Wavelength Measurements of Electron Cyclotron Harmonic Waves in Earth's Magnetotail
Wavelength Measurements of Electron Cyclotron Harmonic Waves in Earth's Magnetotail
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DOI：
10.1029/2022ja030500
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发表时间：
2022-06
期刊：
影响因子：
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通讯作者：
Xu Zhang;V. Angelopoulos;A. Artemyev;Xiao‐jia Zhang;X. An;Jiang Liu
中科院分区：
文献类型：
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作者：
Xu Zhang;V. Angelopoulos;A. Artemyev;Xiao‐jia Zhang;X. An;Jiang Liu
电子回旋谐波（ECH）是极光扩散降水的潜在驱动力，几十年来一直受到广泛的研究。然而，ECH波的产生机制仍然是一个悬而未决的问题。70年代的理论工作已经证明，热等离子体片电子的损失锥分布可以激发ECH波。然而，最近的THEMIS航天器观测表明，波也可以被低能电子束激发。利用干涉测量技术分析THEMIS航天器上电场仪天线对上的单个探针测量的电势之间的相位差，我们计算了波束驱动的ECH波和损耗锥驱动的ECH波的波数。这些波数测量以及从航天器测量获得的其他波的性质证明是符合预期的线性不稳定性分析。这为我们提供了独立的验证的产生机制和线性色散关系的光束驱动和损耗锥驱动的ECH波。我们的统计结果表明，波束驱动ECH波的波矢量的中值，其特征在于波法线角（θB <$，k <$$\theta \left（\stackrel{\righttharpoonup}{B}，\stackrel{\righttharpoonup}{k}\right）$）小于80°时，为0.011 m−1;损失锥驱动的ECH波，其特征是波法向角大于85°，为0.00765 m−1。ECH波的直接波数测量使我们能够更好地了解地球磁层中ECH波和电子之间的相互作用。
Electron cyclotron harmonic (ECH) waves, potential drivers for diffuse aurora precipitation, have been extensively investigated for decades. The generation mechanism of ECH waves, however, remains an open question. Theoretical work in 1970s has demonstrated that ECH waves can be excited by loss cone distributions of hot plasma sheet electrons. Recent THEMIS spacecraft observations, however, indicate that the waves can also be excited by low energy electron beams. Utilizing interferometry techniques to analyze the phase difference between electric potentials measured by individual probes on Electric Field Instrument antenna pairs on THEMIS spacecraft, we compute the wavenumber of both beam‐driven ECH waves and loss‐cone‐driven ECH waves. These wavenumber measurements as well as other wave properties obtained from spacecraft measurements prove to be consistent with expectation from linear instability analysis. This provides us with independent verification of the generation mechanism and linear dispersion relation of beam‐driven and loss‐cone‐driven ECH waves. Our statistical results demonstrate that the median value of the wave vectors of beam‐driven ECH waves, characterized by wave normal angles ( θB⇀,k⇀ $\theta \left(\stackrel{\rightharpoonup }{B},\stackrel{\rightharpoonup }{k}\right)$ ) less than 80°, is 0.011 m−1; and that of loss‐cone‐driven ECH waves, characterized by wave normal angles larger than 85°, is 0.00765 m−1. Direct wavenumber measurements of ECH waves allow us to better understand the interaction between ECH waves and electrons in Earth's magnetosphere.