SOME STUDIES ON VLF ATMOSPHERICS

Abstract

Lightning can be regarded as a transient high-current electric discharge, having path length of several kilometres. It occurs when some region of the atmosphere attains an electric charge sufficiently large that the electric field associated with it causes electrical break-down of the air. Lightning is known to occur in various media like thundercloud, sand and dust storms, volcanic erruptions, cyclones and nuclear explosions. It is also SAo-ea. -----kno-wn to occur on other planets like Venus and Jupiter. On earth, the most common source of lightning is the thunder-cloud. Present studies pertain only to lightning discharges produced by it. The lightning discharge can take place (i) between two opposite charge centres of a single cloud, remaining entirely within the cloud, (ii) between one charge centre of one cloud and opposite charge centre of another cloud and (iii) between lower charge centre of cloud and the ground. These are known as intracloud SIC), intercloud and cloud to ground (CG) discharges respectively. Occasionally, the discharge may occur between the cloud and the surrounding air which is known as 'air dis-charge'. The intracloud discharges, known to be less intense, are mostly hidden within the clouds. Therefore, most of the experimental and theoretical studies reported in literature pertain to the cloud to ground lightning.