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Heres a program from our archives.Tornado - Voice PrintAmbience: TornadoIt's tornado season throughout the south central United States and scientists are trying to find ways to predict tornadoes early enough to give people sufficient time to take cover. One way to detect tornadoes is to listen for the distinctive sounds that they make; and this so called "voice print" may tell us some important things about the type of tornado that could be forming nearby. I'm Jim Metzner, and this is the Pulse of the Planet.Alfred Bedard is a Supervisory physicist with the National Oceanic and Atmospheric Administration.Bedard: OK, there are several types of sounds and people have traditionally spoken of a roaring of a freight train and that's often a description that people use. And that's an audible, very strong sound. It could result from the tornado interacting with the ground itself; it could result from the sound of the wind rushing by obstacles, trees, buildings and cars and everything in its path. And all of these sounds combine to give a very loud, screeching, audible roar. The sounds that we're studying are sub-audible-- you can't hear them. Even though they're true sounds, they travel in the atmosphere, I call them soundless sounds because they're below the range of human hearing.And it may be possible to build a detector which listens for the loud, low frequency voice print of a tornado.Bedard: One theory is that the larger the size of the tornado, the lower the pitch. Which means that if we're detecting the voice print of a tornado at long ranges, we may be able to tell something about the size of the tornado, or even how the size is changing with time, or how many tornadoes are in an area. This archival program is part of our thirtieth anniversary celebration. If you want hear more, check out our podcast. Im Jim Metzner and this is the Pulse of the Planet.