Smoothing of MHD Shocks in Mode Conversion

Pennicott, Jamon D.; Cally, Paul Stuart

doi:10.3847/2041-8213/ab3423

Cited by 12 publications

(18 citation statements)

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“…On the other hand, at nonzero attack angle, the incident wave splits into a combination of slow and fast waves. This is seen in numerous simulations (e.g., Felipe et al 2010), and even persists for shock waves (Pennicott and Cally 2019). Figure 1 illustrates the two mode conversion processes both schematically (upper) and through z − k z dispersion diagrams for representative cases.…”

Section: Introductionmentioning

confidence: 78%

Chromospheric Heating by Magnetohydrodynamic Waves and Instabilities

et al. 2021

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The importance of the chromosphere in the mass and energy transport within the solar atmosphere is now widely recognised. This review discusses the physics of magnetohydrodynamic (MHD) waves and instabilities in large-scale chromospheric structures as well as in magnetic flux tubes. We highlight a number of key observational aspects that have helped our understanding of the role of the solar chromosphere in various dynamic processes and wave phenomena, and the heating scenario of the solar chromosphere is also discussed. The review focuses on the physics of waves and invokes the basics of plasma instabilities in the context of this important layer of the solar atmosphere. Potential implications, future trends and outstanding questions are also delineated.

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Section: Introductionmentioning

confidence: 78%

Chromospheric Heating by Magnetohydrodynamic Waves and Instabilities

et al. 2021

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“…The slow waves are near-transverse and not very compressive. According to recent results by Pennicott & Cally (2019), who studied the behavior of shocks as they cross the β = 1 layer, slow shocks are very weak both in compression ratio and in Mach number. The slow shocks can produce considerable magnetic field shear and change the field direction.…”

Section: Statistical Fourier Analysismentioning

confidence: 99%

Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun

González-Morales

Khomenko

Vitas

et al. 2020

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The partial ionization of the solar plasma causes several nonideal effects such as the ambipolar diffusion, the Hall effect, and the Biermann battery effect. Here we report on the first three-dimensional realistic simulations of solar local dynamo where all three effects were taken into account. The simulations started with a snapshot of already saturated battery-seeded dynamo, where two new series were developed: one with solely ambipolar diffusion and another one also taking into account the Hall term in the generalized Ohm’s law. The simulations were then run for about 4 h of solar time to reach the stationary regime and improve the statistics. In parallel, a purely MHD dynamo simulation was also run for the same amount of time. The simulations are compared in a statistical way. We consider the average properties of simulation dynamics, the generation and dissipation of compressible and incompressible waves, and the magnetic Poynting flux. The results show that, with the inclusion of the ambipolar diffusion, the amplitudes of the incompressible perturbations related to Alfvén waves are reduced, and the Poynting flux is absorbed, with a frequency dependence. The Hall effect causes the opposite action: significant excess of incompressible perturbations is generated and an excess of the Poynting flux is observed in the chromospheric layers. The model with ambipolar diffusion shows, on average, sharper current sheets and slightly more abundant fast magneto-acoustic shocks in the chromosphere. The model with the Hall effect has higher temperatures at the lower chromosphere and stronger and more vertical magnetic field concentrations all over the chromosphere. The study of high-frequency waves reveals that significant power of incompressible perturbations is associated with areas with intense and more vertical magnetic fields and larger temperatures. This behavior explains the large Poynting fluxes in the simulations with the Hall effect and provides confirmation as to the role of Alfvén waves in chromospheric heating in internetwork regions, under the action of both Hall and ambipolar effects. We find a positive correlation between the magnitude of the ambipolar heating and the temperature increase at the same location after a characteristic time of 102 s.

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“…The initial density profile for the MHD and PIP simulations is shown in Figure 1. This initial set up is similar to that of Pennicott & Cally (2019) except here we have the addition of two-fluid effects. Future work will include studying shock behaviour in more realistic atmospheres.…”

Section: Initial Conditionsmentioning

confidence: 99%

“…When the initial conditions feature an angle in the magnetic field, energy can be exchanged between the different wave modes at the β v point and the shock fronts can separate into their fast (perpendicular) and slow (parallel) components (studied in MHD by Pennicott & Cally 2019). Here we present results from a inclined magnetic field with B x = 0.8, B y = 0.6, preserving the total magnetic field strength as unity.…”

Section: Pipmentioning

confidence: 99%

“…It is well known that MHD waves can undergo mode conversion in the solar atmosphere (e.g., Schunker & Cally 2006;Cally & Hansen 2011;Khomenko & Cally 2019), and the same is true of shocks. A recent paper by Pennicott & Cally (2019) studied the propagation of an MHD shock in a stratified, isothermal atmosphere and the separation into slow-and fast-mode shocks above the β v point, which is defined as the height in the atmosphere where the sound and Alfvén speeds are equal. Their results showed that as a shock passes through the β v point it can can undergo mode conversion.…”

Section: Introductionmentioning

confidence: 99%

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Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere

Snow

Hillier

2020

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Context. The plasma of the lower solar atmosphere consists of mostly neutral particles, whereas the upper solar atmosphere is mostly ionised particles and electrons. A shock that propagates upwards in the solar atmosphere therefore undergoes a transition where the dominant fluid is either neutral or ionised. An upwards propagating shock also passes a point where the sound and Alfvén speed are equal. At this point the energy of the acoustic shock can separated into fast and slow components. How the energy is distributed between the two modes depends on the angle of magnetic field. Aims. The separation of neutral and ionised species in a gravitationally stratified atmosphere is investigated. The role of two-fluid effects on the structure of the shocks post-mode-conversion and the frictional heating is quantified for different levels of collisional coupling. Methods. Two-fluid numerical simulations are performed using the (PIP) code of a wave steepening into a shock in an isothermal, partially-ionised atmosphere. The collisional coefficient is varied to investigate the regimes where the plasma and neutral species are weakly, strongly and finitely coupled. Results. The propagation speeds of the compressional waves hosted by neutral and ionised species vary, therefore velocity drift between the two species is produced as the plasma attempts to propagate faster than the neutrals. This is most extreme for a fast-mode shock. We find that the collisional coefficient drastically changes the features present in the system, specifically the mode conversion height, type of shocks present, and the finite shock widths created by the two-fluid effects. In the finitely-coupled regime fast-mode shock widths can exceed the pressure scale height leading to a new potential observable of two-fluid effects in the lower solar atmosphere.

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Smoothing of MHD Shocks in Mode Conversion

Cited by 12 publications

References 13 publications

Chromospheric Heating by Magnetohydrodynamic Waves and Instabilities

Chromospheric Heating by Magnetohydrodynamic Waves and Instabilities

Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun

Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere

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