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Morison, James Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington.
- Rising AO index
- Changes in Arctic region
- Related Primary Literature
- Additional Reading
The Arctic Oscillation (AO) is a unifying description of how atmospheric pressure in northern latitudes fluctuates (oscillates) between positive and negative phases. Recent changes in the Artic Oscillation index appear related to changes in the marine and terrestrial environments of the Arctic. To understand this relation is akin to understanding the phenomenon of the El Niño Southern Oscillation (ENSO). The AO index is an indicator of sea-level pressure variability for the Northern Hemisphere above 20°N. The Arctic Oscillation pressure pattern has a dominant low-pressure region roughly centered over the Arctic Ocean, and positive lobes over the North Pacific and North Atlantic. The pattern of the 50-hectopascal height correlated with the AO index is very similar to the surface pattern of the Arctic Ocean (see illus.). Thus, a positive AO index implies a strengthening of the counterclockwise (cyclonic) polar vortex (spinning ring of air) from the surface to the lower stratosphere. The asymmetries in the pressure pattern mean cool winds sweep east-southeast across eastern Canada, and southwesterly North Atlantic storm tracks bring rain and mild temperatures to northern Europe.
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