磁场拓扑和方向对火星磁尾热电子分布的影响
The Influence of Magnetic Field Topology and Orientation on the Distribution of Thermal Electrons in the Martian Magnetotail
摘要：
热（<1 eV）电子密度测量，来自火星大气和挥发物演化（MAVEN）朗缪尔探测器和波（LPW）仪器，进行了分析，以产生在火星磁尾的热电子人口的第一个统计研究。重合测量的本地磁场被用来证明，靠近火星，热电子人口是最有可能被观察到的圆柱形距离约1.1火星半径（RM）的中央尾部区域的时候，当磁场耀斑向内朝中央尾部，相比之下，约1.3 RM的时候，当磁场耀斑向外远离中央尾部。在磁尾更远的地方也观察到类似的模式，但变化更大。热电子密度在整个磁尾中变化很大;在火星的光学阴影内，平均密度通常为20-50 /cc，而在光学阴影外，平均密度可以达到100 /cc。观察到整个尾部测量的平均密度的标准偏差为100%。对局部磁场拓扑结构的分析表明，在火星光学阴影内观察到的热电子可能来自夜侧电离层，而在光学阴影外观察到的电子可能来自昼侧电离层。最后，当最强的地壳磁场指向太阳时，火星光学阴影内的热电子被观测到的可能性比指向尾部时高出20%。
英文摘要：
Thermal (<1 eV) electron density measurements, derived from the Mars Atmosphere and Volatile Evolution's (MAVEN) Langmuir Probe and Waves (LPW) instrument, are analyzed to produce the first statistical study of the thermal electron population in the Martian magnetotail. Coincident measurements of the local magnetic field are used to demonstrate that close to Mars, the thermal electron population is most likely to be observed at a cylindrical distance of ~1.1 Mars radii (RM) from the central tail region during times when the magnetic field flares inward toward the central tail, compared to ~1.3 RM during times when the magnetic field flares outward away from the central tail. Similar patterns are observed further down the magnetotail with greater variability. Thermal electron densities are highly variable throughout the magnetotail; average densities are typically ~20-50 /cc within the optical shadow of Mars and can peak at ~100 /cc just outside of the optical shadow. Standard deviations of 100% are observed for average densities measured throughout the tail. Analysis of the local magnetic field topology suggests that thermal electrons observed within the optical shadow of Mars are likely sourced from the nightside ionosphere, whereas electrons observed just outside of the optical shadow are likely sourced from the dayside ionosphere. Finally, thermal electrons within the optical shadow of Mars are up to 20% more likely to be observed when the strongest crustal magnetic fields point sunward than when they point tailward.
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