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

Zhelyazkov, I.; Chandra, Ramesh; Srivastava, A. K.

doi:10.1007/s10509-015-2639-2

Cited by 15 publications

(11 citation statements)

References 89 publications

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“…This result is readily applicable to standing waves, as Ruderman (2018) showed that the growth rate of a standing wave is equal to the growth rate of the propagating wave with negative energy minus the damping rate of the propagating wave with positive energy. Zhelyazkov et al (2016) carried out case studies on observed coronal jets and stated that the onset of KHI regarding kink waves depends on whether the plasma jet is incompressible or compressible, as the incompressibility elevates the KHI threshold speed. The magnetic twist of the jet decreases the KHI threshold speed.…”

Section: Negative Energy Wave Effects On Kink Oscillationsmentioning

confidence: 99%

Kink Oscillations of Coronal Loops

et al. 2021

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Kink oscillations of coronal loops, i.e., standing kink waves, is one of the most studied dynamic phenomena in the solar corona. The oscillations are excited by impulsive energy releases, such as low coronal eruptions. Typical periods of the oscillations are from a few to several minutes, and are found to increase linearly with the increase in the major radius of the oscillating loops. It clearly demonstrates that kink oscillations are natural modes of the loops, and can be described as standing fast magnetoacoustic waves with the wavelength determined by the length of the loop. Kink oscillations are observed in two different regimes. In the rapidly decaying regime, the apparent displacement amplitude reaches several minor radii of the loop. The damping time which is about several oscillation periods decreases with the increase in the oscillation amplitude, suggesting a nonlinear nature of the damping. In the decayless regime, the amplitudes are smaller than a minor radius, and the driver is still debated. The review summarises major findings obtained during the last decade, and covers both observational and theoretical results. Observational results include creation and analysis of comprehensive catalogues of the oscillation events, and detection of kink oscillations with imaging and spectral instruments in the EUV and microwave bands. Theoretical results include various approaches to modelling in terms of the magnetohydrodynamic wave theory. Properties of kink oscillations are found to depend on parameters of the oscillating loop, such as the magnetic twist, stratification, steady flows, temperature variations and so on, which make kink oscillations a natural probe of these parameters by the method of magnetohydrodynamic seismology.

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Section: Negative Energy Wave Effects On Kink Oscillationsmentioning

confidence: 99%

Kink Oscillations of Coronal Loops

et al. 2021

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“…It is worth pointing out, however, that for a twisted magnetic field the magnitude of the axial magnetic field component B iz , which is used for computing both ε 1 and v Ai , is less than B i itself. This implies that the reference Alfvén speed v Ai must be corrected along with the magnetic fields ratio b, notably b should be replaced by b twist = b 1 + ε 2 1 and, accordingly, v Ai → v Ai / 1 + ε 2 1 (see Zhelyazkov et al (2016)). The diminished value of v Ai requires a correction of the Alfvén Mach number, too, namely M A should be replaced by M A 1 + ε 2 1 .…”

Section: Dispersion Curves and Growth Rates Of The Unstable M = 2 Mhdmentioning

confidence: 99%

Kelvin–Helmholtz instability in a twisting solar polar coronal hole jet observed by SDO/AIA

Zhelyazkov

Zaqarashvili

Ofman

et al. 2018

Advances in Space Research

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We investigate the conditions under which the fluting (m = 2), m = 3, and m = 12 magnetohydrodynamic (MHD) modes in a uniformly twisted flux tube moving along its axis become unstable in order to model the Kelvin-Helmholtz (KH) instability in a twisting solar coronal hole jet near the northern pole of the Sun. We employed the dispersion relations of MHD modes derived from the linearized MHD equations. We assumed real wavenumbers and complex angular wave frequencies, namely complex wave phse velocities. The dispersion relations were solved numerically at fixed input parameters (taken from observational data) and varying degrees of torsion of the internal magnetic field. It is shown that the stability of the modes depends upon five parameters: the density contrast between the flux tube and its environment, the ratio of the external and internal axial magnetic

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“…There is an unexpected peculiarity-the threshold Alfvén Mach number for instability arising turns out to be lower than that in untwisted flux tube, notably equal to 2.30839, which yields a critical flow speed of ≈308 km s −1 -24 km s −1 less than the average jet speed. An (Zhelyazkov et al, 2016).…”

Section: Kink Mode Propagation Characteristics At a Density Contrast mentioning

confidence: 99%

Solar jet on 2014 April 16 modeled by Kelvin–Helmholtz instability

et al. 2018

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We study here the arising of Kelvin-Helmholtz Instability (KHI) in one fast jet of 2014 April 16 observed by the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) in different UV and EUV wavelengths. The evolution of jet indicates the blob like structure at its boundary which could be the observational evidence of the KHI. We model the jet as a moving cylindrical magnetic flux tube of radius a embedded in a magnetic field B i and surrounded by rest magnetized plasma with magnetic field B e . We explore the propagation of the kink MHD mode along the jet that can become unstable against the KHI if its speed exceeds a critical value.Concerning magnetic fields topology we consider three different configurations, notably of (i) spatially homogeneous magnetic fields (untwisted magnetic flux tube), (ii) internal (label 'i') twisted magnetic field and external homogeneous one (label 'e') (single-twisted flux tube), and (iii) both internal and external twisted magnetic fields (double-twisted magnetic flux tube). Plasma densities in the two media ρ i and ρ e are assumed to be homogeneous. The density contrast is defined in two ways: first as ρ e /ρ i and second as ρ e /(ρ i + ρ e ). Computations show that the KHI can occur at accessible flow velocities in all the cases of untwisted and single-twisted flux tubes. It turns out, however, that in the case of a double-twisted flux tube the KHI can merge at an accessible jet speed only when the density contrast is calculated from the ratio ρ e /(ρ i + ρ e ).Evaluated KHI developing times and kink mode wave phase velocities at wavelength of 4 Mm lie in the ranges of 1-6.2 min and 202-271 km s −1 , respectively-all being reasonable for the modeled jet.

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

Cited by 15 publications

References 89 publications

Kink Oscillations of Coronal Loops

Kink Oscillations of Coronal Loops

Kelvin–Helmholtz instability in a twisting solar polar coronal hole jet observed by SDO/AIA

Solar jet on 2014 April 16 modeled by Kelvin–Helmholtz instability

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