Two-fluid simulations of waves in the solar chromosphere

Abstract

Solar chromosphere consists of a partially ionized plasma, which makes modeling the solar chromosphere a particularly challenging numerical task. Here we numerically model chromospheric waves using a two-fluid approach with a newly developed numerical code. The code solves two-fluid equations of conservation of mass, momentum and energy, together with the induction equation, for the case of the purely hydrogen plasma with collisional coupling between the charged and neutral fluid components. The implementation of a semi-implicit algorithm allows us to overcome the numerical stability constraints due to the stiff collisional terms. We test the code against analytical solutions of acoustic and Alfvén wave propagation in uniform medium in several regimes of collisional coupling.The results of our simulations are consistent with the analytical estimates, and with other results described in the literature. In the limit of a large collisional frequency, the waves propagate with a common speed of a single fluid. In the other limit of a vanishingly small collisional frequency, the Alfvén waves propagate with an Alfvén speed of the charged fluid only, while the perturbation in neutral fluid is very small. The acoustic waves in these limits propagate with the sound speed corresponding to either the charges or the neutrals, while the perturbation in the other fluid component is very small. Otherwise, when the collision frequency is similar to the real part of the wave frequency, the interaction between charges and neutrals through momentum transfer collisions cause alterations of the waves frequencies and damping of the wave amplitudes.

Chromospheric heating and generation of plasma outflows by impulsively generated two-fluid magnetoacoustic waves

“…To describe the low layers of the solar atmosphere we use twofluid equations for ions + electrons ( i,e ) and neutrals ( n ) treated as separate interacting fluids (Zaqarashvili et al 2011a;Leake et al 2014;Oliver et al 2016;Maneva et al 2017;Popescu Braileanu et al 2019):…”

3D numerical simulations of propagating two-fluid, torsional Alfvén waves and heating of a partially ionized solar chromosphere

“…The main goal of the present paper is to investigate the impact of two-fluid effects on (a) propagation, attenuation and dissipation of torsional Alfvén waves, (b) chromospheric heating, and (c) energy transfer to the upper layers of the solar corona. We aim to follow and complement both the previous studies of Popescu Braileanu et al (2019) and Kuźma et al (2019) by taking into account a 3D model of the solar atmosphere, and the study of Soler et al (2019) by taking into account a non-static, time-varying model of propagating Alfvén waves. As we want to focus solely on two-fluid effects on wave propagation and plasma heating, we limited our model by not taking into account non-ideal terms in the induction equation, nor ionization and recombination (Popescu Braileanu et al 2019) and resistivity (Soler et al 2019).…”

“…We aim to follow and complement both the previous studies of Popescu Braileanu et al (2019) and Kuźma et al (2019) by taking into account a 3D model of the solar atmosphere, and the study of Soler et al (2019) by taking into account a non-static, time-varying model of propagating Alfvén waves. As we want to focus solely on two-fluid effects on wave propagation and plasma heating, we limited our model by not taking into account non-ideal terms in the induction equation, nor ionization and recombination (Popescu Braileanu et al 2019) and resistivity (Soler et al 2019). Ultimately, we want to determine and stress the importance of two-fluid effects for processes with time-scales longer than the characteristic time-scales of ion-neutral collisions.…”

Numerical simulations of the lower solar atmosphere heating by two-fluid nonlinear Alfvén waves

“…Indeed, Fig. 6 (top-right) reveals a growth of the plasma temperature close to the bottom boundary up to δT i ≈ 200 K over a timescale of 250 s. We note that acoustic (Kuźma et al 2019) and fast magneto-acoustic waves (Popescu Braileanu et al 2019) behave differently from Alfvén waves, as they contribute to plasma heating in the chromosphere, whereas Alfvén waves directly thermalize their energy in the low photosphere. A first attempt to understand how the heating and cooling processes modify the properties of MHD waves in a fully ionized medium in the case of solar prominence was made by Ballester et al (2016).…”