Study of Plasma Wave Propagation Based on Magnetotail MHD Modelling

基于磁流体力学（MHD）模拟模型，给出了磁场和等离子体密度的自洽模型，阐明了磁尾中各种等离子体波的传播特性。我们首先使用了一个二维MHD模型的等离子体团在磁尾区域。在阐明了各种等离子体波在二维模型中的传播特性后，我们将研究扩展到三维模型。在将MHD模型应用于射线追迹中时，我们引入了一种新的方法，即在离散空间网格点上定义密度和磁场，而在以前的射线追迹研究中，密度和磁场模型是作为解析函数给出的。我们假设在与等离子体团相关的X点重联区域中的等离子体波的源。我们追踪了各种电磁波在所有可能传播角度下的传播路径。我们从射线的空间分布中获得了“射线密度”。我们得到的射线密度的各种电磁波的范围内，从一个非常低的频率小于离子回旋频率的高频率高于电子等离子体频率。通过AVS图形系统对三维模型中的射线密度进行可视化显示，得到了离子回旋波、低杂波、哨声模波、L-O模波在磁尾中的传播特性。基于射线密度数据库，模拟了航天器穿越磁尾等离子体团时观测到的电磁波的动态谱。

We have clarified propagation characteristic of various kinds of plasma waves in the magnetotail based on the MHD simulation model which gives a self-consistent model of the magnetic field and plasma density. We first used a 2D MHD model of a plasmoid in the magnetotail region. After clarifying the propagation characteristics of various kinds of plasma waves in the 2D model, we extended the study to a 3D model. In applying the MHD models to the ray tracing, we introduced a new method to interpolate the plasma density and the magnetic field from those defined at the discrete spatial grid points, while the density and magnetic field models are given as an analytic functions in the previous ray tracing studies. We assumed a source of the plasma waves in the X-point reconnection region associated with the plasmoid. We traced the propagation paths of the various kinds of electromagnetic waves for all possible propagation angles. We obtained a "ray density" from the spatial distribution of the rays. We obtained the ray densities for various electromagnetic waves in the range from a very low frequency less than the ion cyclotron frequency up to the high frequency higher than the electron plasma frequency. Through visualization of the ray densities in the 3D model via the AVS graphic system, we have identified the propagation characteristics of ion cyclotron waves, lower hybrid waves, whistler mode waves, L-O mode waves in the magnetotail. Based on the database of the ray density, we simulated dynamic spectra of electromagnetic waves as observed by a spacecraft which traverses the plasmoid in the magnetotail.