May 7, 2009

Cause of U.S. Dust Bowl proposed

U.S. and Swiss scientists say unusual atmospheric circulation might have caused the 1930s Dust Bowl and could also be responsible for other droughts.

The researchers from the Institute for Atmospheric and Climate Science in Zurich, Switzerland; the Observatory and World Radiation Center in Davos, Switzerland, and the U.S. National Climatic Data Center in Asheville, N.C., said they used historical upper air data, reconstructions and model simulations to analyze atmospheric circulation during the Dust Bowl era.

They said they discovered the Great Plains low level jet, which transports moisture from the Gulf of Mexico to the region, was weaker on its eastern side, shallower and did not extend as far north as during wetter years.

In addition, they found during the Dust Bowl years there was unusually strong ridging in the mid-troposphere above the Great Plains and persistent flow anomalies in the upper troposphere across North America, possibly preventing moisture from reaching the region.

The researchers said their findings suggest oceanic forces triggered the changes. Models that included such forcing reproduced the atmospheric conditions associated with extreme droughts, which implies that droughts in the Midwest could potentially be predictable.

The study appears in the journal Geophysical Research Letters.