Erupting Flux Rope Research Articles

Multi-scale reconnections in a complex CME

A series of three flares of GOES class M, M and C, and a CME were observed on 20 January 2004 occurring in close succession in NOAA 10540. Types II, III, and N radio bursts were associated. We use the combined observations from TRACE, EIT, H α images from Kwasan Observatory, MDI magnetograms, GOES, and radio observations from Culgoora and Wind/ WAVES to understand the complex development of this event. We reach three main conclusions. First, we link the first two impulsive flares to tether-cutting reconnections and the launch of the CME. This complex observation shows that impulsive quadrupolar flares can be eruptive. Second, we relate the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. Finally, we show that reconnection with the magnetic structure of a previous CME launched about 8 h earlier injects electrons into open field lines having a local dip and apex (located at about six solar radii height). This is observed as an N-burst at decametre radio wavelengths. The dipped shape of these field lines is due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains why this is the first N-burst ever observed at long radio wavelengths.

The May 13, 2005 Eruption: Observations, Data Analysis and Interpretation

In this study, we present detailed description and analysis of the May 13, 2005 eruption, the corresponding coronal mass ejection (CME) and intense geomagnetic storm observed near the Earth on May 15, 2005. This isolated two-ribbon M8.0 flare and the very fast CME occurred in a relatively simple magnetic configuration during a quiet period of solar activity, which enabled us to reliably associate the solar surface event with its counterpart observed in the Earth magnetosphere. In our study, we utilized (i) various tools to analyze a multi-wavelength data set that includes ground (BBSO vector magnetograms, Hα) and space (SOHO, TRACE, RHESSI and ACE) based data; (ii) linear force-free modeling to reconstruct the coronal field above the active region and (iii) erupting flux rope (EFR) model to simulate a near-Sun halo CME and a near-Earth interplanetary CME (ICME). Our findings indicate that persisting converging and shearing motions near the main neutral line could lead to the formation of twisted core fields and eventually their eruption via reconnection. In the discussed scenario, the in situ formed erupting loop can be observed as a magnetic cloud (MC) when it reaches the Earth. The EFR model was able to produce both a model halo CME and ICME providing a good global match to the overall timing and components of the magnetic field in the observed MC. The orientation of the model ICME and the sense of the twist, inferred from the EFR model, agree well with the orientation and the magnetic helicity found in the source active region.

Three‐dimensional Simulation Study of Flux Rope Dynamics in the Solar Corona

The three-dimensional stability and the nonlinear dynamics of a flux rope embedded in a magnetic arcade are investigated using magnetohydrodynamic (MHD) simulations, with the goal of understanding the mechanism of filament eruption in the solar corona. The flux rope equilibrium proposed by Forbes in 1990 is adopted as the initial state of the three-dimensional simulation, and we find that the equilibrium is linearly unstable to the kink mode instability, when the system approaches the loss-of-equilibrium state. The three-dimensional simulation demonstrates that when the flux rope is long enough, it can escape from the arcade at an almost constant speed after the accelerated launching phase due to the kink instability. The continuous ascending of the flux rope is driven by the nonlinear growth of several kink modes. In the case of a short flux rope, however, the flux rope ascension fails at some height. This suggests that the flux rope eruption must proceed through the multiple stages, which are driven by the loss of stability in the launching phase and by the loss of equilibrium in the late ascending phase. Since the short rope could not come up to the critical height for the transition from the first to the second stage, the ascending must stop. The role of magnetic reconnection in the late ascending phase and the formation mechanism of density cavity, which corresponds to dimming region observed in CMEs, is also discussed using the simulation results.

