Eruption Of Magnetic Flux Rope Research Articles

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 Confined Two-peaked Solar Flare Observed by EAST and SDO

The solar flare is one of the most violent explosions, and can disturb the near-Earth space weather. Except for commonly single-peaked solar flares in soft X-ray, some special flares show intriguing a two-peak feature that is deserved much more attentions. Here, we reported a confined two-peaked solar flare and analyzed the associated eruptions using high-quality observations from Educational Adaptive-optics Solar Telescope and Solar Dynamics Observatory. Before the flare, a magnetic flux rope (MFR) formed through partially tether-cutting reconnection between two sheared arches. The flare occurred after the MFR eruption that was confined by the overlying strong field. Interestingly, a small underlying filament immediately erupted, which was possibly destabilized by the flare ribbon. The successive eruptions were confirmed by the analysis of the emission measure and the reconnection fluxes. Therefore, we suggest that the two peaks of the confined solar flare are corresponding to two episodes of magnetic reconnection during the successive eruptions of the MFR and the underlying filament.

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.

The Impulsive Acceleration of a Solar Filament Eruption Associated with a B-class Flare

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.

Eruptivity Criteria for Solar Coronal Flux Ropes in Magnetohydrodynamic and Magnetofrictional Models

We investigate which scalar quantity or quantities can best predict the loss of equilibrium and subsequent eruption of magnetic flux ropes in the solar corona. Our models are initialized with a potential magnetic arcade, which is then evolved by means of two effects on the lower boundary: first, a gradual shearing of the arcade, modeling differential rotation on the solar surface; and second, supergranular diffusion. These result in flux cancellation at the polarity inversion line and the formation of a twisted flux rope. We use three model setups: full magnetohydrodynamics (MHD) in cartesian coordinates, and the magnetofrictional (MF) model in both cartesian and polar coordinates. The flux ropes are translationally invariant, allowing for very fast computational times and thus a comprehensive parameter study, comprising hundreds of simulations and thousands of eruptions. Similar flux rope behavior is observed using either magnetofriction or MHD, and there are several scalar criteria that could be used as proxies for eruptivity. The most consistent predictor of eruptions in either model is the squared current in the axial direction of the rope, normalized by the relative helicity, although a variation on the previously proposed eruptivity index is also found to perform well in both the MF and MHD simulations.

The Structure of Coronal Mass Ejections Recorded by the K-Coronagraph at Mauna Loa Solar Observatory

Previous survey studies reported that coronal mass ejections (CMEs) can exhibit various structures in white-light coronagraphs, and ∼30% of them have the typical three-part feature in the high corona (e.g., 2–6 R ⊙), which has been taken as the prototypical structure of CMEs. It is widely accepted that CMEs result from eruption of magnetic flux ropes (MFRs), and the three-part structure can be understood easily by means of the MFR eruption. It is interesting and significant to answer why only ∼30% of CMEs have the three-part feature in previous studies. Here we conduct a synthesis of the CME structure in the field of view (FOV) of K-Coronagraph (1.05–3 R ⊙). In total, 369 CMEs are observed from 2013 September to 2022 November. After inspecting the CMEs one by one through joint observations of the Atmospheric Imaging Assembly, K-Coronagraph, and LASCO/C2, we find 71 events according to the criteria: (1) limb event; (2) normal CME, i.e., angular width ≥30°; (3) K-Coronagraph caught the early eruption stage. All (or more than 90% considering several ambiguous events) of the 71 CMEs exhibit the three-part feature in the FOV of K-Coronagraph, while only 30%–40% have the feature in the C2 FOV (2–6 R ⊙). For the first time, our studies show that 90%–100% and 30%–40% of normal CMEs possess the three-part structure in the low and high corona, respectively, which demonstrates that many CMEs can lose the three-part feature during their early evolutions, and strongly supports that most (if not all) CMEs have the MFR structures.

