Magnetic Flux Rope Research Articles

Laboratory study of the failed torus mechanism in arched, line-tied, magnetic flux ropes

Coronal mass ejections (CMEs) are some of the most energetic and violent events in our solar system. The prediction and understanding of CMEs are of particular importance due to the impact that they can have on Earth-based satellite systems and, in extreme cases, ground-based electronics. CMEs often occur when long-lived magnetic flux ropes (MFRs) anchored to the solar surface destabilize and erupt away from the Sun. One potential cause for these eruptions is an ideal magnetohydrodynamic (MHD) instability, such as the kink or torus instability. Previous experiments on the magnetic reconnection experiment revealed a class of MFRs that were torus-unstable but kink-stable, which failed to erupt. These “failed-tori” went through a process similar to Taylor relaxation, where the toroidal current was redistributed before the eruption ultimately failed. We have investigated this behavior through additional diagnostics that measure the current distribution at the foot points and the energy distribution before and after an event. These measurements indicate that ideal MHD effects are sufficient to explain the energy distribution changes during failed torus events. This excludes Taylor relaxation as a possible mechanism of current redistribution during an event. A new model that only requires non-ideal effects in a thin layer above the electrodes is presented to explain the observed phenomena. This work broadens our understanding of the stability of MFRs and the mechanism behind the failed torus through the improved prediction of the torus instability and through new diagnostics to measure the energy inventory and current profile at the foot points.

Distorted-toroidal Flux Rope Model

The 3D characterization of magnetic flux ropes observed in the heliosphere has been a challenging task for decades. This is mainly due to the limitations on inferring the 3D global topology and physical properties from the 1D time series from any spacecraft. To advance our understanding of magnetic flux ropes whose configuration departs from the typical stiff geometries, here we present an analytical solution for a 3D flux rope model with an arbitrary cross section and a toroidal global shape. This constitutes the next level of complexity following the elliptic-cylindrical (EC) geometry. The mathematical framework was established by Nieves-Chinchilla et al. with the EC flux rope model, which describes a magnetic topology with an elliptical cross section as a first approach to changes in the cross section. In the distorted-toroidal flux rope model, the cross section is described by a general function. The model is completely described by a nonorthogonal geometry and the Maxwell equations can be consistently solved to obtain the magnetic field and relevant physical quantities. As a proof of concept, this model is generalized in terms of the radial dependence of current density components. The last part of this paper is dedicated to a specific function, , to illustrate possibilities of the model. This model paves the way toward the investigation of complex distortions of magnetic structures in the solar wind. Future investigations will explore these distortions in depth by analyzing specific events; studying implications for physical quantities, such as magnetic fluxes, helicity, or energy; and evaluating the force balance with the ambient solar wind that allows such distortions.

Manifestation of Magnetic Flux Ropes in the Structure of Solar Prominences

Manifestation of Magnetic Flux Ropes in the Structure of Solar Prominences

Magnetic predictions

AbstractOliver Rice discusses work in modelling the magnetic field in the solar corona, and one way in which this may be used to predict the eruptions of magnetic flux ropes

Two-step Acceleration of Energetic Electrons at Magnetic Flux Ropes during Turbulent Reconnection

Energetic electrons have been frequently observed during magnetic reconnection in the magnetotail. The acceleration process of the energetic electrons is not fully understood. In this paper, we select for a detailed study a case of energetic electron acceleration from the earlier reported interval of turbulent magnetic reconnection in Earth’s magnetotail observed by the Magnetospheric Multiscale mission. We use the first-order Taylor expansion method to reconstruct the magnetic topology of electron acceleration sites from the data. We find that the energetic electron fluxes increase inside the flux rope forming in front of the magnetic pileup region. We show that the energetic electrons are produced by a two-step process where two different acceleration mechanisms are successively operating outside and inside the flux rope. First, the thermal electrons are energized in the field-aligned direction inside the magnetic pileup region owing to the Fermi mechanism forming a cigar-like distribution. Second, those energized electrons are further accelerated predominately antiparallel to the magnetic field direction by a parallel electric field inside the flux rope. Our findings provide information for a better understanding of the generation of energetic electrons during turbulent reconnection process.

