Modelling observed decay-less oscillations as resonantly enhanced Kelvin-Helmholtz vortices from transverse MHD waves and their seismological application

Abstract

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-Helmholtz instabilities (KHI) often accompany transverse MHD waves. In this work, we combine 3D MHD simulations and forward modelling to show that for currently achieved spatial resolution and observed small amplitudes, an apparent decay-less oscillation is obtained. This effect results from the combination of periodic brightenings produced by the KHI and the coherent motion of the KHI vortices amplified by resonant absorption. Such effect is especially clear in emission lines forming at temperatures that capture the boundary dynamics rather than the core, and reflects the low damping character of the local azimuthal Alfvén waves resonantly coupled to the kink mode. Due to phase mixing, the detected period can vary depending on the emission line, with those sensitive to the boundary having shorter periods than those sensitive to the loop core. This allows to estimate the density contrast at the boundary.

8 pages, 4 figures; Accepted for publication in The Astrophysical Journal Letters

References in corpus (3)

• Nonlinear Instability of kink oscillations due to shear motions
• Fine strand-like structure in the solar corona from MHD transverse oscillations
• Resonant absorption in complicated plasma configurations: applications to multi-stranded coronal loop oscillations

Cited by in corpus (23)

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• Kink oscillations of coronal loops
• Heating by transverse waves in simulated coronal loops
• Excitation of decay-less transverse oscillations of coronal loops by random motions
• Decayless oscillations in solar coronal bright points
• Amplitudes and energy fluxes of simulated decayless kink oscillations
• Magnetohydrodynamic Seismology of Quiet Solar Active Regions
• Wave heating in gravitationally stratified coronal loops in the presence of resistivity and viscosity
• Generating transverse loop oscillations through a steady-flow driver
• What drives decayless kink oscillations in active region coronal loops on the Sun?
• Flare induced decay-less transverse oscillations in solar coronal loops
• Two-Spacecraft Detection of Short-period Decayless Kink Oscillations of Solar Coronal Loops
• An Analytical Model of the Kelvin-Helmholtz Instability of Transverse Coronal Loop Oscillations
• Coronal cooling as a result of mixing by the nonlinear Kelvin--Helmholtz instability
• Transverse loop oscillations via vortex shedding: a self oscillating process
• Coronal loop transverse oscillations excited by different driver frequencies
• Estimating the energy dissipation {from Kelvin-Helmholtz instability induced} turbulence in oscillating coronal loops}
• Novel data analysis techniques in coronal seismology
• 30-min Decayless Kink Oscillations in a Very Long Bundle of Solar Coronal Plasma Loops
• Investigating the damping rate of phase-mixed Alfven waves
• Decayless oscillations in 3D coronal loops excited by a power-law driver
• Temporal evolution of oscillating coronal loops
• Do Periods of Decayless Kink Oscillations of Solar Coronal Loops Depend on Noise?