As charge in one cloud center is dissipated, negative charge from an adjacent charge center moves in to replace it. A dart leader from the second charge center moves to the ground along the original current channel. This produces another return streamer that also travels up to the cloud. Discharging continues until all negative charges in the cloud have been drained off, restoring electrical balance between Earth and atmosphere. Lightning strokes also travel between two clouds, and, in the case of heat lightning, between charge centers in the same cloud.
Thunder follows a lightning flash.
During the electrical discharge, the flow of electricity along the discharge path ionizes the gases of the air and produces great heat. The gases expand violently, causing compression waves that travel outward at the speed of sound. These compression waves produce thunder. The thousands of thunderstorms on Earth each day produce more than 8 million flashes of lightning, most of which occur in tropical and subtropical areas. Most are harmless, but a number of them strike airplanes, buildings, ships, and people.