Redefining flux ropes in heliophysics

Magnetic flux ropes manifest as twisted bundles of magnetic field lines. They carry significant amounts of solar mass in the heliosphere. This paper underlines the need to advance our understanding of the fundamental physics of heliospheric flux ropes and provides the motivation to significantly improve the status quo of flux rope research through novel and requisite approaches. It briefly discusses the current understanding of flux rope formation and evolution, and summarizes the strategies that have been undertaken to understand the dynamics of heliospheric structures. The challenges and recommendations put forward to address them are expected to broaden the in-depth knowledge of our nearest star, its dynamics, and its role in its region of influence, the heliosphere.

Efficient Electron Acceleration Driven by Flux Rope Evolution during Turbulent Reconnection

Magnetic flux ropes or magnetic islands are important structures responsible for electron acceleration and energy conversion during turbulent reconnection. However, the evolution of flux ropes and the corresponding electron acceleration process still remain open questions. In this paper, we present a comparative study of flux ropes observed by the Magnetospheric Multiscale mission in the outflow region during an example of turbulent reconnection in Earth's magnetotail. Interestingly, we find the farther the flux rope is away from the X-line, the bigger the size of the flux rope and the slower it moves. We estimate the power density converted at the observed flux ropes via the three fundamental electron acceleration mechanisms: Fermi, betatron, and parallel electric field. The dominant acceleration mechanism at all three flux ropes is the betatron mechanism. The flux rope that is closest to the X-line, having the smallest size and the fastest moving velocity, is the most efficient in accelerating electrons. Significant energy also returns from particles to fields around the flux ropes, which may facilitate the turbulence in the reconnection outflow region.

An Evolution and Eruption of the Coronal Magnetic Field through a Data-driven MHD Simulation

We present a newly developed data-driven magnetohydrodynamics (MHD) simulation code under a zero-β approximation based on a method proposed by Hayashi et al. 2018 and 2019. Although many data-driven MHD simulations have been developed and conducted, there are not many studies on how accurately those simulations can reproduce the phenomena observed in the solar corona. In this study, we investigated the performance of our data-driven simulation quantitatively using ground-truth data. The ground-truth data was produced by an MHD simulation in which the magnetic field is twisted by the sunspot motions. A magnetic flux rope (MFR) is created by the cancellation of the magnetic flux at the polarity inversion line due to the converging flow on the sunspot, which eventually leads to the eruption of the MFR. We attempted to reproduce these dynamics using the data-driven MHD simulation. The coronal magnetic fields are driven by the electric fields, which are obtained from a time series of the photospheric magnetic field that is extracted from the ground-truth data, on the surface. As a result, the data-driven simulation could capture the subsequent MHD processes, the twisted coronal magnetic field and formation of the MFR, and also its eruption. We report these results and compare them with the ground-truth data, and discuss how to improve the accuracy and optimize the numerical method.

Parallel and Momentum Superdiffusion of Energetic Particles Interacting with Small-scale Magnetic Flux Ropes in the Large-scale Solar Wind

A recently developed time-dependent fractional Parker transport equation is solved to investigate the parallel and momentum superdiffusion of energetic charged particles in an inner heliospheric region containing dynamic small-scale flux ropes (SMFRs). Both types of superdiffusive transport are investigated with fractional transport terms containing a fractional time integral combined with normal spatial or momentum derivatives. Just as for normal diffusion, accelerated particles form spatial peaks with a maximum amplification factor that increases with particle energy. Instead of growth of the spatial peaks until a steady state is reached as for normal diffusion, parallel superdiffusion causes the peaks to dissipate into plateaus followed by a rollover at late times. The peaks dissipate at a faster rate when parallel transport is more superdiffusive. Furthermore, the accelerated particle spectral distribution function inevitably becomes an f 0 ∝ p −3 spectrum at late times in the test particle limit near the particle source despite the potential for spectral steepening from other transport terms. All this is a product of the growing domination of parallel spatial and especially momentum superdiffusion over other transport terms with time. Such extreme late time effects can be avoided by a transition to a normal diffusive state. Finally, fitting spatial peaks observed during SMFR acceleration events with the solution of the fractional Parker transport equation can potentially be used as a diagnostic for estimating the level of spatial and momentum superdiffusion in these events and how the levels of superdiffusion vary with distance from the Sun.

