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My Discovery
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The most familiar and best understood type of lightning comes in the form of cloud-to-ground strikes. These strikes aren't the most common form of lightning, but because they come to ground, they are the most damaging and dangerous. About 90 percent of cloud-to-ground flashes originate in a cloud's negative charge center, in its lower section. A charged streamer, called a stepped leader, then moves toward Earth in discrete steps of about 50 meters each, pausing about 100 microseconds between steps. This leader shoots down to meet with a positively charged streamer surging up from objects on the ground -- trees, buildings, people, etc. --at 60,000 miles per second. If the two connect, they set off a bright flash. Sometimes cloud-to-ground strikes send a positive charge toward Earth. This positive charge typically originates from the cloud's positively charge upper region and tend to be about 10 times more energetic than negative flashes. Researchers now speculate that sprites, which are a type of lightning that occurs above thunderclouds, may result from positive cloud-to-ground strikes.
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