Probing the many mysteries of the tornado
HIS cameras and tripod packed, David Hoadley will set out later this week on a yearly odyssey: chasing tornadoes. Mr. Hoadley, a budget analyst with the US Environmental Protection Agency by trade, is a storm chaser by hobby. Each spring he packs his car and spends two to three weeks of vacation scurrying about the dusty Texas panhandle or rolling prairies of Kansas, searching for one of nature's most powerful and puzzling events.
He is part of a small fraternity of tornado chasers -- perhaps two dozen nationwide -- that risk being buffeted by lightning, hail, and killer winds to learn about these weather extremes. Mr. Hoadley does it mainly for sport (''It's a phenomenon of nature that is untamed and wild,'' he says), but others do it for science.
The latest research, using a host of new tools and techniques, is beginning to resolve some of the riddles how tornadoes form and what makes them tick. The knowledge may lead to better tornado prediction and stormproof building design.
There's certainly need for it. Nature hath no fury like a funnel: Tornado whirlwinds, often roaring like a freight train, are blamed for more deaths each year than almost all other weather disturbances, averaging 102 in the United States.
(The past few years, however, have been quieter -- 64 fatalities in 1983, the same number in '82, and 24 in '81.) Usually they cause more than $500 million a year in property damage, also. Those that ripped through the South and Midwest last week -- and earlier ones in the Carolinas -- were painful reminders of the tornado's fury.
Tornadoes are difficult to study because they don't sit still very long. They are small, short-lived phenomena -- dangerous to get close to. Much of the today's research remains focused on tornado formation -- why some thunderstorms produce twisters and similar ones do not. Scientists understand the general conditions that create them, but they are hazy on the details.
It's like we've got a puzzle dumped out in front of us,'' says John Snow, an assistant professor of geosciences at Purdue University, who recently wrote on tornadoes in Scientific American. ''We have a lot of the peices. But the overall picture isn't there.''
Although tornadoes have occurred in every state, most of the 800-odd funnels reported each year rip through ''tornado alley'' -- an area stretching from northern Texas up through Nebraska. Most (roughly 75 percent) also occur in the spring, from March through June, when the climate conditions are right.
The potential for one to exist develops as warm, moist air, usually from the Gulf of Mexico, bumps into cold, dry air, usually from the West. These conditions create thunderstorms out of which tornadoes can hatch.
In simplified terms, a funnel is believed to be formed when a column of warm air (updraft) begins to rise and gently rotate. As it moves higher in the atmosphere concentrate and speed up the rotation.
Then the same principle that governs a pirouetting skater takes effect: The tighter she tucks her arms, the faster she spins. With the funnel, the column of air narrows and intensifies as it stretches upward and builds down toward the ground. Eventually, a tornado core forms inside the general funnel, spinning fast enough to extend to the ground. But here researchers begin scratching their heads:
* How does the funnel become so concentrated?
* Where does the energy come from to produce such fast rotation?
* How do small tornadoes form? (Most of today's knowledge surrounds large funnel systems -- ones spinning faster than 175 m.p.h. or so.)
One long-held theory hypothesized that electrical activity in the storm provided added energy to sustain the funnel's tightly whirling ''vortex.'' But that idea, says Mr. Snow, has now been discarded.
Researchers are getting a better fix on tornado wind speeds. Some have reached high enough velocity to hurl pieces of straw through telephone poles. Winds inside the funnels were once thought to approach supersonic velocities. Now it is believed they top out at about 300 miles an hour. Most probably swirl at about 100 to 200 m.p.h. Researchers can only make educated guesses: No instruments have yet penetrated a tornado completely unscathed and sent back data.
''The 300 mile-per-hour range appears to be very rare,'' says Richard Peterson, an atmospheric scientist with the Institute for Disaster Research at Texas Technological College in Lubbock.
Readings from the core of the tornado have usually been surmised from motion ictures and study of damage done to structures on the ground. More recently, scientists have begun to enlist another powerful tool, Doppler radar. It vividly displays the motion in funnels by bouncing microwaves off dust particles and water droplets in the atmosphere and then measuring their shift. When teamed with a computer, the radar can guage the size and intensity of a storm as well as the wind speed, direction, and amount of precipitation. A related tool, Doppler lidar, takes readings using laser light.
Attempts to take a tornado's pulse from the inside continue, however. Dr. Stirling Colgate of the Los Alamos National Laboratory in New Mexico has tried to fire small cardboard rockets through tornado funnels. The sensor-laden missiles, lobbed from aircraft, carring tiny instruments to relay information about pressure, temperature, and wind patterns. He has only had partial sucess. Never have all the gauges performed perfectly.
Researchers at the National Severe Storms laboratory in Norman. Okla., among others, will be chasing storms over the nect couple of months in small aircraft fitted with instruments and sensors. They usually take their readings from a few comfortable miles away from the funnel.
On the ground, researchers are using computer modeling to simulate tornado conditions, and intrepid researchers from Texas Tech, the University of Oklahoma , and other centers are chasing them in cars and recordidng them with movie cameras. In some instances, ''storm chasers'' try to anchor instruments in the funnels to collect information.
All of this hould lead to earlier and more localized tornado warnings. The biggest boost is expected to come with greater us of Doppler radar. Forecasters can now issue tornado ''watches'' covering large areas from two to eight hours in advance. Once a network of Doppler radar is set up around the United States -- plans are afoot to install more than 100 units over the next decadde -- weather forecasters should be able to pinpoint better which storms might pawn funnels and to track their paths in the early stages.
''There is still both art and science in forecasting,'' says Dr. Peter Ray, chief of meteorological research at the National Severe torms Laboratory. ''[But ] we now have the tools at hand to help us understand tornadoes.''