Ion-Scale Magnetic Flux Rope Generated From Electron-Scale Magnetopause Current Sheet: Magnetospheric Multiscale Observations.

We present in-depth analysis of three southward-moving meso-scale (ion-to magnetohydrodynamic-scale) flux transfer events (FTEs) and subsequent crossing of a reconnecting magnetopause current sheet (MPCS), which were observed on 8 December 2015 by the Magnetospheric Multiscale spacecraft in the subsolar region under southward and duskward magnetosheath magnetic field conditions. We aim to understand the generation mechanism of ion-scale magnetic flux ropes (ISFRs) and to reveal causal relationship among magnetic field structures, electromagnetic energy conversion, and kinetic processes in magnetic reconnection layers. Results from magnetic field reconstruction methods are consistent with a flux rope with a length of about one ion inertial length growing from an electron-scale current sheet (ECS) in the MPCS, supporting the idea that ISFRs can be generated through secondary reconnection in an ECS. Grad-Shafranov reconstruction applied to the three FTEs shows that the FTEs had axial orientations similar to that of the ISFR. This suggests that these FTEs also formed through the same secondary reconnection process, rather than multiple X-line reconnection at spatially separated locations. Four-spacecraft observations of electron pitch-angle distributions and energy conversion rate suggest that the ISFR had three-dimensional magnetic topology and secondary reconnection was patchy or bursty. Previously reported positive and negative values of , with magnitudes much larger than expected for typical MP reconnection, were seen in both magnetosheath and magnetospheric separatrix regions of the ISFR. Many of them coexisted with bi-directional electron beams and intense electric field fluctuations around the electron gyrofrequency, consistent with their origin in separatrix activities.

Statistical Study of Ejections in Coronal Hole Regions As Possible Sources of Solar Wind Switchbacks and Small-scale Magnetic Flux Ropes

The omnipresence of transient fluctuations in the solar wind, such as switchbacks (SBs) and small-scale magnetic flux ropes (SMFRs), have been well observed by the in situ observation of Parker Solar Probe (PSP), yet their sources are not clear. Possible candidates fall into two categories: solar origin and in situ generation in the solar wind. Among the solar-origin scenarios, the small-scale activities (such as ejections and eruptions) in coronal hole (CH) regions, where solar wind originates, are suggested as candidates. Using full-disk extreme ultraviolet images from Atmospheric Imaging Assembly on board the Solar Dynamic Observatory, we identify small-scale ejections in CH regions during PSP Encounters 5, 7, and 8, and study their statistical properties. These ejections belong to two categories: standard jets and blowout jets. With 27,832 ejections identified in 24 days (about 2/3 of them are blowout jets), we updated the expected frequency for PSP to detect their counterparts in the heliospace. The ejections we identified are comparable to the frequency of PSP-detected SMFRs, but they are insufficient to serve as the only producer of SBs or SB patches. Certain smaller events missed by this study, such as jetlets, may fill the gap.

Manifestation of Magnetic Flux Ropes in the Structure of Solar Prominences

The appearance of quiescent solar prominences most often resembles a wide curtain or a fencemade of a vertical palisade. It is hard to imagine that such a structure can be connected or even formed by amagnetic flux rope, that is, a bundle of force lines twisted into a cylindrical helix, which sometimes clearlymanifests itself in active region filaments. However, with a relatively small activation of the prominences,when the plasma composing them begins to move along the field lines, the structure of the magnetic flux ropecan be discerned. An example of a quiescent prominence is shown, in which rotational motion is observedalong helical trajectories outlining the flux rope. The rotation is clearly visible in the time-distance diagram,which is composed of narrow strips of images of the prominence along the trajectory of motion

Rapid Rotation of an Erupting Prominence and the Associated Coronal Mass Ejection on 13 May 2013

