内磁层中的超低频波作为辐射带能量电子加速的机制之一，一直是磁层物理研究的热点。等离子体层顶处的密度梯度可能对内磁层中超低频波的产生和传播产生重要的影响，尤其是申请人在最近的工作提出等离子体层顶表面波可能与磁力线共振耦合从而激发超低频波，这个机制需要我们进一步的分析和研究。THEMIS卫星搭载了高质量的磁场、电场、等离子体和能量粒子探测仪器，其轨道穿越内磁层，为内磁层中超低频波的研究提供了大量可靠的观测数据。本课题计划利用THEMIS计划的多颗卫星探测数据对等离子体层顶周围的超低频波性质进行详细的研究，争取在下面三个方面取得重要进展：（1）等离子体层顶表面波与磁力线共振的耦合机制；（2）等离子体层顶在共振腔模超低频波激发中的作用；（3）等离子体层顶内外超低频波性质的差异及其对辐射带能量电子的影响。

ULF waves in the inner magnetosphere can have significant influence on energetic particle transport and acceleration. Sharp density gradients at the plasmapause can affect the generation and propagation of ULF waves. Especially, we have recently proposed the mechanism of the generation of ULF waves by the coupling between plasmapause surface wave and field line resonance. Further investigation is required to better understand the mechanism. The THEMIS mission provides unique opportunities to analyze electric and magnetic field measurements in order to derive many of the characteristics of ULF waves. In this project we propose to use THEMIS observations to investigate the characteristics of ULF pulsations around the plasmapause with both electric and magnetic field measurements. Specifically, we strive to address the follow objectives: a) Investigation of the coupling between plasmapause surface wave and field line resonance; b) Investigation of the effect of the plasmapause on the excitation of cavity mode ULF waves; c) Investigation of the difference between the characteristics of the ULF waves outside and inside the plasmapause and its effects on wave-particle interaction.