Storm Chaser Deploys Probe, Makes History
Bijal P. Trivedi
National Geographic Today
|June 27, 2003|
Tuesday night Tim Samaras stood his ground in front of the quarter-mile-wide (400-meter-wide) tornado that would level part of the tiny town of Manchester, South Dakota, When the whirling vortex was only about 100 yards (90 meters) away, he jumped out of his van, dropped a scientific probe next to the road and yelled to his driver to make a swift getaway.
Eighty seconds later the tornado swept over the probe. "It was a direct hit! We haven't slept all night," Samaras says. "This is a historic occasion. But we were definitely too close."
Samaras is a professional storm chaser, which means he spends May and June speeding around Tornado Alleya broad swath of land in the central United States between the Rockies and the Mississippi, where tornadoes are most frequentin a Dodge Caravan outfitted with GPS, radios, scanners, monitors, a wireless Internet connection and satellite tracking instruments.
His harrowing task: to spot tornadoes, try to put himself in their path and then deploy the newly designed probe that will measure humidity, temperature, pressure, wind speed and direction in the vortex of the beast. Then he promptly gets out of the way.
On that Tuesday night, Samaras achieved his most significant feat yet: The probe he helped design measured the biggest pressure drop100 millibarsever recorded in the heart of a tornado.
"This is one of the best measurements ever made," says Erik Rasmussen, a meteorologist with the National Severe Storms Laboratory, based in Norman, Oklahoma. "The data collected will be a gold mine."
"I've been a passionate storm chaser for 15 years," Samaras says, "and this is an opportunity to combine my hobby and professional work." Samaras is an electrical engineer at Applied Research Associates, Inc., based in Denver, Colorado, where he co-designed and built the probe, known as a "turtle" in meteorological circles.
The squat, conical 45-pound (20 kilograms) device is 20 inches (50 centimeters) across, six inches high and crammed full of sensors. Its development was funded by the Department of Commerce. The National Geographic Society supported its use in the field with a grant from the Committee for Research and Exploration.
Even with the most sophisticated weather equipment, tornadoes are tough to spot, because they're too small to be seen by National Weather Service Doppler radar or satellite images. So Samaras looks for supercells, the most dangerous kind of thunderstorm and the most likely to spawn tornadoes.
Supercells are huge, rotating cloud masses 60,000 feet (18,300 meters) tall, and can extend a couple of miles across. "Structurally they are like huge spinning soup cans," says Paul Markowski, a professor of meteorology at Penn State University in University Park. If a portion of this swirling cloud mass touches the ground, a tornado is imminentso when storm chasers like Samaras see that conditions are ripe for supercell formation, the chase begins.
Right Place, Right Time
"The trick is being in the right place at the right time before the storm develops," Samaras says. "That's what everybody struggles with." So far this year he has clocked about 20,000 miles (32,000 kilometers) on his vanstorm chasing is mostly, after all, chasing.
Once Samaras has found his developing storm, he relies less on technology and more on his senses, as surface observations become key.
He pulls over to study the shape and movement of a mass of clouds, looking for clues that the storm might spawn a tornado. As the storm catches up with him, he jumps back in the van and races ahead again, hoping he'll find himself at the right coordinates if a tornado develops.
Samaras gets it right about two out of every seven outings. And a few times he's been right in its path.
"It takes me about 10 seconds to deploy the probe," Samaras says. A videotape shows him racing from the van, dropping the probe on the ground and speeding away as two-and-a-half-inch hail falls around him and the tornado approaches.
In a dispatch sent on Monday, Samaras wrote of the previous night's adventures just west of York, Nebraska. "It was simply amazing! This storm dropped four-and-a-half-inch hail. We watched a beautiful cone funnel drop halfway to the ground last night, got into position just a quarter of a mile away, only to watch the funnel dissipate! I guess that's part of the game."
Predicting Tornado Strength
"Tim's work is essential for the next VORTEX experiment," says Rasmussen. In 1994-1995 Rasmussen led the Verification of the Origin of Rotation in Tornadoes Experimentor VORTEXwhich was a scientific tour de force featuring cars, portable radar devices, planes, balloons and "turtles," with a mission to understand tornado formation.
"There have been successful attempts to measure pressure inside a tornado," Rasmussen says, "but Tim is the first to measure the temperature, humidity, and wind speed and direction."
What practical applications will emerge from these measurements are still unclear. "It is still a bit of a fishing expedition," Rasmussen adds. With more data from a range of tornadoes, he speculates, the measurements may prove useful for predicting the intensity and duration of future tornadoes.
"We currently have about an 80 percent false alarm rate when it comes to predicting which storms will spawn tornadoes," says Penn State's Markowski. "All research we do is directed at reducing that rate, and Tim's work is a step in that direction."
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