Abstract

Discrete spectra of frequencies at 8, 14, 20, 26, … Hz are generated by electromagnetic emission from lightning sources and can be regarded as excitation of AC global circuit. These electromagnetic emissions originating within the Earth-ionosphere waveguide occur in the ULF, ELF and VLF frequency ranges. These include Schuman Resonances (SR), ELF-VLF sferics, sprites etc. During 1990s and later, the scenario with these sub-ionospheric ELF SR waves changed and several new aspects emerged. The SR power varies with respect to the receiver position and the lightning centers, commonly referred as source-observer distance. Both electric and magnetic components of SR intensity vary with the spatial shifts of the thunderstorm regions under El-Niño and La-Niña conditions. The magnitude of the lightning in the lower atmospheric region varies with time of the day. The electromagnetic waves thus generated at SR frequencies resonate due to multiple reflections in the Earth-ionosphere cavity. The total signal may be dependent on the waves from the different lightning sources. In this context, different groups of researchers throughout the globe are working and published few interesting results. In this work, few results of different observatories are discussed. Also, an attempt was made to detect experimentally the discrete signals at Kolkata (Lat. 22.56° N, Long. 88.5° E) from the year 1999. Some frequency changes in the peak values are observed in the recorded data which may be attributed to uncertainty arising from spatial distribution of lightning sources exciting the Schuman Resonance modes. Some of those results are also presented in this paper.

中文翻译：

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舒曼共振现象的研究及最新进展

摘要

闪电产生的电磁辐射会产生频率分别为8、14、20、26，…Hz的离散频谱，这可以看作是对AC全局电路的激励。这些源自地球电离层波导的电磁辐射发生在ULF，ELF和VLF频率范围内。这些包括Schuman共振（SR），ELF-VLF伪像，子画面等。在1990年代及以后，这些电离层ELF SR波的情况发生了变化，出现了几个新的方面。SR功率随接收器位置和闪电中心的变化而变化，通常称为源-观察者距离。在El-Niño和La-Niña条件下，SR强度的电磁成分都随雷暴区域的空间变化而变化。较低大气区域的闪电强度随一天的时间而变化。因此，在SR频率下产生的电磁波由于地球电离层腔中的多次反射而共振。总信号可能取决于来自不同闪电源的波。在这种情况下，全球各地的不同研究人员小组正在工作，并发表了一些有趣的结果。在这项工作中，很少讨论不同天文台的结果。另外，尝试从1999年开始实验检测加尔各答（北纬22.56°，东经88.5°）处的离散信号。在记录的数据中观察到峰值的某些频率变化，这可能是由于雷电的空间分布引起的不确定性激发了舒曼共振模式。