During the positive phase of the North Atlantic Oscillation (NAO), a large pressure gradient across the North Atlantic creates strong winds that drive winter storms across the Atlantic and into Northern Europe. During the negative phase, there is only a small pressure gradient. Southern Europe and Africa receive weak winter storms while Northern Europe and the eastern United States are cold and dry.
Click on image for full size
Courtesy of UCAR

The North Atlantic Oscillation

Will there be lots of snow in New York this winter? Will it be warmer than usual in France? Will the Mediterranean get rainy weather? That will depend on the North Atlantic Oscillation.

Winter weather in the Northern Hemisphere is affected by changes in atmospheric pressure over the North Atlantic called the North Atlantic Oscillation. During the winter, a low pressure system over Iceland and a high pressure system over the Atlantic become stronger or weaker. The changes in pressure cause changes in the amount of wind and the number of winter storms that cross the Atlantic. This affects the weather in North America, Europe, and North Africa.

When the difference in pressure between the high and low is large, strong winds cross the North Atlantic, bringing wet winter storms from eastern North America to northern Europe. This is the positive phase of the North Atlantic Oscillation.

When the difference in pressure is small, there is less wind over the ocean. Eastern North America and northern Europe have fewer winter storms. The weather is rainy in southern Europe and North Africa. This is the negative phase of the North Atlantic Oscillation.

There is evidence of more negative phases during the 1960s and 1970s and more positive phases during the 1980s and 1990s. Scientists are using computer models to figure out whether this change is due to global warming .

The changes in atmospheric pressure associated with the NAO are connected with other patterns of atmospheric pressure including the Arctic Oscillation and the El Nino-Southern Oscillation.

Last modified September 18, 2008 by Lisa Gardiner.

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more


Wind is moving air. Warm air rises, and cool air comes in to take its place. This movement creates different pressures in the atmosphere which creates the winds around the globe. Since the Earth spins,...more

Global Warming: Scientists Say Earth Is Heating Up

Earth’s climate is warming. During the 20th Century Earth’s average temperature rose 0.6° Celsius (1.1°F). Scientists are finding that the change in temperature has been causing other aspects of our planet...more

El Niño and Other Climate Events

Sometimes there is a change in the way air moves through parts of the atmosphere. And there are sometimes changes in the way water moves through the ocean too. This disturbs typical weather patterns, or...more

Teleconnections: Changes in Weather Linked Together

Changes in the atmosphere in one place can affect weather over 1000 miles away. Scientists are trying to sort out how this works so that they can better understand and predict weather patterns worldwide....more

Content for Climate Change Education Courses

Looking for online content that can be used for a climate change education course or module? Pages linked below can be used to support an introductory climate change education for either a unit or a full...more

A New Plan to Help Earth’s Changing Climate

Leaders from 192 countries are meeting in Copenhagen, Denmark December 7-18, 2009 to decide how the world will deal with climate change. They are trying to decide how to limit the amount of greenhouse...more

What Is Climate?

The climate where you live is called regional climate. It is the average weather in a place over more than thirty years. To describe the regional climate of a place, people often tell what the temperatures...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA