Dynamical evolution of a solar coronal magnetic field arcade

Mikić, Z.; Barnes, David; Schnack, D. D.

doi:10.1086/166341

Cited by 240 publications

(119 citation statements)

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“…The other models for the eruption, like the sheared-arcade model (Mikić et al 1988;Mikić and Linker 1994) and the breakout model (Antiochos et al 1999) in which reconnection creates the flux rope, did not explicitly address the development and the other related features/properties of the CS behind the CME probably because either the numerical resistivity was high and the CS is hard to form in the numerical experiments, or the main attention was paid to the triggering of the eruption. In the follow-ups of these works, on the other hand, with the improvement in the numerical techniques and more and more attention being paid on the CS structure, the related works also showed the appearance of a long CS behind the CME in these models, and detailed properties of the CS started to be investigated (e.g., see Linker et al 2003;Riley et al 2007;Karpen et al 2012 for details).…”

Section: Have Convincingly Showed That Both the Reconnection Sites Comentioning

confidence: 99%

“…The transition from the quasi-static to dynamic evolution constitutes the catastrophe, and the corresponding model for solar eruptions are known as the catastrophe model (see Lin et al 2003 for more details). Alternative models to the catastrophe one for triggering eruptions include the sheared arcade model (Mikić et al 1988;Mikić and Linker 1994;Linker et al 2003;Amari et al 2005Amari et al , 2010), the breakout model (Antiochos et al 1999;Lynch et al 2010;Karpen et al 2012), the ideal MHD model on the basis of the kink and torus instability (Titov and Démoulin 1999;Török and Kliem 2005;Kliem and Török 2006;Fan and Gibson 2007;Karlický and Kliem 2010), the tether-cutting model (Moore et al 2001), and so on (see also Shibata and Magara 2011;Yang et al 2012;Schmieder et al 2013;Yan et al 2014).…”

Section: Introductionmentioning

confidence: 99%

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Review on Current Sheets in CME Development: Theories and Observations

et al. 2015

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We introduce how the catastrophe model for solar eruptions predicted the formation and development of the long current sheet (CS) and how the observations were used to recognize the CS at the place where the CS is presumably located. Then, we discuss the direct measurement of the CS region thickness by studying the brightness distribution of the CS region at different wavelengths. The thickness ranges from 10 4 km to about 10 5 km at heights between 0.27 and 1.16 R from the solar surface. But the traditional theory indicates that the CS is as thin as the proton Larmor radius, which is of order tens of meters in the corona. We look into the huge difference in the thickness between observations and theoretical expectations. The possible impacts that affect measurements and results are studied, and physical causes leading to a thick CS region in which reconnection can still occur at a reasonably fast rate are analyzed. Studies in both theories and observations suggest that the difference between the true value and the apparent value of the CS thickness is not significant as long as the CS could be recognised in observations. We review observations that show complex structures and flows inside the CS region and present recent numerical modelling results on some aspects of these structures. Both observations and numerical experiments indicate that the downward reconnection outflows are usually slower than the upward ones in the same eruptive event. Numerical simulations show that the complex structure inside CS and its temporal behavior as a result of turbulence and the Petschek-type slow-mode shock could probably account for the thick CS and fast reconnection. But whether the CS itself is that thick still remains unknown since, for the time being, we cannot measure the electric current directly in that region. We also review the most recent laboratory experiments of reconnection driven by energetic laser beams, and discuss some important topics for future works.

