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Undular Bore rolls across Iowa
• Giant aerial "wave" captured on webcam
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By
Miss Krakatoa, Environment Correspondent
Friday,
2 November, 2007
Undular bores are a type of "gravity wave"—so called because gravity acts as the restoring force essential to wave motion. UK readers familiar with the tidal bore in the Severn river should imagine an aerial equivalent.
A series of giant "undular bore waves" were photographed Oct. 3rd 2007 flowing across the skies of Des Moines, Iowa.(Credit: KCCI-TV Des Moines and Iowa Environmental Mesonet SchoolNet8 Webcam.)
"Wow, that was a good one!" says atmospheric scientist Tim Coleman of the National Space Science and Technology Center (NSSTC) in Huntsville, Alabama. In Iowa"These waves were created by a cluster of thunderstorms approaching Des Moines from the west," he explains.
"At the time, a layer of cold, stable air was sitting on top of Des Moines. The approaching storms disturbed this air, creating a ripple akin to what we see when we toss a stone into a pond."
"We're all familiar with gravity waves caused by boats in water," points out Coleman. "When a boat goes tearing across a lake, water in front of the boat is pushed upward. Gravity pulls the water back down again and this sets up a wave."
Coleman is an expert in atmospheric wave phenomena and he believes bores are more common and more important than previously thought.
Click on the link to see the footage (you will need iplayer installed).
The Naked Reader 2007
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