A Magnetogram-matching Method for Energizing Magnetic Flux Ropes Toward Eruption

We propose a new “helicity-pumping” method for energizing coronal equilibria that contain a magnetic flux rope (MFR) toward an eruption. We achieve this in a sequence of magnetohydrodynamics relaxations of small line-tied pulses of magnetic helicity, each of which is simulated by a suitable rescaling of the current-carrying part of the field. The whole procedure is “magnetogram-matching” because it involves no changes to the normal component of the field at the photospheric boundary. The method is illustrated by applying it to an observed force-free configuration whose MFR is modeled with our regularized Biot–Savart law method. We find that, in spite of the bipolar character of the external field, the MFR eruption is sustained by two reconnection processes. The first, which we refer to as breakthrough reconnection, is analogous to breakout reconnection in quadrupolar configurations. It occurs at a quasi-separator inside a current layer that wraps around the erupting MFR and is caused by the photospheric line-tying effect. The second process is the classical flare reconnection, which develops at the second quasi-separator inside a vertical current layer that is formed below the erupting MFR. Both reconnection processes work in tandem with the magnetic forces of the unstable MFR to propel it through the overlying ambient field, and their interplay may also be relevant for the thermal processes occurring in the plasma of solar flares. The considered example suggests that our method will be beneficial for both the modeling of observed eruptive events and theoretical studies of eruptions in idealized magnetic configurations.

Toward a Unified Explanation for the Three-part Structure of Solar Coronal Mass Ejections

Coronal mass ejections (CMEs) are associated with the eruption of magnetic flux ropes (MFRs), which usually appear as hot channels in active regions and coronal cavities in quiet-Sun regions. CMEs often exhibit a classical three-part structure in the lower corona when imaged with white-light coronagraphs, including a bright front, dark cavity, and bright core. For several decades, the bright core and dark cavity have been regarded as the erupted prominence and MFR, respectively. However, recent studies have clearly demonstrated that both the prominence and hot-channel MFR can be observed as the CME core. The current research presents a three-part CME resulting from the eruption of a coronal prominence cavity on 2010 October 7, with observations from two vantage perspectives, i.e., edge-on from the Earth and face-on from the Solar Terrestrial Relations Observatory (STEREO). Our observations illustrate two important results: (1) for the first time, the erupting coronal cavity is recorded as a channel-like structure in the extreme-ultraviolet passband, analogous to the hot-channel morphology, and is dubbed as the warm channel; and (2) both the prominence and warm-channel MFR (coronal cavity) in the extreme-ultraviolet passbands evolve into the CME core in the white-light coronagraphs of STEREO-A. The results suggest that we are working toward a unified explanation for the three-part structure of CMEs, in which both prominences and MFRs (hot or warm channels) are responsible for the bright core.

Mechanism of the Failed Eruption of an Intermediate Solar Filament

Abstract Solar filament eruptions can generate coronal mass ejections (CMEs), which are huge threats to space weather. Thus, we need to understand their underlying mechanisms. Although many authors have studied the mechanisms for several decades, we still do not fully understand in what conditions a filament can erupt to become a CME or not. Previous studies have discussed extensively why a highly twisted and already erupted filament will be interrupted and considered that a strong overlying constraint field seems to be the key factor. However, few of them study filaments in the weak field, namely, quiescent filaments, as it is too hard to reconstruct the magnetic configuration there. Here we show a case study, in which we can fully reconstruct the configuration of an intermediate filament with the MHD-relaxation extrapolation model and discuss its initial eruption and eventual failure. By analyzing the magnetic configuration, we suggest that the reconnection between the erupting magnetic flux rope (MFR) and the overlying field are the key factors that constrained the eruption of the filament. There is observational evidence that MFRs will reconnect with peripheral field lines. Usually, the reconnection between an MFR and peripheral fields will weaken the overlying constraint and promote further eruption, but in some cases in which the magnetic configuration of an MFR is far different from peripheral fields, the reconnection will play a negative role in MFR eruption.

Evolution of a streamer-blowout CME as observed by imagers on Parker Solar Probe and the Solar Terrestrial Relations Observatory

Context. On 26–27 January 2020, the Wide-field Imager for Solar Probe on Parker Solar Probe (PSP) observed a coronal mass ejection (CME) from a distance of approximately 30 R⊙ as it passed through the instrument’s 95° field-of-view, providing an unprecedented view of the flux rope morphology of the CME’s internal structure. The same CME was seen by Solar Terrestrial Relations Observatory-Ahead (STEREO-A), beginning on 25 January. Aims. Our goal is to understand the origin and determine the trajectory of this CME. Methods. We analyzed data from three well-placed spacecrafts: PSP, STEREO-A, and Solar Dynamics Observatory (SDO). The CME trajectory was determined using a tracking-and-fitting technique and verified using simultaneous images of the CME propagation from STEREO-A. The fortuitous alignment with STEREO-A also provided views of coronal activity leading up to the eruption. Observations from SDO, in conjunction with potential magnetic field models of the corona, were used to analyze the coronal magnetic evolution for the three days leading up to the flux rope ejection from the corona on 25 January. Results. We found that the 25 January CME is likely the end result of a slow magnetic flux rope eruption that began on 23 January and was observed by STEREO-A/Extreme Ultraviolet Imager. The analysis of these observations suggest that the flux rope was apparently constrained in the corona for more than a day before its final ejection on 25 January. STEREO-A/COR2 observations of swelling and brightening of the overlying streamer for several hours prior to eruption on 25 January led us to classify this as a streamer-blowout CME. The analysis of the SDO data suggests that restructuring of the coronal magnetic fields caused by an emerging active region led to the final ejection of the flux rope.

