Lightning
illuminates the sky during a storm in Weld County, Colo. Researchers
have developed a new technique to expose the conditions inside
thunderclouds that lead to lightning strikes. Picture: BRYCE BRADFORD/FLICKR (CC BY-NC-ND 2.0)
Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions in the atmosphere (inside a single thundercloud or cloud-to-cloud) or ground temporarily equalize themselves, causing the instantaneous release of as much as one gigajoule of energy.
Lightning causes thunder, a sound from the shock wave which develops as gases in the vicinity of the discharge experience a sudden increase in pressure.