行星际中间激波的演化

本文采用特征线方法和激波装配法,对磁流体中间激波在行星际空间的演化过程进行数值模拟。主要结论如下:（1） 2→4型中间激波通过向下游发出后向慢压缩波使下游态磁场减幅,通过向上游发出前向快压缩波使上游态磁场增幅,以致2→4型中间激波迅速经导灭激波向慢激波转化;所发出的前向快压缩波经非线性变陡形成快激波。（2）1→3型中间激波首先通过向下游发出前向慢稀疏波而很快变成1→3=4型临界中间激波,并瞬间转变为由前向快激波和前向2→4型中间激波构成的激波系统。其中,2→4型中间激波可在其前导快激波的下游传播较远的距离,有可能为 IAU 附近的飞船观测到,但最终导灭激波转变为慢激波。

EVOLUTION OF MHD INTERMEDIATE SHOCKS IN INTERPLANETARY SPACE

Using the method of characteristics and shock fitting techniques,this paper simulates numerically the evolution of MHD （Magnetohydrodynamic） intermediate shocks in interplanetary space.The main conclusions are:（1） For an intermediate shock of type 2→4,the downstream tangential magnetic strength decreases by launching reverse slow compression waves downstream,whereas the upstream tangential magnetic strength increases by launching forward fast compression waves upstream.Therefore,the intermediate shock of type 2→4 evolves rapidly into a slow shock via a switch-off shock.Meanwhile the forward fast compression waves become a fast shock through nonlinear steepening process.（2） An intermediate shock of type 1→3 becomes a critical intermediate shock of type 1→3=4 by by launching forward slow rarefaction waves downstream,and immediately evolves into a shock system consisting of a forward fast shock and an intermediate shock of type 2→4. The intermediate shock of type 2→4 may propagate a larger heliocentric distance in the downstream side of the leading fast shock and be observed possibly by spacecraft near 1AU,but it eventually becomes a slow shock via a switch off shock. Key words Interplanetary dynamics,Magnetohydrodynamics,MHD shock, Intermediate shock,Numerical simulation