365 Days of Climate Awareness 112 – The North Atlantic Oscillation

 

(Another shorty! A relief after yesterday...)

The North Atlantic Oscillation (NAO) is a surface atmospheric pressure variation between the Icelandic Low and the Azores High, and controls large-scale weather patterns such as westerly winds and storm tracks across the Atlantic basin. It is closely correlated with the Arctic Oscillation (AO), which measures surface air pressure differences between the Arctic and midlatitudes. The AO, however, includes both the Atlantic and Pacific.

General location of the Icelandic High and Azores Low.

The calculation for the index is very complex. A positive NAO index (NAOI) indicates both the Icelandic Low and Azores High are strong, with a large pressure difference between them. A large positive value (>1) predicts warm weather in the eastern United States and northern Europe, and cold weather in southern Europe. It also indicates higher sea level in the northern Atlantic Ocean, due to the lowered air pressure (which allows the seawater to expand). This is important in interpreting paleo-sea level records for the Atlantic basin.

A negative NAOI indicates the high and low features are weak, with a smaller pressure differential between them. A large negative value (<-1) indicates cold temperatures in the eastern United States and northern Europe, and warmer conditions in southern Europe.

Tomorrow: the North Pacific Oscillation.

Be brave, and be well.