Lightning works through a process of charge separation within a thunderstorm cloud. Inside the cloud, turbulent winds move ice particles and water droplets, causing negative charges to gather near the cloud base and positive charges to build near the top. This separation creates strong electric fields between different charged regions in the cloud, and between the cloud and the ground. When the electric field becomes strong enough, a channel of negative charges called a stepped leader descends from the cloud toward the ground in steps of about 50 to 100 meters. At the same time, positive charges rise up from tall objects on the ground. When these two channels connect, an intense flow of electric current called the return stroke shoots upward from the ground to the cloud. This return stroke is what we see as the bright flash of lightning. The lightning process happens very quickly, in less than a second, and often consists of several strokes following the same or slightly different paths, causing flickering or dancing appearances. The return stroke heats the air around the channel to extreme temperatures, causing the air to expand rapidly, creating a shockwave that produces the sound of thunder. Lightning can strike from cloud to ground, within a cloud, or between clouds. The typical cloud-to-ground lightning involves a plasma channel several kilometers long with currents in the tens of thousands of amperes and temperatures up to 30,000 °C (54,000 °F).
