2004 Hurricane Season
Photo of live blogging

Detecting Tornadoes with Atmospheric Infrasound

Next speaker is Dr Al Bedard, Boulder CO.

Sub audible sound well below range of human hearing has some promise for tornado detection and warning. Range around 1Hz. 0.1 to 10Hz tornadic sound occurs in that range. Slide of sensor. Looks like an old fashioned lawn sprinkler. Total area sampling diameter of 50 feet. Each sensor surrounded by an eddy fence about 6 feet hight. Designed to break up eddies to allow for continuous monitoring. Use 4 sensors. Infrasonic Observatory can detect other sounds such as avalanches, Fires, Earthquakes, ocean waves. In Boulder can detect sounds in both Atlantic and Pacific ocean. Could detect sounds of Tsunami in Boulder.

What can we do with Tornado Detection? Shear along the core creates freight train roaring sound. Not detecting that. Can detect the core vibrating radially. First detection in 1995. Detected sound about 30 minutes before tornado sighted, and touched down.

Talks about other examples. (Maybe this is why no animals were caught up in the Tsunami? Animals have different hearing thresholds. We know that these events create sound. What an amazing and noisy world we live in?)

Need a national network. Problem with detection is delay times and location of sensors.

Question from audience: encountered false positives? Yes.

Communicating results and analysis of signals to weather folks. Overlay on radar data a polar plot. Sites: Pueblo, Boulder and Kansas. Put on website and fed back to weather folks. Actual display WFO's - radar, radar reflexity. Not yet made public. Option of displaying 3 pass bands.

Question from audience: how do we handle sim events? Tornadic sounds are random sporadic sound bursts, and can detect both.

Technique is useful for tornado detection - update frequency and time ever 5 seconds. Can provide information on small vortices and rotation on a limited extent. Use of overlapping stations. 1 station costs about $50,000. Still in R&D. Design of network and propogation effects still needs to be dealt with.

30% related to storms with tornados, 33% represented false alarms. 36% related to severe weather. 67 signals corresponded in direction and timing with storm data reports of tornados. Challenges: need improved verification, need feedback from storm chasing community to determine type of storm. Closer signals mask more distant signals. Need to increase density of network. Weather Service not routinely using data, because need to improve how it is displayed and portrayed. Demonstrates how data may look in real time. May be other uses for this technology.

Question from audience about animal sensitivities. Anecdotal evidence about elephants detecting tsunami wave sounds. Talks about animals, birds detecting infrasound. We see the world and have limited hearing. What if the world could only be detected through sound? We would "see" objects and each other by the sounds they produce.

Question: Switch frequency so can hear it audibly? Yes. May use it as a playback option on website.


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