Lightning serves to neutralize the charge imbalances that build up in thunderstorms over time. Through the induction process
, lightning transfers the stored electrical energy of the electrified cloud into electrical currents that traverse the conductive ionized lightning channels. Most of the lightning energy goes into heating the atmospheric constituent gases, which causes them to undergo dissociation
, and recombination
. This generates intense emissions at atomic lines for the atmospheric gases. The rapidly expanding gases surrounding the channel also generate a shock wave
that we perceive acoustically as thunder
. Because sound
travels more slowly than light
through the air, the thunder will be appreciably delayed. The time difference between the flash of light and clap of thunder can be used to gauge the distance to the flash. Only when the leader connects to the ground does the ground potential wave (return stroke
) affect the lightning process.
The appearance of lightning to human observers and lightning-detecting instruments depends on the types of discharge processes involved. Observers have long described lightning as streak lightning
, forked lightning
, bead lightning
, sheet lightning
, or spider lightning
, among other terms, depending on the behavior of the leaders as they propagate through the clouds or make their way toward the ground. Cases of self-initiated upward lightning and lightning-triggered upward lightning have also been documented that resemble cloud-to-ground flashes that originate from a tall object on the ground and strike the cloud. The largest flashes—known as megaflashes
—can develop horizontally over hundreds of kilometers through the cloud while initiating multiple cloud-to-ground strokes
along their paths. Distant lightning that is too far away for the thunder to be heard has been called heat lightning
and other terms that do not represent distinct types of lightning. Reports of ball lightning
have also been made, but the existence of this phenomenon and its underlying physical processes have not been verified.
In addition to neutralizing local charge imbalances within the thunderstorm, lightning is also linked to the broader Earth
–atmosphere system through the global electric circuit
. The global circuit provides a framework for measuring and tracking changes in convective weather
worldwide over a long period of time, making lightning measurements a useful tool for climate monitoring
Term edited 3 March 2022.
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