What is the North Atlantic Oscillation index?

The North Atlantic Oscillation Index describes changes in the strength of two recurring pressure patterns in the atmosphere over the North Atlantic: a low near Iceland, and a high near the Azores Islands. Positive NAOI values indicate these features are strong, creating a big pressure difference between them.

What does the North Atlantic Oscillation effect?

North Atlantic Oscillation (NAO), an irregular fluctuation of atmospheric pressure over the North Atlantic Ocean that has a strong effect on winter weather in Europe, Greenland, northeastern North America, North Africa, and northern Asia.

How is the NAO index calculated?

The standard NAO Index is calculated by taking the difference between normalized surface pressure anomaly from a 30 years mean of a northern and a southern station (Equation 1).

What happens during a weakening of the NAO?

Simply put the negative NAO creates an “atmospheric road block.” The westerly winds weaken, resulting in limited upper air flow over the entire North Atlantic extending all the way to the US East Coast.

How is North Atlantic Oscillation calculated?

The value of this difference is calculated by subtracting the measured surface air pressure over Iceland from the measured surface air pressure at the Azores. Comparison of this instantaneous value with the long-term average pressure difference yields the North Atlantic Oscillation Index.

Why is NAO important?

Especially during the months of November to April, the NAO is responsible for much of the variability of weather in the North Atlantic region, affecting wind speed and wind direction changes, changes in temperature and moisture distribution and the intensity, number and track of storms.

What does a positive NAO mean?

The positive phase of the NAO reflects below-normal heights and pressure across the high latitudes of the North Atlantic and above-normal heights and pressure over the central North Atlantic, the eastern United States and western Europe.

What is NAO region?

North Atlantic Oscillation. The NAO is the dominant mode of winter climate variability in the North Atlantic region ranging from central North America to Europe and much into Northern Asia. The NAO is a large scale seesaw in atmospheric mass between the subtropical high and the polar low.