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The Arctic Oscillation (AO) is compares 1000 mb height anomalies pole of 20N to those across the middle latitudes.
- A positive AO suggests a stronger polar vortex with lower pressures near the pole, allowing the middle latitude jet stream to blow strongly and consistently from west to east, keeping colder air locked in the polar region.
- A negative AO suggests higher pressures in the polar region, weaker zonal winds and the potential for acrtic air to move south into the middle latitudes. (1998 David WJ Thompson and John Michael Wallace)
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