Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind

Zaqarashvili, T. V.; Vörös, Z.; Zhelyazkov, I.

doi:10.1051/0004-6361/201322808

Cited by 45 publications

(61 citation statements)

References 43 publications

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“…Therefore, the gradient of the pressure perturbation is retained in the momentum equation, while the time derivative of density perturbations is neglected in the continuity equation (Chandrasekhar 1961). After straightforward calculations, the total (thermal + magnetic) pressure perturbations are governed by the Bessel equation (Goossens et al 1992;Zaqarashvili et al 2014Zaqarashvili et al , 2015 which has a solution in terms of Bessel functions. The continuity of the Lagrangian total pressure and displacement results in the dispersion equation where ω is the angular frequency, w Ai and w Ae are the Alfvén frequencies inside and outside the tube respectively, m is the azimuthal wave number, k z is the longitudinal wavenumber, and r i and r e are the densities inside and outside the tube, respectively.…”

Section: Khi: Theorymentioning

confidence: 99%

“…The continuity of the Lagrangian total pressure and displacement results in the dispersion equation where ω is the angular frequency, w Ai and w Ae are the Alfvén frequencies inside and outside the tube respectively, m is the azimuthal wave number, k z is the longitudinal wavenumber, and r i and r e are the densities inside and outside the tube, respectively. Furthermore, (see Zaqarashvili et al 2014). The dispersion relation (1) is a transcendental equation for the complex wave frequency, ω, whose imaginary part indicates an instability process in the system, in particular, the growth rate of unstable harmonics.…”

Section: Khi: Theorymentioning

confidence: 99%

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Kelvin–helmholtz Instability in Solar Chromospheric Jets: Theory and Observation

Kuridze

Zaqarashvili

Henriques³

et al. 2016

ApJ

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Using data obtained by the high-resolution CRisp Imaging SpectroPolarimeter instrument on the Swedish 1 m Solar Telescope, we investigate the dynamics and stability of quiet-Sun chromospheric jets observed at the disk center. Small-scale features, such as rapid redshifted and blueshifted excursions, appearing as high-speed jets in the wings of the Hα line, are characterized by short lifetimes and rapid fading without any descending behavior. To study the theoretical aspects of their stability without considering their formation mechanism, we model chromospheric jets as twisted magnetic flux tubes moving along their axis, and use the ideal linear incompressible magnetohydrodynamic approximation to derive the governing dispersion equation. Analytical solutions of the dispersion equation indicate that this type of jet is unstable to Kelvin-Helmholtz instability (KHI), with a very short (few seconds) instability growth time at high upflow speeds. The generated vortices and unresolved turbulent flows associated with the KHI could be observed as a broadening of chromospheric spectral lines. Analysis of the Hα line profiles shows that the detected structures have enhanced line widths with respect to the background. We also investigate the stability of a larger-scale Hα jet that was ejected along the line of sight. Vortex-like features, rapidly developing around the jet's boundary, are considered as evidence of the KHI. The analysis of the energy equation in the partially ionized plasma shows that ion-neutral collisions may lead to fast heating of the KH vortices over timescales comparable to the lifetime of chromospheric jets.

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Section: Khi: Theorymentioning

confidence: 99%

Section: Khi: Theorymentioning

confidence: 99%

Kelvin–helmholtz Instability in Solar Chromospheric Jets: Theory and Observation

Kuridze

Zaqarashvili

Henriques³

et al. 2016

ApJ

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“…For the particular case of turbulent plumes in prominences, Soler et al (2012) concluded that sub-Alfvénic flow velocities can trigger the KH instability thanks to the ion-neutral coupling. Zaqarashvili, Vörös & Zhelyazkov (2014a) in exploring the KH instability of twisted cylindrical magnetic flux tubes in the solar wind have obtained that twisted magnetic flux tubes can be unstable to KH instability when they move with regard to the solar wind stream. It was found also that the external axial magnetic field stabilizes KH instability, therefore, the tubes moving along Parker spiral are unstable only for super-Alfvńic motions.…”

