Abstract

In September 2019, two out-of-service power transmission lines were used as a horizontal emitting antenna in an experiment conducted on the Kola Peninsula to generate ultra-low-frequency (ULF, 0.38–6.4 Hz) and extremely low–frequency (ELF, 9.4–194 Hz) signals during nighttime hours. The current ranged from 240 A at low frequencies (LF, 0.382 Hz) to 20 A at the highest frequencies (194 Hz). The results of the recording of ULF signals at Staraya Pustyn magnetic station, which is 1610 km away from the transmission line, are presented. The recorded signals had frequencies of 0.6–6.4 Hz and amplitudes normalized to the value of the emitter current ~0.4–0.7 fT/A. Three models were used for theoretical estimates: (1) formulas based on the theory of ELF field excitation over a conducting surface; (2) a numerical model of the ULF field in the atmosphere and ionosphere generated by a linear surface current of infinite length, and (3) a numerical model of a horizontal dipole in the multilayer Earth–atmosphere–ionosphere medium. Model 2 is based on the numerical solution of the system of Maxwell equations in the vertically inhomogeneous atmosphere and ionosphere; its fundamental feature is that it takes into account the contribution of ionospheric waveguide propagation to the excited field at large distances. Model 3 demonstrated the best agreement with the amplitudes of the recorded signals. However, contrary to the predictions of models 1 and 3, the frequency dependence of the amplitude of artificial signals in the 2–8 Hz range is non-monotonic, which may be a manifestation of the effects of waveguide propagation along the ionosphere.

中文翻译：

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在 FENICS-2019 实验期间在 Staraya Pustyn 磁站检测人工 ULF 信号

摘要

2019 年 9 月，在科拉半岛进行的一项实验中，两条停运的输电线路被用作水平发射天线，以产生超低频（ULF，0.38-6.4 Hz）和极低频（ELF） , 9.4–194 Hz) 在夜间发出信号。电流范围从低频 (LF, 0.382 Hz) 的 240 A 到最高频率 (194 Hz) 的 20 A。介绍了距输电线路 1610 公里的 Staraya Pustyn 磁站记录超低频信号的结果。记录的信号频率为 0.6–6.4 Hz，振幅归一化为发射极电流值 ~0.4–0.7 fT/A。三个模型用于理论估计：（1）基于导电表面上极低频场激励理论的公式；(2) 由无限长的线性表面电流产生的大气和电离层中超低频场的数值模型，以及 (3) 地球-大气-电离层多层介质中水平偶极子的数值模型。模型 2 基于麦克斯韦方程组在垂直非均匀大气和电离层中的数值解；它的基本特点是考虑了电离层波导传播对远距离激发场的贡献。模型 3 展示了与记录信号幅度的最佳一致性。然而，与模型 1 和 3 的预测相反，2-8 Hz 范围内人工信号幅度的频率依赖性是非单调的，这可能是波导沿电离层传播效应的表现。