Two X-class solar flares occurred on 2017 September 6 from active region NOAA 12673: the first one is a confined X2.2 flare, and it is followed only $\sim 3$ hours later by the second one, which is the strongest flare in solar cycle 24, reaching X9.3 class and accompanied with a coronal mass ejection. Why these two X-class flares occurred in the same position with similar magnetic configurations, but one is eruptive while the other is not? Here we track the coronal magnetic field evolution via nonlinear force-free field extrapolations from a time sequence of vector magnetograms with high cadence. A detailed analysis of the magnetic field shows that a magnetic flux rope (MFR) forms and grows gradually before the first flare, and shortly afterwards, the MFR's growth is significantly enhanced with a much faster rise in height, from far below the threshold of torus instability to above it, while the magnetic twist only increases mildly. Combining EUV observations and the magnetic field extrapolation, we found that overlying the MFR is a null-point magnetic topology, where recurrent brightening is seen after the first flare. We thus suggest a scenario to interpret the occurrence of the two flares. The first flare occurred since the MFR reached a high enough height to activate the null point, and its continuous expansion forces the null-point reconnection recurrently. Such reconnection weakens the overlying field, allowing the MFR to rise faster, which eventually crosses the threshold of torus instability and triggers the second, eruptive flare.
Zipper reconnection has been proposed as a mechanism for creating most of the twist in the flux tubes that are present prior to eruptive flares and coronal mass ejections. We have conducted a first numerical experiment on this new regime of reconnection, where two initially untwisted parallel flux tubes are sheared and reconnected to form a large flux rope. We describe the properties of this experiment, including the linkage of magnetic flux between concentrated flux sources at the base of the simulation, the twist of the newly formed flux rope and the conversion of mutual magnetic helicity in…
The interaction between interplanetary small-scale magnetic flux ropes and the magnetic field in the ambient solar wind is an important topic to understand- ing the evolution of magnetic structures in the heliosphere. Through a survey of 125 previously reported small flux ropes from 1995 to 2005, we find that 44 of them reveal clear signatures of Alfvenic fluctuations, and thus classify them into Alfven wave trains rather than flux ropes. Signatures of magnetic reconnection, generally including a plasma jet of ~30 km/s within a magnetic field rotational region, are clearly present at boundarie…
Large-scale solar eruptive activities have a close relationship with coronal magnetic flux ropes. Previous numerical studies have found that the equilibrium of a coronal flux rope system could be disrupted if the axial magnetic flux of the rope exceeds a critical value, so that the catastrophe occurs, initiating the flux rope to erupt. Further studies discovered that the catastrophe does not necessarily exist: the flux rope system with certain photospheric flux distributions could be non-catastrophic. It is noteworthy that most previous numerical studies are under the ideal magnetohydrodynamic…
The nature of three-dimensional reconnection when a twisted flux tube erupts during an eruptive flare or coronal mass ejection is considered. The reconnection has two phases: first of all, 3D "zipper reconnection" propagates along the initial coronal arcade, parallel to the polarity inversion line (PIL), then subsequent quasi-2D "main phase reconnection" in the low corona around a flux rope during its eruption produces coronal loops and chromospheric ribbons that propagate away from the PIL in a direction normal to it. One scenario starts with a sheared arcade: the zipper reconnection creates …
Parker's magnetostatic theorem extended to astrophysical magnetofluids with large magnetic Reynolds number supports ceaseless regeneration of current sheets and hence, spontaneous magnetic reconnections recurring in time. Consequently, a scenario is possible where the repeated reconnections provide an autonomous mechanism governing emergence of coherent structures in astrophysical magnetofluids. In this work, such a scenario is explored by performing numerical computations commensurate with the magnetostatic theorem. In particular, the computations explore the evolution of a flux-rope governed…
Numerical simulations of the helical ($m\!=\!1$) kink instability of an arched, line-tied flux rope demonstrate that the helical deformation enforces reconnection between the legs of the rope if modes with two helical turns are dominant as a result of high initial twist in the range $Φ\gtrsim6π$. Such reconnection is complex, involving also the ambient field. In addition to breaking up the original rope, it can form a new, low-lying, less twisted flux rope. The new flux rope is pushed downward by the reconnection outflow, which typically forces it to break as well by reconnecting with the ambi…
