EUV observations made by the Atmospheric Imaging Assembly on board Solar Dynamics Observatory. First, we complement the initiation process by showing that the initiation occurred together with material falling from a large-scale overlying prominence, a signature of drainage instability. The usual downward and upward motions of the microwave and X-ray sources are observed from their evolution. However, the microwave source’s height shows a recurrent decrease and increase during its overall upward motion; it shows a kind of recurrent contraction and expansion. The time period of the recurrent contraction and expansion corresponds to the period of post-contraction oscillation of EUV loops, and the oscillatory motions are closely correlated with four microwave/hard X-ray peaks that unusually increased nonthermal emission levels by several times. X-ray spectra get hardened during the oscillation. In addition, the rapid contraction of magnetic loops located on the outside of the erupting flux rope occurs 5 minutes after the onset of the flare, showing that the contraction of the peripheral magnetic loops is more likely due to the vortex and sink flows generated by an upward erupting magnetic flux rope rather than a coronal implosion. The results can provide more insight into the physics of dynamic coronal magnetic field and particle acceleration during solar flares.

Numerical simulations of prominence oscillations triggered by external perturbations

Context. Several energetic disturbances have been identified as triggers of large-amplitude oscillations (LAOs) in prominences. Observations show that Moreton or extreme ultraviolet waves excite prominence oscillations of the longitudinal, transverse, or mixed polarities. However, the mechanisms for the excitation of LAOs by these waves are not well understood. Aims. In this study, we aim to investigate mechanisms behind the triggering of LAOs via self-consistent perturbation produced by an eruption and via energetic waves coming from a distant energy source. Methods. We performed time-dependent numerical simulations in 2.5D and 2D setups, using the magnetohydrodynamic code MANCHA3D, involving a flux rope and dipped arcade magnetic configurations with an artificially loaded prominence mass in the magnetic dips. Two types of disturbances were applied to excite prominence oscillations. The first type involves perturbations produced self-consistently by an eruption, while the second type of perturbation is associated with the waves caused by an artificial energy release. Results. In the simulations of the eruption, we find that this eruption by itself does not produce LAOs in the prominence located in its vicinity. Its only effect is in inclining the magnetic configuration of the prominence. While the erupting flux rope rises, an elongated current sheet forms behind it. This current sheet becomes unstable and breaks into plasmoids. The downward-moving plasmoids cause perturbations in the velocity field by merging with the post-reconnection loops. This velocity perturbation propagates in the surroundings and enters the flux rope, causing the disturbance of the prominence mass. The analysis of the oscillatory motions of the prominence plasma reveals the excitation of small-amplitude oscillations (SAOs), which are a mixture of longitudinal and vertical oscillations with short and long periods. In the simulations with a distant artificial perturbation, a fast-mode shock wave is produced and it gradually reaches two flux rope prominences at different distances. This shock wave excites vertical LAOs as well as longitudinal SAOs with similar amplitudes, periods, and damping times in both prominences. Finally, in the experiment with the external triggering of LAOs of solar prominences by an artificial perturbation in a dipped arcade prominence model, we find that although the vector normal to the front of a fast-mode shock wave is parallel to the spine of the dipped arcade well before the contact, this wave does not excite longitudinal LAOs. When the wave front approaches the prominence, it pushes the dense plasma down, establishing vertical LAOs and motions due to compression and rarefaction along the magnetic field. Conclusions. The external triggering of prominence oscillations is a complex process that excites LAOs or SAOs of the longitudinal or transverse polarizations or a mix of both types. It is not an easy task to produce LAOs in prominences because the triggering event requires a sufficient amount of energy. The orientation of the prominence axis with respect to the driving event may play a crucial role in triggering a certain type of LAOs.