MHD equilibrium and stability properties of a bipolar current loop

Xue, Ming; Chen, James

doi:10.1007/bf00157450

Cited by 27 publications

(14 citation statements)

References 11 publications

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“…III G 1) were found to constrain ð p À p c Þ and B p =B t in such a way as to render the flux ropes stable. 310 Linearly, local Suydam stability 348 and the external kink stability 349 are both satisfied. Nonlinearly, 3-D flux rope tends to become more stable to the kink as it expands because twist per unit length tends to decrease.…”

Section: Mhd Stability Of Flux Ropesmentioning

confidence: 99%

“…I A), which led to a broad rejection of flux ropes as CMEs. The application of the hoop force to solar flux ropes 85,310 was also regarded as a "laboratory" technique inapplicable to solar structures. With the new LASCO observations, however, the consensus shifted to the flux rope geometry (Fig.…”

Section: E Flux-rope Cmesmentioning

confidence: 99%

“…323 The application to plasma structures was originally derived for axisymmetric equilibria in tokamaks 299,324 and introduced into the solar physics literature in a study of macroscopic equilibrium of 3-D solar loops with nonzero pressure. 310 It was later extended to the dynamics of nonaxisymmetric flux ropes with stationary footpoints. 85 For the solar application, the minor radial dynamics, minor radial variation along the flux rope, and the stationary footpoints during expansion are found to be essential.…”

Section: F Dynamics Of Solar Flux Ropesmentioning

confidence: 99%

“…The finite ambient pressure, p c 6 ¼ 0, means that b p < 0 is possible, which allows equilibrium flux ropes even with B c ¼ 0 without violating the virial theorem. 310 In axisymmetric structures, there is no counterpart of the length scale S f .…”

Section: Mhd Forces On Solar Flux Ropes: Equations Of Motionmentioning

confidence: 99%

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Physics of erupting solar flux ropes: Coronal mass ejections (CMEs)—Recent advances in theory and observation

Chen

2017

Physics of Plasmas

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Solar eruptions, observed as flares and coronal mass ejections (CMEs), are the most energetic visible plasma phenomena in the solar system. CMEs are the central component of solar eruptions and are detected as coherent magnetized plasma structures expanding in the solar wind (SW). If they reach the Earth, their magnetic fields can drive strong disturbances in the ionosphere, causing deleterious effects on terrestrial technological systems. The scientific and practical importance of CMEs has led to numerous satellite missions observing the Sun and SW. This has culminated in the ability to continuously observe CMEs expanding from the Sun to 1 AU, where the magnetic fields and plasma parameters of the evolved structures ("ejecta") can be measured in situ. Until recently, the physical mechanisms responsible for eruptions were major unanswered questions in solar and by extension stellar physics. New observations of CME dynamics and associated eruptive phenomena are now providing more stringent constraints on models, and quantitative theory-data comparisons are helping to establish the correct mechanism of solar eruptions, particularly the driving force of CMEs and the evolution of their magnetic fields in three dimensions. Recent work has demonstrated that theoretical results can simultaneously replicate the observed CME position-time data, temporal profiles of associated solar flare soft X-ray emissions, and the magnetic field and plasma parameters of CME ejecta measured at 1 AU. Thus, a new theoretical framework with testable predictions is emerging to model eruptions and the coupling of CME ejecta to geomagnetic disturbances. The key physics in CME dynamics is the Lorentz hoop force acting on toroidal "flux ropes," scalable from tokamaks and similar laboratory plasma structures. The present paper reviews the latest advances in observational and theoretical understanding of CMEs with the emphasis on quantitative comparisons of theory and observation. Published by AIP Publishing.

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Section: Mhd Stability Of Flux Ropesmentioning

confidence: 99%

Section: E Flux-rope Cmesmentioning

confidence: 99%

Section: F Dynamics Of Solar Flux Ropesmentioning

confidence: 99%

Section: Mhd Forces On Solar Flux Ropes: Equations Of Motionmentioning

confidence: 99%

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Physics of erupting solar flux ropes: Coronal mass ejections (CMEs)—Recent advances in theory and observation

Chen

2017

Physics of Plasmas

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“…This work was applied to coronal loop equilibria (Xue & Chen 1983) and extended to the dynamics of nonaxisymmetric solar flux ropes with quasi-stationary footpoints (Chen 1989). The fundamental assumption is that the force is governed by the local curvature, which was rigorously demonstrated by Garren & Chen (1994) for R/a 1.…”

Section: Driving Forces In Cme Modelsmentioning

confidence: 99%

Temporal and Physical Connection Between Coronal Mass Ejections and Flares

Chen

Kunkel

2010

ApJ

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The physical connection between the eruption of coronal mass ejections (CMEs) and associated flare energy release is examined. The trajectories of five CMEs are determined using LASCO/SOHO or SECCHI/STEREO data, and the associated soft X-ray (SXR) light curves are obtained from GOES 1-8 Å data. As the theoretical description of CME physics, the existing erupting flux-rope model is used in which an initial flux rope is driven out of equilibrium by the increasing poloidal magnetic flux Φ p (t) (poloidal "flux injection"). Mathematically, this is represented by dΦ p (t)/dt. For each CME, this function is adjusted to obtain the solution that best fits the observed height-time data. The resulting dΦ p (t)/dt is shown to be strongly constrained by the CME height data. This function and the attendant electromotive force (EMF) given by E(t) ≡ −(1/c)dΦ p (t)/dt constitute predictions of the theory for each CME trajectory. It is shown that the best-fit solutions fit the CME trajectories within 1%-2% of the CME height data and that the temporal profile of the predicted dΦ p (t)/dt is correlated with that of the associated X-ray light curve regardless of the flare duration. Specifically, we find that the observed duration of SXR emission ΔT SXR is comparable to and scales with the predicted duration ΔT p of poloidal flux injection, i.e., ΔT SXR ΔT p . Neither the predicted dΦ p (t)/dt nor the input CME height data contain any information on X-ray data. Thus, the correlation is nontrivial, constituting evidence that poloidal flux injection is physically connected to flare energy release. It is suggested that this connection is provided by the EMF that produces electric fields to accelerate particles.

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Reconnection in Sheared Magnetic Fields in Space and Astrophysics

Drake

1985

Unstable Current Systems and Plasma Instabilities in Astrophysics

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MHD equilibrium and stability properties of a bipolar current loop

Cited by 27 publications

References 11 publications

Physics of erupting solar flux ropes: Coronal mass ejections (CMEs)—Recent advances in theory and observation

Physics of erupting solar flux ropes: Coronal mass ejections (CMEs)—Recent advances in theory and observation

Temporal and Physical Connection Between Coronal Mass Ejections and Flares

Reconnection in Sheared Magnetic Fields in Space and Astrophysics

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