Twisters Still Hold Mysteries for Chasers
After two years of studying tornadoes, scientists have found that reams of data take them in new directions
The vans and compact cars looked like refugees from Mystery Science Theater 3000 as they took to the highway in search of tornadoes. Wind gauges spun, and weather vanes swung erratically from poles anchored to rooftop racks as the caravan headed out.Skip to next paragraph
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The scientists inside the vehicles aimed to use the instrument-laden squadron to take close-up readings that would help them pry open the secrets of how such destructive wind storms form. In the year since their final foray - part of a two-year effort known as the VORTEX project - researchers who roamed from Texas to Kansas in search of twisters have begun poring through the data they've gathered.
VORTEX, which involved more than 75 researchers from 10 universities and several federal agencies in the United States and Canada, returned a wealth of observations that participants estimate will take several years to interpret. The ultimate goal: to help save lives by improving the lead time and accuracy of tornado warnings.
North America is not the only tornado hot spot. Australia and Bangladesh also account for a large number of the world's tornadoes. Last week, for example, a twister packing winds estimated at 125 miles an hour spent half an hour leveling 80 Bangladeshi villages, leaving an estimated 615 dead and 34,000 injured.
The United States has the dubious distinction of being the tornado capital of the world. Last year set a record, with 1,233 confirmed sightings in states ranging from Texas to New Hampshire and Florida to Oregon. Since 1950, no state has been spared. Indeed, Southern California experiences as many tornadoes as the Oklahoma City area, says Roger Wakimoto, a professor of meteorology at the University of California at Los Angeles. The difference, he quickly adds, is that California's twisters are much weaker and shorter-lived.
Although tornadoes can occur during any season, they become most active from late winter to early summer, starting near the Gulf of Mexico in March and moving north and east as the seasons progress. Outbreaks typically peak in May and June in Kansas, Iowa, and Nebraska.
Weaker tornadoes, with wind speeds of around 110 miles an hour, last less than 10 minutes. They cut a swath roughly 100 yards wide for about a mile before they disappear. Strong tornadoes have been known to last for up to two hours or more, cutting a path up to 1,000 yards wide and more than 100 miles long. Estimates of the maximum wind speeds in the strongest tornadoes have reached as high as 280 miles an hour.
Because they can develop suddenly and vanish just as fast, tornadoes pose a particularly thorny problem for forecasters.
VORTEX, which stands for Verification of the Origin of Rotation in Tornadoes Experiment, was designed to test current notions of how tornadoes form, as well as provide new information that could be fed into computer models that try to simulate and forecast tornadoes.
During the springs of 1994 and '95, a small army of scientists and graduate students chased storms and tried to surround tornadoes with their armada of specially instrumented cars. They dotted the landscape ahead of tornadoes with small instrument packages called "turtles," in hopes a twister would inhale one and give researchers the inside story. Mobile Doppler radar yielded unique close-up images of storm circulation patterns, while sounding balloons and the National Oceanic and Atmospheric Administration's hurricane hunter aircraft rounded out the assault force.
In the end, the team bagged 10 tornadoes - including a severe twister that hit Dimmitt, Texas, and became the most monitored tornado in history. They also probed numerous thunderstorms with tornado potential.
"VORTEX was able to get more information about tornadoes from more points" than ever before, says Charles Doswell, a scientist at the National Severe Storms Laboratory at the University of Oklahoma in Norman. From a scientific standpoint, he says, the VORTEX data are exciting - and humbling.
Going into the project "we had some sense that we knew what was going on," he explains. Instead, "we saw enough variability in the way tornadoes form that ... each one was unique.... As one of my colleagues put it, we've defined the depths of our ignorance."
As daunting as the VORTEX data may be, the understanding of conditions that lead to tornado-generating thunderstorms has come a long way since Benjamin Franklin saddled up to chase dust devils. "Even before radar and traditional meteorology started after World War II, people thought that a tornado's rotation developed within a storm and then fell to the ground," explains Dr. Wakimoto, a member of the VORTEX team. After all, that's what people saw - a dark funnel cloud descending from the base of a thunderstorm.