NASA Technology Putting A New Twist On Early Detection of Twisters

Just as NASA research during the Apollo program led to the development of home smoke alarms, research into vibrations on the Space Shuttle now promises to provide a tornado warning system to homes and communities.

Tornadoes can strike anywhere in the United States and at anytime of the day or night. NEXRAD, or doppler radar, can detect the tornadic vortex signature at distances of 100 miles but cannot tell when a tornado is in contact with the ground. Once the deadly funnel clouds reach the ground, they can cause untold death and destruction. While tornadoes that occur during the daylight hours can be seen a mile or so away on the ground, there is often little or no warning of tornadoes spawned from storms at night.

Dr. Frank Tatom, president of Engineering Analysis, Inc., of Huntsville, Ala., recently completed a study for the Department of Commerce’s National Oceanic and Atmospheric Administration that may provide a valuable early warning system for approaching twisters.

“My research has its origins in a study done for NASA’s Marshall Space Flight Center in 1991 to calculate turbulent pressure fluctuations on the surface of the Space Shuttle during atmospheric flight. These fluctuations produce noise and vibrations inside the Space Shuttle,” Dr. Tatom said. “This prompted me to examine the possibility that turbulent pressure fluctuations inside of a tornado in contact with the ground should produce seismic waves.”

“From earthquake studies, we know that seismic waves can travel long distances and can be detected by instruments called seismometers. If earthquake vibrations can be detected, tornadic vibrations also should be identifiable, I reasoned. I set out to first make certain there were ground vibrations associated with tornadoes in contact with the ground, and then to devise a way of filtering these vibrations from others – such as might be caused by heavy trucks or passing trains. If the signature of vibrations from a tornado in contact with the ground could be isolated and identified,” he said, “a warning system for tornadoes in contact with the ground – tuned to that frequency range and combined with appropriate filters – should be feasible.”

“I began my studies into the vibration phenomenon right here at home. The city of Huntsville has been hit by several tornadoes – the two worst in 1974 and in 1989. Several others have passed by very close to the city’s limits. I went to interview people who had been at the scene when the twisters struck. Those I interviewed along the 1989 tornado’s path down Airport Road in Huntsville reported feeling strong ground vibrations long before seeing the tornado. A police officer, who was about to step out of his patrol car when the tornado touched down, said he could feel vibrations in the foot that was on the ground but not from the foot still in the vehicle. Residents living on Monte Sano, an elevation on the city’s eastern border, reported feeling the entire mountain shake during the 1974 tornado. Corroborating reports from on-scene witnesses elsewhere in the U.S. strengthened my belief that I was onto a significant discovery,” he said.

“Eyewitness reports, regardless of their number, are not hard evidence,” Dr. Tatom continued. “I needed something more – something I found in a graveyard in Tennessee.

“Tornadoes produce wind noise – lots of it. This noise is background clutter for seismologists trying to spot earthquakes,” Dr. Tatom explained. “Ebenezer Cemetery is the site of a University of Memphis seismometer that had been in operation when a tornado passed within a mile of it. When I checked the data it had recorded at the time, the tornado’s ‘wind noise’ signature was plain to see. More evidence came from the University of Memphis, where a seismic sensor had caught the noise signature of a funnel cloud that passed through Memphis. More evidence came from researching old data from a University of Mississippi seismic sensor in Oxford, Miss. It had caught the distinctive signature of the 1971 tornado there.”

“This research showed to me that clearly the tornadic turbulence was creating ground pressure fluctuations that were being transmitted to seismic sensors. With a network of sensors tuned to the frequency range of tornadoes,” Dr. Tatom said, “it will be possible, I believe, to detect the exact moment a funnel cloud touches the ground and identify its distance, direction, and path up to 10 miles away from the closest sensors. “This very valuable information,” Dr. Tatom said, “will make possible a truly accurate tornado warning system that should save countless lives, once it is in operation.”

Dr. Tatom envisions two types of devices. A regional network warning system with on the order of 20 or more sites; each possessing one or more geophones, a microprocessor, a communications link, an independent power supply, and a security system to protect it from vandals – would be linked to city or county emergency centers. This regional system would be used in conjunction with Doppler radar. The other type of device would be a residential model for homes and workplaces. It would consist of a geophone, a processor and a link to a home alarm system – something akin to a smoke alarm but with a different type of signal so as to make it easy to distinguish between them. A variant of the residential model would serve mobile home parks, which are notoriously susceptible to tornado damage.

Dr. Tatom developed his first proof-of-concept instruments using his own company’s funds. “The US Weather Service has instrument packages to measure meteorological properties of tornadoes, which look like mine, that it calls ‘turtles,’” Dr. Tatom said. “I call my seismic sensors ‘snails.’” Dr. Tatom has built six ‘snails’, each weighing about 35 pounds and pre-packed in its own shipping container. These have been provided to tornado storm chasers in several regions in the mid-western US in time for the Spring 1997 tornado season.

“The ‘snails’ don’t have to be run over by a tornado,” Dr. Tatom said, “just placed near the path the tornado takes.” Each ‘snail’ comes with a ‘snail handlers’ manual. The geophone is attached to the main unit via an 18-inch long cord. The geophone’s sensor prongs are inserted into the ground by foot pressure. The data they pick up is transmitted to the recorder’s built-in 386 computer. Once data has been captured, the entire instrument is recovered by the ‘snail handler’ and returned to Engineering Analysis, Inc., for downloading. The data is studied while the downloaded recorder is returned to the tornado chaser in the field.

Contingent on Department of Commerce funding, Dr. Tatom’s research is ready to enter its second phase. If results continue to be as positive as they have been, commercialization of the tornado alarm system is expected in the next decade, possibly sooner.