May 10, 1999 This Week's Oklahoma Tornadoes Provide Highest-Resolution-Ever Data
Mobile Doppler radar instruments funded by the National Science Foundation (NSF) and deployed by scientists Howard Bluestein and Joshua Wurman of the University of Oklahoma and Andrew Pazmany of the University of Massachusetts are edging ever closer to the funnel clouds of tornadoes -- including last week's devastating storms in Oklahoma. One of these storms passed within a half-mile of the mobile units.
NSF supports the two complementary projects with the goal of understanding how tornadoes form and "decay," and the damage that might be expected from them. The first project supports the "Doppler on Wheels," which has been jointly developed by the University of Oklahoma and the NSF-sponsored National Center for Atmospheric Research in Boulder, Colorado. These two mobile radars -- one painted pink and yellow, the other blue and green -- are mounted on two flat-bed trucks. Sporting the radar instruments, the trucks become odd-looking configurations of generators, equipment and operator cabins. According to Wurman, who directs this project, these radars are ideally suited to provide detailed information on the three-dimensional wind and precipitation distribution in the near vicinity of the tornado vortex. The Doppler on Wheels team collected extensive data on the genesis of the tornado that struck Moore, Oklahoma.
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.
"The biggest advantage of the mobile Doppler radars is that scientists can collect more data with better precision," says Steve Nelson, program manager in NSF's atmospheric sciences division, which funds the mobile Doppler research. "Storms like tornadoes and hurricanes rarely move in the path of ideally spaced Doppler systems. Since we can't move the storm, it's pretty convenient that we can move the radars."
The second radar system is managed by Bluestein and Pazmany and transmits at a higher radio frequency. In practical terms, this means that while this radar can not cover as much area as the Doppler on Wheels, it does provide finer details of the tornado. In the storms that struck Oklahoma City, Bluestein and Pazmany estimate that the radar resolution ranged between 6 and 15 meters. Due to the close proximity of the radar to the vortex, unprecedented data was collected at the contact point of the vortex with the ground. The airflow in this lowest level is believed by scientists to hold the key to many questions on tornado structure and life cycle.
"On Monday, May 3rd," Bluestein relates, "which was my first day out with the new system, we collected data from a tornado a little more than an hour before it moved through Oklahoma City, wreaking devastation as it went." The monster storm tracked by the scientists exhibited what is called "multivortex structure" -- several funnels -- which within minutes turned into a large single tornado. "Luckily," says a relieved Bluestein, "when we were probing this storm, it was out over open country. It did, however, remove a house from its foundation a little under a mile away."
Bluestein, Pazmany and Wurman hope to compare data from this week's efforts with those of other colleagues also tracking the storms. Notes Bluestein, "We should soon have a much better picture of the inner workings of a tornado."
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