Coronal cooling as a result of mixing by the nonlinear Kelvin--Helmholtz instability

Abstract

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 this paper we develop a simple phenomenological model of nonlinear Kelvin--Helmholtz mixing, using it to determine the characteristic density and temperature of the mixing layer, which for the case under study with constant pressure across the two fluids are ${\rho }_{\mathrm{mixed}}=\sqrt{{\rho }_1{\rho }_2}$ and $T_{\mathrm{mixed}}=\sqrt{T_1{T}_2}$. One result from the model is that it provides an accurate, as determined by comparison with simulation results, determination of the kinetic energy in the mean velocity field. A consequence of this is that the magnitude of turbulence, and with it the energy that can be dissipated on fast time-scales, as driven by this instability can be determined. For the prominence-corona system, the mean temperature rise possible from turbulent heating is estimated to be less than 1\% of the characteristic temperature (which is found to be $10^5$\,K). These results highlight that mixing, and not heating, are likely to be the cause of the observed transition between cool to warm material in Okamoto et. al (2015). One consequence of this result is that the mixing creates a region with higher radiative loss rates on average than either of the original fluids, meaning that this instability could contribute a net loss of thermal energy from the corona, i.e. coronal cooling.

17 pages, 9 figures, accepted for publication in ApJ

References in corpus (11)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Nonlinear Instability of kink oscillations due to shear motions
• Fine strand-like structure in the solar corona from MHD transverse oscillations
• Heating by transverse waves in simulated coronal loops
• Damping of nonlinear standing kink oscillations: a numerical study
• The Kelvin-Helmholtz Instability at CME-Boundaries in the Solar Corona: Observations and 2.5D MHD Simulations
• Modelling observed decay-less oscillations as resonantly enhanced Kelvin-Helmholtz vortices from transverse MHD waves and their seismological application
• Quiescent prominence dynamics observed with the Hinode Solar Optical Telescope . II. Prominence Bubble Boundary Layer Characteristics and the Onset of a Coupled Kelvin-Helmholtz Rayleigh-Taylor Instability
• Energetics of the Kelvin-Helmholtz instability induced by transverse waves in twisted coronal loops
• An Analytical Model of the Kelvin-Helmholtz Instability of Transverse Coronal Loop Oscillations
• Investigating prominence turbulence with Hinode SOT Dopplergrams

Cited by in corpus (13)

• Multiphase Gas and the Fractal Nature of Radiative Turbulent Mixing Layers
• Cloudy with A Chance of Rain: Accretion Braking of Cold Clouds
• Estimating the energy dissipation {from Kelvin-Helmholtz instability induced} turbulence in oscillating coronal loops}
• Better Together: The Complex Interplay Between Radiative Cooling and Magnetic Draping
• The Anatomy of a Turbulent Radiative Mixing Layer: Insights from an Analytic Model with Turbulent Conduction and Viscosity
• Entrainment of Hot Gas into Cold Streams: The Origin of Excessive Star-formation Rates at Cosmic Noon
• Shocks and instabilities in the partially ionised solar atmosphere
• Mixing, heating and ion-neutral decoupling induced by Rayleigh-Taylor instability in prominence-corona transition regions
• Magnetising galaxies with cold inflows
• Identification of Nonlinear Damping of Transverse Loop Oscillations by KHI-induced Turbulence
• SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation
• Magnetic reconnection and the Kelvin-Helmholtz instability in the solar corona
• Small-scale Turbulent Motion of the Plasma in a Solar Filament as the Precursor of Eruption