Studies on Schumann Resonance Phenomena and Some Recent Advancements

Аннотация

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.