VORTEX Sets Sights on Tornado Formation Process

by Bob Henson, NCAR Staff Notes (bhenson@ucar.edu)

NORMAN, Oklahoma: The largest net of weather instruments ever deployed to trace the process of tornado development will be in place next month across the Southern Plains as storm season heats up. The instruments are part of the Verification of the Origin of Rotation in Tornadoes Experiment (VORTEX), based in Norman from April 1 through June 15. VORTEX is serving as a test bed for several innovative new Doppler radar systems, two of which were developed through collaborations with the National Center for Atmospheric Research (NCAR), which is funded by the National Science Foundation (NSF).

This year marks the second spring of field activity in the two-year program. VORTEX's target is supercells: long-lived severe thunderstorms with circulation patterns especially favorable for producing tornadoes. Although supercells produce the most violent tornadoes on earth, less than half of them produce any tornadoes at all. On a given day, VORTEX aims to deploy as many as 20 instrument-studded vehicles at various positions around a single supercell, moving with the storm and documenting it over several hours. The vehicles are each topped by compact weather stations that report position and weather data every few seconds to a mobile command post through Global Positioning System (GPS) technology.

Three aircraft will probe the storms: a P-3 from NOAA that features airborne Doppler radar; an armor-plated T-28 from the South Dakota School of Mines and Technology that will fly through intense hail and updrafts; and NSF's Electra aircraft, which is operated by NCAR. This will be the first test at full capacity for the Electra's dual-Doppler radar (ELDORA). Developed by NCAR and the French government, ELDORA features a rapid-scanning technology that will permit a resolution in time and space unprecedented for airborne radar.

Another radar being tested in VORTEX is Doppler on Wheels, a joint development between NCAR and the University of Oklahoma (OU) that is being coordinated by OU associate professor Joshua Wurman. If all goes well, this portable Doppler radar may allow the most precise measurement to date of winds in and near tornadoes. Its resolution--as fine as 50 meters--will permit measurement of small but intense wind structures that cannot be detected by other Doppler units. Also to be deployed in VORTEX is a portable Doppler radar operated by OU professor Howard Bluestein that detected 286-mile-per-hour winds in an Oklahoma tornado in 1991.

Based at NOAA's National Severe Storms Laboratory (NSSL) in Norman, VORTEX is jointly sponsored by NOAA and NSF and is a component of the U.S. Weather Research Program, a federal interagency program aimed at improving short-term weather forecasts. More than 100 participants will be on hand from the above institutions as well as the University of Alabama in Huntsville; University of California, Los Angeles; Universities of Illinois, Massachusetts, and West Virginia; the New Mexico Institute of Mining and Technology; Texas A & M and Texas Tech universities; the University Corporation for Atmospheric Research (UCAR) Office of Field Project Support; the Center for the Analysis and Prediction of Storms, based at OU; the U.S. National Weather Service; and Canada's Atmospheric Environment Service (AES). NCAR's Morris Weisman is one of the 18 principal investigators.

Forecasters on assignment to VORTEX from the National Severe Storms Forecast Center, other NOAA sites, and AES, will issue one- and two-day outlooks from an experimental forecast facility at NSSL and from the Norman NWS forecast office.

Last year's field phase of VORTEX tracked three tornadic and eight nontornadic supercells. One of the biggest surprises for VORTEX scientists was the storm that produced a tornado near Archer City, Texas, on May 29, 1994. With winds estimated at close to 200 miles per hour, the twister moved west, then northeast, than northwest, defying the usual eastward movement of tornadoes. Analysis of airborne Doppler radar data of the Archer City storm by UCLA's Roger Wakimoto showed that the tornado's parent circulation developed very rapidly--in less than five minutes--in a manner quite different from that normally thought to produce major tornadoes. Such results, though puzzling, will help VORTEX researchers address the 22 hypotheses on tornado development that the experiment is designed to confirm or refute.

UCAR operates NCAR under a cooperative agreement with NSF.

NOTE TO EDITORS: A VORTEX media day will be held in Norman on the morning of Thursday, 30 March. Principal investigators will be on hand to answer questions, and instrumentation and vehicles will be available for photos or filming. For more details, contact Dane Konop, NOAA Public Affairs, 301-713-2483, e-mail dkonop@rdc.noaa.gov. Media also are invited to join the VORTEX field operations once the experiment begins. One car of reporters will be allowed to accompany the field workers each day. Reporters interested in the field work, or who would like to visit the operations center at NSSL on days when the experiment is not operating because of calm weather, should contact Dane Konop. Further information concerning the U.S. Weather Research Program can be obtained from William Hooke, head of the USWRP Program Office, 301-713-0460.