An effective matrix-free implicit scheme for the magnetohydrodynamic solar wind simulations

Abstract

The magnetohydrodynamics (MHD) modeling of the steady solar wind is an essential and important ingredient in numerical space weather study. Numerically solving the MHD equation system is not an easy work due to its complexity by combining the Euler equations of gas dynamics with the Maxwells equations of electromagnetics and the solenoidal constraint. Moreover, the vast physical temporal and spatial scales of the solar wind simulation propose harsh requirements for computational efficiency and memory storage. Considering these factors, we develop an easily implemented finite volume (FV) scheme using the GMRES algorithm with an LU-SGS preconditioner for the three-dimensional (3D) MHD-based simulation. The steady-state solar wind from 1 Rs to 20 Rs during Carrington rotation (CR) 2051 is simulated for the validation of the proposed matrix-free implicit solver. Compared with the explicit solver, the implicit one can effectively enlarge the CFL number to 100 and achieve speedup ratios of 31.27 × and 28.05 × , which reduces the computational time for the steady-state study from several days to only a few hours. The simulation captures main features of the solar corona and the mapped in-situ solar wind measurements. The scheme proposed here provides a promising choice to conduct the 3D MHD simulation of the solar wind background from the Sun to the Earth beyond.