DISCUSSION: Tornadoes are one of the most dangerous and destructive meteorological phenomena on Earth (e.g., tornado pictured above damaged parts of Tuscaloosa, AL in April 2011). However, tornadoes are small-scale features that are difficult to observe. The primary means of observing these features are with radar and visual confirmation. Given the limited number of fixed radars and the fact that radar beams increase in height with distance from the radar, tornadoes rarely occur close enough to a radar such that their associated surface circulation can be directly observed. In addition, in places like the southeast United States with some terrain and abundant tree cover, sightlines to a tornado may be limited. Thus, it would be helpful if there was another way to detect tornadoes more reliably and at greater distances.
A research group at the University of Mississippi developed microphones that are sensitive to infrasound (i.e., sound with frequencies too low to be detected by the human ear). The original purpose of these microphones was to detect infrasound emitted from illegal nuclear weapons tests. However, the research group recently discovered that tornadoes or the thunderstorms that produce them emit infrasound that can be detected by these microphones up to 50 miles away.
There is promise that these infrasound microphones could be an additional tool to detect tornadoes, but many questions need to be answered before this tool could be used operationally. For example, what specifically is producing the sound, the tornado or some other aspect of the parent thunderstorm? Do non-tornadic thunderstorms also produce infrasound? Can infrasound produced from tornadoes be confused with other sources, or do tornadoes have a unique acoustic signature? If there is a unique tornadic signature, do all tornadoes emit such a signature?
In summary, microphones initially designed to detect acoustic signals from nuclear weapons explosions may provide another tool to help detect tornadoes that is complementary to existing detection methods. These microphones may be able to provide earlier detection of tornadoes which may lead to warnings with greater lead times, potentially helping to save lives. Ongoing work seeks to learn more about the application of this tool to tornado detection before the method can be used operationally.
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©2020 Meteorologist Dr. Ken Leppert II