Using the cold plasma dispersion relation and whistler mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument
Using the cold plasma dispersion relation and whistler mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument
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DOI：
10.1002/2016ja022501
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发表时间：
2016-05
期刊：
影响因子：
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通讯作者：
D. Hartley;Craig A. Kletzing;W. Kurth;S. Bounds;T. Averkamp;G. Hospodarsky;J. Wygant;J. Bonnell;O. Santolík;Clare E. J. Watt
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文献类型：
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作者：
D. Hartley;Craig A. Kletzing;W. Kurth;S. Bounds;T. Averkamp;G. Hospodarsky;J. Wygant;J. Bonnell;O. Santolík;Clare E. J. Watt
当根据电场观测来近似哨声模式磁场波功率时，通常假设冷等离子体理论和平行波传播。目前的研究是第一个包括波法向角从电场和磁场仪器套件和集成科学包板上的货车艾伦探针在转换因子，从而允许这些假设的准确性进行量化。结果表明，删除平行传播的假设并没有显着影响计算等离子体层嘶嘶声波功率。因此，并行传播的假设是有效的。对于合唱波，包含在转换因子中的波法向角导致波功率比（观测/计算）分布的显着改变;高估的百分比减少，低估的百分比增加，值的传播显着减少。平均而言，计算出的等离子体层嘶嘶声波功率是一个很好的估计所观察到的，而计算出的合唱波功率持续和系统地低估。波功率比（观察/计算）的调查，作为频率和等离子体密度的函数，揭示了一个结构与信号衰减一致，通过形成一个等离子体鞘周围的电场和波球形双探头仪器。为了量化电场天线和等离子体界面之间的可变阻抗的影响，开发了一个简单的密度相关模型。这种鞘层阻抗模型，然后被证明是成功的显着提高计算和观察到的功率谱和波功率之间的协议。
Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/ calculated); the percentage of overestimates decreases, the percentage of underestimates increases, and the spread of values is significantly reduced. Calculated plasmaspheric hiss wave powers are, on average, a good estimate of those observed, whereas calculated chorus wave powers are persistently and systematically underestimated. Investigation of wave power ratios (observed/calculated), as a function of frequency and plasma density, reveals a structure consistent with signal attenuation via the formation of a plasma sheath around the Electric Field and Waves spherical double probes instrument. A simple, density‐dependent model is developed in order to quantify this effect of variable impedance between the electric field antenna and the plasma interface. This sheath impedance model is then demonstrated to be successful in significantly improving agreement between calculated and observed power spectra and wave powers.