Modeling Solar Atmosphere Dynamics with MAGEC

TL;DR

The paper introduces MAGEC, a finite-volume radiative MHD code that merges Mancha3D and MAGNUS with MPI parallelization to model the solar atmosphere’s multi-layer dynamics. It details the conservative MHD formulation, HRSC numerical methods, anisotropic and hyperbolic thermal conduction, a Saha-based equation of state, LTE radiative losses with optically thin losses at high temperatures, and a method to estimate numerical resistivity and viscosity. Through 2D magneto-convection simulations with open and closed magnetic configurations, the authors show that open fields produce hotter coronal regions, quantify energy contributions across heights, and demonstrate the role of perpendicular thermal conduction in reconnection zones. The results validate MAGEC as a reliable, efficient tool for self-consistent radiative MHD simulations of the solar atmosphere and point toward future 3D extensions and inclusion of additional non-ideal effects to further capture coronal heating processes.

Abstract

Modeling the solar atmosphere is challenging due to its layered structure and multi-scale dynamics. We aim to validate the new radiative MHD code MAGEC, which combines the MANCHA and MAGNUS codes into a finite-volume, shock-capturing framework, and to test its performance through 2D simulations of magneto-convection. MAGEC is MPI-parallelized and includes improvements for coronal modeling, such as LTE radiative losses and a hyperbolic treatment of thermal conduction that mitigates restrictive time steps. We also estimated its numerical viscosity and resistivity. To assess robustness, we performed 2D simulations covering a domain from 2 Mm below the surface to 18.16 Mm into the corona, using both open and closed magnetic-field configurations. For each case, we analyzed steady-state temperature profiles and the contributions to the internal-energy balance at different heights. A separate experiment examined the role of perpendicular thermal conduction. MAGEC reproduced the expected temperature stratification set by boundary conditions and magnetic geometry, and all simulations reached thermal equilibrium. Open-field cases produced higher coronal temperatures than closed, arcade-like fields. Analysis of the explicit and implicit energy terms clarified their relative effects on heating and cooling. Perpendicular thermal conduction, often neglected in coronal models, was found to influence plasma dynamics near reconnection; although local effects are small, they can cumulatively modify the average coronal temperature. These results show that MAGEC is a reliable and efficient tool for radiative MHD simulations, well suited to capturing the shocks and dynamic processes of the solar atmosphere.

Figures (16)

• Figure 1: Density-averaged radiative loss rate $\Lambda$(T) from the CHIANTI 10.1 database with photospheric abundances.
• Figure 2: Graphical estimation of numerical resistivity (top panel) and numerical viscosity (bottom panel). Each dot represents the maximum magnetic field ($B_\text{max}$) or velocity ($V_\text{max}$) obtained from a simulation with a specific explicit value of $\eta$ or $\nu$. The blue solid line is a fit to these data points. Two horizontal lines are shown: one corresponds to the $B_\text{max}/V_\text{max}$ value for the case with $\eta=0$ and $\nu = 0$, and the other marks the threshold of numerical noise. The intersection of this threshold with the fitted curve defines the estimated numerical resistivity or viscosity, indicated by the vertical line.
• Figure 3: Initial profiles of density and temperature as functions of height.
• Figure 4: Initial plasma-beta profiles as a function of height, evaluated at the center of the domain in the $x-$direction, for both the vertical and arcade magnetic field configurations after field implantation.
• Figure 5: Colormap of the temperature from the baseline hydrodynamic simulation at $t=1000$ s. Arrows indicate the velocity field, with lengths proportional to the local flow speed. The full temporal evolution is available as an online movie (see links in Table \ref{['tab:description']}).