Oscillatory reconnection is a process that has been suggested to underlie several solar and stellar phenomena, and is likely to play an important role in transient events such as flares. Quasi-periodic pulsations (QPPs) in flare emissions may be a manifestation of oscillatory reconnection, but the underlying mechanisms remain uncertain. In this paper, we present 2D magnetohydrodynamic (MHD) simulations of two current-carrying magnetic flux ropes with an out-of-plane magnetic field undergoing oscillatory reconnection in which the two flux ropes merge into a single flux rope. We find that oscill…
We firstly report the simultaneous activities of a slipping motion of flare loops and a slipping eruption of a flux rope in 131 Å and 94 Å channels on 2014 February 02. The east hook-like flare ribbon propagated slippingly at a speed of about 50 km s$^{-1}$, which lasted about 40 min and extended by more than 100 Mm, but the west flare ribbon moved in the opposite direction with a speed of 30 km s$^{-1}$. At the later phase of the flare activity, a "bi-fan" system of flare loops was well developed. The east footpoints of the flux rope showed an apparent slipping motion along the hook of the ri…
We present the quasi-periodic slipping motion of flux rope structures prior to the onset of an eruptive X-class flare on 2015 March 11, obtained by the \emph{Interface Region Imaging Spectrograph} (\emph{IRIS}) and the \emph{Solar Dynamics Observatory} (\emph{SDO}). The slipping motion occurred at the north part of the flux rope and seemed to successively peel off the flux rope. The speed of the slippage was 30$-$40 km s$^{-1}$, with an average period of 130$\pm$30 s. The Si {\sc iv} 1402.77 Å line showed a redshift of 10$-$30 km s$^{-1}$ and a line width of 50$-$120 km s$^{-1}$ at the west le…
Reconnection Jets Detected during the Footpoint Drift of a CME Flux Rope: New Signatures of Ongoing 3D Arcade-Flux Rope Reconnection
School of Physics and Astronomy, Yunnan University（云南大学物理与天文学院）；Department of Astronomy, Key Laboratory of Astroparticle Physics of Yunnan Province, Yunnan University（云南大学天文学系、云南省天体粒子物理重点实验室）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）
Using a 3D MHD simulation, we model the quasi-static evolution and the onset of eruption of a coronal flux rope. The simulation begins with a twisted flux rope emerging at the lower boundary and pushing into a pre-existing coronal potential arcade field. At a chosen time the emergence is stopped with the lower boundary taken to be rigid. Then the coronal flux rope settles into a quasi-static rise phase during which an underlying, central sigmoid-shaped current layer forms along the so called hyperbolic flux tube (HFT), a generalization of the X-line configuration. Reconnections in the dissipat…
We present results from 3D magnetohydrodynamic (MHD) simulations of the emergence of a twisted convection zone flux tube into a pre-existing coronal dipole field. As in previous simulations, following the partial emergence of the sub-surface flux into the corona, a combination of vortical motions and internal magnetic reconnection forms a coronal flux rope. Then, in the simulations presented here, external reconnection between the emerging field and the pre-existing dipole coronal field allows further expansion of the coronal flux rope into the corona. After sufficient expansion, internal reco…
We study the early evolution of a hot-channel-like magnetic flux rope (MFR) toward eruption. Combining with imaging observation and magnetic field extrapolation, we find that the hot channel possibly originated from a pre-existing seed MFR with a hyperbolic flux tube (HFT). In the precursor phase, three-dimensional tether-cutting reconnection at the HFT is most likely resulting in the heating and buildup of the hot channel. In this process, the forming hot channel was rapidly enlarged at its spatial size and slipped its feet to two remote positions. Afterward, it instantly erupted outwards wit…
Using high-resolution observations from the 1.6 m New Solar Telescope (NST) operating at the Big Bear Solar Observatory (BBSO), we report direct evidence of merging/reconnection of cool H$α$ loops in the chromosphere during two homologous flares (B- and C-class) caused by a shear motion at the footpoint of two loops. The reconnection between these loops caused the formation of an unstable flux rope which showed counterclockwise rotation. The flux rope could not reach the height of torus instability and failed to form a coronal mass ejection. The HMI magnetograms revealed rotation of the negati…
One of the major discoveries of Hinode's Extreme-ultraviolet Imaging Spectrometer (EIS) is the presence of upflows at the edges of active regions. As active regions are magnetically connected to the large-scale field of the corona, these upflows are a likely contributor to the global mass cycle in the corona. Here we examine the driving mechanism(s) of the very strong upflows with velocities in excess of 70 km/s, known as blue-wing asymmetries, observed during the eruption of a flux rope in AR 10977 (eruptive flare SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations combined wit…
Radio, X-ray, and EUV signatures of internal and external reconnection of an erupting flux rope
Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；University of Applied Sciences and Arts Northwestern Switzerland（瑞士西北应用科学与艺术大学）；Space Sciences Laboratory, University of California Berkeley（加州大学伯克利分校空间科学实验室）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；Astronomical Institute, Slovak Academy of Sciences（斯洛伐克科学院天文研究所）
Using high-resolution images from 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO), we report the direct evidence of chromospheric reconnection at the polarity inversion line (PIL) between two small opposite polarity sunspots. Small jet-like structures (with velocities of ~20-55 km/s) were observed at the reconnection site before the onset of the first M1.0 flare. The slow rise of untwisting jets was followed by the onset of cool plasma inflow (~10 km/s) at the reconnection site, causing the onset of a two-ribbon flare. The reconnection between two sheared J-shaped cool H$α…
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 Lunquist 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 oscillati…
The structure of magnetic flux ropes injected into the solar wind during reconnection in the coronal atmosphere is explored with particle-in-cell simulations and compared with in situ measurements of magnetic "switchbacks" from the Parker Solar Probe. We suggest that multi-x-line reconnection between open and closed flux in the corona injects flux ropes into the solar wind and that these flux ropes convect outward over long distances before eroding due to reconnection. Simulations that explore the magnetic structure of flux ropes in the solar wind reproduce the following key features of the sw…
The solar corona is frequently disrupted by coronal mass ejections (CMEs), whose core structure is believed to be a flux rope made of helical magnetic field. This has become a "standard" picture although it remains elusive how the flux rope forms and evolves toward eruption. While 1/3 of the ejecta passing through spacecrafts demonstrate a flux-rope structure, the rest have complex magnetic fields. Are they originating from a coherent flux rope, too? Here we investigate the source region of a complex ejecta, focusing on a flare precursor with definitive signatures of magnetic reconnection, i.e…
Magnetic reconnection is essential to release the flux rope during its ejection. The question remains: how does the magnetic reconnection change the flux rope structure? Following the original study of \citet{Qiu2007}, we compare properties of ICME/MC flux ropes measured at 1 AU and properties of associated solar progenitors including flares, filaments, and CMEs. In particular, the magnetic field-line twist distribution within interplanetary magnetic flux ropes is systematically derived and examined. Our analysis shows that for most of these events, the amount of twisted flux per AU in MCs is …
The kinetic features of secondary magnetic reconnection in a single flux rope undergoing internal kink instability are studied by means of three-dimensional Particle-in-Cell simulations. Several signatures of secondary magnetic reconnection are identified in the plane perpendicular to the flux rope: a quadrupolar electron and ion density structure and a bipolar Hall magnetic field develop in proximity of the reconnection region. The most intense electric fields form perpendicularly to the local magnetic field, and a reconnection electric field is identified in the plane perpendicular to the fl…
We present an analysis of the formation of atmospheric flux ropes in a magnetohydrodynamic (MHD) solar flux emergence simulation. The simulation domain ranges from the top of the solar interior to the low corona. A twisted magnetic flux tube emerges from the solar interior and into the atmosphere where it interacts with the ambient magnetic field. By studying the connectivity of the evolving magnetic field, we are able to better understand the process of flux rope formation in the solar atmosphere. In the simulation, two flux ropes are produced as a result of flux emergence. Each has a differe…
In this paper, we present multiwavelength observations of the triggering of a failed-eruptive M-class flare from the active region NOAA 11302, and investigate the possible reasons for the associated failed eruption. Photospheric observations and Non-Linear Force Free Field extrapolated coronal magnetic field revealed that the flaring region had a complex quadrupolar configuration with a pre-existing coronal null point situated above the core field. Prior to the onset of the M-class flare, we observed multiple periods of small-scale flux enhancements in GOES and RHESSI soft X-ray observations, …
Triggering mechanisms of solar eruptions have long been a challenge. A few previous case studies have indicated that preceding gentle filament merging via magnetic reconnection may launch following intense eruption, according with the tether-cutting (TC) model. However, detailed process of TC reconnection between filaments has not been exhibited yet. In this work, we report the high resolution observations from the Interface Region Imaging Spectrometer (IRIS) of TC reconnection between two sheared filaments in NOAA active region 12146. The TC reconnection commenced since 15:35 UT on 2014 Augus…
