Kelvin-Helmholtz {instability induced} turbulence is one promising mechanism by which loops in the solar corona can be heated by MHD waves. In this paper we present an analytical model of the dissipation rate of {Kelvin-Helmholtz instability induced} turbulence $\varepsilon_{\rm D}$, finding it scales as the wave amplitude ($d$) to the third power ($\varepsilon_{\rm D}\propto d^3$). Based on the concept of steady-state turbulence, we expect the turbulence heating throughout the volume of {the} loop to match the total energy injected through its footpoints. In situations where this holds, the wave amplitude has to vary as the cube-root of the injected energy. Comparing the analytic results with those of simulations shows that our analytic formulation captures the key aspects of the turbulent dissipation from the numerical work. Applying this model to the observed characteristics of decayless kink waves we predict that the amplitudes of these observed waves is insufficient to turbulently heat the solar corona.
The Kelvin-Helmholtz instability has been proposed as a mechanism to extract energy from magnetohydrodynamic (MHD) kink waves in flux tubes, and to drive dissipation of this wave energy through turbulence. It is therefore a potentially important process in heating the solar corona. However, it is unclear how the instability is influenced by the oscillatory shear flow associated with an MHD wave. We investigate the linear stability of a discontinuous oscillatory shear flow in the presence of a horizontal magnetic field within a Cartesian framework that captures the essential features of MHD osc…
Prominences are incredibly dynamic across the whole range of their observable spatial scales, with observations revealing gravity-driven fluid instabilities, waves, and turbulence. With all these complex motions, it would be expected that instabilities driven by shear in the internal fluid motions would develop. However, evidence of these have been lacking. Here we present the discovery in a prominence, using observations from the Interface Region Imaging Spectrograph (IRIS), of a shear flow instability, the Kelvin-Helmholtz sinusoidal-mode of a fluid channel, driven by flows in the prominence…
Solar wind plasma is supposed to be structured in magnetic flux tubes carried from the solar surface. Tangential velocity discontinuity near the boundaries of individual tubes may result in Kelvin-Helmholtz instability, which may contribute into the solar wind turbulence. While the axial magnetic field may stabilize the instability, a small twist in the magnetic field may allow to sub-Alfvenic motions to be unstable. We aim to study the Kelvin-Helmholtz instability of twisted magnetic flux tube in the solar wind with different configurations of external magnetic field. We use magnetohydrodynam…
In the Hall magnetohydrodynamics, the onset condition of the Kelvin Helmholtz instability is solely determined by the Hall effect and is independent of the nature of shear flows. In addition, the physical mechanism behind the super and sub Alfvenic flows becoming unstable is quite different: the high frequency right circularly polarized whistler becomes unstable in the super Alfvenic flows whereas low frequency, left circularly polarized ion-cyclotron wave becomes unstable in the presence of sub Alfvenic shear flows. The growth rate of the Kelvin Helmholtz instability in the super Alfvenic cas…
The Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory observed a coronal mass ejection with an embedded filament on 2011 February 24, reavealing quasi-periodic vortex-like structures at the northern side of the filament boundary with a wavelength of approximately 14.4 Mm and a propagation speed of about 310 +- 20 km/s. These structures could result from the Kelvin-Helmholtz instability occurring on the boundary. We perform 2.5D numerical simulations of the Kelvin-Helmholtz instability and compare the simulated characteristic properties of the instability with the observations…
There has been interest in recent years to assess the ability of astrophysical hydrodynamics codes to correctly model the Kelvin-Helmholtz instability. Smoothed particle hydrodynamics (SPH), in particular, has received significant attention, though there has yet to be a clear demonstration that SPH yields converged solutions that are in agreement with other methods. We have performed SPH simulations of the Kelvin-Helmholtz instability using the test problem put forward by Lecoanet et al (2016). We demonstrate that the SPH solutions converge to the reference solution in both the linear and non-…
