3D Magnetohydrodynamics Numerical Simulation Of The Solar Wind In The Interplanetary Background

Solar wind is a stream of charged particles released from the upper atmosphere of the Sun,called the corona.This plasma consists of mostly electrons,protons and alpha particles.It is the link between the Sun and the Earth.The study of solar wind has the great significance in theory and practical application.Three-dimensional magnetohydrodynamic(MHD)numerical simulation have now become an important tool for solar wind research and operational prediction.Since 1980 s,a lot of models for interplanetary background solar wind simulation have been established,However these models still have some problems.In this paper,the COIN-TVD MHD model has been greatly improved in many aspects.In the new model,the inner boundary is set at 0.1 astronomical unit(AU),the ideal MHD equations are solved by TVD Lax-Friedrichs scheme in a six-component mesh grid system,the divergence of magnetic field is eliminated by diffusion method,and the density and pressure are kept positive by the combination of the first-order scheme and the high-precision scheme,the outer boundary are specified by the characteristic boundary conditions.The model is written in Fortran programming language;in addition,OpenMP and MPI technique are used to parallelize the code.At the inner boundary,a set of self-consistent boundary conditions is proposed for the numerical simulation of interplanetary background solar wind.The model takes the observed magnetic map of solar photospheric from Solar Global Oscillation Monitoring Network(GONG)as the input data,and uses the WSA(Wang-Sheeley-Arge)empirical relationship to determine the velocity distribution at the inner boundary.The energy flux of the solar wind limits the distribution of the density.The temperature distribution is calculated according to the positive correlation between temperature and velocity.The polarity of the interplanetary magnetic field is specified by the surface model of the magnetic field potential field source surface model.There are five adjustable parameters at the boundary conditions,of which three are retained by WSA model and the other two are based on the observations of the satellites at the first Lagrange point.The free parameters make it convenient for simulating solar wind in different solar activity periods.The model is used to simulate the background solar wind over an 11-year period from2007 to 2017,covering four different solar activity periods.The simulation results not only capture most of the high-speed streams at 1 AU,but also accurately predict the polarity of the interplanetary magnetic field.Moreover,the solar wind density,temperature and intensity of the interplanetary magnetic field are not significantly overestimated or underestimated.This model can reproduce the three-dimensional distribution of the background solar wind in interplanetary space.Because the model has fewer adjustable parameters with the smaller value range,and these parameters can be kept unchanged for a long time(several Carrington Rotations to several years)according to the simulation of the past 11 years,it is easy to be operated and can be applied for the prediction/forecast of the solar wind parameters near the Earth.