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Section: Have Convincingly Showed That Both the Reconnection Sites Comentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Review on Current Sheets in CME Development: Theories and Observations

et al. 2015

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“…The formation of a plasmoid from a single arcade (Inhester, Birn, & Hesse 1992) is a loss-ofequilibrium bifurcation related to tearing instability of the current sheet which forms at the center of the arcade when it is sheared strongly (Finn & Guzdar 1993). In addition, it has been shown that plasmoid formation can occur directly as a consequence of linear instability when multiple arcades exist (Mikic et al 1988 ;Biskamp & Welter 1989 ;Finn, Guzdar, & Chen 1992).…”

Section: Imitation On Increase Of T Wistmentioning

confidence: 99%

“…561 1991, 1995Mikic, Barnes, & Schnack 1988 ;Finn & Chen 1990 ;Sturrock, Antiochos, & Roumeliotis 1995). The direct application of those studies to accretion disks has been fairly recent (e.g., Appl & Camenzind 1993 ;& Konigl Ruden 1993 ;LB94 ;Lynden-Bell 1996 ;Bardou & Heyvaerts 1996 ;Goodson, & Winglee 1999 ;Uzdensky, Bohm, & Litwin 2001).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Helix Formation Driven by Keplerian Disk Rotation in an External Plasma Pressure: The Initial Expansion Stage

Lovelace

Finn

et al. 2001

ApJ

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We study the evolution of a magnetic arcade that is anchored to an accretion disk and is sheared by the di †erential rotation of a Keplerian disk. By including an extremely low external plasma pressure at large distances, we obtain a sequence of axisymmetric magnetostatic equilibria and show that there is a fundamental di †erence between Ðeld lines that are a †ected by the plasma pressure and those that are not (i.e., force free). Force-free Ðelds, while being twisted by the di †erential rotation of the disk, expand outward at an angle of D60¡ away from the rotation axis, consistent with the previous studies. These force-free Ðeld lines, however, are enclosed by the outer Ðeld lines, which originate from small disk radii and come back to the disk at large radii. These outer Ðelds experience most of the twist, and they are also a †ected most by the external plasma pressure. At large cylindrical radial distances, magnetic pressure and plasma pressure are comparable so that any further radial expansion of magnetic Ðelds is prevented or slowed down greatly by this pressure. This hindrance to cylindrical radial expansion causes most of the added twist to be distributed on the ascending portion of the Ðeld lines, close to the rotation axis. Since these Ðeld lines are twisted most, the increasing ratio of the toroidal component to the B Õ poloidal component eventually results in the collimation of magnetic energy and Ñux around the B R,z rotation axis. We discuss the difficulty with adding a large number of twists within the limitations of the magnetostatic approximation.

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“…A better method is therefore to turn the problem into a hyperbolic one and to solve an additional evolution equation for the velocity correction where the driving force is the Lorentz force. This approach is sometimes called the "force-free model" (FFM), even though the field in this model is never exactly force-free anywhere (Mikić et al 1988;Ortolani & Schnack 1993). In the context of force-free magnetic field extrapolations this method is also known as the stress-and-relax method (Valori et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Surface appearance of dynamo-generated large-scale fields

Warnecke

Brandenburg

2010

A&A

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Aims. Twisted magnetic fields are frequently seen to emerge above the visible surface of the Sun. This emergence is usually associated with the rise of buoyant magnetic flux structures. Here we ask how magnetic fields from a turbulent large-scale dynamo appear above the surface if there is no magnetic buoyancy. Methods. The computational domain is split into two parts. In the lower part, which we refer to as the turbulence zone, the flow is driven by an assumed helical forcing function leading to dynamo action. Above this region, which we refer to as the exterior, a nearly force-free magnetic field is computed at each time step using the stress-and-relax method. Results. Twisted arcade-like field structures are found to emerge in the exterior above the turbulence zone. Strong current sheets tend to form above the neutral line, where the vertical field component vanishes. Time series of the magnetic field structure show recurrent plasmoid ejections. The degree to which the exterior field is force free is estimated as the ratio of the dot product of current density and magnetic field strength to their respective rms values. This ratio reaches values of up to 95% in the exterior. A weak outward flow is driven by the residual Lorentz force.

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Dynamical evolution of a solar coronal magnetic field arcade

Cited by 240 publications

References 0 publications

Review on Current Sheets in CME Development: Theories and Observations

Review on Current Sheets in CME Development: Theories and Observations

Magnetic Helix Formation Driven by Keplerian Disk Rotation in an External Plasma Pressure: The Initial Expansion Stage

Surface appearance of dynamo-generated large-scale fields

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