行星际空间MHD模拟激波跃变关系分析

ANALYZING OF THE INTERPLANETARY SIMULATION MHD SHOCK WITH THE SHOCK JUMP CONDITION

分析了模拟得到的可以传播到1 AU以远的日地空间磁流体力学激波与Rankine-Hug-noniot跃变关系的符合程度.通过对模拟激波的结构及其在传播过程中的演化进行的分析,提出了模拟激波的定位方法;基于所提出的定位方法,利用向长青提出的确定MHD激波局地参数的方法计算了模拟得到的激波与Rankine-Hugnoniot跃变关系的偏差.结果表明在激波传播到100Rs以后,激波对中前向快激波与Rankine-Hugnoniot关系的符合达到很高的程度,相对误差在10-2数量级以内;并且在激波传播到150 Rs以后,相对误差在10-3数量级以内.这个结果说明文中所使用的有限差分数值格式能较好地模拟激波.

The agreement between Rankine-Hugnoniot equations and the simulation of interplanetary MHD shock that can arrive 1AU or further is investigated. A method to locate the position of the forward fast shock in the shock pair structure is proposed in this paper. The method is composed of two main steps. First, by analyzing topology of the simulated MHD shock and its evolution during its propagating forward, it is identified that the discontinuity structure in the computational domain is in fact shock pair structure. According to this judgment, a method to locate the shock in the computation domain is developed. The second step is to select the proper time levels where the space between the shock and the grids is minimal, so as to minimize the errors that the shock is not exactly on the grids. By using this method to locate the shock and the method that was proposed in Reference [14] to determine the local parameters of the shock, it is found that the forward fast shock in the shock pair structure matches the Rankine-Hugoniot relations perfectly with the relative difference limited in the scale, when the shock propagates to or farther, and that the discrepancy between them is limited in the scale when the shock propagates to or farther. This result confirms that the finite-difference numerical solutions can describe the shock accurately. And as to clear out the cause of the discrepancy, the relationship between the discrepancy and the evolution of the shock structure as well as the relationship between the discrepancy and the polytropic index is discussed.