Transversal oscillations of spicules axes may be related to the propagation of magnetohydrodynamic waves along them. These waves may become unstable and the instability can be of the Kelvin-Helmholtz type. We use the dispersion relation of kink mode derived from linearized magnetohydrodynamic equations. The input parameters of the derived dispersion equation, namely, spicules and their ambient medium densities ratios as well as their corresponding magnetic fields ratios, are considered to be within the range $0-1$. By solving the dispersion equation numerically, we show that for higher densiti…
Recent observations show cool, oscillating prominence threads fading when observed in cool spectral lines and appearing in warm spectral lines. A proposed mechanism to explain this evolution is that the threads were heated by turbulence driven by the Kelvin--Helmholtz instability that developed as a result of wave-driven shear flows on the surface of the thread. As the Kelvin--Helmholtz instability is an instability that works to mix the fluids, in the solar corona it can be expected to work by mixing the cool prominence material with that of the hot corona to form a warm boundary layer. In th…
Over the last few years it became clear that turbulent magnetic reconnection and magnetized turbulence are inseparable. It was not only shown that reconnection is responsible for violating the frozen-in condition in turbulence, but also that stochastic reconnection in 3D generates turbulence by itself. The actual mechanism responsible for this driving is still unknown. Processes such tearing mode or Kelvin-Helmholtz, among other plasma instabilities, could generate turbulence from irregular current sheets. We address the nature of driving mechanism for this process and consider a relative role…
Recent high resolution AIA/SDO images show evidence of the development of the Kelvin-Helmholtz instability, as coronal mass ejections (CMEs) expand in the ambient corona. A large-scale magnetic field mostly tangential to the interface is inferred, both on the CME and on the background sides. However, the magnetic field component along the shear flow is not strong enough to quench the instability. There is also observational evidence that the ambient corona is in a turbulent regime, and therefore the criteria for the development of the instability are a-priori expected to differ from the lamina…
The main aim of this submission is to investigate the effects of some parameters like wave number, shear velocity, magnetic field and temperature for the growth rate of the magnetized Kelvin-Helmholtz instability (KHI) with incessant profiles through interface of two viscous fluid layer occurred in the solar atmosphere using the model of Hoshoudy, Cavus and Mahdy (2019). In this examination, the presence of KHI is identified for the various cases of wave number, magnetic field, shear velocity and temperature in the solar atmosphere. The sensible values of these parameters were acquired.
The linear MHD Kelvin-Helmholtz instability (KHI) in an anisotropic plasma concerning the direction of an external magnetic field is examined in detail. For this purpose, the MHD equations are used to describe the motion of plasma as a fluid, which is derived from 16 moments of Boltzmann-Vlasov kinetic equations for collisionless plasma. In addition, the heat flux along the magnetic field is taken into account. The growing rates of KHI are calculated as functions of the anisotropic plasma properties for a shear flow along the magnetic field at supersonic velocities. On the other hand, the quas…
Using two-dimensional simulations, we numerically explore the dependences of Kelvin-Helmholtz instability upon various physical parameters, including viscosity, width of sheared layer, flow speed, and magnetic field strength. In most cases, a multi-vortex phase exists between the initial growth phase and final single-vortex phase. The parametric study shows that the evolutionary properties, such as phase duration and vortex dynamics, are generally sensitive to these parameters except in certain regimes. An interesting result is that for supersonic flows, the phase durations and saturation of v…
