Twisted Coronal Magnetic Loops

Klimchuk, J. A.; Antiochos, S. K.; Norton, D. A.

doi:10.1086/309527

Cited by 54 publications

(64 citation statements)

References 31 publications

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“…Dymova & Ruderman (2005) showed that kink oscillations of thin magnetic tubes with the density varying along the tube can be described by the wave equation with the phase speed equal to the local kink speed. Although typically the coronal loop expansion is relatively small, the ratio of the loop cross-section radii at the apex and at the footpoints can still reach a value of 1.5 Klimchuk et al 2000). It is surprising that in the chromosphere the expansion of vertical magnetic flux tubes can reach a value of up to a few hundred (e.g.…”

Section: Introductionmentioning

confidence: 99%

Kink oscillations of cooling coronal loops with variable cross-section

Shukhobodskiy

Erdélyi

2017

A&A

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We study kink waves and oscillations in a thin expanding magnetic tube in the presence of flow. The tube consists of a core region and a thin transitional region at the tube boundary. In this region the plasma density monotonically decreases from its value in the core region to the value outside the tube. Both the plasma density and velocity of background flow vary along the tube and in time. Using the multiscale expansions we derive the system of two equations describing the kink oscillations. When there is no transitional layer the oscillations are described by the first of these two equations. We use this equation to study the effect of plasma density variation with time on kink oscillations of an expanding tube with a sharp boundary. We assume that the characteristic time of the density variation is much greater than the characteristic time of kink oscillations. Then we use the Wentzel-Kramer-Brillouin (WKB) method to derive the expression for the adiabatic invariant, which is the quantity that is conserved when the plasma density varies. The general theoretical results are applied to the kink oscillations of coronal magnetic loops. We consider an expanding loop with the half-circle shape and assume that the plasma temperature inside a loop decays exponentially with time. We numerically calculated the dependences of the fundamental mode frequency, the ratio of frequencies of the first overtone and fundamental mode, and the oscillation amplitude on time. We obtained that the oscillation frequency and amplitude increase and the frequency ratio decreases due to cooling. The amplitude increase is stronger for loops with a greater expansion factor. This effect is also more pronounced for higher loops. However, it is fairly moderate even for loops that are quite high.

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Section: Introductionmentioning

confidence: 99%

Kink oscillations of cooling coronal loops with variable cross-section

Shukhobodskiy

Erdélyi

2017

A&A

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“…This represents a natural stressing mechanism of the magnetic field that eventually leads to a relaxation and a release of magnetic energy (e.g., Golub et al 1980;Klimchuk et al 2000;López Fuentes et al 2003). …”

Section: Introductionmentioning

confidence: 99%

3d MHD Modeling of Twisted Coronal Loops

Reale

Orlando

Guarrasi

et al. 2016

ApJ

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We perform MHD modeling of a single bright coronal loop to include the interaction with a non-uniform magnetic field. The field is stressed by random footpoint rotation in the central region and its energy is dissipated into heating by growing currents through anomalous magnetic diffusivity that switches on in the corona above a current density threshold. We model an entire single magnetic flux tube in the solar atmosphere extending from the high-β chromosphere to the low-β corona through the steep transition region. The magnetic field expands from the chromosphere to the corona. The maximum resolution is ∼30 km. We obtain an overall evolution typical of loop models and realistic loop emission in the EUV and X-ray bands. The plasma confined in the flux tube is heated to active region temperatures (∼3 MK) after ∼2/3 hr. Upflows from the chromosphere up to ∼100 km s −1 fill the core of the flux tube to densities above 10 9 cm. More heating is released in the low corona than the high corona and is finely structured both in space and time.

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“…For curved flux tube models previous work has addressed how the current sheets formed (e.g. Török et al 2004), how the loops responded to twist being injected through foot points (Van Hoven et al 1995;Amari et al 1996;Amari & Luciani 1999;Klimchuk et al 2000;Török & Kliem 2003;Tokman & Bellan 2002;Gerrard et al 2004;Aulanier et al 2005) and how kink unstable loops erupt through overlaying arcades (e.g. Török & Kliem 2005;Fan 2005).…”

Section: Introductionmentioning

confidence: 99%

Observational properties of a kink unstable coronal loop

Haynes

Arber

2007

A&A

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Aims. Previous work on the dynamics of the kink instability has concentrated on the evolution of the magnetic field and associated current sheets. Here we aim to determine the observational consequences of the kink instability in short coronal loops, particularly what images TRACE would record of such an instability. This paper concentrates on the internal m = 1 mode where the kink structure of the instability may not be apparent from the global field shape. This is most relevant to the observation of active region brightenings and coronal bright points.Methods. An existing fluid code was modified to include the TRACE temperature response function in order to calculate temporally and spatially averaged, line of sight images in the 171, 195 and 284 Å band passes for straight, kink unstable flux tubes. Results. Two new fluid effects of the kink instability are discovered: the circular enhancement of the density at the foot points and the appearance of a low density band running across the flux tube. The second of these effects is shown to be imagable by TRACE and hence would be a good candidate observational signature for an internal m = 1 kink unstable loop.

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Twisted Coronal Magnetic Loops

Cited by 54 publications

References 31 publications

Kink oscillations of cooling coronal loops with variable cross-section

Kink oscillations of cooling coronal loops with variable cross-section

3d MHD Modeling of Twisted Coronal Loops

Observational properties of a kink unstable coronal loop

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