In this paper, we report the multiwavelength observations of an erupting prominence and the associated coronal mass ejection (CME) on 13 May 2013. The event occurs behind the western limb in the field of view of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) spacecraft. The prominence is supported by a highly twisted magnetic flux rope and shows rapid rotation in the counterclockwise direction during the rising motion. The rotation of the prominence lasts for ∼ 47 minutes. The average period, angular speed, and linear speed are ∼ 806 sec, ∼ 0.46 rad min−1, and ∼ 355 km s−1, respectively. The total twist angle reaches ∼ 7 $\pi$ , which is considerably larger than the threshold for kink instability. Writhing motion during 17:42 – 17:46 UT is clearly observed by SWAP in 174 Å and Extreme-UltraViolet Imager (EUVI) on board the behind Solar Terrestrial Relations Observatory (STEREO) spacecraft in 304 Å after reaching an apparent height of ∼ 405 Mm. Therefore, the prominence eruption is most probably triggered by kink instability. A pair of conjugate flare ribbons and post-flare loops are created and observed by STA/EUVI. The onset time of writhing motion is consistent with the commencement of the impulsive phase of the related flare. The 3D morphology and positions of the associated CME are derived using the graduated cylindrical shell (GCS) modeling. The kinetic evolution of the reconstructed CME is divided into a slow-rise phase (∼ 330 km s−1) and a fast-rise phase (∼ 1005 km s−1) by the writhing motion. The edge-on angular width of the CME is a constant (60∘), while the face-on angular width increases from 96∘ to 114∘, indicating a lateral expansion. The latitude of the CME source region decreases slightly from ∼ 18∘ to ∼ 13∘, implying an equatorward deflection during propagation.

The mechanism of magnetic flux rope rotation during solar eruption

Solar eruptions often show the rotation of filaments, which is a manifestation of the rotation of erupting magnetic flux rope (MFR). Such a rotation of MFR can be induced by either the torque exerted by a background shear-field component (which is an external cause) or the relaxation of the magnetic twist of the MFR (an internal cause). For a given chirality of the erupting field, both the external and internal drivers cause the same rotation direction. Therefore, it remains elusive from direct observations which mechanism yields the dominant contribution to the rotation. In this paper, we exploit a full MHD simulation of solar eruption by tether-cutting magnetic reconnection to study the mechanism of MFR rotation. In the simulation, the MFR’s height–rotation profile suggests that the force by the external shear-field component is a dominant contributor to the rotation. Furthermore, the torque analysis confirms that it is also the only factor in driving the counterclockwise rotation. On the contrary, the Lorentz torque inside the MFR makes a negative effect on this counterclockwise rotation.

Statistics of geometrical invariants of magnetic field gradient tensors in the turbulent magnetosheath based on magnetospheric multiscale mission

Geometrical invariants of magnetic field gradient tensors are used to classify the topological structures of a magnetic field. This study presents a statistical analysis on the geometrical invariants of magnetic field gradient based on high-quality data measured by magnetospheric multiscale mission in turbulent magnetosheath. The method for the classification of velocity field topologies cannot be applied to magnetic field with strong intensity directly because the magnetic field cannot be transformed to zero by selecting a co-moving reference frame in which the velocity is zero. During a strong magnetic field, flux ropes and tubes are the most possible magnetic structures. Statistics in the plane formed by geometrical invariants show that about 23% are force-free structures comprised of 20.5% flux tubes and 79.5% flux ropes. The remaining actively evolved structures are comprised of 30% flux tubes and 70% flux ropes. Moreover, the conditional average of current density and Lorentz force decomposition in geometrical invariants plane are investigated. The results show that flux ropes carried more current density than flux tubes for the same geometrical invariants, and flux ropes tend to associate with magnetic pressure force and flux tubes tend to associate with magnetic tension.

Multi-dimensional incoherent Thomson scattering system in PHAse Space MApping (PHASMA) facility.

A multi-dimensional incoherent Thomson scattering diagnostic system capable of measuring electron temperature anisotropies at the level of the electron velocity distribution function (EVDF) is implemented on the PHAse Space MApping facility to investigate electron energization mechanisms during magnetic reconnection. This system incorporates two injection paths (perpendicular and parallel to the axial magnetic field) and two collection paths, providing four independent EVDF measurements along four velocity space directions. For strongly magnetized electrons, a 3D EVDF comprised of two characteristic electron temperatures perpendicular and parallel to the local magnetic field line is reconstructed from the four measured EVDFs. Validation of isotropic electrons in a single magnetic flux rope and a steady-state helicon plasma is presented.

