Margaret Colosimo, age 15, of Hiawatha, Utah; . for her question:
What makes a whirlwind?
A whirlwind can do its merry dance almost anywhere, but it is more likely to dance for us in the desert. On a summers day, you may see a whole ballet troupe of whirlwinds whirling over the deserts and prairies. Actually, of course, we do not see a whirlwind. We see the dust and leaves, scraps of paper and other debris caught up in its swirling dance.
A frisky whirlwind can carry a sheet of newspaper spiraling up 20, 30, or 40 feet. It may waltz with its dancing partner a block or more down the street. `then it tires. Paper and leaves, dust and leaves and other dancing debris are dropped to the ground in a swirling heap. Rarely, if ever, is a whirlwind strong enough to do any serious damage.
A whirlwind is a weather event. But compared with the winds and storms that sweep over the world, it is just a kitten with all the playful antics of a kitten. However, even the smallest weather event is caused by temperature changes and circulation in the air.
The air, as we know, is warmest near the ground and the higher we go the cooler it gets. Warm air expands, becoming thinner and lighter. This is the airs s method for cooling off on a hot day, for as it expands it loses some of its heat. Warm air will expand in all possible directions, but a patch of warm air near the ground tends to expand upward and rise.
On a summer day, the sun heats up many patches of ground, some more than others. A sandy hillside, say, gets hotter than a shady gully. And the air gets its heat from the ground it touches. Here and there we get a small mass of warm air which begins to expand in a rising column.
Around it, cooler air flows in to replace it and the inflowing breezes star to spiral around and aloft. Dusty debris is pulled along with the whirlwind breezes and "c small weather event begins to take a shape that we can see. It is a rising, twirling column of dust and small fragments of debris. Soon the playful whirlwind may waltz away from its birth place and dance along in a zig zag path. Meantime, the small weather event is mixing batches of light and heavy, warm and cool air. When the mixture is properly blended, the whirlwind dies down. Its little dancing partners are dropped on the ground, perhaps a mile from where they started.
Whirlwinds may twirl in any direction and in a small way they may help to cool off the blistering heat of a summer day. They begin, remember, at the ground and carry a batch of the warmest air aloft to cooler regions. Even 100 of these kittenish weather events cannot do much to reduce the heat, but a sweltering day on the desert would be somewhat worse without them.