The nonlinear magnetic Kelvin-Helmholtz instability (KHi), and the turbulence it creates, appears in many astrophysical systems. This includes those systems where the local plasma conditions are such that the plasma is not fully ionised, for example in the lower solar atmosphere and molecular clouds. In a partially ionised system, the fluids couple via collisions which occur at characteristic frequencies, therefore neutral and plasma species become decoupled for sufficiently high-frequency dynamics. Here we present high-resolution 2D two-fluid simulations of the nonlinear KHi for a system that…
The shear-flow-driven instability can play an important role in energy transfer processes in coronal plasma. We present for the first time the observation of a kink-like oscillation of a streamer probably caused by the streaming kinkmode Kelvin-Helmholtz instability. The wave-like behavior of the streamer was observed by Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 and C3 aboard SOlar and Heliospheric Observatory (SOHO). The observed wave had a period of about 70 to 80 minutes, and its wavelength increased from 2 Rsun to 3 Rsun in about 1.5 hours. The phase speeds of its cre…
We report here, for the first time, an observed instability of a Kelvin-Helmholtz (KH) nature occurring in a fully three-dimensional (3D) current-vortex sheet at the fan plane of a 3D magnetic null point. The current-vortex layer forms self-consistently in response to foot point driving around the spine lines of the null. The layer first becomes unstable at an intermediate distance from the null point, with the instability being characterized by a rippling of the fan surface and a filamentation of the current density and vorticity in the shear layer. Owing to the 3D geometry of the shear layer…
I show that after the "helium flash" abruptly ends its first ascent red giant evolution, a solar-type star is powered primarily by gravitational contraction of its helium core, rather than by nuclear fusion. Because this energy is released in the core rather than the envelope, the overall structure of the star, and so its luminosity, is driven toward that of a red clump star from its initial position at the tip of the red giant branch (TRGB). This occurs on a first (and well recognized) Kelvin-Helmholtz timescale t_{KH,1} ~ E_env/L_TRGB ~ 1e4 yrs., where E_env is the thermal energy stored in t…
We investigate conditions under which kink magnetohydrodynamic waves propagating along photospheric uniformly twisted flux tubes with axial mass flows become unstable as a consequence of the Kelvin-Helmholtz instability. We employed the dispersion relations of kink waves derived from the linearised magnetohydrodynamic equations. We assumed real wave numbers and complex angular wave frequencies, namely complex wave phase velocities. The dispersion relations were solved numerically at fixed input parameters and several mass flow velocities. We show that the stability of the waves depends upon fo…
Context. The magnetic Kelvin-Helmholtz instability (KHI) has been proposed as a means of generating magnetohy- drodynamic turbulence and encouraging wave energy dissipation in the solar corona, particularly within transversely oscillating loops. Aims. Our goal is to determine whether the KHI encourages magnetic reconnection in oscillating flux tubes in the solar corona. This will establish whether the instability enhances the dissipation rate of energy stored in the magnetic field. Methods. We conducted a series of three-dimensional magnetohydrodynamic simulations of the KHI excited by an osci…
We explore magnetic-field amplification due to the Kelvin-Helmholtz instability during binary neutron star mergers. By performing high-resolution general relativistic magnetohydrodynamics simulations with a resolution of $17.5$ m for $4$--$5$ ms after the onset of the merger on the Japanese supercomputer "K", we find that an initial magnetic field of moderate maximum strength $10^{13}$ G is amplified at least by a factor of $\approx 10^3$. We also explore the saturation of the magnetic-field energy and our result shows that it is likely to be $\gtrsim 4 \times 10^{50}$ erg, which is $\gtrsim 0…
We present observations of the formation, propagation and decay of vortex- shaped features in coronal images from the Solar Dynamics Observatory (SDO) associated with an eruption starting at about 2:30UT on Apr 8, 2010. The series of vortices formed along the interface between an erupting (dimming) region and the surrounding corona. They ranged in size from several to ten arcseconds, and traveled along the interface at 6-14 km/s. The features were clearly visible in six out of the seven different EUV wavebands of the Atmospheric Imaging Assembly (AIA). Based on the structure, formation, propag…
