Listen Up! Infrasound is Talking

A global infrasound network is recording what we can't see or hear — and researchers are listening more intently every day. While many of these listening stations were constructed to detect secret nuclear tests, the inaudible sound waves are also telling scientists exciting stories about funneling tornadoes, erupting volcanoes and approaching objects from space. The impact of this current "Infrasound Renaissance" will continue to grow as more researchers discover how these inaudible sound waves can benefit their research.

Large atmospheric explosions, natural and anthropogenic, generate infrasound pulses that travel great distances over the earth, often circling the globe at least once. The International Monitoring System (IMS) for Comprehensive Nuclear-Test-Ban Treaty Verification is implementing 60 ground-based infrasonic arrays (stations) distributed uniformly over the surface of the globe to identify explosions from nuclear tests. This network triggers false alarms when sufficiently energetic bolides enter Earth's atmosphere. Douglas Revelle of the Los Alamos National Laboratory has new predictions for how often incoming bolides from space will trigger the nuclear test warning system.

Beyond false alarms, Al Bedard of the NOAA/Environmental Technology Laboratory describes the role infrasound plays in state-of-the-art tornado detection and warning systems. Infrasound can help meteorologists differentiate between thunderstorms likely to generate tornadoes and those storms that probably will not. In addition, Bedard notes that infrasound may help scientists understand "sprites," mysterious and colorful above-cloud lightning.

Milton Garces is using infrasound to answer deep questions — literally deep questions. Garces uses infrasound to study the physical and chemical evolution of volcanic eruptions. "Volcanic infrasound provides a valuable tool for monitoring and forecasting volcanic eruptions," he says. The benefits from volcanic infrasound may reach beyond the communities affected by lava flows, according to Garces. "A warning system would be useful not only for communities adjacent to an eruption area but also for redirecting airline traffic away from ash-rich regions."

—Daniel Kane

13 February 2003

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