What is lightning?

   A simple answer is: it is a naturally occurring electrical discharge whose length is measured in kilometers. Most of you would have seen electrical sparks as, for example, when a short circuit occurs. Also when welding is done. Imagine that spark (or arc) to be as long as a few kilometers! You have some idea of lightning. There is, of course, a complication. A single lightning flash consists of more than one electrical discharge. It usually consists of three or four partial electrical discharges; these partial discharges are known as strokes. Each stroke consists of two parts: (1) a discharge travelling down from thunder cloud towards ground and (2) a discharge travelling from ground towards the cloud. The first is called the “leader stroke” because it initiates the flash and the second is called the “return stroke”. When this leader touches the ground, a blindingly intense discharge follows which is the return....