STEPPED LEADER (LIGHTNING)

A stepped leader is faint luminous light which is seen to propagate in discrete 50 meter steps with a short pause between each step; it branches downward from the cloud base to the ground before a lightning flash. Propagating at 1/3,000 the speed of light, it deposits about 5 coulombs of charge (usually negative) along its path and is associated with a 100- to 200-ampere current. Once one of the stepped leader's branches nears the ground, the increase in the electrical field causes a return stroke along the path of that branch (but in the opposite direction).