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

Abstract

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.

Influence of ambipolar and Hall effects on vorticity in three-dimensional simulations of magneto-convection

“…The aim of the current work is to start filling this gap and to provide an initial study of the influence of non-ideal effects on vorticity in realistic three-dimensional simulations of small-scale solar dynamo in the saturated regime. We continue the study from Khomenko et al [34] (Paper I) and González-Morales et al [40] (Paper II) on the action of the ambipolar diffusion and Hall effect in three-dimensional models of solar magneto-convection, with a special emphasis on the vorticity generation and dissipation, and on modifications of the average magnetic structure of the atmosphere due to the Hall effect.…”

“…In Paper I and II we split the compressible and incompressible perturbations by computing the divergence and the curl of the velocity field parallel to the magnetic field lines. This separation works well independently of plasma β , and the incompressible perturbation can be associated with Alfvén waves [34,40,51]. The behaviour of Alfvén waves and the vorticity is intimately related [28,52].…”

“…The simulations that we analyse in this paper were previously used in Paper II [40], and represent a continuation of the battery-excited small-scale solar dynamo series from Khomenko et al [41] and Paper I [34]. The simulations are obtained with the mancha3d code [42–44] and are fully described in the publications mentioned above.…”

Chromospheric Heating by Magnetohydrodynamic Waves and Instabilities

“…The ambipolar diffusion has been studied extensively in the context of chromospheric heating and structure formation, both using the analytical theory or idealized, and even realistic, numerical simulations (see the review by Ballester et al, 2018). It has been shown that ambipolar diffusion allows to dissipate into heat incompressible magnetic waves (e.g., Alfvén waves; Khomenko et al, 2018;González-Morales et al, 2020). Resistive dissipation of Alfvén waves, enhanced through ion-neutral interaction, has been considered by Song and Vasyliūnas (2011); Tu and Song (2013); Shelyag et al (2016), andMartínez-Sykora et al (2016).…”

“…Gonzalez‐Morales et al. (2020) find that ambipolar diffusion near‐surface battery‐excited dynamo reduces the flux of Alfvén waves generated, whilst the Hall effect substantially enhances chromospheric Alfvén fluxes. Heating aspects of waves in the large‐scale solar chromosphere is discussed in details in Section 4.…”