In past decades, much progress has been achieved on the origin and evolution of coronal mass ejections (CMEs). In-situ observations of the counterparts of CMEs, especially magnetic clouds (MCs) near the Earth, have provided measurements of the structure and total flux of CME flux ropes. However, it has been difficult to measure these properties in the erupting CME flux rope, in particular in the pre-existing flux rope. In this work, we propose a model to estimate the toroidal flux of the pre-existing flux rope by subtracting the flux contributed by magnetic reconnection during the eruption fro…
In this letter, we present a spectacular eruptive flare (X8.2) associated with a coronal mass ejection (CME) on 2017 September 10 at the west limb of the Sun. A flux rope eruption is followed by the inflow, the formation of a current sheet and a cusp structure, which were simultaneously observed during the occurrence of this flare. The hierarchical layers of the cusp-shaped structure are well observed in 131 Å observation. The scenario that can be created from these observations is very consistent with the predictions of some eruptive models. Except for the characteristics mentioned above in t…
A standard model for eruptive flares aims at describing observational 3D features of the reconnecting coronal magnetic field. Extensions to the 2D model require the physical understanding of 3D reconnection processes at the origin of the magnetic configuration evolution. However, the properties of 3D reconnection without null point and separatrices still need to be analyzed. We focus on magnetic reconnection associated with the growth and evolution of a flux rope and associated flare loops during an eruptive flare. We aim at understanding the intrinsic characteristics of 3D reconnection in the…
Existing 3D extensions to the standard model show that flux-rope footpoints are surrounded by curved-shaped QSL-footprints that can be related with hook-shaped flare-ribbons. We build upon this finding and further address the joint questions of their time-evolution, and of the formation of flare loops at the ends of flaring PILs of the erupting bipole, which are both relevant for flare understanding in general and for ICME studies in particular. We calculate QSLs and relevant field lines in an MHD simulation of a torus-unstable flux-rope. The evolving QSL footprints are used to define the oute…
Context. Some of the most dynamic active regions are associated with complex photospheric magnetic configurations such as quadrupolar regions, and especially ones with 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. 3D MHD simulations of the partial emergence of a highly twisted flux tube from the solar interior into a non-magnetized stratified atmosphere. Results. We emerge two $Ω$-shaped loops forming a quadrupolar region. The emerging flux forms two initially separated bipo…
Solar filament eruptions play a crucial role in triggering coronal mass ejections (CMEs). More than 80 % of eruptions lead to a CME. This correlation has been studied extensively during the past solar cycles and the last long solar minimum. The statistics made on events occurring during the rising phase of the new solar cycle 24 is in agreement with this finding. Both filaments and CMEs have been related to twisted magnetic fields. Therefore, nearly all the MHD CME models include a twisted flux tube, called a flux rope. Either the flux rope is present long before the eruption, or it is built u…
We investigated the dynamic evolution of a 3-dimensional (3D) flux rope eruption and magnetic reconnection process in a solar flare, by simply extending 2-dimensional (2D) resistive magnetohydrodynamic simulation model of solar flares with low $β$ plasma to 3D model. We succeeded in reproducing a current sheet and bi-directional reconnection outflows just below the flux rope during the eruption in our 3D simulations. We calculated four cases of a strongly twisted flux rope and a weakly twisted flux rope in 2D and 3D simulations. The time evolution of a weakly twisted flux rope in 3D simulation…
Coronal mass ejections (CMEs) are large-scale explosions of the coronal magnetic field. It is believed that magnetic reconnection significantly builds up the core structure of CMEs, a magnetic flux rope, during the eruption. However, the quantitative evolution of the flux rope, particularly its toroidal flux, is still unclear. In this paper, we study the evolution of the toroidal flux of the CME flux rope for four events. The toroidal flux is estimated as the magnetic flux in the footpoint region of the flux rope, which is identified by a method that simultaneously takes the coronal dimming an…
The slow solar wind exhibits strong variability on timescales from minutes to days, likely related to magnetic reconnection processes in the extended solar corona. Higginson2017b presented a numerical magnetohydrodynamic simulation which showed interchange magnetic reconnection is ubiquitous and most likely responsible for releasing much of the slow solar wind, in particular along topological features known as the Separatrix-Web (S-Web). Here, we continue our analysis, focusing on two specific aspects of structured slow solar wind variability. The first type is present in the slow solar wind f…
