Answer to "thunder and lightning" question

THUNDER & LIGHTNING -- Tania Louviere from Hammond, LA contacted us with following question: "My daughter, Lena, wants to know how lightning is made. She also wants to know what makes the thunder sound. My nephew, who is eight years old, told her that the thunder is caused when the clouds hit together. Isn't that cute?

We would just like to learn what really happens. All the kids are curious now, not to mention her Dad and myself. Thank You." -- 6/25/00

Your question is quite interesting, because when I grew up, my mother used to tell me that it was the clouds bumping together, too. And when I looked up in the sky to see the towering thunderclouds form, I could see the clouds merging (or bumping together).

Unfortunately, that isn't what happens....although it makes a nice story.

In the thunderstorm clouds, raindrops of different sizes, hailstones, and snowflakes all rub against each other. (That's right, there can be snow and ice in thunderstorms; the top of thunderstorms are very cold, sometimes the temperature at the top of clouds can be -60 degrees Fahrenheit or colder.) When the precipitation rubs inside the cloud, electric charges start to separate. This is much like what happens in a clothes dryer. As the clothes tumble around each other (and rub into each other), static electricity develops. When the clothes come out of the dryer, they "cling" to each other. It may not happen much in Louisiana, but sometimes in the winter, you can shuffle across a carpeted floor and touch a doorknob; "zap", you can get a small electric shock (more static electricity). And if you rub your fingers carefully in front of TV set that is on, you'll literally hear the electricity crackling!

Back to the thunderstorm. As all this rubbing takes place, electric charges tend to cluster in different parts of the thunderstorm cloud and on the ground near the thunderstorm. When the charge separation between positive charges and negative charges gets very large, it overrides the insulating capacity of the air in between and you see the result instantly - a giant electric spark, called lightning.

Now, lightning is hot. It can be up to 50,000 degrees Fahrenheit hot. So, as it passes through the air, it quickly heats the air. As air is heated, it expands, and this heated air bumps into the air nearby that isn't heated. The resulting sound wave moves through the air at about 1 mile every 5 seconds. So, if you count "1 Mississippi...." you can figure out about how close the lightning was to you. For every 5 seconds counted, it is another mile away.

Because lighting sometimes takes very odd paths as it snakes across the sky, the resulting thunder can also have a strange sound pattern. Some thunder is sharp, like a cracked whip. Other thunder rumbles for several seconds.

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