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Those giant waves—"undular bore waves"—were photographed Oct. 3rd 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. Coleman is an expert in atmospheric wave phenomena and he believes bores are more common and more important than previously thought.But first, 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."Undular bores are a type of "gravity wave"—so called because gravity acts as the restoring force essential to wave motion. Analogy: "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."Playing the role of boat, the thunderstorms tearing across Iowa on Oct. 3rd spawned a train of four waves. "To read more go to:
As in the days of Noah....
