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As the tornado turns.

Packing enough power to uproot trees and toss freight trains from their tracks, tornadoes are the most violent weather phenomena on Earth. Who would ever think they're made of . . . clouds?

Find out more by turning the page.

HOW DOES A TORNADO GET ITS SHAPE?

You could say the "twisted" shape is the result of a skyway "accident," a smash-up between two air masses coming at each other from different directions (A). One is a warm and moist air mass traveling along the ground (red); the other is a cold and dry one higher in the atmosphere (blue).

The collision comes when the warm air rises--as warm air inevitably does. If it rises just as the cold front blows in, the collisions between warm and cold air molecules can set the rising air spinning.

Now you've got a powerful thunderstorm, called a supercell (B). But in order for a supercell to spawn a tornado, it has to build up a lot more energy.

WHERE DOES IT GET THE ENERGY?

It turns out that the winds in the rising spiral of air reduce the pressure inside the spiral. That adds heat energy to the storm in two ways:

* It creates suction, which draws more warm, moist air up from the ground. That heat and moisture feed the storm.

* It reduces the temperature of the air inside the spiral. That cooling increases the rate at which moisture in the rising air condenses (to form rain). The process of condensation releases even more heat.

SO WHAT DOES THE STORM DO WITH ALL THAT ENERGY?

It uses it to grow and to push in on the spinning air, forcing it into a tighter and tighter spiral. The tighter the spiral gets, the faster the winds swirl, further reducing the pressure and temperature inside. Eventually the air at ground level (C) is being sucked up into the storm so fast that the pressure and temperature there drop enough for water vapor to condense. It's this condensed water vapor, swirling violently as it gets sucked into the storm, that you see as a funnel-shaped vortex cloud--a tornado.

CAN MORE THAN ONE TORNADO HIT THE SAME PLACE AT THE SAME TIME?

Sure. A single thunderstorm can produce any number of tornadoes. Plus, individual twisters can split into three or four separate funnels that can hit the same structure all at once.

HOW CAN A TORNADO DESTROY ONE HOUSE AND NOT THE ONE RIGHT NEXT DOOR?

Some tornadoes, though quite powerful, are only 20-30 feet wide at the base. They take out whatever is in their path, but leave what they don't touch undisturbed. Bigger tornadoes, some a mile wide, cause more widespread damage. So funnel size really determines whether the twister takes the town block by block, house by house, or shoe by shoe (see "Twister Sisters" opposite page).

IF I SEE A TWISTER COMING, SHOULD I TRY TO OUTRUN IT?

Not unless you can do 70mph--that's how fast a tornado can travel. The winds inside the funnel can swirl even faster--as fast as 300mph. With winds like that it's no wonder most tornado deaths are the result of flying debris (see photos, above).

WHAT SHOULD I DO?

If you see the twister, get away from windows, head for a basement, inside hallway, or into a bathtub, and cover yourself with pillows or a mattress for protection. Most tornadoes last only 10 to 20 minutes, so you shouldn't have to stay in your shelter too long.

If you haven't seen the twister but you have heard a tornado watch, that means the weather conditions in your area could lead to tornadoes. Be ready to take cover. A tornado warning means a twister has already been spotted nearby.

WHAT CAUSES THE SPINNING WINDS TO FINALLY STOP?

Eventually, cool air from high up in the storm clouds sinks to the ground. That cuts off the supply of warm, moist air needed to keep the storm raging.

TWISTER SISTERS

April 26, 1991, was a typical day for Misty Storrer of Andover, Kansas--until her dad called from work to say the weather was doing "funny things." Shortly after the call, 15-year-old Misty looked out the living room window and saw a tornado almost touching ground just a few houses away.

Misty grabbed her 11-year-old sister, Kelsey, the family's two dogs, Ebony and Congo, and Onyx the cat, and headed for the basement. "A minute later we heard doors flying, glass breaking, and a very loud noise," she says.

Suddenly, almost as soon as it had hit, the twister passed.

"We went upstairs," Misty remembers, "and all that was left [of our house] was the concrete foundation. There was no carpet, no furniture. . . only one piece of linoleum tile from the kitchen floor. . . ."

The girls saw their mother running through the street. She had been at a teachers' meeting at the school when the twister struck.

"She didn't know where she was--or if she was even on our street--because the neighborhood was torn up," says Misty. "She asked us, 'Where is our house?' and I cried, 'It's gone!'

"Later, my mom looked for a pair of shoes, because she had kicked off her heels when she ran to get us. But the tornado had taken all the left-foot shoes and left the right-foot ones behind. So she wore one right shoe and a slipper she found in the rubble."

The Storrer's home is rebuilt now, on the same plot--the closets restocked with pairs of shoes. And Misty hopes she's seen the last of sinister twisters.
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Article Details
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Title Annotation:includes related articles; weather phenomenon
Author:Todd, Marie
Publication:Science World
Date:Mar 12, 1993
Words:922
Previous Article:Clearly cola?
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