Large‐Scale Activities Associated with the 2003 October 29 X10 Flare

We present a multiwavelength study focusing on the large-scale activities associated with the 2003 October 29 X10 flare and a halo CME. This event was strong enough to clearly show several large-scale activities, such as remote brightenings, Moreton waves at Hα off-bands, and type II radio bursts, which offers an excellent opportunity to clarify the relationship among them. The remote brightenings were found near two coronal holes more than 2 × 105 km from the main flare in eastern and southern directions, respectively. Coronal dimmings were seen at the locus of the remote brightenings right after the flare at both EUV and soft X-ray wavelengths. The Moreton waves propagated both northeastward and southward, toward the aforementioned remote regions, at speeds of approximately 1100 and 1900 km s-1, respectively. Our analyses show that the Moreton waves, the type II radio bursts, and the CME started almost simultaneously, but were not cotemporal with the remote brightenings. The remote brightenings are rather consistent with the flare hard X-ray emissions within the active region, although they have much smaller scales. We therefore conclude that the two remote brightening regions were magnetically connected to the flaring active region, and that the remote brightenings, as well as all other activities, were due to the interaction of an erupting flux rope at the core of the flare with magnetic field overlying the region. In this scenario, the large overlying loops should open to allow the flare activity underneath them, which points to a picture similar to the magnetic break-out process in such a large scale.

Flux Rope Model of the 2003 October 28–30 Coronal Mass Ejection and Interplanetary Coronal Mass Ejection

A numerical model of an erupting solar flux rope is shown to reproduce both quantitative near-Sun properties of the 2003 October 28 coronal mass ejection and the timing, strength, and orientation of the fields measured in situ at 1 AU. Using a simple erupting flux rope model, we determine the best-fit parameters for this event. Our analysis shows that the orientation of the magnetic axis of the flux rope in this case rotates smoothly through approximately 50 � as thefluxropeapex expandsfromthe solar surface to1AU. Using aglobal magnetospheric simulation code,we further show that the resulting model solar wind properties at 1 AU produce a magnetospheric response comparable to that computed using the actual solar wind data.

MHD Numerical Simulation of Interdependent Flares and CMEs

Using time-dependent resistive magnetohydrodynamic simulations, we study a flux rope eruption caused by magnetic reconnection with implication in coexistent flare-CME events. Without the resistance the flux rope system presents a double catastrophe. We use the first catastrophic state as the initial condition, in which an isolated flux rope coexists with two current sheets: a vertical one below and a transverse one above the flux rope. The flux rope erupts when reconnection starts in the current sheets, and the flux rope dynamics depends on the reconnection sequence in the two current sheets. We obtain three cases: reconnection occurs (1) simultaneously in the two current sheets, (2) first in the transverse one and then in the vertical, and (3) in an order opposite to case 2. Such a model exhibits characteristics of both magnetic breakout model for CME initiation and standard flare model. We argue that both breakout-like and tether-cutting reconnections may be important for CME eruptions.

Two–Current‐Sheet Reconnection Model of Interdependent Flare and Coronal Mass Ejection

Time-dependent resistive magnetohydrodynamic simulations are carried out to study a flux rope eruption caused by magnetic reconnection with implication in coexistent flare-CME (coronal mass ejection) events. An early result obtained in a recent analysis of double catastrophe of a flux rope system is used as the initial condition, in which an isolated flux rope coexists with two current sheets: a vertical one below and a transverse one above the flux rope. The flux rope erupts when reconnection takes place in the current sheets, and the flux rope dynamics depends on the reconnection sequence in the two current sheets. Three cases are discussed: reconnection occurs (1) simultaneously in the two current sheets, (2) first in the transverse one and then in the vertical, and (3) in an order opposite to case 2. Such a two-current-sheet reconnection exhibits characteristics of both magnetic breakout for CME initiation and standard flare model. We argue that both breakout-like and tether-cutting reconnections may be important for CME eruptions and associated surface activities.

Slow‐Rise and Fast‐Rise Phases of an Erupting Solar Filament, and Flare Emission Onset

