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Giant Atmospheric Waves Over Iowa

Undular bore waves over Iowa, Oct. 3, 2007. Click here to see the animation

Iowa, USA
Giant atmospheric waves over Iowa. Giant waves -"undular bore waves"- were photographed Oct. 3rd flowing across the skies of Des Moines, Iowa. "These waves were created by a cluster of thunderstorms approaching Des Moines from the west. 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. "We're all familiar with gravity waves caused by boats in water. 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. Undular bores may play a surprising role in severe weather. "For one thing, we believe undular bores can amplify tornadoes. Furthermore undular bores may be a source of thunderstorms." That's right, thunderstorms make undular bores and undular bores return the favor. "These waves churn up the atmosphere, causing instabilities that can initiate and sustain severe storms." Typical waves measure 5 miles from peak to peak and race across the sky at 10 to 50 mph. "An undular bore passes over any given point in the United States about once a month," a scientist estimates
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