磁层中电子各向异性综述：对太阳风压力和Kp的依赖性
A Survey of Electron Anisotropies in the Magnetosphere: Dependence on Solar Wind Pressure and Kp
- Space Sciences Laboratory, University of California, Berkeley（加州大学伯克利分校空间科学实验室）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本综述基于THEMIS数据调查磁层电子各向异性的空间分布及其对太阳风压力和Kp的依赖，发现平行各向异性集中于低能日侧，垂直各向异性集中于高能晨侧，并随活动增强向低L移动。
AI中文摘要：
我们展示了一项基于THEMIS卫星在地球赤道磁层内L值≤14处测量的电子分布调查。特别关注电子分布函数中磁场平行和垂直各向异性的空间分布和出现情况，以及这些各向异性如何依赖于太阳风动压力和磁层活动。利用THEMIS A和D卫星的161,300个3秒分辨率的电子测量数据，我们发现磁场平行各向异性在低能量（30--200 eV）下最为显著，并几乎出现在所有L和MLT范围内，其最大值集中在日侧/午后等离子层中；而垂直各向异性在高能量（1--30 keV）下占主导，并在L~5--10的较窄带内最大且最可能出现，具有明显的日侧/午前偏差。在黎明附近4≲L≲8--9的局部区域，在整个30--200 eV波段内通常缺乏磁场平行电子。两种各向异性类型在太阳风动压力和Kp升高时都向较低L壳层移动并变得更可能出现，且它们的空间和能量依赖性在很大程度上是互补的：垂直各向异性在空间上与准平行合声波的产生区域重合，而磁场平行各向异性与斜合声波和时域结构（TDS）的产生区域重合。除了作为电子种群类型的有用诊断工具外，我们的结果为与由这些各向异性产生的波模式的全球分布进行比较提供了有用的基础，并提供了一个基于各向异性的观测框架，用于解释它们对磁层活动的依赖性。
英文摘要：
We present a survey of electron distributions measured by THEMIS within Earth's equatorial magnetosphere at $L$ values $\le$ 14. Particular attention is focused on the spatial distribution and occurrence of magnetic field-aligned and perpendicular anisotropies in electron distribution functions and how these depend on solar wind dynamic pressure and magnetospheric activity. Using 161,300 3-s resolution electron measurements from THEMIS A and D, we find that field-aligned anisotropies are most prominent at low energies (30--200 eV) and occur over nearly all $L$ and MLT, with the largest values concentrated in the dayside/postnoon plasmasphere, while perpendicular anisotropies dominate at higher energies (1--30 keV) and are largest and most probable in a narrower band from $L \sim$ 5--10 with a pronounced dayside/prenoon bias. A localized region near dawn at $4\lesssim L\lesssim 8$--9 is found to be typically devoid of field-aligned electrons over the entire 30--200~eV band. Both anisotropy types shift toward lower $L$ shell and become more probable under elevated solar wind dynamic pressure and Kp, and their spatial and energy dependence is largely complementary: perpendicular anisotropies coincide spatially with regions of quasi-parallel chorus generation, while field-aligned anisotropies coincide with oblique chorus and time domain structure (TDS) generation regions. In addition to being a useful diagnostic for electron population types, our results provide a useful basis for comparison with global distributions of wave modes which arise from these anisotropies, and offer an anisotropy-based observational framework for interpreting their dependence on magnetospheric activity.
