Hall-coupling of Slow and Alfvén Waves at Low Frequencies in the Lower Solar Atmosphere

Raboonik, Abbas; Cally, Paul Stuart

doi:10.1007/s11207-019-1544-1

Cited by 16 publications

(10 citation statements)

References 48 publications

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“…This seems to be in agreement with the geometrical mode transformation theory (Cally & Goossens 2008;Khomenko & Cally 2012a). Ambipolar diffusion can, in principle also affect waves by degrading the fast wave flux entering the transformation zone Raboonik & Cally 2019). This needs to be further investigated.…”

Section: High-frequency Wavessupporting

confidence: 84%

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

González-Morales

Khomenko

Vitas

et al. 2020

A&A

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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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Section: High-frequency Wavessupporting

confidence: 84%

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

González-Morales

Khomenko

Vitas

et al. 2020

A&A

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“…There are two significant nuances in the present study in contrast with Raboonik & Cally (2019). First, the incorporated realistic anisothermal atmospheric model, and second, here we dispense with the 'small Hall parameter 𝜖 𝐻 ' assumption which was crucial to the semi-analytical solutions in that paper.…”

Section: Mathematical Modelmentioning

confidence: 99%

“…Since its discovery by Alfvén (1942), many observational and theoretical studies have been launched to corroborate the existence and perhaps preponderance of Alfvén waves in the upper atmosphere and explain the extreme temperature of the corona (Alfvén 1947;Kuperus et al 1981;Poedts 2002;Cranmer & van Ballegooĳen 2005;De Pontieu et al 2005Tomczyk et al 2007). While some works concentrate on uninterrupted transmission of energy by Alfvén waves from photospheric heights all the way to the corona (Cranmer & van Ballegooĳen 2005), others have been investigating the significance of mode converted Alfvén waves elicited from originally magnetoacoustic oscillations (Cally & Goossens 2008;Cally 2017;Cally & Khomenko 2015, 2018González-Morales et al 2019;Raboonik & Cally 2019).…”

Section: Introductionmentioning

confidence: 99%

Benchmarking Hall-Induced Magnetoacoustic to Alfvén Mode Conversion in the Solar Chromosphere

Raboonik¹,

Cally²

2021

Preprint

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A 2.5D numerical model of magnetoacoustic-Alfvén linear mode conversions in the partially ionised low solar atmosphere induced by the Hall effect is surveyed, varying magnetic field strength and inclination, and wave frequency and horizontal wave number. It is found that only the magnetic component of wave energy is subject to Hall-mediated conversions to Alfvén wave-energy via a process of polarisation rotation. This strongly boosts direct mode conversion between slow magnetoacoustic and Alfvén waves in the quiet low chromosphere, even at mHz frequencies. However, fast waves there, which are predominantly acoustic in nature, are only subject to Hall-induced conversion via an indirect two-step process: (i) a geometry-induced fast-slow transformation near the Alfvén-acoustic equipartition height 𝑧 eq ; and (ii) Hall-rotation of the fast wave in 𝑧 > 𝑧 eq . Thus, for the two-stage process to yield upgoing Alfvén waves, 𝑧 eq must lie below or within the Hall-effective window 0 𝑧 700 km. Magnetic field strengths over 100 G are required to achieve this. Since the potency of this Hall effect varies inversely with the field strength but directly with the wave frequency, only frequencies above about 100 mHz are significantly affected by the two-stage process. Increasing magnetic field inclination 𝜃 generally strengthens the Hall convertibility, but the horizontal wavenumber 𝑘 𝑥 has little effect. The direct and indirect Hall mechanisms both have implications for the ability of MHD waves excited at the photosphere to reach the upper chromosphere, and by implication the corona.

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“…2009Soler at al. , 2015Cally & Khomenko 2015;Shelyag et al 2016;Khomenko 2017;Martínez-Gómez et al 2017;Martínez-Sykora et al 2017;Ballester et al 2018;Cally & Khomenko 2018;Raboonik & Cally 2019;Muthsam et al 2021;Khomenko et al 2021;Raboonik & Cally 2021). Thus the canonical picture that emerges from the recent research suggests that with increasing altitude the solar atmosphere changes from weakly ionized and weakly magnetized Ohm dominated photosphere to moderately ionized and highly magnetized ambipolar dominated chromosphere with the overlapping Ohm-Hall and Hall-ambipolar regions sandwiched in the middle (Pandey & Wardle 2012, 2013.…”

Section: Introductionmentioning

confidence: 99%

The non-ideal finite Larmor radius effect in the solar atmosphere

Pandey,

Wardle

2022

Preprint

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The dynamics of the partially ionized solar atmosphere is controlled by the frequent collision and charge exchange between the predominant neutral Hydrogen atoms and charged ions. At signal frequencies below or of the order of either of the collision or charge exchange frequencies the magnetic stress is felt by both the charged and neutral particles simultaneously. The resulting neutral-mass loading of the ions leads to the rescaling of the effective ioncyclotron frequency-it becomes the Hall frequency, and the resultant effective Larmor radius becomes of the order of few kms. Thus the finite Larmor radius (FLR) effect which manifests as the ion and neutral pressure stress tensors operates over macroscopic scales. Whereas parallel and perpendicular (with respect to the magnetic field) viscous momentum transport competes with the Ohm and Hall diffusion of the magnetic field in the photosphere-chromosphre, the gyroviscous effect becomes important only in the transition region between the chromosphere and corona, where it competes with the ambipolar diffusion. The wave propagation in the gyroviscous effect dominated medium depends on the plasma β (a ratio of the thermal and magnetic energies). The abundance of free energy makes gyro waves unstable with the onset condition exactly opposite of the Hall instability. However, the maximum growth rate is identical to the Hall instability. For a flow gradient ∼ 0.1 s −1 the instability growth time is one minute. Thus, the transition region may become subject to this fast growing, gyroviscous instability.

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Hall-coupling of Slow and Alfvén Waves at Low Frequencies in the Lower Solar Atmosphere

Cited by 16 publications

References 48 publications

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

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

Benchmarking Hall-Induced Magnetoacoustic to Alfvén Mode Conversion in the Solar Chromosphere

The non-ideal finite Larmor radius effect in the solar atmosphere

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