We observe the eruption of an active-region solar filament on 1998 July 11 using high time cadence and high spatial resolution EUV observations from the TRACE satellite, along with soft X-ray images from the soft X-ray telescope (SXT) on the Yohkoh satellite, hard X-ray fluxes from the BATSE instrument on the CGRO satellite and from the hard X-ray telescope (HXT) on Yohkoh, and ground-based magnetograms. We concentrate on the initiation of the eruption in an effort to understand the eruption mechanism. Prior to eruption the filament undergoes a slow upward movement in a slow-rise phase with an approximately constant velocity of ≈15 km s-1 that lasts about 10 minutes. It then erupts in a fast-rise phase, accelerating to a velocity of ≈200 km s-1 in about 5 minutes and then decelerating to ≈150 km s-1 over the next 5 minutes. EUV brightenings begin about concurrently with the start of the filament's slow rise and remain immediately beneath the rising filament during the slow rise; initial soft X-ray brightenings occur at about the same time and location. Strong hard X-ray emission begins after the onset of the fast rise and does not peak until the filament has traveled to a substantial altitude (to a height about equal to the initial length of the erupting filament) beyond its initial location. Our observations are consistent with the slow-rise phase of the eruption resulting from the onset of "tether cutting" reconnection between magnetic fields beneath the filament, and the fast rise resulting from an explosive increase in the reconnection rate or by catastrophic destabilization of the overlying filament-carrying fields. About 2 days prior to the event, new flux emerged near the location of the initial brightenings, and this recently emerged flux could have been a catalyst for initiating the tether-cutting reconnection. With the exception of the sudden transition from the slow-rise phase to the fast-rise phase in our event, our filament's height-time profile is qualitatively similar to the plot of the erupting flux rope height as a function of time recently computed by Chen and Shibata for a model in which the eruption is triggered by reconnection between an emerging field and another field under the flux rope.

Confined and Ejective Eruptions of Kink-unstable Flux Ropes

The ideal helical kink instability of a force-free coronal magnetic flux rope, anchored in the photosphere, is studied as a model for solar eruptions. Using the flux rope model of Titov and D?moulin as the initial condition in MHD simulations, both the development of helical shape and the rise profile of a confined (or failed) filament eruption (on 2002 May 27) are reproduced in very good agreement with the observations. By modifying the model such that the magnetic field decreases more rapidly with height above the flux rope, a full (or ejective) eruption of the rope is obtained in very good agreement with the developing helical shape and the exponential-to-linear rise profile of a fast coronal mass ejection (CME) on 2001 May 15. This confirms that the helical kink instability of a twisted magnetic flux rope can be the mechanism of the initiation and the initial driver of solar eruptions. The agreement of the simulations with properties that are characteristic of many eruptions suggests that they are often triggered by the kink instability. The decrease of the overlying field with height is a main factor in deciding whether the instability leads to a confined event or to a CME.

A slow coronal mass ejection with rising X-ray source

An eruptive event, which occurred on 16th April 2002, is discussed. Using images from the Transition Region and Coronal Explorer (TRACE) at 195 A, we observe a lifting flux rope which gives rise to a slow coronal mass ejection (CME). There are supporting velocity observations from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO), which illustrate the helical nature of the structure. Additionally a rising coronal hard X-ray source, which is observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), is shown to follow the flux rope with a speed of ∼60 km s −1 . It is also sampled by the CDS slit, although it has no signature in the Fe XIX band. Following the passage of this source, there is evidence from the CDS for down-flowing (cooling) material along newly reconnected loops through Doppler velocity observations, combined with magnetic field modeling. Later, a slow CME is observed with the Large Angle and Spectroscopic Coronagraph (LASCO). We combine a height-time profile of the flux rope at lower altitudes with the slow CME. The rising flux rope speeds up by a factor of 1.7 at the start of the impulsive energy release and goes through further acceleration before reaching 1.5 solar radii. These observations support classical CME scenarios in which the eruption of a filament precedes flaring activity. Cusped flare loops are observed following the erupting flux rope and their altitude increases with time. In addition we find RHESSI sources both below and above the probable location of the reconnection region.

A Full View of EIT Waves

Early observations by the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory indicated that propagating diffuse fronts, now conventionally referred to as can often be seen on the solar disk with a propagation velocity several times smaller than that of Hα Moreton waves. They are almost always associated with coronal mass ejections. We have previously confirmed the existence of such a phenomenon with numerical simulations, which indicate that there does exist a slower moving much behind the coronal counterpart of the Hα Moreton wave. Further observations have disclosed many new features of the EIT waves: the waves stop near the separatrix between active regions, sometimes they experience acceleration from the active region to the quiet region, and so on. Here we report on MHD simulations performed to demonstrate how the typical features of EIT waves can all be accounted for within our theoretical model, in which the EIT waves are thought to be formed by successive stretching or opening of closed field lines driven by an erupting flux rope. The relationship between EIT waves, Hα Moreton waves, and type II radio bursts is discussed, with an emphasis on reconciling the discrepancies among different views of the wave phenomenon.

