]> A rare and randomly occurring bright ball of light observed floating or moving through the atmosphere close to the ground. A particular aspect of a normal lightning flash occasionally seen when the observer happens to view end-on a number of segments of the irregular channel (zigzag lightning) and hence receives an impression of higher luminosity at a series of locations along the channel. Weakly luminous upward propagating discharges, blue in color, emanating from the tops of thunderstorms. The process by which negative charge centers at successively more distant locations in a thundercloud are tapped for discharge by successive strokes of cloud-to-ground lightning. Lightning is a transient, high-current electric discharge with pathlengths measured in kilometers. The most common source of lightning is the electric charge separated in ordinary thunderstorm clouds. The intense luminosity that propagates upward from earth to cloud base in the last phase of each lightning stroke of a cloud-to-ground discharge. The sound emitted by rapidly expanding gases along the channel of a lightning discharge.