行星际激波特性的数值研究

NUMERICAL STUDY ON PROPAGATION PROPERTIES OF INTERPLANETARY SHOCKS

采用二维二分量 ＭＨＤ模型，应用 ＰＰＭ格式，研究内日球赤道面内 １ＡＵ附近激波波阵面参数的分布特性，以及太阳风速、扰动源宽度、扰动源初始传播方向和行星际电流片对分布的影响．结果指出：（１）均匀背景情况下激波阵面西侧为强磁场区，东侧的动压差比西侧大，而密度比和气压比基本对称；（２）背景太阳风流速和扰动源初始传播方向对参量分布影响较大；扰动源宽度影响不大；（３）当扰动源中心处于电流片东侧或西侧时，密度比、气压比和磁场比峰值均西偏，而动压差峰值和扰动源处于同侧；当扰动源中心与电流片重合时，激波阵面东西两侧都出现峰值，为双峰分布，东侧动力学参数大，西侧磁场强．上述结论与观测资料的统计结果趋势上是一致的．

A two-dimensional, two-component MHD model and the PPM scheme are used in this paper to investigate distribution of the density ratio (ρ_2/ρ_1), magnetic field strength ratio (B_2/B_1), gas pressure ratio (P_2/P_1), and kinetic pressure jump (Pk_2- Pk_1) along the shock wave front at 1AU in the heliospheric equatorial plane (the subscripts 1 and 2 represent the upstream and downstream sides respectively). Effects of the background solar wind, the width and initial propagation direction of the disturbance source, and the presence of the interplanetary current sheet on the distribution are also studied. The main conclusions are as follows. (1) In an axisymmetric background, the stronger magnetic field region is situated at the western part of the shock wave front whereas the kinetic pressure jump is larger at the eastern part. On the other hand, the density and gas pressure ratios are essentially symmetrical with respect to the normal across the source center. (2) The velocity of the background solar wind exerts a great influence on the kinetic pressure jump and the magnetic field strength ratio. The width of the disturbance source has no appreciable effect, but the initial propagation direction of the disturbance has a significant effect on the distribution of the relevant parameters. (3) The Presence of the current sheet directly affects the distribution of the parameters along the shock wave front. When the initial position of the current sheet does not coincide with the disturbance source, the peaks of the ratios of density, gas pressure and magnetic field strength deviate westward in longitude, whereas the Peak of the kinetic pressure jump and the normal across the source center are located at the same side of the current sheet. When the center coincides with the current sheet there exists a peak on each part of the shock wave front i.e. a double peak structure, and moreover, the kinetic pressure jump is larger on the eastern part while the magnetic field strength is stronger on the western pall.