Way the wind blows predicted

December 17, 1999

Winter cold snaps might be forecast weeks in advance if predictions from the first simulation of the climate-dictating polar vortex are born out by further observations.

Oxford scientist Paul McCloghrie presented to the American Geophysical Union meeting this week a model showing how westward prevailing high altitude winds around the arctic can abruptly break down.

This great anti-clockwise swirl of wind keeps freezing arctic air bound up tight in high latitudes. However, it periodically collapses, ultimately resulting in a plunge in ground temperatures and bouts of cold weather.

The process starts with a sudden heating of the stratosphere, 10-30 miles above the surface. It takes several weeks for the impact of this temperature rise to unravel the polar vortex until cold air from the arctic is unleashed southwards into Europe and North America.

John Wallace, an atmospheric scientist at the University of Washington, Seattle, United States, said it was becoming increasingly obvious that this linking between stratophere and troposphere was of great importance to climate and weather in the northern hemisphere.

"Scientists should be able to use model simulations like Mr McCloghrie's to figure out how events 30km up are able to influence weather far below," said Professor Wallace.

The early stages of the process can be viewed from microwave satellite images and could one day be used to improve forecasting, possibly giving experts an advance warning of big shifts in winter weather patterns well before their effects appear on the ground.

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