The Emergence of a Twisted Magnetic Flux Tube into a Preexisting Coronal Arcade

Fan, Yuhong; Gibson, S. E.

doi:10.1086/375834

Cited by 191 publications

(206 citation statements)

References 13 publications

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“…For instance, an equilibrium coronal loop becomes unstable if its length is stretched beyond a critical value, or if it is twisted by photospheric motions (Priest 1978). For twisted magnetic field configurations, different critical thresholds were found within numerical experiments, including uniformly twisted toroidal or periodic, line-tied cylindrically symmetric configurations (Hood and Priest 1981;Baty and Heyvaerts 1996) and locally twisted configurations (Baty and Heyvaerts 1996;Mikić et al 1990;Fan and Gibson 2003;Török and Kliem 2003). Note, the results of all of these model experiments agree fairly well on the critical amount of twist: the field lines must perform more than one full turn (T > 2π) about the center of the flux tube for it to become kink unstable, which would be observed as an eruption under coronal conditions.…”

Section: Magnetic Shear and Twistmentioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

172

125

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This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.

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Section: Magnetic Shear and Twistmentioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

172

125

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“…For example, an emerging flux trigger (Chen & Shibata 2000), flux cancellation (Amari et al 2003a(Amari et al ,b, 2010, tether cutting (Moore et al 2001), and breakout models (Antiochos et al 1999;Lynch et al 2004;Karpen et al 2012) require magnetic reconnection below or above the flux rope. On the other hand, numerical MHD simulations of the kink instability suggest that if the twist of the flux rope exceeds a critical value (∼1.75 field line turns), then it becomes unstable (Fan & Gibson 2003Kliem et al 2004;Török & Kliem 2003;Török et al 2004). Alternatively, the decrease of an overlying magnetic field (B) with height (H; decay index n = −d(log B)/d(log H) > 1.5, condition for torus instability) above the eruption site alone can decide whether the eruption of a flux rope is successful or fails Aulanier et al 2010;Olmedo & Zhang 2010).…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength observation of a large-scale flux rope eruption above a kinked small filament

Kumar

Cho

2014

A&A

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We analyzed multiwavelength observations of a western limb flare (C3.9) that occurred in AR NOAA 111465 on 30 April 2012. The high-resolution images recorded by SDO/AIA 304, 1600 Å and Hinode/SOT Hα show the activation of a small filament (rising speed ∼ 40 km s −1 ) associated with a kink instability and the onset of a C-class flare near the southern leg of the filament. The first magnetic reconnection occurred at one of the footpoints of the filament and caused the breaking of its southern leg. The filament shows unwinding motion of the northern leg and apex in counterclockwise direction and failed to erupt. A flux-rope structure (visible only in hot channels, i.e., AIA 131 and 94 Å and Hinode/SXT) appeared along the neutral line during the second magnetic reconnection that occurred above the kinked filament. The formation of the RHESSI hard X-ray source (12−25 keV) above the kinked filament and the simultaneous appearance of the hot 131 Å loops associated with photospheric brightenings (AIA 1700 Å) indicates the particle acceleration along these loops from the top of the filament. In addition, extreme ultraviolet disturbances or waves observed above the filament in 171 Å also show a close association with magnetic reconnection. The flux rope rises slowly (∼100 km s −1 ), which produces a very large twisted structure possibly through reconnection with the surrounding sheared magnetic fields within ∼15−20 min, and showed an impulsive acceleration reaching a height of about 80-100 Mm. AIA 171 and SWAP 174 Å images reveal a cool compression front (or coronal mass ejection frontal loop) surrounding the hot flux rope structure.

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“…Fan & Gibson (2003) studied the kink motion of the tube and its interaction with an ambient coronal field. Titov & Démoulin (1999) constructed a force-free model of an anchored twisted flux tube with an arch-like shape embedded in an external potential magnetic field.…”

Section: Introductionmentioning

confidence: 99%

The emergence of toroidal flux tubes from beneath the solar photosphere

Hood¹,

Archontis²,

Galsgaard³

et al. 2009

A&A

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Context. Models of flux emergence frequently use a twisted cylindrical loop as the initial starting configuration and ignore the coupling between the radiation field and plasma. In these models, the axis of the original tube never emerges through the photosphere. Without the axis emerging, it is very difficult to form a realistic sunspot. Aims. The aim is to use a toroidal flux loop, placed beneath the solar photosphere and study whether the axis of the system emerges fully into the atmosphere. The toroidal curvature means that the plasma can drain more effectively than in a straight cylindrical tube. Methods. Three-dimensional magnetohydrodynamic numerical simulations of an emerging magnetic flux tube are presented for an initial toroidal loop model. The simulations use a Lagrangian-Remap code that is particularly suited to dealing with shocks and strong current sheets. Results. The evolution of the toroidal loop is followed and the characteristics of the emergence process are compared with the traditional cylindrical loops. The flux sources seen at the photosphere are more circular, and there are less shearing motions in the upper photosphere. When the initial magnetic field strength is relatively weak the evolution of the system is similar to the cylindrical loop case, with the formation of a new flux rope above the photosphere. A striking result is that for large values of field strength the axial field of the toroidal loop emerges fully into the corona. This is reported for the first time in experiments of flux emergence in a highly stratified atmosphere that do not solve self-consistently the radiation transfer problem. In addition, the new flux rope forms below the original axis of the toroidal tube when the field strength is sufficiently strong.

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The Emergence of a Twisted Magnetic Flux Tube into a Preexisting Coronal Arcade

Cited by 191 publications

References 13 publications

The magnetic field in the solar atmosphere

The magnetic field in the solar atmosphere

Multiwavelength observation of a large-scale flux rope eruption above a kinked small filament

The emergence of toroidal flux tubes from beneath the solar photosphere

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