North Atlantic Oscillation (NAO)

The North Atlantic Oscillation (NAO) is the leading mode of atmospheric variability over the North Atlantic, defined by the normalized sea-level-pressure difference between the Azores High and the Icelandic Low. The positive phase has a strong pressure gradient, stronger and more northward westerlies, mild wet winters in northern Europe, and dry conditions in the Mediterranean. The negative phase weakens and shifts the storm track south. The NAO is the regional expression of the Northern Annular Mode and influences ocean heat flux, sea ice, and the subpolar gyre.