Pc3 ULF波是磁层中一种常见的超低频等离子体波动，它在粒子输运、加速以及磁层-电离层耦合过程中起着非常重要的作用。Pc3 ULF波的产生机制和能量变化与电离层密切相关，ULF波的波矢量、偏振等特性在穿越电离层前后会有显著变化。由于电离层的复杂性和电离层内部波动观测较少等原因，理论模型计算与地面实际观测结果有较大差异，波动的电离层效应随地方时、经纬度以及电离层高度的变化规律未明。本项目拟利用SWARM和CHAMP低轨道卫星以及地面地磁台站的联合观测，通过个例、统计及理论对比分析，系统研究Pc3 ULF波矢量、偏振以及传播特性，弄清Pc3 ULF波动穿过电离层前后的波动特性变化规律及其随电离层高度、地方时以及纬度的依赖性。项目的实施将有助于揭示ULF波动在电离层中的传播机制，为诊断磁层空间中的等离子体性质提供重要的参考信息。

The Pc3 ULF waves are the waves with ultra low frequency and common phenomena in the magnetosphere. It plays an important role in the particle transportation, acceleration, and coupling between magnetosphere and ionosphere. The generation mechanism and energy change of the ULF wave are closely related to the ionosphere. The wave vector and polarization will change significantly when crossing the ionosphere. However, due to the complexity of the ionosphere and less observation on the wave in the ionosphere. The local time and latitude dependences of the changes of the wave characteristics are still not fully understand. In this project, based on joint observations from SWARM, CHAMP, and ground in a whole solar cycle, we will systematically study the wave vector, polarization and the propagation of the ULF waves. By the analysis of typical event, statistics analysis and comparing the observations from both spacecraft and ground stations, we will make a systematic research on the wave vector, polarization, and propagation. It is expected to understand the characteristics of the ULF waves when crossing the ionosphere. In addition, the dependence on ionospheric height, local time, and latitude will be also discussed. The project will help us understand the mechanism of the ULF wave propagation and provide important information for magnetospheric plasma diagnostics on the ground.