Field Line Resonance in the Hermean Magnetosphere: Structure and Implications for Plasma Distribution
Field Line Resonance in the Hermean Magnetosphere: Structure and Implications for Plasma Distribution
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DOI：
10.1029/2018ja025920
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发表时间：
2019-01-01
影响因子：
2.8
通讯作者：
Bunce, Emma J.
中科院分区：
文献类型：
--
作者：
James, Matthew K.;Imber, Suzanne M.;Bunce, Emma J.
首次利用来自整个月球表面、空间环境、地球化学和测距使命的磁强计数据对磁力线共振事件进行了统计调查。超低频波是Hermean磁层磁震学的重要工具，这项研究提供了一个全新的窗口，共振结构和等离子体密度分布在Hermean磁层。在这里，我们评估共振事件从两个类别的环形共振特性的经典图片FLR在地球磁层驱动的开尔文-亥姆霍兹不稳定性和一个更全面的方法，包括所有观察到的横向共振更宽松的极化标准。二百二十三个环形FLR的特征与开尔文-亥姆霍兹驱动的FLR一致，发现在日侧Hermean磁层。这些波的基本频率被用来提供等离子体质量密度的估计，其范围类似于1-650 amu/cm（3）。进一步的343横向共振发现，提供非常相似的密度估计地球一样的FLR人口。来自所有566个事件的基频和谐波频率被用来拟合沿场线沿着的等离子体质量密度的幂律。赤道等离子体的质量密度预计约与R-7.5。赫敏偶极子在北方半球的偏移导致驻波结构的显著不对称。由于水星磁层的极端翘曲（远离偶极配置）的太阳风，基本环向模式被预测为振荡的频率明显低于基本极向模式，相反的相对环向和极向频率为地球的磁层建模。
The first statistical survey of field line resonance (FLR) events is presented using magnetometer data from the entire MErcury Surface, Space ENvironment, GEochemistry and Ranging mission. Ultralow-frequency waves are an important tool for the magnetoseismology of the Hermean magnetosphere; this study provides a completely new window onto the resonance structures and plasma density distribution in the Hermean magnetosphere. Here we assess resonance events from two categories-toroidal resonances characteristic of the classical picture of FLRs in the terrestrial magnetosphere driven by the Kelvin-Helmholtz instability and a more comprehensive approach including all observed transverse resonances with more relaxed polarization criteria. Two hundred twenty-three toroidal FLRs with characteristics consistent with Kelvin-Helmholtz-driven FLRs are found in the dayside Hermean magnetosphere. The fundamental frequencies of these waves are used to provide estimates of plasma mass density in the range of similar to 1-650 amu/cm(3). A further 343 transverse resonances are found which provide very similar density estimates to the Earth-like FLR population. Fundamental and harmonic frequencies from all 566 events are used to fit a power law to plasma mass density along the field lines. The equatorial plasma mass density is predicted to vary approximately with R-7.5. The offset of the Hermean dipole into the northern hemisphere causes significant asymmetries in the standing wave structure. Due to the extreme warping (away from a dipolar configuration) of Mercury's magnetosphere by the solar wind, the fundamental toroidal mode is predicted to oscillate with a notably lower frequency than the fundamental poloidal mode, contrary to relative toroidal and poloidal frequencies modeled for Earth's magnetosphere.