Michael Rotnicke, age 11, of Sapleton, Iowa, for his question:
Why is a tornado hollow in the middle?
The central funnel of a tornado is almost an empty vacuum yet this hollow space packs a mighty wallop. Actually, it is a column of thinner ¬than thin air, sucking in winds and. moveable objects as it rises aloft. For its size, the tornado is the wildest storm in the world any: it demon¬strates that weather events work somewhat like engines, driven by moving currents of air.
This year, Americans had more than their share of destructive torna¬dos. As usual the wild little storms hatched in batches and struck down from cloudy skies. As usual, they formed along weather fronts that built up ahead of advancing cyclones, or low pressure cells. meteorologists ex¬plain that tornados occur in certain regions when weather conditions of this sort create enormous contrasts in temperature and air pressure.
Weather fronts tend to create contrasting pockets of warm and cool, light and dense air. In tornado territory, perhaps a down slope wind or some other factor enters the feathery turmoil. In any case, here and there a pocket of very light air forms in the weather front.
This small mass of very light air expands, but not through the denser air around it. It rises aloft and the denser air around is pulled in toward the rising column of thin light air. Nature we are told, abhors a vacuum of empty space and even a near vacuum filled with very thin air. A household vacuum cleaner uses a fan to create a near vacuum of thin air. This exerts a pulling force to fill the thin space and the pulling force ;bags in the dust.
An embryo tornado begins to act like a vacuum cleaner while it is still up there in the cloudy sky. As its hollow center of thin thin air continues to rise, denser air rushes toward it. This creates a circle of strong breezes blowing inward toward the rising updraft. The motion of the spinning earth twists these winds to spiral toward the center. They form a funnel of dark clouds around the hollow in the middle.
As this mighty little vacuum engine grows stronger, its dusky funnel dips down to the ground. Several of these dangling funnels may form in an advancing weather front. Fortunately, most of theca never get up enough strength to reach down and touch the ground. But the one that does creates a disaster. Both its hollow center and its spiraling winds work like en¬gines of destruction.
When the hollow center envelops a building, it sucks up the air and the rooms become near vacuums of low low pressure. The denser air outside crushes in and causes the walls to collapse. The rising updraft in the center also can lift people, iceboxes and other objects, carry them along and drop them maybe 100 yards from home. meantime the wild winds uproot trees and remove roofs as the air spirals inward to be whisked aloft in the hollow center.