On a recent crisp autumn afternoon in Iowa, video cameras captured an unusual and visually dramatic result of two air masses colliding. Clouds split into a series of stripes and swept across the sky.
These so-called undular bores are created by atmospheric conditions that destabilize the air in a particular way.
|An undular bore caught by satellite over the Arabian Sea on May 8th, 2007.
In the case of Des Moines, Iowa, they formed on Oct. 3 when a group of thunderstorms approached the city.
"At the time, a layer of cold, stable air was sitting on top of Des Moines," said atmospheric scientist Time Coleman of the National Space Science and Technology Center in Alabama. "The approaching storms disturbed the air, creating a ripple akin to what we see when we toss a stone into a pond."