地球磁尾尾瓣超低频波产生机制和特征的研究

Ultra-low frequency waves (referred to as ULF waves) play an important role in the transmission and dissipation of energy and particle acceleration in the magnetosphere. There are a large number of ULF waves in the magnetotail plasma sheet, while ULF waves can also be observed in the magnetotail lobe with lower plasma density. The ULF waves in the lobe can be generated by the solar wind and dynamic processes in the plasma sheet and plasma sheet boundary layer. However, the explanation of the fact that the solar wind velocity driving ULF waves in the lobe currently lacks direct observational evidences and the specific physical process of dynamic processes in the magnetosphere driving ULF waves in the lobe remains unclear. In this project, we plan to use many years of satellite data to obtain observational evidences that the solar wind velocity perturbation drives ULF waves in the lobe, and clarifie the response process of the plasma sheet to the solar wind velocity. We investigate the basic characteristics of fluctuations in the Pi2-band frequency range before and after the substorm onset to explore their source region and mechanisms, and study the physical process of the bursty bulk flow driving Pi2-band waves in the lobe. We also plan to study the relation between the Pi2-band wave in the lobe and Pi2 pulsations in the polar cap, and clarify the role of these Pi2-band waves during substorms. These results will help us to deeply understand the role of ULF waves in the lobe in the magnetosphere.

超低频波（简称ULF波）在磁层能量传输和耗散以及粒子加速等方面发挥着重要作用。在磁尾等离子体片中存在着大量的ULF波，而在等离子体密度更低的尾瓣中也能观测到ULF波。尾瓣中的ULF波可由太阳风及等离子体片和等离子体片边界层中的动力学过程产生。然而，太阳风速度在尾瓣中产生ULF波的这一解释目前缺乏直接观测证据，而磁层内部的动力学过程在尾瓣中产生ULF波的具体物理过程仍不清楚。本项目拟利用多年的卫星数据，获得太阳风速度扰动在尾瓣中产生ULF波的观测证据，明确等离子体片对太阳风速度的响应过程；分析亚暴爆发前后Pi2频段波动的基本特征，探究这些波动在等离子体片中的源区和产生机制，明确爆发性整体流在尾瓣中产生Pi2频段波动的具体物理过程；研究尾瓣Pi2频段波动与极盖区Pi2脉动的关系，明确尾瓣Pi2频段波动在磁层亚暴期间的作用。这些结果将有助于我们深入认识尾瓣ULF波在磁层中的作用。

地球磁尾存在丰富的超低频波动，这些波动在磁层能量传输和耗散以及粒子加速等方面发挥着重要的作用。因此，对磁尾中超低频波的研究有助于我们深入理解磁层中的动力学过程。一些超低频波产生与太阳风扰动相关。此外，太阳风扰动也能激发磁尾电流片形成拍动，然而其具体的行程机制尚不清楚。针对这些问题，我们利用MMS卫星所提供的高精度场和等离子体数据，对磁尾电流片拍动开展了细致研究。我们发现，太阳风速度扰动可以在磁尾南北尾瓣之间行程压力差，该压力差可导致电流片在南北方向上运动，从而形成电流片拍动。此外，我们对电流片拍动期间的场向电流开展了深入研究。场向电流在磁层-电离层耦合过程中发挥着极为重要的作用。我们发现电子在磁尾中性片附近可以达到非磁化状态，其磁矩不再守恒；电子的混沌运动可将垂直电流转向场向，从而形成场向电流。该研究成果对深入理解磁层-电离层耦合具有重要意义。