Do All Interplanetary Coronal Mass Ejections Have a Magnetic Flux Rope Structure Near 1 au?

Abstract Interplanetary coronal mass ejections (ICMEs) often consist of a shock wave, sheath region, and ejecta region. The ejecta regions are divided into two broad classes: magnetic clouds (MCs) that exhibit the characteristics of magnetic flux ropes, and non-magnetic clouds (NMCs) that do not. As CMEs result from eruption of magnetic flux ropes, it is important to answer why NMCs do not have the flux rope features. One claims that NMCs lose their original flux rope features due to the interactions between ICMEs or ICMEs and other large-scale structures during their transit in the heliosphere. The other attributes this phenomenon to the geometric selection effect; i.e., when an ICME has its nose (flank, including leg and non-leg flanks) pass through the observing spacecraft, the MC (NMC) features will be detected along the spacecraft trajectory within the ejecta. In this Letter, we examine which explanation is more reasonable through the geometric properties of ICMEs. If the selection effect leads to different ejecta types, MCs should have narrower sheath region compared to NMCs from the statistical point of view, which is confirmed by our statistics. In addition, we find that NMCs have similar sizes in solar cycles 23 and 24, and NMCs are smaller than MCs in cycle 23 but larger than MCs in cycle 24. This suggests that most NMCs have their leg flank pass through the spacecraft. Our geometric analyses support that all ICMEs should have a magnetic flux rope structure near 1 au.

Eruptions and flaring activity in emerging quadrupolar regions

Context. Solar observations suggest that some of the most dynamic active regions are associated with complex photospheric magnetic configurations such as quadrupolar regions, and especially those that have a δ-spot configuration and a strong polarity inversion line (PIL). Aims. We study the formation and eruption of magnetic flux ropes in quadrupolar regions. Methods. We performed 3D magnetohydrodynamics simulations of the partial emergence of a highly twisted flux tube from the solar interior into a non-magnetised stratified atmosphere. We introduced a density deficit at two places along the length of the subphotospheric flux tube to emerge as two Ω-shaped loops, forming a quadrupolar region. Results. At the photosphere, the emerging flux forms two initially separated bipoles, which later come in contact, forming a δ-spot central region. Above the two bipoles, two magnetic lobes expand and interact through a series of current sheets at the interface between them. Two recurrent confined eruptions are produced. In both cases, the reconnection between sheared low-lying field lines forms a flux rope. The reconnection between the two lobes higher in the atmosphere forms field lines that retract down and push against the flux rope, creating a current sheet between them. It also forms field lines that create a third magnetic lobe between the two emerged lobes, that later acts as a strapping field. The flux rope eruptions are triggered when the reconnection between the flux ropes and the field above the ropes becomes efficient enough to remove the tension of the overlying field. These reconnection events occur internally in the quadrupolar system, as the atmosphere is non-magnetised. The flux rope of the first, weaker, eruption almost fully reconnects with the overlying field. The flux rope of the second, more energetic, eruption is confined by the overlying strapping field. During the second eruption, the flux rope is enhanced in size, flux, and twist, similar to confined-flare-to-flux-rope observations. Proxies of the emission reveal the two erupting filaments channels. A flare arcade is only formed in the second eruption owing to the longer lasting and more efficient reconnection at the current sheet below the flux rope.

Solar Magnetic Flux Rope Eruption Simulated by a Data-driven Magnetohydrodynamic Model

Abstract The combination of magnetohydrodynamic (MHD) simulation and multi-wavelength observations is an effective way to study the mechanisms of magnetic flux rope eruption. We develop a data-driven MHD model using the zero-β approximation. The initial condition is provided by a nonlinear force-free field derived from the magneto-frictional method based on vector magnetic field observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The bottom boundary uses observed time series of the vector magnetic field and the vector velocity derived by the Differential Affine Velocity Estimator for Vector Magnetograms. We apply the data-driven model to active region 11123 observed from 06:00 UT on 2010 November 11 to about 2 hr later. The evolution of the magnetic field topology coincides with the flare ribbons observed in the 304 and 1600 Å wavebands by the Atmospheric Imaging Assembly. The morphology, propagation path, and propagation range of the flux rope are comparable with the observations in 304 Å. We also find that a data-constrained boundary condition, where the bottom boundary is fixed to the initial values, reproduces a similar simulation result. This model can reproduce the evolution of a magnetic flux rope in its dynamic eruptive phase.

