A New Twist in Tornadoes

Roaring in unexpectedly from the Gulf of Mexico, a swirl of tornadoes cut across central Florida last week, killing ten persons, injuring 300 and causing $30 million worth of damage. Weather Bureau meteorologists were as surprised as the victims. They had predicted storms confidently enough, but their maps showed no sign of the ominous low pressure areas that usually accompany tornadoes. An official warning was not issued until half an hour after the first twister hit the Tampa--St. Petersburg area, a delay that was a devastating reminder of how little is known about the monstrous forces that produce the whirling storms.

Indoor Whirlwind. While Florida was still cleaning up its storm damage, another tornado started spinning in Washington, D.C. But this one was manmade, and it whirled with promise. Generated in a laboratory at Catholic University by Chinese-born Dr. Chieh-Chein Chang, head of the university's space sciences department, the indoor twister probably came closer to simulating a real tornado than any other artificial storm ever produced. By carefully analyzing its characteristics, Chang hopes to learn how to build structures that will better withstand the deadly twisters and perhaps point the way toward more accurate prediction and even prevention of tornadoes.

To reap his whirlwind, Chang started a smoke generator installed beneath a screened cylindrical cage 9 ft. high and 6 ft. in diameter. After the smoke was drawn toward the top of the cage by a powerful exhaust fan, the cage itself began to revolve. As the screen approached six revolutions per minute, it imparted a rotary motion to the air being drawn through it by the fan. The rising smoke gradually turned into a column that rotated at 1,200 r.p.m., whistling around in the cage at speeds up to 40 m.p.h. Pieces of confetti on the floor of the cage--and then a cardboard model of a house--were sucked up into the whirling column.

Top & Bottom. Using tiny temperature, velocity and pressure recorders, Chang has already gathered some basic data on his miniature storm and discovered that it conforms to tornado dynamics in two ways: the motion of the column is faster at the top than the bottom, and pressure at the bottom of the funnel, surrounding the low-pressure "eye," is considerably greater than at the top. It is this extremely low pressure in the eye and the high-velocity winds in the funnel that make the tornado so deadly. To better determine the forces at work, Chang intends to build a larger cage that will produce winds of more than 100 m.p.h. --a velocity that he believes is high enough to simulate natural tornadoes more realistically.

An expert in fluid dynamics and aerodynamics, Chang has worked on nuclear reactors for space propulsion, plasma studies for controlled nuclear fusion reactions, and new structural techniques for aircraft. But ever since he saw an aircraft factory in Nanking destroyed by a sudden twister 35 years ago, he has been determined to unlock the secrets and tame the fury of tornadoes. His artificial storm has now given him his first hope of success.

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