North Atlantic Oscillation

First published: 2021

Brief summary

UCAR explanation of NAO pressure patterns and climate variability.

Article

The North Atlantic Oscillation describes fluctuations in the atmospheric pressure difference between the subtropical North Atlantic and the region near Iceland. Changes in this pressure gradient affect the strength and path of the prevailing westerly winds across the North Atlantic.

In the positive phase, the subtropical high and Icelandic low are both relatively strong. The increased pressure gradient supports stronger westerly winds and a storm track that tends to bring mild, wet winters to northern Europe and drier conditions to parts of southern Europe.

In the negative phase, the pressure centres are weaker and the west-to-east pressure gradient is reduced. Storm tracks can shift southward, increasing the likelihood of colder conditions in parts of northern Europe and eastern North America while altering rainfall around the Mediterranean.

The NAO varies from days to decades and does not follow a fixed periodic schedule. It is measured with pressure-based indices and is influenced by interactions among the atmosphere, ocean, sea ice and stratosphere.

Source details and credits

• Source / publisher: UCAR
• Source type: Educational article
• URL type: WWW
• Credits: UCAR
• URL: https://scied.ucar.edu/learning-zone/how-climate-works/north-atlantic-oscillation