Section: Waves and Instabilities In Twisted Solar Magnetic Structuresmentioning

confidence: 99%

On Modeling the Kelvin–Helmholtz Instability in Solar Atmosphere

Zhelyazkov

2015

J Astrophys Astron

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Abstract.In the present review article, we discuss the recent developments in studying the Kelvin-Helmholtz (KH) instability of magnetohydrodynamic (MHD) waves propagating in various solar magnetic structures. The main description is on the modeling of KH instability developing in the coronal mass ejections (CMEs), and contributes to the triggering of wave turbulence subsequently leading to the coronal heating. KH instability of MHD waves in coronal active regions recently observed and imaged in unprecedented detail in EUV high cadence, highresolution observations by SDO /AIA, and spectroscopic observations by Hinode/EIS instrument, is posing now challenge for its realistic modeling. It is shown that considering the solar mass flows of CMEs as moving cylindrical twisted magnetic flux tubes, the observed instability can be explained in terms of unstable m = −3 MHD mode. We also describe the occurrence of the KH instability in solar jets. The obtained critical jet speeds for the instability onset as well as the linear wave growth rates are in good agreement with the observational data of solar jets.

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“…Dispersion relations of MHD waves propagating on cylindrical untwisted and twisted plasma jets are generally well-known and here we will only give their final form-their derivation the reader can see in Zhelyazkov 2012a; Zhelyazkov & Zaqarashvily 2012;Zaqarashvili et al 2014 and references therein. We recall that all perturbed quantities associated with the waves are proportional to exp[−i(ωt − mφ − k z z)], where ω is the wave angular frequency, m the azimuthal wave mode number, and k z the axial wavenumber (as usual, we assume that waves propagate in z direction).…”

Section: Introductionmentioning

confidence: 99%

“…As we will demonstrate shortly, the kink mode can become unstable against the KH instability. As one can expect, the dispersion relation of MHD modes propagating on a moving twisted flux tube is more complicated and has the form (Zhelyazkov & Zaqarashvily 2012;Zaqarashvili et al 2014)…”

Section: Introductionmentioning

confidence: 99%

Kelvin–Helmholtz instability in an active region jet observed with Hinode

Zhelyazkov

Chandra

Srivastava

2016

Astrophys Space Sci

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Over past ten years a variety of jet-like phenomena were detected in the solar atmosphere, including plasma ejections over a range of coronal temperatures being observed as extreme ultraviolet (EUV) and X-ray jets. We study the possibility for the development of Kelvin-Helmholtz (KH) instability of transverse magnetohydrodynamic (MHD) waves traveling along an EUV jet situated on the west side of NOAA AR 10938 and observed by three instruments on board Hinode on 2007 January 15/16 (Chifor et al., Astron. Astrophys. 481, L57 (2008)). The jet was observed around Log T e = 6.2 with up-flow velocities exceeded 150 km s −1 . Using Fe XII λ186 and λ195 line ratios, the measured densities were found to be above Log N e = 11. We have modeled that EUV jet as a vertically moving magnetic flux tube (untwisted and weakly twisted) and have studied the propagation characteristics of the kink (m = 1) mode and the higher m modes with azimuthal mode numbers m = 2, 3, 4. It turns out that all these MHD waves can become unstable at flow velocities in the range of 112-114.8 km s −1 . The lowest critical jet velocity of 112 km s −1 is obtained when modeling the jet as compressible plasma contained in an untwisted magnetic flux tube. When the jet and its environments are treated as incompressible media, the critical jet velocity becomes higher, namely 114.8 km s −1 . A weak twist of the equilibrium magnetic field in the same approximation of incompressible plasmas slightly decreases the threshold Alfvén Mach number, M cr A , and consequently the corresponding critical velocities, notably to 114.4 km s −1 for the kink mode and to 112.4 km s −1 for the higher m modes. We have also compared two analytically found criteria for predicting the threshold Alfvén Mach number for the onset of KH instability and have concluded that one of them yields reliable values for M cr A . Our study of the nature of stable and unstable MHD modes propagating on the jet shows that in a stable regime all the modes are pure surface waves, while the unstable kink (m = 1) mode in untwisted compressible plasma flux tube becomes a leaky wave. In the limit of incompressible media (for the jet and its environment) all unstable modes are non-leaky surface waves.

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Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind

Cited by 45 publications

References 43 publications

Kelvin–helmholtz Instability in Solar Chromospheric Jets: Theory and Observation

Kelvin–helmholtz Instability in Solar Chromospheric Jets: Theory and Observation

On Modeling the Kelvin–Helmholtz Instability in Solar Atmosphere

Kelvin–Helmholtz instability in an active region jet observed with Hinode

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