How does lightning form?
Lightning, one of the most dangerous weather phenomena, strikes the earth millions of times per day.
Lightning | © Mike Hollingshead | SuperStock | Corbis
Lightning is one of nature's most impressive weather phenomena and one of the most dangerous. A lightning bolt can contain as many as a billion volts of electricity, making every flash a potential killer. Lightning strikes the surface of the Earth roughly 8 million times per day. It can strike clouds and air as well, but the ground strikes are what can cause damage to property and people.
Lightning bolts are caused by an imbalance between positive and negative charges. A series of negative charges, known as a stepped leader, make their way down from a storm cloud toward the ground. When the last of these negative charges, which are about 150 feet long, comes within 150 feet of a positively charged object (such as a building, tree or person), it is met by a charge of positive electricity called a streamer. When the leader and streamer connect, a return stroke travels back to the cloud. You see a lightning flash occur after about 20 return strokes travel along the same path. Each return stroke travels at approximately 60,000 mph.
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There would be no thunder without lightning. A lightning channel heats the surrounding air to 18,000 degrees Fahrenheit. This causes the air to rapidly expand, generating the sound wave of thunder. You can estimate the distance of lightning by counting how many seconds elapse before you hear a thunder clap. If you hear thunder five seconds after seeing a lightning flash, the lightning is one mile away.
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Lightning is most likely to occur during the summer months in warm climates. The highest frequency of lightning occurs in Florida between Orlando and Tampa because of the high moisture content and high surface temperatures. The West Coast has the lowest frequency of cloud-to-ground lightning strikes. Lightning often strikes tall objects such as skyscrapers and mountains, but it doesn't necessarily gravitate toward the nearest high point — it can strike the ground in an open field with a tree line nearby.
5 quick facts about lightning
- Lightning can occur in volcanic eruptions, intense forest fires and nuclear detonations.
- There is a still a scientific debate about how a cloud builds up electrical charges.
- A typical lightning flash could power a fluorescent light bulb for a year.
- Being underneath a tree is the second leading cause of lightning deaths.
- New York's Empire State Building is struck by lightning nearly 100 times a year.