内磁层“鼻状”离子谱结构的空间分布和时间演化

The “Nose-like” ion spectral structures are formed by ions in the near-Earth plasma sheet penetrating into the inner magnetosphere. Many studies had shown that the distribution of the Nose structures was controlled by the large-scale convection electric field, gradient-curvature drift and corotation electric field in the inner magnetosphere during geomagnetic quiet condition. However, during geomagnetic active periods, especially during the storms and substorms, the spatial and temporal characteristics and formation mechanism are still under debate. The formation mechanism of the nose structures for different ions is still an open question. In this project, joint observations from Van Allen Probes, THEMIS, and Cluster will be used to statistically study the spatial distribution and temporal evolution of the “Nose-like” ion spectral structures in the inner magnetosphere. By comparing the differences of the nose structures between the protons and oxygen ions during storm periods and with the numerical calculations, respectively, we will analyze the physical mechanism of the differences. The project will help us understand the injection mechanism of the ions from the plasma sheet into the inner magnetosphere and the relation between the storm and substorm, and thus provide important information for ring current formation.

内磁层“鼻状”离子谱结构是指近磁尾等离子片中离子注入至内磁层形成的一种特殊的离子能量谱分布结构。已有的研究认为，在地磁平静时期，“鼻状”结构在内磁层的分布特征依赖于磁层大尺度对流电场、曲率-梯度漂移以及内磁层旋转电场的共同作用。然而，在地磁活动时期，特别是磁暴与亚暴发生期间，这种离子结构的时空特性及其形成机制仍然备受争议，不同离子（氢离子和氧离子）所形成“鼻状”谱结构的差异及形成原因仍有待研究。本项目拟利用Van Allen Probes、THEMIS,和Cluster卫星在内磁层的联合观测，通过个例、统计及理论分析，系统研究“鼻状”离子谱结构在内磁层的空间分布特性以及时间演化规律，比较磁暴期间不同离子“鼻状”谱结构的异同，与数值计算结果进行对比，分析造成这种差异的物理成因。项目的实施将有助于揭示暴时近磁尾离子向内磁层的注入机制以及磁暴与亚暴的关系，为环电流的形成机制提供重要的参考信息。