An upcoming episode of the PBS TV series 'NOVA' will focus on the search for understanding nature's most violent tornadoes, from daredevil storm chasing in tornado alley to simulating severe weather with the computational resources and visualization expertise of the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign. "Hunt for the Supertwister," produced by Thomas Lucas Productions, Inc. for NOVA, was created in High Definition TV format (HDTV) and will air nationally on Tuesday, March 30 at 7 p.m. Central Standard Time (8 p.m. EST) on PBS stations across the country (check local listings). The show will feature data-driven tornado visualizations produced by NCSA's Experimental Technologies Division. In a typical year, 1,200 tornadoes cause 70 fatalities and 1,500 injuries nationwide. Most of the damage, deaths, and injury are due to a very small percentage of these tornadoes, the powerful so-called "supertwisters." Ideally, forecasters would be able to provide enough advance warning that people could protect themselves from these killer storms, but accurately predicting when and where tornadoes will strike is a feat that continues to elude forecasters. "Hunt for the Supertwister" details scientists' efforts, both in the field and in the lab, to understand the most violent tornadoes. Scientists know that the strongest tornadoes are generated by a particular type of rotating thunderstorm called a supercell. The constantly swirling winds of a supercell can produce tornadoes, but not all supercells lead to tornadoes, and not all tornadoes become supertwisters. Why some storms spawn tornadoes while others don't—and why some tornadoes become extraordinarily strong supertwisters—is not yet well understood. In an effort to pinpoint what triggers tornadoes, researchers create computer simulations of evolving storms. Just as physicians use X-rays and CAT scans to diagnose disease, storm researchers use simulations and visualization to analyze tornado formation. "The big problem in storm science is that with the instrumentation we have we can't sense all the things that we need to know," explains Lou Wicker, a researcher at the NOAA National Severe Storms Laboratory in Oklahoma. "From the field, we can't figure out completely what's going on, but we think the computer model is a reasonable approximation of what's going on, and with the model we can capture the entire story." Wicker developed a model called NCOMMAS (NSSL Collaborative Model for Multiscale Atmospheric Simulation) to computationally simulate thunderstorms and their associated tornadoes. NCOMMAS is based upon an earlier model developed by Robert Wilhelmson, NCSA research scientist and University of Illinois professor of atmospheric sciences. The simulation begins with data describing the pre-tornado weather conditions—wind speed, atmospheric pressure, humidity, etc. From these initial variables, a virtual storm is born. Wilhelmson's research team used NCOMMAS to simulate a supertwister similar to the one whose 200 mph winds ripped through tiny Manchester, South Dakota, in the summer of 2003. Lucas and his crew caught the Manchester supertwister on HDTV video, so the real and simulated storms will be juxtaposed in the NOVA special. Starting with the recorded pre-storm conditions near Manchester, the simulation followed the erupting thunderstorm and resulting powerful tornado as it evolved in a 100 x 100 x 25 km domain. The calculations were performed on NCSA's IBM p690 computing cluster in November 2003. To simulate about two and a half hours of "cloud time" required the use of 16 processors for 10 days. The simulation produced 650 billion bytes of data. These snapshots of the evolving storm consist of wind temperature, humidity, and precipitation data at various intervals. NCSA's visualization team—Robert Patterson, Stuart Levy, Matt Hall, Alex Betts, Lorne Leonard, and team director Donna Cox—translated the data into a dynamic, high-definition animated visualization of the tornado's birth and growth. "It's a very human-intensive, iterative process," stressed Cox, the leader of NCSA's Experimental Technologies Division. At each stage of the process, human intelligence is required to make decisions about what data are most descriptive and how best to draw meaning from the data. The members of the visualization team frequently consulted with one another and the storm scientists, making adjustments and re-adjustments in the visualization. "This has been a very hard-working, collaborative renaissance team," Cox added. In the final visualization as it will be seen by NOVA viewers, a swirling blue-gray cape of isosurfaces represents the body of the tornado, while swaying cones tilt to show wind speed and direction at ground level. Balls and tubes of varying colors indicate the tornado's pressure and rotation rate. Atmospheric scientist Matthew Gilmore, a member of Wilhelmson's research team, describes the visualization as a "three-dimensional virtual storm chase." The events that occur with blinding speed in the field can be slowed to a crawl for close study. The scientists can interrogate the data in many ways, looking at cross-sections, employing different points of view, and zooming in on small-scale effects. "We are in hot pursuit of the reasons why some supercells produce tornadoes and some do not," Wilhelmson concludes. "Visualization helps us understand the meaning behind the billions of numbers produced by model simulations." Press information and promotional photography for NOVA "Hunt for the Supertwister" can be downloaded at http://pressroom.wgbh.org/pages/nova.html. NCSA (National Center for Supercomputing Applications) is a national high-performance computing center that develops and deploys cutting-edge computing, networking and information technologies. Located at the University of Illinois at Urbana-Champaign, NCSA is funded by the National Science Foundation. Additional support comes from the state of Illinois, the University of Illinois, private sector partners and other federal agencies. For more information, see http://www.ncsa.uiuc.edu/. Now in its thirty-first year of broadcasting, NOVA is produced for PBS by the WGBH Science Unit. The director of the WGBH Science Unit and senior executive producer of NOVA is Paula S. Apsell. NOVA is closed captioned for deaf and hard-of-hearing viewers, and described for people who are blind or visually impaired by the Media Access Group at WGBH. The descriptive narration is available on the SAP channel of stereo TVs and VCRs. Major funding for NOVA is provided by the Park Foundation, Sprint, and Microsoft. Additional funding is provided by the Corporation for Public Broadcasting and public television viewers. Courtesy of the National Center for Supercomputing Applications (NCSA) and the Board of Trustees of the University of Illinois.