Threshold of Non-potential Magnetic Helicity Ratios at the Onset of Solar Eruptions

Abstract The relative magnetic helicity is a quantity that is often used to describe the level of entanglement of non-isolated magnetic fields, such as the magnetic field of solar active regions. The aim of this paper is to investigate how different kinds of photospheric boundary flows accumulate relative magnetic helicity in the corona and if and how well magnetic-helicity-related quantities identify the onset of an eruption. We use a series of three-dimensional, parametric magnetohydrodynamic simulations of the formation and eruption of magnetic flux ropes. All the simulations are performed on the same grid, using the same parameters, but they are characterized by different driving photospheric flows, i.e., shearing, convergence, stretching, and peripheral- and central- dispersion flows. For each of the simulations, the instant of the onset of the eruption is carefully identified by using a series of relaxation runs. We find that magnetic energy and total relative helicity are mostly injected when shearing flows are applied at the boundary, while the magnetic energy and helicity associated with the coronal electric currents increase regardless of the kind of photospheric flows. We also find that, at the onset of the eruptions, the ratio between the non-potential magnetic helicity and the total relative magnetic helicity has the same value for all the simulations, suggesting the existence of a threshold in this quantity. Such a threshold is not observed for other quantities as, for example, those related to the magnetic energy.

Two Scenarios for the Eruption of Magnetic Flux Ropes in the Solar Atmosphere

Eruptions of material from lower to upper layers of the solar atmosphere can be divided into two classes. The first class of eruptions maintain their (usually loop-like) shapes as they increase in size (eruptive prominences), or display a sudden expansion of fairly shapeless clumps of plasma in all directions (flare sprays). The second class refers to narrow, collimated flows of plasma on various scales (spicules, surges, jets). It is obvious that the magnetic configurations in which these phenomena develop differ: for the first class they form closed structures that confine the plasma, and in the second class open structures directing flows of plasma in a particular direction, as a rule, upward. At the same time, the mechanisms initiating eruptions of both classes could be similar, or even practically identical. This mechanism could be instability of twisted magnetic tubes (flux ropes), leading to different consequences under different conditions. It is shown that the results of eruptive instability are determined by the ratio of the scales of the magnetic flux rope and the confining coronal field, and also by the configuration of the ambient magnetic field in the corona. Observations of both types of eruptions are analyzed, the conditions for their develoment are examined, and phenomenological models are proposed.

Quasi-periodic Oscillations in Flares and Coronal Mass Ejections Associated with Magnetic Reconnection

Abstract We propose a mechanism for quasi-periodic oscillations of both coronal mass ejections (CMEs) and flare loops as related to magnetic reconnection in eruptive solar flares. We perform two-dimensional numerical MHD simulations of magnetic flux rope eruption, with three different values of the global Lundquist number. In the low Lundquist number run, no oscillatory behavior is found. In the moderate Lundquist number run, on the other hand, quasi-periodic oscillations are excited both at the bottom of the flux rope and at the flare loop top. In the high Lundquist number run, quasi-periodic oscillations are also excited; in the meanwhile, the dynamics become turbulent owing to the formation of multiple plasmoids in the reconnection current sheet. In high and moderate Lundquist number runs, thin reconnection jets collide with the flux rope bottom or flare loop top and dig them deeply. Steep oblique shocks are formed as termination shocks where reconnection jets are bent (rather than decelerated) in the horizontal direction, resulting in supersonic backflows. The structure becomes unstable, and quasi-periodic oscillations of supersonic backflows appear at locally confined high-beta regions at both the flux rope bottom and flare loop top. We compare the observational characteristics of quasi-periodic oscillations in erupting flux ropes, post-CME current sheets, flare ribbons, and light curves with corresponding dynamical structures found in our simulation.