We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the Solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find that the flux rope dynamo is more than an order of magnitude more efficient at converting mechanical energ…
We report on observations of the two newly-identified reconnection geometries involving erupting flux ropes. In 3D, a flux rope can reconnect either with a surrounding coronal arcade (recently named "ar-rf" reconnection) or with itself ("rr-rf" reconnection), and both kinds of reconnection create a new flux rope field line and a flare loop. For the first time, we identify all four constituents of both reconnections in a solar eruptive event, the filament eruption of 2011 June 07 observed by SDO/AIA. The ar-rf reconnection manifests itself as shift of one leg of the filament by more than 25" no…
The relaxation of field-line tension during magnetic reconnection gives rise to a universal Fermi acceleration process involving the curvature drift of particles. However, the efficiency of this mechanism is limited by the trapping of energetic particles within flux-ropes. Using 3D fully kinetic simulations, we demonstrate that the flux-rope kink instability leads to strong field-line chaos in weak-guide-field regimes where the Fermi mechanism is most efficient, thus allowing particles to transport out of flux-ropes and undergo further acceleration. As a consequence, both ions and electrons de…
The X1 flare and associated filament eruption occurring in NOAA Active Region 12017 on SOL2014-03-29 has been the source of intense study. In this work, we analyse the results of a series of non linear force free field extrapolations of the pre and post flare period of the flare. In combination with observational data provided by the IRIS, Hinode and SDO missions, we have confirmed the existence of two flux ropes present within the active region prior to flaring. Of these two flux ropes, we find that intriguingly only one erupts during the X1 flare. We propose that the reason for this is due t…
We performed magnetohydrodynamic simulation of a formation process of coronal mass ejections (CMEs), focusing on interaction (reconnection) between an ejecting flux rope and its ambient field. We examined three cases with different ambient fields: no ambient field, and cases with dipole field of two opposite directions which are parallel and anti-parallel to that of the flux rope surface. As a result, while the flux rope disappears in the anti-parallel case, in other cases the flux ropes can evolve to CMEs and show different amounts of rotation of the flux rope. The results imply that the inte…
The work extends the computational model EULAG-MHD to include Hall magnetohydrodynamics (HMHD)---important to explore physical systems undergoing fast magnetic reconnection at the order of the ion inertial length scale. Examples include solar transients along with reconnections in magnetosphere, magnetotail and laboratory plasmas. The paper documents the results of two distinct sets of implicit large-eddy simulations in the presence and absence of the Hall forcing term, initiated with an unidirectional sinusoidal magnetic field. The HMHD simulation while benchmarking the code also emphasizes t…
Flux rope formation through flux cancellation of sheared coronal arcades in a 3D convectively-driven MHD simulation
University of Oslo（奥斯陆大学）；Sorbonne Université, Observatoire de Paris-PSL, École Polytechnique, IP Paris, CNRS, Laboratoire de Physique des Plasmas（索邦大学，巴黎天文台-PSL，巴黎综合理工学院，IP巴黎，法国国家科学研究中心，等离子体物理实验室）
Evolution of reconnection flux during eruption of magnetic flux ropes
Indian Institute of Astrophysics（印度天体物理研究所）；Joint Astronomy Programme and Department of Physics, Indian Institute of Science（印度科学学院天文联合项目与物理系）；University of Helsinki（赫尔辛基大学）；Amrita School of Physical Science, Amrita Vishwa Vidyapeetham（阿莫瑞塔维斯瓦维德亚佩坦姆大学阿莫瑞塔理学院）
We study the magnetic field structures of hard X-ray sources and flare ribbons of the M1.1 flare in active region NOAA 10767 on 2005 May 27. We have found in a nonlinear force-free field extrapolation, over the same polarity inversion line, a small pre-eruptive magnetic flux rope located next to sheared magnetic arcades. Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Transition Region and Coronal Explorer (TRACE) observed this confined flare in the X-ray bands and ultraviolet (UV) 1600 Å\ bands, respectively. In this event magnetic reconnection occurred at several locations. It fir…
We perform a numerical study of the evolution of a Coronal Mass Ejection (CME) and its interaction with the coronal magnetic field based on the May 12, 1997, CME event using a global MagnetoHydroDynamic (MHD) model for the solar corona. The ambient solar wind steady-state solution is driven by photospheric magnetic field data, while the solar eruption is obtained by superimposing an unstable flux rope onto the steady-state solution. During the initial stage of CME expansion, the core flux rope reconnects with the neighboring field, which facilitates lateral expansion of the CME footprint in th…
