Kink instability of solar coronal loops as the cause of solar flares

Hood, A. W.; Priest, E. R.

doi:10.1007/bf00151441

Cited by 352 publications

(217 citation statements)

References 16 publications

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“…The magnetic reconnection in twisted coronal loops atmosphere after kink instability has been described in many earlier studies (see Hood & Priest 1979;Baty & Heyvaerts 1996;Browning & Van der Linden 2003;Hood et al 2009;Gordovskyy & Browning 2012;Bareford et al 2016), while the evolution of thermal and non-thermal radiation from such systems is considered by Botha et al (2012), Gordovskyy et al (2013, Pinto et al (2016). Essentially, a loop experiences two different types of reconnection simultaneously: the reconnection between field lines of twisted fluxtube, resulting in twist reduction, and the reconnection of twisted field lines with the ambient field, resulting in the radial expansion of twisted loops (Fig.…”

Section: Main Features Of the Considered Flare Modelmentioning

confidence: 64%

Plasma motions and non-thermal line broadening in flaring twisted coronal loops

Gordovskyy

Kontar

Browning

2016

A&A

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Context. Observation of coronal extreme ultra-violet (EUV) spectral lines sensitive to different temperatures offers an opportunity to evaluate the thermal structure and flows in flaring atmospheres. This, in turn, can be used to estimate the partitioning between the thermal and kinetic energies released in flares. Aims. Our aim is to forward-model large-scale (50-10 000 km) velocity distributions to interpret non-thermal broadening of different spectral EUV lines observed in flares. The developed models allow us to understand the origin of the observed spectral line shifts and broadening, and link these features to particular physical phenomena in flaring atmospheres. Methods. We use ideal magnetohydrodynamics (MHD) to derive unstable twisted magnetic fluxtube configurations in a gravitationally stratified atmosphere. The evolution of these twisted fluxtubes is followed using resistive MHD with anomalous resistivity depending on the local density and temperature. The model also takes thermal conduction and radiative losses in the continuum into account. The model allows us to evaluate average velocities and velocity dispersions, which would be interpreted as non-thermal velocities in observations, at different temperatures for different parts of the models. Results. Our models show qualitative and quantitative agreement with observations. Thus, the line-of-sight (LOS) velocity dispersions demonstrate substantial correlation with the temperature, increasing from about 20-30 km s −1 around 1 MK to about 200-400 km s −1 near 10-20 MK. The average LOS velocities also correlate with velocity dispersions, although they demonstrate a very strong scattering compared to the observations. We also note that near footpoints the velocity dispersions across the magnetic field are systematically lower than those along the field. We conclude that the correlation between the flow velocities, velocity dispersions, and temperatures are likely to indicate that the same heating mechanism is responsible for heating the plasma, its turbulisation, and expansion/evaporation.

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Section: Main Features Of the Considered Flare Modelmentioning

confidence: 64%

Plasma motions and non-thermal line broadening in flaring twisted coronal loops

Gordovskyy

Kontar

Browning

2016

A&A

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“…This is the definition used by Hood and Priest (1979) when analysing the kink instability. The link between this definition of twist and the integral expression t w (which is the value of the force-free parameter, α, times the length of the field line) is often unclear (see the detailed theoretical comparison in Appendix C of Liu et al, 2016, and the discussion therein).…”

Section: Appendix A: Comparison Of Twist Measuresmentioning

confidence: 99%

Flux Rope Formation Due to Shearing and Zipper Reconnection

2018

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Zipper reconnection has been proposed as a mechanism for creating most of the twist in the flux tubes that are present prior to eruptive flares and coronal mass ejections. We have conducted a first numerical experiment on this new regime of reconnection, where two initially untwisted parallel flux tubes are sheared and reconnected to form a large flux rope. We describe the properties of this experiment, including the linkage of magnetic flux between concentrated flux sources at the base of the simulation, the twist of the newly formed flux rope, and the conversion of mutual magnetic helicity in the sheared pre-reconnection state into the self-helicity of the newly formed flux rope.

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“…This mechanism has been suggested to be at the origin of solar flares of different types (both confined Movies associated to Figs. 4 and 5 are available in electronic form at http://www.aanda.org and ejective) and at different spatial scales (from nano-flares to X class flares; Hood & Priest 1979;Linton et al 1996;Galsgaard & Nordlund 1997;Lionello et al 1998;Shibata & Yokoyama 1999;Török & Kliem 2005;Rappazzo et al 2013, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Soft X-ray emission in kink-unstable coronal loops

Pinto

Vilmer

Brun

2015

A&A

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Context. Solar flares are associated with intense soft X-ray emission generated by the hot flaring plasma in coronal magnetic loops. Kink-unstable twisted flux-ropes provide a source of magnetic energy that can be released impulsively and may account for the heating of the plasma in flares. Aims. We investigate the temporal, spectral, and spatial evolution of the properties of the thermal continuum X-ray emission produced in such kink-unstable magnetic flux-ropes and discuss the results of the simulations with respect to solar flare observations. Methods. We computed the temporal evolution of the thermal X-ray emission in kink-unstable coronal loops based on a series of magnetohydrodynamical numerical simulations. The numerical setup consisted of a highly twisted loop embedded in a region of uniform and untwisted background coronal magnetic field. We let the kink instability develop, computed the evolution of the plasma properties in the loop (density, temperature) without accounting for mass exchange with the chromosphere. We then deduced the X-ray emission properties of the plasma during the whole flaring episode. Results. During the initial (linear) phase of the instability, plasma heating is mostly adiabatic (as a result of compression). Ohmic diffusion takes over as the instability saturates, leading to strong and impulsive heating (up to more than 20 MK), to a quick enhancement of X-ray emission, and to the hardening of the thermal X-ray spectrum. The temperature distribution of the plasma becomes broad, with the emission measure depending strongly on temperature. Significant emission measures arise for plasma at temperatures higher than 9 MK. The magnetic flux-rope then relaxes progressively towards a lower energy state as it reconnects with the background flux. The loop plasma suffers smaller sporadic heating events, but cools down globally by thermal conduction. The total thermal X-ray emission slowly fades away during this phase, and the high-temperature component of the emission measure distribution converges to the power-law distribution EM ∝ T −4.2 . The twist deduced directly from the X-ray emission patterns is considerably lower than the highest magnetic twist in the simulated flux-ropes.

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Kink instability of solar coronal loops as the cause of solar flares

Cited by 352 publications

References 16 publications

Plasma motions and non-thermal line broadening in flaring twisted coronal loops

Plasma motions and non-thermal line broadening in flaring twisted coronal loops

Flux Rope Formation Due to Shearing and Zipper Reconnection

Soft X-ray emission in kink-unstable coronal loops

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