James Matthew K, Bunce Emma J, Yeoman Timothy K, Imber Suzanne M, Korth Haje
Department of Physics and Astronomy University of Leicester Leicester UK.
Department of Physics and Astronomy University of Leicester Leicester UK; Department of Atmospheric, Oceanic and Space Sciences University of Michigan Ann Arbor Michigan USA.
J Geophys Res Space Phys. 2016 Sep;121(9):8755-8772. doi: 10.1002/2016JA023103. Epub 2016 Sep 28.
We present a statistical survey of ultralow-frequency wave activity within the Hermean magnetosphere using the entire MErcury Surface, Space ENvironment, GEochemistry, and Ranging magnetometer data set. This study is focused upon wave activity with frequencies <0.5 Hz, typically below local ion gyrofrequencies, in order to determine if field line resonances similar to those observed in the terrestrial magnetosphere may be present. Wave activity is mapped to the magnetic equatorial plane of the magnetosphere and to magnetic latitude and local times on Mercury using the KT14 magnetic field model. Wave power mapped to the planetary surface indicates the average location of the polar cap boundary. Compressional wave power is dominant throughout most of the magnetosphere, while azimuthal wave power close to the dayside magnetopause provides evidence that interactions between the magnetosheath and the magnetopause such as the Kelvin-Helmholtz instability may be driving wave activity. Further evidence of this is found in the average wave polarization: left-handed polarized waves dominate the dawnside magnetosphere, while right-handed polarized waves dominate the duskside. A possible field line resonance event is also presented, where a time-of-flight calculation is used to provide an estimated local plasma mass density of ∼240 amu cm.
我们利用水星表面、空间环境、地球化学和测距（MErcury Surface, Space ENvironment, GEochemistry, and Ranging，MESSENGER）磁力计的完整数据集，对水星磁层内的超低频波活动进行了统计调查。本研究聚焦于频率小于0.5赫兹的波活动，该频率通常低于当地离子回旋频率，以确定是否可能存在类似于在地球磁层中观测到的场线共振。利用KT14磁场模型，将波活动映射到磁层的磁赤道平面以及水星的磁纬度和地方时上。映射到行星表面的波功率表明了极盖边界的平均位置。在磁层的大部分区域，压缩波功率占主导，而靠近日侧磁层顶的方位波功率则表明磁鞘与磁层顶之间的相互作用（如开尔文-亥姆霍兹不稳定性）可能正在驱动波活动。这一点在平均波极化中得到了进一步证实：左旋极化波在晨侧磁层占主导，而右旋极化波在昏侧占主导。还展示了一个可能的场线共振事件，其中飞行时间计算用于估计当地等离子体质量密度约为240原子质量单位/立方厘米。