Why are there stationary EIT wave fronts

EIT waves are often observed to be propagating EUV enhancements followed by an expanding dimming region after the launch of CMEs. It was widely assumed that they are the coronal counterparts of the chromospheric Moreton waves, though the former are three or more times slower. The existence of a stationary “EIT wave” front in some events, however, posed a big challenge to the wave explanation. Simulations are performed to reproduce the stationary “EIT wave” front, which is exactly located near the footpoint of the magnetic separatrix, consistent with observations. The formation of the stationary front is explained in the framework of our model where “EIT waves” are supposed to be generated by successive opening of the field lines covering the erupting flux rope in CMEs.

Magnetic Reconnection Rate and Flux‐Rope Acceleration of Two‐Ribbon Flares

Forbes & Lin derived simple equations to link the properties of magnetic reconnection in the corona to observed signatures of solar flares. We measured the photospheric magnetic fields and the flare ribbon separation speeds then applied these equations to derive two physical terms for the magnetic reconnection rates: the rate of magnetic flux change rec involved in magnetic reconnection in the low corona and the electric field Erec inside the reconnecting current sheet (RCS) that is generated during magnetic reconnection. The central interest in this work is to investigate and quantify the statistical correlation between the magnetic reconnection rate and the corresponding flux-rope acceleration. From a sample of 13 well-observed two-ribbon flares, which are associated with filament eruptions or coronal mass ejections (CMEs), the acceleration of erupting filaments is found mainly in the range of 0.05-0.4 km s-2, up to 3 km s-2. Correspondingly, the maximum Erec and rec mostly occur in the range of 0.2-5 V cm-1 and 0.5-6 × 1018 Mx s-1, respectively. A positive and strong correlation is found with a cross-correlation coefficient of 0.94-0.97 between the magnetic reconnection rate and the acceleration of erupting filaments that represents the early stages of flux-rope eruptions in the low corona. However, the inferred reconnection rate is not correlated to the acceleration of CME fronts measured by the Large Angle and Spectrometric Coronagraph (LASCO) observations in the range of 2-30 solar radii (the correlation coefficient is less than 0.2). A reasonable correlation is found between the reconnection rate and the velocity of CMEs, which indicates the cumulative acceleration of CMEs from the low corona to the LASCO C2 field of view. The temporal correlation between the magnetic reconnection rate and the flare nonthermal emissions has also been verified in this paper.

Properties of Remote Flare Ribbons Associated with Coronal Mass Ejections

To understand the large-scale structure of flares and coronal mass ejections, we studied the motion and properties of remote flare ribbons of three major events: 2003 May 27 X1.3, 2000 November 24 X1.8, and 2000 November 25 X1.9 flares. The remote ribbons are in addition to the typical two-ribbon pairs in the flare cores. We found two common properties of these three events. First, the flare core occurs at the edge of a major sunspot, associated with flux emergence parallel to the edge. Such a flux emergence formed complicated magnetic channel structure. Second, three flare ribbons are visible for each event. The first two make up a typical two-ribbon structure near the flare core. The third ribbon (remote ribbon) moves away from the flare site at a speed between 30 and 100 km s-1, several times larger than the nominal two-ribbon separation speed of flares. It is interesting to note that for the 2000 November 25 event, the remote ribbon first moved away in the same manner as the other two events; it then retracted after the flare emission peaked. We compared such an expansion/retraction motion with a limb event observed on 2001 April 15. We interpret the observed motion of remote ribbons by the interaction between the erupting flux rope in the flare core region and the overlying large-scale magnetic fields. For the 2000 November 25 event, the overlying field and flare core fields interacted twice, during the outward and inward motions.

