Nongyrotropic electron velocity distribution functions near the lunar surface
Nongyrotropic electron velocity distribution functions near the lunar surface
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DOI：
10.1029/2012ja017642
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发表时间：
2011-12
影响因子：
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通讯作者：
Y. Harada;S. Machida;Yoshifumi Saito;S. Yokota;K. Asamura;M. Nishino;H. Tsunakawa;H. Shibuya;F. Takahashi;M. Matsushima;H. Shimizu
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文献类型：
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作者：
Y. Harada;S. Machida;Yoshifumi Saito;S. Yokota;K. Asamura;M. Nishino;H. Tsunakawa;H. Shibuya;F. Takahashi;M. Matsushima;H. Shimizu
[1]我们分析了在月球表面附近获得的非地转电子速度分布函数（VDFs）。由Kaguya在太阳风和地球磁层中在100 -100公里高度测量的电子VDF显示出与“陀螺仪损耗”效应相关的非地转空区;即，月球表面的电子吸收与电子回旋运动相结合。粒子示踪计算使我们能够推导出理论上的电子VDFs中的禁区，从而考虑到由于抗磁电流系统，月球表面充电和垂直于磁场的电场引起的不均匀磁场的修改。所观察到的空区域与理论推导出的禁止区域之间的比较表明，各种组件修改的非共沸电子VDFs的特性取决于周围的等离子体条件。在月面的磁尾叶，负表面电位略有减少的大小的禁区，但没有明显的影响，无论是抗磁电流或垂直电场。在太阳风的昼侧，观测结果表明存在抗磁电流或太阳风对流电场效应，或两者兼而有之。在地球等离子体片中，所有这三种机制都可以大大改变禁带的特性。这些观察结果表明存在至少5 mV/m的局部电场，尽管负责产生这种强电场的机制尚不清楚。分析与固体表面附近的陀螺损耗效应相关的非共沸VDFs可以促进对近表面等离子体环境和等离子体-固体-表面相互作用的更好理解。
[1] We have analyzed nongyrotropic electron velocity distribution functions (VDFs) obtained near the lunar surface. Electron VDFs, measured at ∼10–100 km altitude by Kaguya in both the solar wind and the Earth's magnetosphere, exhibit nongyrotropic empty regions associated with the ‘gyroloss’ effect; i.e., electron absorption by the lunar surface combined with electron gyromotion. Particle-trace calculations allow us to derive theoretical forbidden regions in the electron VDFs, thereby taking into account the modifications due to nonuniform magnetic fields caused by diamagnetic-current systems, lunar-surface charging, and electric fields perpendicular to the magnetic field. Comparison between the observed empty regions with the theoretically derived forbidden regions suggests that various components modify the characteristics of the nongyrotropic electron VDFs depending on the ambient-plasma conditions. On the lunar nightside in the magnetotail lobes, negative surface potentials slightly reduce the size of the forbidden regions, but there are no distinct effects of either the diamagnetic current or perpendicular electric fields. On the dayside in the solar wind, the observations suggest the presence of either the diamagnetic-current or solar wind convection electric field effects, or both. In the terrestrial plasma sheet, all three mechanisms can substantially modify the characteristics of the forbidden regions. The observations imply the presence of a local electric field of at least 5 mV/m although the mechanism responsible for production of such a strong electric field is unknown. Analysis of nongyrotropic VDFs associated with the gyroloss effect near solid surfaces can promote a better understanding of the near-surface plasma environment and of plasma–solid-surface interactions.