A major player in the world's efforts to learn about and live with extreme weather is the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, funded by NSF's Division of Atmospheric Sciences. Central to NCAR's activities is the use of supercomputers to develop large-scale simulations of atmospheric and ocean dynamics. These models help to explain the formation of tornadoes, windstorms, and hurricanes, as well as more mundane climatic events. For example, in the late 1970s, NCAR researcher Joseph Klemp, working with Robert Wilhelmson of the NSF-funded supercomputing center at the University of Illinois, developed the first successful model of the most dangerous of all thunderstorms, the "supercell" storm. In a thunderstorm, air moves up and down in a turbulent mix. A single-cell storm means that there is just one updraft/downdraft component, which generally produces only moderately severe weather. A multicell storm can kick out the occasional tornado, but sometimes a main, intensely rotating updraft develops within a multicell storm and transforms it into a supercell storm capable of producing the most devastating weather, complete with violent tornadoes, raging winds, hail, and flooding.
The model developed by Klemp and Wilhelmson confirmed other researchers' observations that this special, rotating brand of thunderstorm could develop by splitting into two separate storm cells. According to their simulation, the southern storm in the pair was the most likely to concentrate its powers to make a tornado. Meteorological modelers have since improved these simulations to the point where researchers can study the ability of rotations midway up in a thunderstorm to develop tornado-like whirls at the ground. Such work, coupled with NSF-sponsored ground reconnaissance of tornadoes, may eventually solve the mystery of how tornadoes are born, which, in turn, could lead to better warning systems.
Warning systems can save lives, but whether or not a building survives a tornado's onslaught depends largely on how it was constructed. Since the 1970s, scientists and engineers at the NSF-funded Texas Tech (University) Institute for Disaster Research have been picking through the aftermath of tornadoes' fury for clues about what predisposes a structure to survival. When the researchers first began their work, it was common for emergency preparedness manuals to recommend that during a tornado building residents open their windows so that pressure inside the building could equalize with the low-pressure interior of the approaching twister. But after much dogged detective work, the Texas Tech researchers were surprised to learn that rather than exploding from unequal pressure, the walls of homes destroyed by tornadoes appeared to flatten when winds pried up the roof, just as aerodynamic forces will lift up an airplane wing. Wind was also discovered to contribute to structural damage by blowing debris from poorly built homes into homes that were otherwise sound.
The key to survivable housingat least in all but the worst cases of tornadoesturns out to be roofs that are firmly anchored to walls and walls that are firmly anchored to foundations. Wide eaves along the roofline, which can act as handles for powerful winds, should be avoided. And the researchers found that weak points in the structure, such as garage doors and opened windows, actually increase the risk of damage by inviting in winds that will blow down the opposing walls, exposing people to injury from breaking glass and flying wreckage. The advice might be simpleshut your windows during a tornado rather than open thembut it is rooted in the long investigation of complex physical forces.