Imaging Observations of Magnetic Reconnection in a Solar Eruptive Flare

Abstract Solar flares are among the most energetic events in the solar atmosphere. It is widely accepted that flares are powered by magnetic reconnection in the corona. An eruptive flare is usually accompanied by a coronal mass ejection, both of which are probably driven by the eruption of a magnetic flux rope (MFR). Here we report an eruptive flare on 2016 March 23 observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The extreme-ultraviolet imaging observations exhibit the clear rise and eruption of an MFR. In particular, the observations reveal solid evidence of magnetic reconnection from both the corona and chromosphere during the flare. Moreover, weak reconnection is observed before the start of the flare. We find that the preflare weak reconnection is of tether-cutting type and helps the MFR to rise slowly. Induced by a further rise of the MFR, strong reconnection occurs in the rise phases of the flare, which is temporally related to the MFR eruption. We also find that the magnetic reconnection is more of 3D-type in the early phase, as manifested in a strong-to-weak shear transition in flare loops, and becomes more 2D-like in the later phase, as shown by the apparent rising motion of an arcade of flare loops.

A TWO-RIBBON WHITE-LIGHT FLARE ASSOCIATED WITH A FAILED SOLAR ERUPTION OBSERVED BYONSET,SDO, andIRIS

Two-ribbon brightenings are one of the most remarkable characteristics of an eruptive solar flare and are often used for predicting the occurrence of coronal mass ejections (CMEs). Nevertheless, it was called in question recently whether all two-ribbon flares are eruptive. In this paper, we investigate a two ribbon-like white-light (WL) flare that is associated with a failed magnetic flux rope (MFR) eruption on 2015 January 13, which has no accompanying CME in the WL coronagraph. Observations by \textit{Optical and Near-infrared Solar Eruption Tracer} and \textit{Solar Dynamics Observatory} reveal that, with the increase of the flare emission and the acceleration of the unsuccessfully erupting MFR, two isolated kernels appear at the WL 3600 {\AA} passband and quickly develop into two elongated ribbon-like structures. The evolution of the WL continuum enhancement is completely coincident in time with the variation of \textit{Fermi} hard X-ray 26--50 keV flux. Increase of continuum emission is also clearly visible at the whole FUV and NUV passbands observed by \textit{Interface Region Imaging Spectrograph}. Moreover, in one WL kernel, the \ion{Si}{4}, \ion{C}{2}, and \ion{Mg}{2} h/k lines display significant enhancement and non-thermal broadening. However, their Doppler velocity pattern is location-dependent. At the strongly bright pixels, these lines exhibit a blueshift; while at moderately bright ones, the lines are generally redshifted. These results show that the failed MFR eruption is also able to produce a two-ribbon flare and high-energy electrons that heat the lower atmosphere, causing the enhancement of the WL and FUV/NUV continuum emissions and chromospheric evaporation.

TRACKING THE EVOLUTION OF A COHERENT MAGNETIC FLUX ROPE CONTINUOUSLY FROM THE INNER TO THE OUTER CORONA

The magnetic flux rope (MFR) is believed to be the underlying magnetic structure of coronal mass ejections (CMEs). However, it remains unclear how an MFR evolves into and forms the multi-component structure of a CME. In this paper, we perform a comprehensive study of an extreme-ultraviolet (EUV) MFR eruption on 2013 May 22 by tracking its morphological evolution, studying its kinematics, and quantifying its thermal property. As EUV brightenings begin, the MFR starts to rise slowly and shows helical threads winding around an axis. Meanwhile, cool filamentary materials descend spirally down to the chromosphere. These features provide direct observational evidence of intrinsically helical structure of the MFR. Through detailed kinematical analysis, we find that the MFR evolution experiences two distinct phases: a slow rise phase and an impulsive acceleration phase. We attribute the first phase to the magnetic reconnection within the quasi-separatrix-layers surrounding the MFR, and the much more energetic second phase to the fast magnetic reconnection underneath the MFR. We suggest that the transition between these two phases be caused by the torus instability. Moreover, we identify that the MFR evolves smoothly into the outer corona and appears as a coherent structure within the white light CME volume. The MFR in the outer corona was enveloped by bright fronts that originated from plasma pile-up in front of the expanding MFR. The fronts are also associated with the preceding sheath region followed the outmost MFR-driven shock.

Eruption of magnetic flux ropes during flux emergence

Aims: We investigate the formation of flux ropes in a flux emergence region and their rise into the outer atmosphere of the Sun. Methods: We perform 3D numerical experiments solving the time-dependent and resistive MHD equations. Results: A sub-photospheric twisted flux tube rises from the solar interior and expands into the corona. A flux rope is formed within the expanding field, due to shearing and reconnection of field lines at low atmospheric heights. If the tube emerges into a non-magnetized atmosphere, the flux rope rises, but remains confined inside the expanding magnetized volume. On the contrary, if the expanding tube is allowed to reconnect with a preexisting coronal field, the flux rope experiences a full eruption with a rise profile which is in qualitative agreement with erupting filaments and Coronal Mass Ejections.