Multi-fluid Modeling of Magnetosonic Wave Propagation in the Solar Chromosphere: Effects of Impact Ionization and Radiative Recombination

Abstract

In order to study chromospheric magnetosonic wave propagation including, for the first time, the effects of ionneutral interactions in the partially ionized solar chromosphere, we have developed a new multi-fluid computational modelaccounting for ionization and recombination reactions in gravitationally stratified magnetized collisional media. The two-fluid model used in our 2D numerical simulations treats neutrals as a separate fluid and considers charged species (electrons and ions) within the resistive MHD approach with Coulomb collisions and anisotropic heat flux determined by Braginskiis transport coefficients. The electromagnetic fields are evolved according to the full Maxwell equations and the solenoidality of the magnetic field is enforced with a hyperbolic divergence-cleaning scheme. The initial density and temperature profiles are similar to VAL III chromospheric model in which dynamical, thermal, and chemical equilibrium are considered to ensure comparison to existing MHD models and avoid artificial numerical heating. In this initial setup we include simple homogeneous flux tube magnetic field configuration and an external photospheric velocity driver to simulate the propagation of MHD waves in the partially ionized reactive chromosphere. In particular, we investigate the loss of chemical equilibrium and the plasma heating related to the steepening of fast magnetosonic wave fronts in the gravitationally stratified medium.

Two-fluid simulations of waves in the solar chromosphere

“…Alternatively, Maneva et al (2017) used a fully implicit scheme which has no restriction for the time-step and is generally more stable. It must be noted that despite the advantage of the stability, implicit schemes are more expensive computationally, because, generally, the matrix inversions needed in the implicit part are usually implemented by iterations, increasing the computational time.…”

“…However, their realism is rather limited. Maneva et al (2017) modeled magneto-acoustic wave propagation in the solar stratified chromosphere including effects of impact ionization and radiative recombination. These authors found numerous difficulties in constructing an equilibrium model atmosphere for the wave propagation, and in interpreting the results of their simulations in comparisons to more standard, single fluid models.…”

Fully-implicit finite volume method for the ideal two-fluid plasma model

“…In the present work we present a novel numerical method for the simulation of laboratory and/or space plasmas, which solves for the ideal two-fluid model coupled to the purely hyperbolic full Maxwell's equations [22]. We extend the fully-implicit finite volume method for unstructured meshes proposed in [23], that has been used for the study of reactive and collisional chromospheric flows [24,25], to the ideal two-fluid plasma model. Compared to the previous two-fluid plasma finite volume schemes, our work proposes the following novelties:…”

“…The scheme developed in this work is implemented into COOLFluiD [29][30][31][32][33][34], an open-source object-oriented platform for scientific high-performance computing. The code is publicly available (https://github.com/andrealani/COOLFluiD) and is currently able to handle parallel multi-physics simulations including, in particular, complex compressible/incompressible flows in thermochemical equilibrium or nonequilibrium [35][36][37][38][39][40], and astrophysical plasmas [41][42][43]24,25] with a wide range of spatial discretization algorithms and time marching methods.…”

Time-Dependent Two-Fluid Magnetohydrodynamic Model and Simulation of the Chromosphere

“…Soler et al (2013) studied Alfvén-wave propagation in partially ionized plasma while taking a generalized approach with free parameters with the lower solar atmosphere case as an example. Maneva et al (2017) and Wójcik, Murawski, and Musielak (2018) studied acoustic-wave propagation using a collisional two-fluid approach as well. Three-fluid simulations, with electrons being the third fluid, were carried out to study reconnection events in the chromosphere (Leake, Lukin, and Linton, 2013).…”