We perform simulations of the Kelvin-Helmholtz instability using smoothed particle hydrodynamics (SPH). The instability is studied both in the linear and strongly non-linear regimes. The smooth, well-posed initial conditions of Lecoanet et al. (2016) are used, along with an explicit Navier-Stokes viscosity and thermal conductivity to enforce the evolution in the non-linear regime. We demonstrate convergence to the reference solution using SPH. The evolution of the vortex structures and the degree of mixing, as measured by a passive scalar `colour' field, match the reference solution. Tests wit…
We report on a three-dimensional MHD numerical experiment of a small scale coronal mass ejection (CME) -like eruption propagating though a non-magnetized solar atmosphere. We find that the Kelvin-Helmholtz instability (KHI) develops at various but specific locations at the boundary layer between the erupting field and the background atmosphere, depending on the relative angle between the velocity and magnetic field. KHI develops at the front and at two of the four sides of the eruption. KHI is suppressed at the other two sides of the eruption. We also find the development of Alfvénic vortex sh…
Observations show various jets in the solar atmosphere with significant rotational motions, which may undergo instabilities leading to heat ambient plasma. We study the Kelvin-Helmholtz (KH) instability of twisted and rotating jets caused by the velocity jumps near the jet surface. We derive a dispersion equation with appropriate boundary condition for total pressure (including centrifugal force of tube rotation), which governs the dynamics of incompressible jets. Then, we obtain analytical instability criteria of Kelvin-Helmholtz instability in various cases, which were verified by numerical …
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, high-resolution observations by SDO/AIA, and spectroscopic observ…
Context: Magnetic null points are associated with high-energy coronal phenomena such as solar flares and are often sites of reconnection and particle acceleration. Dynamic twisting of a magnetic null point can generate a Kelvin-Helmholtz instability (KHI) within its fan plane and, under continued twisting, can instigate spine-fan reconnection and an associated collapse of the null point. Aim: This article aims to compare the effects of isotropic and anisotropic viscosity in simulations of the KHI and collapse in a dynamically twisted magnetic null point. Methods: Simulations were performed usi…
The Kelvin-Helmholtz Instability (KHI) has been observed in the solar atmosphere. Ion-neutral collisions may play a relevant role for the growth rate and evolution of the KHI in solar partially ionized plasmas as in, e.g., solar prominences. Here, we investigate the linear phase of the KHI at an interface between two partially ionized magnetized plasmas in the presence of a shear flow. The effects of ion-neutral collisions and compressibility are included in the analysis. We obtain the dispersion relation of the linear modes and perform parametric studies of the unstable solutions. We find tha…
We perform two-dimensional resistive magnetohydrodynamic simulations of coronal jets driven by flux emergence along the lower boundary. The reconnection layers are susceptible the formation of blobs that are ejected in the jet. Our simulation with low plasma $β$ (Case I) shows that magnetic islands form easily and propagate upwards in the jet. These islands are multithermal and thus are predicted to show up in hot channels (335 Å\, and 211 Å) and the cool channel (304 Å) in observations by the Atmospheric Imaging Assembly (AIA) on the \emph{Solar Dynamics Observatory}. The islands have maximum…
The presence of dust grains profoundly affects the diffusion of the magnetic field in molecular clouds. When the electrons and ions are well coupled to the magnetic field and charged grains are only indirectly coupled, emergent Hall diffusion may dominate over all the other non ideal magnetohydrodynamic (MHD) effects in a partially ionized dusty cloud. The low frequency, long wavelength (0.01 t0 1 pc) dispersive MHD waves will propagate in such a medium with the polarization of the waves determined by the dust charge density or the dust size distribution. In the presence of shear flows, these …
