[P-EM16] Space Plasma Physics: Theory and Simulation

[PEM16-11] Development of approximate Riemann solvers for non-isothermal MHD

*Sotaro Shigekuni¹, Takahiro Miyoshi¹ (1.Graduate School of Advanced Science and Engineering, Hiroshima University)

Keywords:approximate Riemann solver, non-isothermal magnetohydrodynamics, solar atmosphere

The spatial and temporal fluctuations of the magnetic field in the solar atmosphere are considered to play an important role in explosive phenomena such as solar flares. Data-driven MHD simulations where a time sequence of photospheric magnetic fields from observational data is used as the boundary condition have recently been attempted to reveal the mechanism of the solar flare. In the data-driven MHD simulation, it is necessary to include the whole solar atmosphere above the photosphere in an active region. In particular, in the photosphere and chromosphere, unlike the corona, the effects of the pressure and gravity (finite beta effect) cannot be ignored. Although Jiang et al. (2021) performed an MHD simulation including the finite beta effect, the effect in the lower atmosphere becomes small in that simulation because an isothermal model with the coronal temperature is adopted in the whole domain. On the other hand, MHD simulations including heating and cooling processes in the solar atmosphere have not been established yet.
The purpose of this study is to elucidate the finite beta effect on the flare trigger mechanism using a non-isothermal MHD model (NIMHD) where a steady temperature distribution in the vertical direction is assumed. In particular, we developed a new HLLD approximate Riemann solver for NIMHD in this paper. We extended the HLLD approximate Riemann solver (Miyoshi & Kusano, 2005), which is widely used in space and astrophysical MHD simulations, and the HLLD approximate Riemann solver for isothermal MHD (IMHD) (Mignone, 2007) to solvers for NIMHD. A shock tube test with non-isothermal distribution showed that the solver based on the HLLD for IMHD produces numerical oscillations, whereas the solver based on the original HLLD suppresses those. We also confirmed that numerical solutions obtained from the solvers developed here are equivalent to those obtained from the HLLD for IMHD in the isothermal distribution.