Generation of electrostatic waves by discontinuous electron distributions
Generation of electrostatic waves by discontinuous electron distributions
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通过不连续的电子分布产生静电波
DOI：
10.1029/1999ja900128
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发表时间：
1999
影响因子：
--
通讯作者：
W. Paterson
中科院分区：
文献类型：
--
作者：
L. Yin;M. Ashour‐Abdalla;R. Richard;L. Frank;W. Paterson
本文研究了远瓣区的窄带静电波以及弓形激波和慢模激波中的静电波。从尾波瓣区进行的GeoTail测量显示，在与波瓣NEN发射相关的平行电子分布的低能区，呈现出双峰特征。在我们的线性色散和模拟研究中发现了不稳定波，并用测量的电子分布进行了初始化。波能量密度、波频和波形与航天器观测结果相当。利用平顶和单峰随有效电子热速度量级漂移的平行电子分布模型函数，研究了电子对弓形激波和慢模激波谱的贡献。该模型假定平行分布中可能存在不连续。模型的结果包括频率高于离子等离子体频率(ωpi)但远低于电子等离子体频率(ωpe)的波，以及延伸到ωpe的宽带高频波。此外，在冲击波侵彻过程中，随着峰偏移速度的增加和峰高的减小，波的频率增加，增长率和波能密度减小。在我们的研究中，我们从线性理论和模拟两个方面得到了色散。不稳定波有较宽的k范围，kλD大于1。对于频率远低于ωpe的波，随着电子分布的演化，频率进一步降低。
This paper presents studies of narrowband electrostatic waves (NEN) in the distant lobe region and electrostatic waves in the bow shock and slow mode shocks. Geotail measurements from the tail lobe region show a two-humped feature in the low-energy region of the parallel electron distributions correlated with lobe NEN emissions. Unstable waves were found in our linear dispersion and simulation studies initialized with the measured electron distributions. The wave energy density, wave frequency, and waveform were comparable with those from spacecraft observations. The electron contribution to bow shock and slow mode shock wave spectra was examined with the use of a parallel electron distribution model function that featured flat tops and single peaks drifting with speeds of the order of the effective electron thermal speed. The model assumed a possible discontinuity in the parallel distribution. Results from the model included waves with frequencies above the ion plasma frequency (ω pi ) but well below the electron plasma frequency (ω pe ) as well as broadband, higher-frequency waves extending to ω pe . In addition, wave frequencies increased and growth rates and wave energy density decreased as the peak offset speed increased and the peak height decreased during a shock penetration. Dispersions from both linear theory and simulation were obtained in our studies. The unstable waves had a broad k range with kλ D exceeding unity. For waves with frequencies well below ω pe , the frequency decreased further during the evolution of the electron distribution.