charged regions (Williams 90; MacGorman & Rust 49-53).
One of the problems in explaining the physics of lightning is the scale range of the phenomena in question. Electrification of storm clouds takes place at the atomic level, on scales of 10-13 kilometer, whereas the movement of the air which completes the cloud charging may occur on a scale of tens or hundreds of kilometers (Williams 88).
The typical duration of a lightning discharge, called a flash, is 0.2 sec., and it is often made up of one or more partial discharges, called strokes, which are measured in tenths of milliseconds (Uman 3-4). Flashes occur most frequently within the thundercloud itself, but the one most often and easily observed is the cloud to ground flash. There are two categories of ground flash: natural and artificially induced. The natural flash occurs because of electrification of the environment, whereas the artificially induced flash involves very tall buildings and structures, airplanes, and rockets. These ground flashes are described as forked lightning, which portrays a flash for a nearly vertical channel or multiple channels; ribbon flash, when the channel is displaced by the wind; and bead flash, when the decaying channel breaks down into light and dark spots. Ball lightning, a luminous sphere associated with the location of a ground strike, has been described, but never explained (MacGorman & Rust 83-86).
Modern research on the physics of lightning began early in this century with the work of C. T. R. Wilson, who also received the Nobel Prize for his invention of the cloud chamber. He was the first to infer the charge structure of thunderclouds and the amount of charge involved in lightning, and he did this by making remote measurements of thunderstorm electric fields. In the 1930s, lightning research was fueled primarily by the need to reduce the effects of lightning on electric power systems, and the pace of such research rema...