It is well known that solar flares have broad impacts on the low atmosphere, but it is largely unknown how they affect sunspot waves and oscillations. It is also under debate as to whether the flare-induced photospheric changes are due to the momentum conservation with coronal mass ejections or due to magnetic reconnection. To shed light on the so-called "back reaction" of solar eruptions, we investigated how running penumbral waves (RPWs) at one foot of an erupting magnetic flux rope (MFR) responds to the rope buildup and subsequent erosion. During the rope-buildup stage, the western foot of …
We present the multi-wavelength observations of a flux rope that was trying to erupt from NOAA AR 11045 and the associated M-class solar flare on 12 February 2010 using space and ground based observations from TRACE, STEREO, SOHO/MDI, Hinode/XRT and BBSO. While the flux rope was rising from the active region, an M1.1/2F class flare was triggered nearby one of its footpoints. We suggest that the flare triggering was due to the reconnection of a rising flux rope with the surrounding low-lying magnetic loops. The flux rope reached a projected height of ~0.15 Rs with a speed of ~90 km/s while the …
The nature of various plausible causal links between sympathetic events is still a controversial issue. In this work, we present multi-wavelength observations of sympathetic eruptions, associated flares and coronal mass ejections (CMEs) occurring on 2013 November 17 in two close-by active regions. Two filaments i.e., F1 and F2 are observed in between the active regions. Successive magnetic reconnections, caused by different reasons (flux cancellation, shear and expansion) have been identified during the whole event. The first reconnection occurred during the first eruption via flux cancellatio…
We present evidence that a magnetic flux rope was formed before a coronal mass ejection (CME) and its associated long-duration flare during a pair of preceding confined eruptions and associated impulsive flares in a compound event in NOAA Active Region 12371. Extreme-ultraviolet images and the extrapolated nonlinear force-free field show that the first two, impulsive flares, SOL2015-06-21T01:42, result from the confined eruption of highly sheared low-lying flux, presumably a seed flux rope. The eruption spawns a vertical current sheet, where magnetic reconnection creates flare ribbons and loop…
Context: Many previous studies have shown that the magnetic precursor of a coronal mass ejection (CME) takes the form of a magnetic flux rope, and a subset of them have become known as `hot flux ropes' due to their emission signatures in $\sim$10 MK plasma. Aims: We seek to identify the processes by which these hot flux ropes form, with a view of developing our understanding of CMEs and thereby improving space weather forecasts. Methods: Extreme-ultraviolet observations were used to identify five pre-eruptive hot flux ropes in the solar corona and study how they evolved. Confined flares were o…
Imaging microwave observations of an eruptive, partially occulted solar flare on 18 April 2001 suggest that the global structure of the event can be described by the helical kink instability of a twisted magnetic flux rope. This model is suggested by the inverse gamma shape of the source exhibiting crossing legs of a rising flux loop and by evidence that the legs interact at or near the crossing point. The interaction is reflected by the location of peak brightness near the crossing point and by the formation of superimposed compact nonthermal sources most likely at or near the crossing point.…
We propose a reconnection-condensation model in which topological change in a coronal magnetic field via reconnection triggers radiative condensation, thereby resulting in prominence formation. Previous observational studies have suggested that reconnection at a polarity inversion line of a coronal arcade field creates a flux rope that can sustain a prominence; however, they did not explain the origin of cool dense plasmas of prominences. Using three-dimensional magnetohydrodynamic simulations including anisotropic nonlinear thermal conduction and optically thin radiative cooling, we demonstra…
Multiple Extreme Ultraviolet Peaks Attributed to Three-dimensional Magnetic Reconnection in a Long-duration Solar Flare
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；State Key Laboratory of Solar Activity and Space Weather, National Space Science Center, Chinese Academy of Sciences（中国科学院国家空间科学中心太阳活动与空间天气国家重点实验室）；CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China（中国科学技术大学地球物理和行星科学系地空间环境中国科学院重点实验室）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文学和天体物理学重点实验室（南京大学））；Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven（荷语鲁汶大学数学系数学等离子体天体物理中心）；LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot（巴黎天文台LESIA实验室（CNRS、UPMC、巴黎第七大学））；Astronomical Institute, Czech Academy of Sciences（捷克科学院天文研究所）
Solar flares are often associated with coronal eruptions, but there are confined ones without eruption, even for some X-class flares. How such large flares occurred and why they are confined are still not well understood. Here we studied a confined X2.2 flare in NOAA 12673 on 2017 September 6. It exhibits two episodes of flare brightening with rather complex, atypical ribbons. Based on topology analysis of extrapolated coronal magnetic field, we revealed that there is a two-step magnetic reconnection process during the flare. Prior to the flare, there is a magnetic flux rope (MFR) with one leg…
