Contact: Dane Konop                      FOR IMMEDIATE RELEASE
                                         May 11, 1998

A team of government and university scientists in mobile meteorological stations and with truck-mounted radars will attempt to intercept severe storms in the Great Plains through mid-June to get very close-up observations of a developing tornado, the National Oceanic and Atmospheric Administration announced today.

The radar data and other information collected could give researchers a three- dimensional view of the complete life cycle of a tornado and ultimately help improve NOAA forecasts and warnings of severe weather.

Based at NOAA's National Severe Storms Laboratory and the University of Oklahoma in Norman, Okla., the researchers will use the latest meteorological information to target a large thunderstorm with a rotating updraft, called a "supercell," that could produce tornadoes within a day's drive. When a likely storm system is forecast, the scientists will set out to intercept the supercell with three truck-mounted Doppler radars and in six sedans equipped with meteorological sensors, cameras and communications gear to stay in contact with other team members and reports of general weather conditions.

The team will intercept the supercell and position their two 8-foot-diameter truck- mounted radar dishes, called "Doppler on Wheel" or DOWs, about a mile outside the storm to scan the entire area of rotating air every 30-90 seconds. Other team members will use a third, shorter wavelength truck-mounted radar to make finer scale measurements. The team will then attempt to send one or more of the three instrumented "probe vehicles" inside the hook, the rotating center of the supercell that looks like an inverted question mark in radar images and often signals a tornado is about to form. Still other team members will attempt to photograph and measure the rear flank downdraft of winds in the storm, since the scientists believe this is the region of a storm that often triggers a tornado.

The research is a follow-up to the VORTEX project in 1994 and 1995, in which scientists from NOAA, the University of Oklahoma and other universities intercepted and studied 10 tornadoes from as close as three miles away, and last year's SubVORTEX, in which for the first time the team intercepted a tornado with the dual DOWs.

"We are calling one of our experiments this spring 'SubVORTEX-RFD',--short for rear flank downdraft,--because we want to document the origin and evolution of a supercell's rear flank downdraft by measuring variations in these winds just before and just after a tornado forms. To do this, we will have to carefully position some of the probe vehicles beneath the most strongly rotating part of the storm, an area storm chasers call 'the bear's cage'. This is something that has never been done before, at least not on purpose," said principal investigator Erik Rasmussen of the NOAA-University of Oklahoma Cooperative Institute for Mesoscale Meteorology Studies in Boulder, Colo.

According to Rasmussen, "Early in a tornadic thunderstorm, the pressure falls due to increasing rotation. This causes the inflowing wind near the ground to accelerate as it rises toward the updraft. This is what our fictional counterparts in Twister called the tornado's 'suck zone'." A few thousand feet above the ground, this inflowing updraft of air collides with air overtaking the storm from the rear in a region where evaporating raindrops are cooling the air, causing a strong downdraft to form.

"We think it is possible that when this outwardly flowing downdraft, which is typically produced by thunderstorms, reaches ground level, it can sometimes wrap around this circulating, inflowing updraft, thus focusing the updraft's rotation into a tightly confined area, increasing momentum and speed just as a figure skater does when she pulls in her arms to increase the speed of her spin. For a tornado to form, it appears that this process must occur at ground level, where friction with the earth's surface creates the actual tornado itself. This is the process we plan to document."

The team includes scientists and meteorology students from the University of Oklahoma operating the DOWs, developed jointly by the University of Oklahoma, NOAA and the National Center for Atmospheric Research, and a higher-frequency truck-mounted radar developed by the University of Massachusetts. In addition to Rasmussen, the project's other principal investigators are Robert Davies-Jones of the National Severe Storms Laboratory and Joshua Wurman, Howard Bluestein and Jerry Straka of the University of Oklahoma.

"In another experiment in our joint project, which we are calling--ROTATE, short for Radar Observations of Tornadoes and Thunderstorms Experiment,--we will study the whole tornado genesis process, tornado maintenance, tornado death and tornado structure using the dual-DOW network," said Wurman.

NOTE TO EDITORS: To obtain a copy of VORTEX and SubVORTEX research video highlights, in either VHS or a broadcast-quality format, call 301-881-0270. For additional information about tornadoes and other severe weather, visit the following World Wide Web sites: http://www.nssl.noaa.gov and http://aaron.ou.edu/rotate.html.