Sep. 26, 1998 When a hurricane's spinning mass of rain, lightning and wind reaches shore the last thing you want to do is drive a truck directly into its path. Unless you are atmospheric scientist Joshua Wurman, that is, and you have mounted a large Doppler radar unit on the back of your truck.
For the second time this summer, Wurman and a research team from the University of Oklahoma will drive two such "Doppler on Wheels" units into the face of a hurricane reaching landfall--Hurricane Georges. With funding from the National Science Foundation (NSF), Wurman studies patterns in hurricane winds that may help in forecasting the evolution of these storms once they hit land.
"Hurricanes spawn damaging winds well inland," said Wurman, "but they can also cause tornadoes and flooding. We are trying to figure out how patterns of winds and rain develop in hurricanes, and determine why and where a storm will produce floods and funnel clouds."
For many years, meteorologists have used Doppler radar at fixed locations to monitor weather patterns, as seen in weather forecasts on television. Due to advances in technology, Doppler radar has evolved to the point where it can be mounted to mobile platforms like Wurman's "Doppler on Wheels."
The vehicle itself is an odd-looking configuration of generators, equipment and an operator cabin welded to a large flatbed truck. The most prominent feature, however, is the large conical base and wide dish of the Doppler radar. "Considering that one radar unit is pink and yellow, and the other is blue and green, we do get our fair share of funny looks as we're heading to a storm," said Wurman.
"The biggest advantage of 'Doppler on Wheels' is that Wurman can collect more data with better precision," said Stephan Nelson, program manager in the NSF's division of atmospheric sciences, which funds Wurman's research. "Hurricanes rarely oblige to move in the path of two correctly spaced Doppler systems. Since we can't move the storm, it's awfully convenient that we can move the radar."
In addition to studying hurricanes, these trucks have also been used to study tornadoes. Since the project began in 1995, researchers have taken advantage of the mobility of "Doppler on Wheels" to map, for the first time, tornado winds. With these Doppler maps of tornadoes, they gained new insight into how tornadoes form and evolve.
In August, Wurman's team took the mobile radar systems to meet Hurricane Bonnie in North Carolina. While riding through 12 hours of storm, these researchers were the first to observe hurricane wind streaks, intense bursts of wind over a short distance. The wind streaks detected in Bonnie were similar to those that Wurman initially observed during his first hurricane mission in 1996. "These are probably the hallmarks of a landing hurricane," said Wurman.
Wind streaks, he hypothesized, are probably caused by boundary layer rolls, portions of the storm where the wind is influenced by the friction between the earth's surface and storm. Peak speeds of these wind streaks can be as much as 50 miles per hour (mph) higher than average winds. "Obviously, short bursts of 120-mph winds can do a lot more damage to houses and trees than 70-mph winds can," Wurman says.
Wurman will have another chance to collect data this year as Hurricane Georges reaches the continental United States.
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