Thunder and lightning explained

This is the season of thunderstorms. When great masses of air move across the continent, some hot, some cold, the places where they meet are areas of great upheaval and turmoil in the atmosphere.
Much of these great, magnificent, awe-inspiring displays can be explained by simple physics. On the other hand, a lot is not simple, by any means.
When two great air masses meet, one hot, one cold, we have a great deal of turbulence.
The hot air rises rapidly, probably drawing a lot of cool air with it.
These huge updrafts may go as high as 70,000 or 80,000 feet. As moist air rises quickly, it cools, and the moisture condenses.
So we have the buildup of those black, towering, menacing clouds, when the storm is on its way.
This is the “thunderhead,” shaped like the old fashioned blacksmith’s anvil.
The other effect which comes about by the rapid movement of air is the electric charge built up on the clouds.
This is “static electricity’, the same as you get when you stroke the cat, or walk on a carpet.
These static charges are really huge, perhaps up to 20 million volts. (Compare this with the 110 volts which runs your home vacuum cleaner)
The bottom of the cloud usually has a negative charge and the top, positive.
The action which bothers us, though, is between the cloud and the earth.
The charge on the cloud bottom courses another charge, of the same size, to form on the earth directly beneath it.
This is an induced charge. Maybe you remember this from your high school physics.
So we have two gigantic charges, with air in between, and those are the ingredients for a monstrous electric spark, and that’s what lightning really is.
When the two charges are big enough, we get a very powerful, fast, electrical discharge between the clouds and the earth—lightning.
We think we see a single stroke, but the electricity really runs back and forth several times in a fraction of a second.
The electric current in a single flash may be up to 90,000 amperes. (Again, compare this with the ½ ampere or so, which operates that vacuum cleaner).
The electricity in a lightning flash does indeed move this “lightning speed”—about 300 miles per second.
There are several kinds of lightning. Fork lightning is one, where the current branches out into several paths.
Bolt lightning is another, where there is only one strong path, with no branches.
Sheet lightning or heat lightning usually happens between two clouds, and is no threat at all to anything on earth.
The thunder? When air is superheated by the electrical discharge, it expands tremendously, almost creating a vacuum.
The air around it collapses into this vacuum immediately.
Both of these effects are accompanied by a lot of noise, especially the collapsing part. And this is the familiar sound of thunder.
That is briefly how thunder and lightning are formed.
The next article will talk a bit about the myths, dangers, and precautions about lightning.

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