lightning, electrical discharge accompanied by thunder, commonly occurring during a thunderstorm. The discharge may take place between one part of a cloud and another part (intracloud), between one cloud and another (intercloud), between a cloud and the earth, or earth and cloud; more rarely observed is the electrical discharge sometimes called "upward lightning," a superbolt between a cloud and the atmosphere tens of thousands of feet above the cloud. Lightning may appear as a jagged streak (forked lightning), as a vast flash in the sky (sheet lightning), or, rarely, as a brilliant ball (ball lightning). Illumination from lightning flashes occurring near the horizon, often with clear skies and the accompanying thunder too distant to be audible, is referred to as heat lightning. Charges are believed to accumulate in cloud regions as ice particles and droplets collide and transfer electric charges, with smaller, lighter ice particles and droplets carrying positive charges higher and heavier particles and droplets carrying negative charges lower. In a lightning strike on the ground, a negatively charged leader propagates from a negatively charged cloud region in a series of steps toward the ground; once it gets close to the ground a positively charged streamer rises to meet it. When the streamer meets the leader, an electrical discharge flows along the completed channel, creating the lighting flash. Long-lasting lightning flashes with lower current are more damaging to nature and humans than shorter flashes with higher currents. Lightning may also be produced in snowstorms or in ash clouds created by volcanic eruptions. Space probes have photographed lightning on Jupiter and recorded indications of it on Venus, Saturn, Uranus, and Neptune. Benjamin Franklin, in his kite experiment (1752), proved that lightning and electricity are identical. See also lightning rod.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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