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WHAT IS THE NORTH ATLANTIC OSCILLATION?

The term 'North Atlantic Oscillation' is used to refer to variations in the large-scale surface pressure gradient in the North Atlantic region.

In the average state of the atmosphere, the North Atlantic surface pressure is relatively high in the subtropics at latitudes 20°N to 40°N ('the Azores High').

It is lower further North at latitudes 50°N to 70°N (the 'Icelandic Low'). 

The North-South pressure difference determines the strength of the westerly winds across the Atlantic and is known as the North Atlantic Oscillation (NAO).

When the pressure difference is large, the NAO is positive and the westerly winds are strong and storms tend to be stronger, more frequent and travel across northwestern Europe. 

When the pressure difference is small, they travel across southern Europe. 

The NAO is also associated with changes in temperature and rainfall in Europe and North America.

The fluctuations in the NAO occur on a wide range of time-scales. 

There are day-to-day changes associated with weather systems, and slower changes associated with seasonal and longer term variability, which is predictable from November for the coming winter.

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FILE - In this Sept. 2, 2016, file photo, a friend's basket of clams sit in the water as Mike Suprin, of Rollinsford, N.H., calls it a day after filling his basket with softshell clams at Cape Porpoise in Kennebunkport, Maine. A study by National Oceanic and Atmospheric Administration scientists released in 2018 concluded that valuable species of shellfish, including softshell clams, have become harder to find on the East Coast because of degraded habitats caused by a warming environment. (AP Photo/Robert F. Bukaty, File) Shellfish are DYING out on the East Coast of the US because climate change is warming the Atlantic and making them vulnerable to predators

Shellfish researchers for the National Oceanic and Atmospheric Administration studied declines in harvests of four valuable shelffish...

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