Lightning occurs when the lower part of a cloud becomes negatively charged and the earth becomes positively charged by induction, forming a capacitor. For a lightning discharge to occur between the cloud and earth, the air must break down when the electric field reaches 10 kV/cm due to the high moisture content and low pressure in storm clouds. A pilot streamer ionizes the air as it travels from the cloud to earth at 0.16 m/μs, branching into a stepped leader of 50 m segments that reaches earth in microseconds. A return stroke then moves rapidly up the already ionized path, neutralizing the cloud's negative charge in a bright flash. Additional charged regions in the cloud can produce dart leaders through the path in hot