地球磁尾偶极化锋面附近的波粒相互作用的研究

Dipolarization front is a unique magnetic field structure, embedded in fast flow in Earth’s magnetotail. It plays a key role in transport of magnetotail’s mass and energy. The wave near dipolarization front can cause the acceleration and loss of energetic particle, the transport of magnetotail’s energy. Study on the wave-particle interaction near dipolarization front can help us to understand the generation mechanism of energetic particle as well as the processes of energy transport and dissipation in Earth’s magnetotail. Based on the datas of Cluster and THEMIS spacecrafts, this program will study the interaction between wave and particle near dipolarization front, investigate the relationship between dipolarization front and the braking of plasma flow, reveal the generation mechanism of energetic particle, and illuminate the mechanism of the energy transport and dissipation in the vicinity of dipolarization front, by using the wave analysis methods such as MVA (Minimum Variance Analysis) method, Timing method and k-filtering method. The detailed research contents include: the wave-particle interaction before the dipolarizaiton front; the interaction between the wave and ion behind the dipolarizaiton front, the processes of ion thermalization and acceleration; the evolution process of wave near dipolarization front during the dipolarizaiton front propagating toward Earth. These results can be helpful to reveal the role of the dipolarization front on the magnetotail’s energy transport and dissipation processes.

偶极化锋面是位于地球磁尾高速流的一种特殊的磁场结构，其对磁尾的物质和能量的传输有重要的作用。偶极化锋面附近的波动可以导致高能粒子的加速、损失和磁尾能量的传输。探究偶极化锋面附近的波粒相互作用，既有助于理解高能粒子的产生机制，又有助于理解磁尾的能量传输和耗散过程。本项目拟利用Cluster卫星和THEMIS卫星的观测数据，结合最小变量分析法，时序分析法和k滤波方法等波动分析方法，进行偶极化锋面附近波动和粒子之间相互作用的研究，探究偶极化锋面和等离子体流减速之间的关系，揭示偶极化锋面附近高能粒子的产生机制，阐明偶极化锋面附近的能量传输和耗散机制。具体研究内容包括：偶极化锋面前的波动与粒子之间的相互作用；偶极化锋面后的波动和离子之间的作用，以及离子加热和加速的过程；在偶极化锋面地向传播的过程中偶极化锋面附近波动的演化过程。研究结果有助于揭示偶极化锋面在磁尾能量传输和耗散过程中的作用。

基于卫星的观测数据和数值模拟技术，研究了偏离赤道的偶极化锋面处的波动，在同一个偶极化锋面的不同区域我们发现了三种不同频率的等离子体波动，分别为离子回旋波，低混杂漂移波和静电孤立波，这说明偶极化锋面可能存在精细的结构。另一方面，我们离子回旋波是由电流驱动的kink-like不稳定性激发的，静电孤立波可以认为是多维的电磁电子洞。研究了偶极化锋面前的镜像波模，在镜像波模的凹陷区发现了低混杂漂移波，这种波动可以加热电子。另外，在本项目的支持下，研究了低电离层的加热。讨论了考虑电子吸附效应的低电离层加热；建立了低电离层二维加热模型，研究了加热后电子温度和电子密度扰动的二维分布特性及电子温度和电子密度的二维饱和时间效应，从而得到电子温度和电子密度的扰动峰值，电子温度和电子密度的饱和时间的变化特性。