Global winds could explain record rains, tornadoes

Two talks at a scientific conference this week will propose a common root for an enormous deluge in western Tennessee in May 2010, and a historic outbreak of tornadoes centered on Alabama in April 2011. Both events seem to be linked to a relatively rare coupling between the polar and the subtropical jet streams, says Jonathan Martin , a University of Wisconsin-Madison professor of atmospheric and oceanic sciences. But the fascinating part is that the change originates in the western Pacific, about 9,000 miles away from the intense storms in the U.S. midsection, Martin says. The mechanism that causes the storms originates during spring or fall when organized complexes of tropical thunderstorms over Indonesia push the subtropical jet stream north, causing it to merge with the polar jet stream. The subtropical jet stream is a high-altitude band of wind that is normally located around 30 degrees north latitude. The polar jet stream is normally hundreds of miles to the north. Martin calls the resulting band of wind a "superjet." Jet streams in the northern hemisphere blow from the west at roughly 140 miles per hour, and are surrounded by a circular whirlwind that looks something like a tornado pushed on its side.