Recent numerical simulations have demonstrated that transverse coronal loop oscillations are susceptible to the Kelvin-Helmholtz (KH) instability due to the counter-streaming motions at the loop boundary. We present the first analytical model of this phenomenon. The region at the loop boundary where the shearing motions are greatest is treated as a straight interface separating time-periodic counter-streaming flows. In order to consider a twisted tube, the magnetic field at one side of the interface is inclined. We show that the evolution of the displacement at the interface is governed by Mat…
We study the evolutionary conditions for Kelvin-Helmholtz (KH) instability in a H-alpha solar surge observed in NOAA AR 8227 on 1998 May 30. The jet with speeds in the range of 45-50 km/s, width of 7 Mm, and electron number density of 3.83 x 10^{10} cm^{-3} is assumed to be confined in a twisted magnetic flux tube embedded in a magnetic field of 7 G. The temperature of the plasma flow is of the order of 10^5 K while that of its environment is taken to be 2 x 10^6 K. The electron number density of surrounding magnetized plasma has a typical for the TR/lower corona region value of 2 x 10^{9} cm^…
Recent observations support the propagation of a number of magnetohydrodynamic (MHD) modes which, under some conditions, can become unstable and the developing instability is the Kelvin--Helmholtz instability (KHI). In its nonlinear stage the KHI can trigger the occurrence of wave turbulence which is considered as a candidate mechanism for coronal heating. We review the modeling of tornado-like phenomena in the solar chromosphere and corona as moving weakly twisted and spinning cylindrical flux tubes, showing that the KHI rises at the excitation of high-mode MHD waves. The instability occurs w…
Kelvin-Helmholtz instability (KHI) is a basic physical process in fluids and magnetized plasmas, with applications successfully modelling e.g. exponentially growing instabilities observed at magnetospheric and heliospheric boundaries, in the solar or Earth's atmosphere and within astrophysical jets. Here, we report the discovery of the KHI in solar blowout jets and analyse the detailed evolution by employing high-resolution data from the Interface Region Imaging Spectrograph (IRIS) satellite launched in 2013. The particular jet we focus on is rooted in the surrounding penumbra of the main nega…
Context. Recent observations of solar prominences show the presence of turbulent flows that may be caused by Kelvin-Helmholtz instabilites (KHI). However, the observed flow velocities are below the classical threshold for the onset of KHI in fully ionized plasmas. Aims. We investigate the effect of partial ionization on the onset of KHI in dense and cool cylindrical magnetic flux tubes surrounded by a hotter and lighter environment. Methods. The linearized governing equations of a partially ionized two-fluid plasma are used to describe the behavior of small-amplitude perturbations superimposed…
Magnetospheric Multiscale (MMS) observations of plasma turbulence generated by a Kelvin-Helmholtz (KH) event at the Earth's magnetopause are compared with a high-resolution two-dimensional (2D) hybrid direct numerical simulation (DNS) of decaying plasma turbulence driven by large-scale balanced Alfvénic fluctuations. The simulation, set up with four observation-driven physical parameters (ion and electron betas, turbulence strength, and injection scale) exhibits a quantitative agreement on the spectral, intermittency, and cascade-rate properties with in situ observations, despite the different…
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. Using a twisting jet of 2010 August 21 by \emph{SDO}/AIA and other observations of coronal jets we set the parameters of our theoretical model and have obtained that in a twisted magnetic flux tube of radius of $9.8$~Mm, at a density contrast of $0.474$ and fixed Alfvén Mach numbe…
In the present paper, we study the evolutionary conditions for Kelvin--Helmholtz (KH) instability in a high-temperature solar surge observed in NOAA AR11271 using the Solar Dynamics Observatory data on 2011 August 25. We study the propagation of normal MHD modes in a flux tube considering the two cases, notably of untwisted magnetic flux tube and the twisted one. The numerical solution to the dispersion relation shows that the kink ($m = 1$) wave traveling in an untwisted flux tube becomes unstable if the jet speed exceeds $1060$ km\,s$^{-1}$ -- a speed which is inaccessible for solar surges. …