2 1/2-Dimensional Reconnection Model and Energy Release in Solar Flares

We employ a 2 1/2-dimensional reconnection model to analyse different aspects of the energy release in two-ribbon flares. In particular, we investigate in which way the systematic change of inflow region variables, associated with the vertical elongation of current sheet, affects the flare evolution. It is assumed that as the transversal magnetic field decreases, the ambient plasma-to-magnetic pressure ratio increases, and the reconnection rate diminishes. As the transversal field decreases due to the arcade stretching, the energy release enhances and the temperature rises. Furthermore, the magnetosonic Mach number of the reconnection outflow increases, providing the formation of fast mode standing shocks above the flare loops and below the erupting flux rope. Eventually, in the limit of a very small transversal field the reconnection becomes turbulent due to a highly non-linear response of the system to small fluctuations of the transversal field. The turbulence results in the energy release fragmentation which increases the release efficiency, and is likely to be responsible for the impulsive phase of the flare. On the other hand, as the current sheet stretches to larger heights, the ambient plasma-to-magnetic pressure ratio increases which causes a gradual decrease of the reconnection rate, energy release rate, and temperature in the late phase of flare. The described magnetohydrodynamical changes affect also the electron distribution function in space and time. At large reconnection rates (impulsive phase of the flare) the ratio of the inflow-to-outflow magnetic field strength is much smaller than at lower reconnection rates (late phase of the flare), i.e., the corresponding loss-cone angle becomes narrower. Consequently, in the impulsive phase a larger fraction of energized electrons can escape from the current sheet downwards to the chromosphere and upwards into the corona – the dominant flare features are the foot-point hard X-ray sources and type III radio bursts. On the other hand, at low reconnection rates, more particles stay trapped in the outflow region, and the thermal conduction flux becomes strongly reduced. As a result, a superhot loop-top, and above-the-loop plasma appears, as sometimes observed, to be a dominant feature of the gradual phase.

The Catastrophe of Coronal Magnetic Flux Ropes in CMEs

A brief review is given on the progress made in the study of the catastrophe of coronal magnetic flux ropes with implication in coronal mass ejections (CMEs). Relevant studies have been so far limited to 2.5-D cases, with a flux rope levitating in the corona, either parallel to the photosphere in Cartesian geometry or encircling the Sun like a torus in spherical geometry. The equilibrium properties of the system depend on the features of the flux rope and the surrounding background state. Under certain circumstances, the flux rope exhibits a catastrophic behavior, namely, the rope loses equilibrium and erupts upward upon an infinitesimal variation of any control parameter associated with the background state or the flux rope. The magnetic energy of the system right at the catastrophic point may exceed the corresponding open field energy so that after the background field is opened up by the erupting flux rope, a certain amount of magnetic free energy is left for the heating and acceleration of coronal plasma against gravity. The flux rope model has been used to reveal the common features of CMEs and to simulate typical CME events, proving to be a promising mechanism for the initiation of CMEs. Incidentally, the Aly conjecture on the maximum magnetic energy of force-free fields places a serious constraint on 2.5-D flux models. Nevertheless, current sheets must form during a catastrophe on the Alfven timescale, and magnetic reconnection across the newly formed current sheets may contribute to circumventing such a constraint. In this sense, the catastrophe simply plays a role of driver for the fast magnetic reconnection, and a combination of them is thus responsible for the initiation of CMEs.

Formation of Opposite-Sign Magnetic Helicity by an Erupting Filament in a Coronal Mass Ejection

Abstract It is unclear whether it is possible for magnetic helical fields of opposite signs to co-exist in a coronal mass ejection (CME). During filament eruption with high-cadence observations for the initial stage, evidence is found for the formation of right-handed helical fields in a rising dextral filament that is embedded in a CME with helical fields in a left-handed sense. The data include Mees multi-off-band $\mathrm{H}\alpha$ observations with 16 s cadence and TRACE 1600 Å observations of 2 s cadence. The filament material is ejected outward and is associated with the expanding CME, suggesting that both of the opposite-sign helical fields are injected into interplanetary space. In this paper, we consider the key observational features, including the formation of a coil-like structure (due to barb reconnections) and the alignment of reconnected field lines with the primary axis of the filament. It is found that they are consistent with the predicted changes during filament eruption by the filament model of Martin and McAllister. However, our results do not reject the filament model of Rust and Kumar. Moreover, a model that reconciles both of them seems to be more convenient for understanding the complicated observations. Therefore, the formation of opposite-sign helicity in an eruptive flux rope should be common for such types of filament eruptions.

