Paula Van Loons age 11. of Berkeley ‑
How is a whirlwind caused?
A little whirlwind is a pleasure to watch. It appears on a hot summers day. It is most likely to start its spinning dance in a dry or desert region. Sometimes you may see a dozen of them kicking up the dust over a stretch of desert.
The whirlwind is no relative of the furious whirling tornado. The tornado starts in a cloud above and dips in a funnel down to the ground. The little whirlwind starts on the ground and winds itself upwards. At times it may be wild enough to tear down a bough or rip a shingle off a roof. But is never blows up to the fury of the tornado.
Certain things are necessary to start the whirlwind dancing. The hot sun is usually glaring down on the ground. A hundred feet up or thereabouts the air must be fairly cool. The layer of air close to the ground must be much hotter than the layer of air above it.
A desert region is fine for these conditions. The ground cools off fast after a hot day. It cools the airy above it night air tends to be chilly even over a scorching desert. Come morning the ground gets its quota of heat and soon begins to warm the low layer of air above it. Hot air tends to rise. As it rises it expands and as it expands it cools. Sop very often the hot air on the face of the desert is covered by a layer of cooler air above. Hence the stage is often set for a ballet of jigging whirlwinds.
The fun begins when a small patch of warm air rises straight up in a column. This makes a straight column of lighter air. When you scoop a cup of water out of a pails the surrounding water flows in to fill up the hole. The heavier air around the column of light air behaves in much the same way.
It rushes in from all directions. The jig is on. Because the brig earth is spinning. the inflowing air spins around in a spiral. But unlike the tornado the tornado. the whirlwind can spin around in either direction. It stirs up the dust and whirls away leaves and debris. The dust rises and falls and trips along as the merry little whirlwind dances hither and thither.
Strange to say. the little dancer is really cooling the hot desert. It carries aloft the scorching air near the ground: This air cools as it rises and expands: Cooler air is mixed with the desert heat. True this does not make a great deal of difference to the temperature of a scorching desert. But the desert would be somewhat hotter without it. The whirlwind stirs up a small local breeze; But the breeze is not much use when it comes to fanning the weary traveler. All he feels is a face full of whirling dust.