STUDIES ON THE VLF EMISSIONS FROM LIGHTNING

Abstract

Lightning, generally defined as a transient, high current, long gap electric discharge, is known to emit electromagnetic radiations in the whole electromagnetic spectrum from a few hertz in ELF range to beyond the visible region. The visible radiation is utilized in photographic and spectroscopic observations, while VLF and ELF waves can be used for propagation studies, as man made transmitters are not easily available in these ranges. Since the return stroke of a lightning discharge radiates maximum electromag-netic energy in,the VLF range, it can be widely used for source location, short term weather forecasting and studies of the propagation characteristics of these waves to large distances in the earth-ionosphere waveguide. The knowledge of the propagation characteristics of VLF waves can be helpful in long range communication and navigation systems. Further, the VLF radiations, which have a higher wavelength compared, to the VHF or HF radiations, can penetrate deep into the earth's crust and can be used in geophysical exploration and ground water detection. However, no attempt, to the author's knowledge, has yet been made in this direction. Previous workers (21,42,74,138,144) have considered a perfectly conducting ground in their calculations of electric fields of lightning. However, the ground is known to be finitely conducting, which the present author takes into..............