Locally Generated ULF Waves in the Martian Magnetosphere: MAVEN Observations
Locally Generated ULF Waves in the Martian Magnetosphere: MAVEN Observations
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DOI：
10.1029/2019ja027312
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发表时间：
2019-11
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通讯作者：
Y. Harada;S. Ruhunusiri;J. Halekas;J. Espley;G. DiBraccio;J. Mcfadden;D. Mitchell;C. Mazelle;G. Collinson;D. Brain;T. Hara;Masahito Nosé;S. Oimatsu;K. Yamamoto;B. Jakosky
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作者：
Y. Harada;S. Ruhunusiri;J. Halekas;J. Espley;G. DiBraccio;J. Mcfadden;D. Mitchell;C. Mazelle;G. Collinson;D. Brain;T. Hara;Masahito Nosé;S. Oimatsu;K. Yamamoto;B. Jakosky
我们研究了由火星弓激波下方的局部等离子体不稳定性产生的火星超低频电磁波。最近对火星大气和挥发分演化(MAVEN)的观测表明，在火星弓激波上游产生的ULF波可以向下传播到电离层上层，可能通过加热电离层等离子体来促进重离子从火星逃逸。与上游质子回旋频率附近的上游波不同，我们从MAVEN数据中识别出频率接近局部质子回旋频率(FCP(LOCAL))的窄带超低频磁场波动。除了预期在磁鞘中局部产生的质子回旋波外，我们新发现了日侧上电离层和夜侧磁尾中FCP(局地)附近的压缩窄带发射(在某些情况下还包括其谐波)。白天波优先在太阳极端紫外线(EUV)较高的条件下观测到，并且经常与磁鞘起源的环状/壳状热质子有关，存在着冷密的电离层质子。夜间波表现出明显的偏爱高太阳EUV、强太阳风的条件，在这种条件下，暖质子和冷质子都得到了增强。观测到的这些纵波的性质与质子速度分布函数的正垂直斜率驱动的质子Bernstein模不稳定性基本一致。激发波可以引起热质子的垂直加热，从而将能量从沉淀的热质子转移到冷电离层质子。
We investigate Martian ultralow frequency (ULF) electromagnetic waves generated by local plasma instabilities below the Martian bow shock. Recent Mars Atmosphere and Volatile EvolutioN (MAVEN) observations have shown that ULF waves generated upstream of the Martian bow shock can propagate down to the upper ionosphere, possibly facilitating heavy ion escape from Mars by heating the ionospheric plasma. In contrast to the upstream waves oscillating near the upstream proton cyclotron frequency, we identify narrow band ULF magnetic field fluctuations with frequencies near the local proton cyclotron frequency (fcp(local)) from MAVEN data. In addition to expected proton cyclotron waves locally generated in the magnetosheath, we newly identify compressional narrow band emissions near fcp(local) (and its harmonics for some cases) in the dayside upper ionosphere and in the nightside magnetotail. The dayside waves are preferentially observed for high solar extreme ultraviolet (EUV) conditions and are often associated with ring/shell‐like, hot protons of magnetosheath origin in the presence of cold, dense ionospheric protons. The nightside waves exhibit distinct preference for high‐solar‐EUV, strong‐solar‐wind conditions, under which both warm and cold protons are enhanced. The observed properties of these compressional waves are generally consistent with a proton Bernstein mode instability driven by a positive perpendicular slope in proton velocity distribution functions. The excited waves can cause perpendicular heating of thermal protons, thereby transferring energy from precipitating hot protons to cold ionospheric protons.