Lightning is a discharge of atmospheric electricity that is triggered by a buildup of differing charges within a cloud. The result is a sudden release of energy that causes a distinctive bright flare, followed by a thunderclap. Lightning is most common around the equatorial regions of the world, although it can potentially strike anywhere, and it appears in a variety of guises, depending on atmospheric conditions.
There are several competing theories to explain why differing electrical charges appear in clouds, although scientists suspect that it may be related to the presence of ice crystals. Typically, the bottom of a cloud becomes negatively charged, and it sends out what is known as a “leader” that seeks a positive charge, either in another cloud or on the earth. As the leader approaches an area that is positively charged, a positively charged streamer emerges, meeting the leader, sealing the connection, and generating a bolt of lightning.
After the lightning travels to the ground or another cloud, it may strike again several times within a fraction of a second. These re-strikes are so fast that people cannot register them with the naked eye; instead, they appear as a single strike. The electricity moves so quickly that it superheats the surrounding air, causing a sudden rapid expansion that creates a shockwave. Shockwaves are responsible for thunder; because thunder is so closely associated with lightning, some people attempt to judge the distance of a storm by counting the time which elapses between a strike and a thunderclap.
Most lightning travels from cloud to cloud, or from a cloud to the ground. In rare circumstances, however, the charges will be reversed, and lightening will emanate from the ground. This is known as “positive lightning,” and it is rare and extremely dangerous. It is often triggered by human activities, such as the liftoff of a rocket or the detonation of a nuclear device.
Many people associate classically jagged streaks in the sky with lightning, but it can also appear in bursts known as bead lightning, or it can reflect from the clouds, making sheet lightning. Some people may also be familiar with ball lightning, an unusual manifestation that is rarely observed.
An individual who is caught outside during a thunderstorm and who cannot take shelter in a car or house should hunch his body close together, making himself a small target, with only his feet touching the ground. People who are indoors should stay away from phones and plumbing, as lightning can sometimes travel through phone wires or plumbing systems.