A new time-dependent three-dimensional magnetohydrodynamics (MHD) simulation model for the trans-sonic/Alfvenic solar wind from 2.5Rs

Our new magnetohydrodynamics (MHD) simulation model of the solar corona and solar wind and its new capabilities are presented. This model covers the range of heliocentric distance from 2.5 solar radii (Rs) up to 1 AU and beyond. Starting the simulation from 2.5 Rs, our Sun-to-Earth MHD model can utilize straightforwardly the information on the coronal mass ejection (CME) and its associated magnetic flux rope at their earliest phase.

This model is constructed by introducing the characteristic-based boundary treatment to our existing H3DMHD model [e.g. Wu+ (2015) JGR 121:1839]. The characteristic-based boundary treatment [e.g. Nakagawa+ (1987) A&Ap 197:354; Wu & Wang (1987) CMAME 64:267] can treat the temporal variations of MHD variables on the sub-sonic/Alfvenic boundary surface in a mathematically and physically consistent manner and enhances the computational robustness. In tailoring a set of characteristic equations for this new model, we assume that the coronal magnetic field is open to the interplanetary space and the solar coronal plasma is flowing outward everywhere at 2.5 Rs. Without the characteristic-based boundary treatment, we often fail to obtain the quasi-steady state of the solar corona and solar wind.

This new model can introduce various types of the numerical perturbation mimicking the CME initiation to the quasi-steady state of the trans-sonic/Alfvenic solar wind. For example, an outward-moving and expanding CME structure can be introduced as the time-dependent boundary values by calculating the MHD variables of the CME structures on the 2.5-Rs intersection. In the present model, the characteristic-based boundary treatment is not used for the boundary grids the CME is passing through, for simplicity; although, it is possible to construct a new set of characteristic equations incorporating with the CME model.

In this presentation, the details of the characteristic-based boundary treatment for the middle of the corona (hence, named CharM) are provided. The results of test simulations with various choices of parameters for the background steady trans-sonic/Alfvenic solar wind and the CME perturbations are compared to assess the dynamics of the CME evolution in the earliest period of the Sun-to-Earth disturbance propagation.