Aims - Investigate the effects of resistivity and viscosity on the onset and growth of the Kelvin-Helmholtz instability (KHI) in an oscillating coronal loop. Methods - We modelled a standing kink wave in a density-enhanced loop with the three dimensional (3-D), resistive magnetohydrodynamics code, Lare3d. We conducted a parameter study on the viscosity and resistivity coefficients to examine the effects of dissipation on the KHI. Results - Enhancing the viscosity and resistivity acts to suppress the KHI. Larger values delay the formation of the instability and, in some cases, prevent the onset…
In the highly structured solar corona, resonant absorption is an unavoidable mechanism of energy transfer from global transverse MHD waves to local azimuthal Alfvén waves. Due to its localised nature, a direct detection of this mechanism is extremely difficult. Yet, it is the leading theory explaining the observed fast damping of the global transverse waves. However, at odds with this theoretical prediction, recent observations indicate that in the low amplitude regime such transverse MHD waves can also appear decay-less, a yet unsolved phenomenon. Recent numerical work has shown that Kelvin-H…
We analyze solar quiescent prominence bubble characteristics and instability dynamics using Hinode/Solar Optical Telescope (SOT) data. We measure bubble expansion rate, prominence downflows, and the profile of the boundary layer brightness and thickness as a function of time. The largest bubble analyzed rises into the prominence with a speed of about 1.3 km/s until it is destabilized by a localized shear flow on the boundary. Boundary layer thickness grows gradually as prominence downflows deposit plasma onto the bubble with characteristic speeds of 20 - 35 km/s. Lateral downflows initiate fro…
Hard X-ray (HXR) sources are frequently observed near the top of solar flare loops, and the emission is widely ascribed to bremsstrahlung. We here revisit an alternative scenario which stresses the importance of inverse Compton processes and the Kelvin- Helmholtz instability (KHI) proposed by Fang et al. (2016). This scenario adds a novel ingredient to the standard flare model, where evaporation flows from flare-impacted chromospheric foot-points interact with each other near the loop top and produce turbulence via KHI. The turbulence can act as a trapping region and as an efficient accelerato…
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 disk center. Small-scale features, such as Rapid Redshifted and Blueshifted Excursions, appearing as high speed jets in the wings of the H$α$ 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 tube…
The Kelvin-Helmholtz (KH) instability is commonly found in many astrophysical, laboratory, and space plasmas. It could mix plasma components of different properties and convert dynamic fluid energy from large scale structure to smaller ones. In this study, we combined the ground-based New Vacuum Solar Telescope (NVST) and the Solar Dynamic Observatories (SDO) / Atmospheric Imaging Assembly (AIA) to observe the plasma dynamics associated with active region 12673 on 09 September 2017. In this multi-temperature view, we identified three adjacent layers of plasma flowing at different speeds, and d…
We use multiwavelength imaging observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to study the evolution of Kelvin-Helmholtz (K-H) instability in a fan-spine magnetic field configuration. This magnetic topology exists near an active region AR12297 and is rooted in a nearby sunspot. In this magnetic configuration, two layers of cool plasma flow in parallel and interact with each other inside an elongated spine. The slower plasma flow (5 $km s^{-1}$) is the reflected stream along the spine field lines from the top, which interacts with the impul…
In addition to their jet-like dynamic behaviour, spicules usually exhibit strong transverse speeds, multi-stranded structure and heating from chromospheric to transition region temperatures. In this work we first analyse \textit{Hinode} \& \textit{IRIS} observations of spicules and find different behaviours in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models or long wavelength to…
We investigate the conditions at which high-mode magnetohydrodynamic (MHD) waves propagating in a spinning solar macrospicule can become unstable with respect to the Kelvin--Helmholtz instability (KHI). We consider the macrospicule as a weakly twisted cylindrical magnetic flux tube moving along and rotating around its axis. Our study is based on the dispersion relation (in complex variables) of MHD waves obtained from the linearized MHD equations of an incompressible plasma for the macrospicule and cool ($β= 0$, rate of the plasma to the magnetic pressure) plasma for its environment. This disp…
