North Atlantic Oscillation

North Atlantic Oscillation

North Atlantic Oscillation

Climate statistics encompass more than just the mean state for climate. They also include measures of natural variability, including the location, timing, and strength of oscillations within the climate system. For example, fully coupled models generate variability on the same time and spatial scales as ENSO, the North Atlantic Oscillation (NAO), and Pacific Decadal variability, among others.

This is a plot of one mode of variability found in the climate system, the North Atlantic Oscillation (NAO), which is a pressure oscillation between the Arctic region and the subtropics. The plot on the left shows the annual mean NAO in the real atmosphere from 1900 to 2008, while the plot on the right shows the annual mean NAO in a fully coupled model over a 109-year period. The results are strikingly similar.

Positive and negative phases of the wintertime North Atlantic Oscillation (NAO).

It's important to note that this variability is not externally forced. This is a natural mode of variability of the Earth's climate system that happens to play a very important role for seasonal weather. Here we see typical global weather patterns associated with positive and negative modes of NAO.

Photo of Snow in Barcelona, Spain

From 2008 to 2011, a tendency toward a strongly negative phase of NAO resulted in extremely cold winters in Europe. Having a climate model generate this sort of variability is important because that variability goes into the statistics of weather that comprise climate for the Northern Hemisphere.