Magnetic Reconnection and Mass Acceleration in Flare–Coronal Mass Ejection Events

An observational relationship has been well established among magnetic reconnection, high-energy flare emissions and the rising motion of erupting flux ropes. In this paper, we verify that the rate of magnetic reconnection in the low corona is temporally correlated with the evolution of flare nonthermal emissions in hard X-rays and microwaves, all reaching their peak values during the rising phase of the soft X-ray emission. In addition, however, our new observations reveal a temporal correlation between the magnetic reconnection rate and the directly observed acceleration of the accompanying coronal mass ejection (CME) and filament in the low corona, thus establishing a correlation with the rising flux rope. These results are obtained by examining two well-observed two-ribbon flare events, for which we have good measurements of the rise motion of filament eruption and CMEs associated with the flares. By measuring the magnetic flux swept through by flare ribbons as they separate in the lower atmosphere, we infer the magnetic reconnection rate in terms of the reconnection electric field Erec inside the reconnecting current sheet (RCS) and the rate of magnetic flux convected into the diffusion region. For the X1.6 flare event, the inferred Erec is ~5.8 V cm-1 and the peak mass acceleration is ~3 km s-2, while for the M1.0 flare event Erec is ~0.5 V cm-1 and the peak mass acceleration is 0.2-0.4 km s-2.

Observational Evidence of a Magnetic Flux Rope Eruption Associated with the X3 Flare on 2002 July 15

We present the study of an eruption from the low solar atmosphere (photosphere/chromosphere) as seen in Transition Region and Coronal Explorer 1600 Angstrom images and with the Solar and Heliospheric Observatory Michelson Doppler Imager. The eruption reached its maximum at 20: 08 UT on 2002 July 15 in the NOAA Active Region 10030 ( N19degrees, W01degrees), accompanied by an X3 flare and followed by a fast-halo coronal mass ejection. The main observational results from the data are as follows: ( 1) the erupting plasma was in a rapidly rising, twisted ropelike structure; ( 2) the eruption occurred just preceding the onset of its driven flare; and (3) the morphology and magnetic flux of one slender footpoint (similar to9000 km in length) of the rope developed rapidly on the photosphere. This structure disappeared in white light and in the magnetograms within 60 minutes. This evidence supports the erupting flux rope model. Our data favor the idea that a catastrophic loss of MHD equilibrium can be the primary driving mechanism for the rapid ejection of a flux rope. This conclusion is based on the judgment that the ambient fields of the flux rope were partly opened as a result of the magnetic reconnection.

Core and Large‐Scale Structure of the 2000 November 24 X‐Class Flare and Coronal Mass Ejection

In this paper, we present three important aspects of the XI .8 flare and the associated coronal mass ejection (CME) that occurred on 2000 November 24: (1) The source of the flare is clearly associated with a magnetic channel structure, as was noted in a study by Zirin & Wang , which is due to a combination of flux emergence inside the leading edge of the penumbra of the major leading sunspot and proper motion of the sunspot group. The channel structure provides evidence for twisted flux ropes that can erupt, forming the core of a CME, and may be a common property of several superactive regions that have produced multiple X-class flares in the past. (2) There are actually three flare ribbons visible. The first can be seen moving away from the flare site, while the second and third make up a stationary ribbon near the leader spot. The moving ribbons could be due to a shock associated with the erupting flux rope or due to the interaction of erupting rope and the surrounding magnetic fields. In either case, the ribbon motion does not fit the classical Kopp-Pneuman model, in which the separation of ribbons is due to magnetic reconnection at successively higher and higher coronal altitudes. (3) From the coronal dimming observed with the EUV Imaging Telescope (EIT), the CME involved a much larger region than the initial X-class flare. By comparing high-resolution full-disk Ha and EIT observations, we found that a remote dimming area is cospatial with the enhanced Ha emission. This result is consistent with the recent model of Yokoyama & Shibata that some dimming areas near footpoints may be due to chromospheric evaporation.