Investigating Pre-eruptive Magnetic Properties at the Footprints of Erupting Magnetic Flux Ropes

It is well established that solar eruptions are powered by free magnetic energy stored in the current-carrying magnetic field in the corona. It has also been generally accepted that magnetic flux ropes (MFRs) are a critical component of many coronal mass ejections. What remains controversial is whether MFRs are present well before the eruption. Our aim is to identify progenitors of MFRs, and investigate pre-eruptive magnetic properties associated with these progenitors. Here we analyze 28 MFRs erupting within 45° from the disk center from 2010 to 2015. All MFRs’ feet are well identified by conjugate coronal dimmings. We then calculate the magnetic properties at the feet of the MFRs, prior to their eruptions, using Helioseismic and Magnetic Imager vector magnetograms. Our results show that only 8 erupting MFRs are associated with significant nonneutralized electric currents, 4 of which also exhibit pre-eruptive dimmings at the footprints. Twist and current distributions are asymmetric at the two feet of these MFRs. The presence of pre-eruption dimmings associated with nonneutralized currents suggests the preexisting MFRs. Furthermore, the evolution of conjugate dimmings and electric currents within the footprints can provide clues about the internal structure of MFRs and their formation mechanism.

Evolution of Magnetic Fields and Energy Release Processes during Homologous Eruptive Flares

We explore the processes of the repetitive buildup and the explosive release of magnetic energy, together with the formation of magnetic flux ropes, which eventually resulted in three homologous eruptive flares of successively increasing intensities (i.e., M2.0, M2.6, and X1.0). The flares originated from NOAA active region 12017 between 2014 March 28 and 29. EUV observations and magnetogram measurements, together with coronal magnetic field modeling, suggest that the flares were triggered by the eruption of flux ropes that were embedded in a densely packed system of loops within a small part of the active region. In X-rays, the first and second events show similar evolutions, with single compact sources, while the third event exhibits multiple emission centroids, with a set of strong nonthermal conjugate sources at 50–100 keV during the hard X-ray peak. Over an interval of ≈ 44 hr, the photospheric magnetic field encompassing the three flares undergoes important phases of emergence and cancellation, together with significant changes near the polarity inversion lines within the flaring region. Our observations point toward the tether-cutting mechanism being the plausible triggering process of the eruptions. Between the second and third events, we observe a prominent phase of flux emergence that temporally correlates with the buildup phase of free magnetic energy in the active region corona. In conclusion, our analysis reveals efficient coupling between the rapidly evolving photospheric and coronal magnetic fields in the active region, leading to a continued phase of the buildup of free energy, which results in the homologous flares of successively increasing intensities.

Division of Magnetic Flux Rope via Magnetic Reconnection Observed in the Magnetotail

AbstractUsing high‐resolution data from Magnetospheric Multiscale (MMS) mission, we report an intense current layer at the center of a flux rope (FR) in the magnetotail. The intense current layer is caused by the compression of the ion bulk flows at the center of a FR rather than two interlaced flux tubes reported at the magnetopause previously. The intense current layer has been identified as an electron diffusion region of the magnetic reconnection, and the hall magnetic field generated by magnetic reconnection makes the FR show crater‐shaped. The reconnecting current layer is supported by the poloidal magnetic field of the FR, and it is dividing the FR into two secondary FRs. The observations suggest that magnetic FR can be compressed easily to excite instability inside it as it is propagating in the magnetotail current sheet, thus changing its magnetic topology.

Influence of magnetic reconnection on the eruptive catastrophes of coronal magnetic flux ropes

Introduction: 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 (MHD) condition, so that it is still elusive whether there is the catastrophe associated with the critical axial flux if magnetic reconnection is included in the flux rope system.Methods: In this paper, we carried out numerical simulations to investigate the evolutions of coronal magnetic rope systems under the ideal MHD and the resistive condition.Results and discussions: Under the ideal MHD condition, our simulation results demonstrate that the flux rope systems with either too compact or too weak photospheric magnetic source regions are non-catastrophic versus varying axial flux of the rope, and thus no eruption could be initiated; if there is magnetic reconnection in the rope system, however, those flux rope systems could change to be capable of erupting via the catastrophe associated with increasing axial flux. Therefore, magnetic reconnection could significantly influence the catastrophic behaviors of flux rope system. It should be both the magnetic topology and the local physical parameters related to magnetic reconnection that determine whether the increasing axial flux is able to cause flux rope eruptions.