地球弓激波的三维模拟

Simulation of Three-dimensional Earth's Bow Shock

利用磁流体动力学(MHD)全球模拟结果,根据弓激波的跃变特性确定出弓激波位置,建立了一个新的综合考虑了快磁声马赫数、太阳风动压、行星际磁场强度以及磁层顶曲率半径的弓激波三维位型模型.将新模型与以往模型的模拟结果进行比较发现,新的弓激波全球模型结果可靠,解决了部分现有模型不能描述弓激波三维位型的问题.研究结果表明,在行星际磁场北向时,随着快磁声马赫数的增大,弓激波日下点距离减小,但是在行星际磁场南向时,快磁声马赫数的变化对弓激波日下点距离影响不大;弓激波位型在赤道面与子午面上存在明显的不对称性,而且随着行星际磁场的转向,这种非对称性也会发生相应改变;行星际磁场南向,Bz值较小时,子午面内弓激波位型已经不是简单的抛物线,出现了明显的类似于极尖区磁层顶的凹陷变化区.

We use a physics-based global Magnetohydrodynamic(MHD) model to investigate the location and shape of the Earth's bow shock.The bow shock locations in the simulations are identified by an automated search algorithm and is fitted by simple analytical functions.A global three dimensional bow shock model is constructed to include the effect of magnetopause and is parameterized by the fast magnetosonic Mach number,solar wind ram pressure,interplanetary magnetic field strength,and magnetopause curvature radius.The model results are compared and agree well with the previous empirical and simulation models.We also find that both the shock standoff distance and the shock flaring angle decrease monotonically with increasing the fast magnetosonic Mach number.The size and location of bow shock on the equatorial plane and the meridian plane show obvious asymmetry.