Frequency-time spectra of magnetospherically reflecting whistlers in the plasmasphere
Frequency-time spectra of magnetospherically reflecting whistlers in the plasmasphere
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等离子体层中磁层反射哨声的频率-时间谱
DOI：
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发表时间：
2003
期刊：
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通讯作者：
T. Bell
中科院分区：
文献类型：
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作者：
J. Bortnik;U. Inan;T. Bell
[1]我们提出了一种数值方法来模拟磁层中任意位置的观测频率-时间(f-t)谱图，该谱图是由地球上任何给定纬度的闪电引起的。使用二维射线跟踪程序，我们计算了5330条哨声射线的轨迹，这些哨声射线有效地采样了闪电的频谱和围绕震源的纬向传播，然后使用这些所谓的样本射线创建了�1.2亿条内插射线，每条射线都根据其频率和注入纬度赋予了能量度量。使用朗道阻尼计算和实际的超热电子通量，这种能量沿着射线的轨迹逐渐衰减。在等离子体层中定义了一个探测区域，穿过该区域的射线被用来构建代表在该区域的卫星上将观察到的东西的f-t谱图。我们研究了闪电源纬度、观测位置和等离子体层电子密度结构对模拟f-t谱图外观的影响，结果表明，这三个参数都表现出明显和明确的影响。特别是，我们重点讨论了等离子体层的电子密度结构，并解释了这些结构与光谱图中特定观测特征的出现之间的联系。利用这一分析，也许可以从观测到的磁层反射哨声光谱图中粗略地推断出源和等离子体层的某些特征。索引词：6964无线电科学：无线电波传播；6939无线电科学：磁层物理；7843空间等离子体物理：数值模拟研究；7871空间等离子体物理：波和不稳定性；关键词：磁层反射、非导管、哨声、等离子体层、甚低频、频谱图
[1] We present a numerical method of simulating at any location in the magnetosphere, the observed frequency versus time ( f-t) spectrogram resulting from a lightning strike at any given latitude on Earth. Using a two-dimensional ray tracing code, we calculate the trajectories of 5330 whistler rays that effectively sample the lightning strike’s frequency spectrum and latitudinal spread about the source and then use these so-called ‘‘sample rays’’ to create � 120 million interpolated rays, each weighted with a measure of energy according to its frequency and injection latitude. This energy is progressively attenuated along the ray’s trajectory using a Landau damping calculation with realistic suprathermal electron fluxes. A detection area is defined in the plasmasphere, and rays that cross this area are used to construct the f-t spectrogram representative of what would be observed on a satellite located in that region. We investigate the role that the lightning source latitude, observation location, and plasmaspheric electron density structures have on the appearance of the simulated f-t spectrograms and show that all three parameters exhibit distinct and well-defined effects. In particular, we focus on plasmaspheric electron density structures and explain the connection between these structures and the appearance of specific observed features in the spectrograms. Using this analysis, it may be possible to crudely infer certain features of the source and plasmasphere from observed magnetospherically reflecting whistler spectrograms. INDEX TERMS: 6964 Radio Science: Radio wave propagation; 6939 Radio Science: Magnetospheric physics; 7843 Space Plasma Physics: Numerical simulation studies; 7871 Space Plasma Physics: Waves and instabilities; KEYWORDS: magnetospherically reflecting, nonducted, whistlers, plasmasphere, VLF, spectrograms