The Processes that Form Lightning

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  • 0:04 What Is Lightning?
  • 1:19 Thunderstorm Development
  • 2:03 Lightning Formation
  • 3:33 Categories & Types of…
  • 5:43 Lesson Summary
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Lesson Transcript
Instructor: Linda Fye
Understand how lightning is formed within a thunderstorm and the different stages involved in development. Learn about different types of lightning in thunderstorms and some not associated with storms.

What Is Lightning?

Have you ever seen lightning, then counted until you heard the thunder to see how far away a storm is? This is not just a game for children to play. It's actually a very real way to estimate the distance. Lightning travels at the speed of light, but thunder travels at the much slower speed of sound. So, a five-second delay between lightning and thunder means that a storm is about one mile away. This is actually very hand information, because lightning is quite a danger to humans. There are over 8.5 million lightning bolts a day that are 100,000 times the power we use in our houses, so it is a very real danger when thunderstorms are around.

But what exactly is lightning and how is it formed? Lightning is a very quick electrical discharge that occurs between a cloud and the ground, between two clouds, or within a cloud. It can be seen as a bright flash and is followed by the sound of thunder. Lightning is usually associated with thunderstorms. To understand how lightning forms in a storm, you must first understand how a thunderstorm develops.

Thunderstorm Development

A thunderstorm is a localized storm that has lightning and thunder and is short-lived. In the beginning of a storm's development, air rises in updrafts above the freezing level in the atmosphere. The water droplets in the cloud freeze, get heavier, and begin to fall, creating a downdraft. The droplets leave the bottom of the storm as heavy precipitation. This is the part of the storm when severe weather can occur. During this stage, both updrafts and downdrafts occur, which are what start the development of lightning. So this stage is when lightning and thunder may occur. Eventually, the updraft stops and only the downdraft remains. The storm weakens and finally ends.

Lightning Formation

Lightning is a bit of a mystery because the exact way electricity develops in a storm is not very well understood by scientists. But what we do know is that the way a thunderstorm develops causes electrical charges to be separated. This is known as charge separation. The updraft of air in a storm carries positively charged water droplets with it. The downdraft of precipitation carries negatively charged water drops downward to the bottom of the cloud. The negative charges on the bottom attract positive charges on Earth's surface, directly below the thunderstorm. The difference in charges on the bottom of the cloud and on the ground grow stronger and stronger until there must finally be a release. A finger of negative electricity, known as a leader, shoots down from the cloud searching for a way to meet the positive charges on the ground. Usually, the leader can't make a connection the first time, so this happens repeatedly until a finger of positive electricity shoots up from the ground to meet the leader. Once this occurs, a conduit or tunnel for electricity to pass from cloud to the ground opens up. This is when the lightning stroke occurs and a surge of electricity strikes downward and is visible for us to see. This may happen several times in rapid succession until all negative charges are gone from the bottom of the cloud. These are known as flashes and they happen so quickly that we can't see each individual stroke. Instead, the lightning appears to flicker.

Categories and Types of Lightning

The kind of lightning just discussed is called cloud-to-ground. It only makes up about 20% of lightning in a storm, but it is the most destructive. Some other categories of lightning that occur within a storm are intra-cloud lightning within the same cloud and cloud-to-cloud, between two clouds. The separation of the charges in the same cloud or different clouds forms lightning and storms in the same way as cloud-to-ground, only the discharge doesn't go to the ground.

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