Low-Frequency Sound Can Reveal That a Tornado Is On Its Way

Scientists are exploring infrasound, low-frequency sound waves produced by tornadoes to develop more accurate early warning systems for these destructive storms. The hope is that eavesdropping on infrasound signals, which travel for hundreds of miles, could provide up to two hours of advance warning. The BBC reports: Scientists have been listening to tornadoes and trying to work out whether they produce a unique sound since the 1970s. Experimental evidence suggests that low-frequency infrasound, with a frequency range of 1-10Hz , is produced while a tornado is taking shape and throughout its life. One recent set of measurements from a tornado near Lakin, Kansas in May 2020 revealed that the twister produced a distinct, elevated signal between 10Hz and 15Hz. In some cases arrays of infrasound detecting microphones have been shown to pick up the noise produced by tornadoes from more than 100km (60 miles) away and have also indicated that the infrasound is produced before tornadogenesis even begins. Researchers hope that by eavesdropping on these noises, it may be possible to not only hear a tornado coming but perhaps even predict them up to two hours before they form. Since 2020, a team from Oklahoma State University has been testing infrasound's predictive powers using equipment installed in tornado-chasing vehicles. Their portable kit, the Ground-based Local Infrasound Data Acquisition, or "Glinda", system, references a character from The Wizard of Oz. They hope the equipment will help storm chasers to better monitor the development of tornadoes in real time, but requires the equipment to be deployed to the right place at the right time. Some researchers, however, are working on systems that can be left to permanently monitor for tornadoes. One group, led by Roger Waxler, principal scientist at the National Centre for Physical Acoustics (NCPA) based at the University of Mississippi, are planning to deploy four permanent arrays of high-tech sensors in south Mississippi to detect infrasound signals. They hope the system will provide a way of consistently monitoring and detecting tornadoes. [...] Waxler and his team hope their decade-long experiment will lead to an effective early warning system for tornadoes, particularly when combined with other sources such as doppler radar. "It's not unreasonable that we could localize a tornado to half a football field," adds Waxler. "I envision seeing a map on an app with a dot that shows there's a tornado coming up South Lamar [Avenue, for example]." Warnings have improved in recent decades: from 2003 to 2017, 87% of deadly tornadoes were preceded by an advance warning, but people still have an average of just 10-15 minutes to find shelter. A study based on interviews with 23 survivors of two deadly tornadoes found that people tried to evaluate and respond to the risk of a tornado as the situation evolved, but some did not have a place to shelter easily. Experts believe tornado warnings are too often ignored due to "warning fatigue" created by false alarms and hours of televised storm coverage. One study found 37% of people surveyed did not understand the need for taking precautionary measures during a tornado warning. Waxler hopes that a more accurate early warning system could change the way people respond when they hear a storm is approaching. "Rather than going to hide in your bathtub or cellar, it might be a better idea to get in your car and drive if you know where a tornado is. "The goal is to save lives."

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