North Atlantic Oscillation Index

The North Atlantic Oscillation (NAO) is one of the major modes of variability of the Northern Hemisphere atmosphere. It is particularly important in winter, when it exerts a strong control on the climate of the Northern Hemisphere. In terms of measurement, the NAO is a fairly simple thing-it is an index created by comparing the pressures in the Azores and in Iceland. For the NAO a high index signifies low pressure around Iceland and the reverse off Portugal a situation that gives rise to strong westerly winds In winter - which is when these signals are strongest - these westerlies bring heat from the ocean's surface into the European continent, along with storms.

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Data Source NOAA

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