Arctic oscillation

The Arctic oscillation (AO) is the dominant pattern of non-seasonal sea-level pressure (SLP) variations north of 20N, and it is characterized by SLP anomalies of one sign in the Arctic and anomalies of opposite sign centered about 37-45N. The North Atlantic oscillation (NAO) is a close relative of the AO and there exist arguments about whether one or the other is more fundamentally representative of the atmosphere's dynamics.
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