High and low index Arctic Oscillation (AO)
The 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. Additional information is available for the Arctic Oscillation (AO) and for the North
Atlantic Oscillation (NAO), a close relative of the AO.
The following figures are from Hodges (2000, National
Fluctuations in the AO can be seen in the time
series of SLP anomalies for the North Pole
The "high index" of the AO is defined as periods of below normal Arctic SLP, enhanced
surface westerlies in the north Atlantic, and warmer and wetter than
normal conditions in northern Europe. This is depicted as the "warm
phase" in the following figure. "Low index" AO conditions are described
in the "cool phase" panel.
Hodges, Glenn, 2000. The new cold war. Stalking arctic climate change by submarine. National
Geographic, March, 30-41.
Todd Mitchell (email@example.com)