What does a negative NAO mean?

The negative NAO phase represents the reverse with a weaker than usual difference in pressure. Winds from the east and north-east are more frequent, bringing with them cold air, while the adjusted position of the jet stream leads to weaker and less frequent storms.

What happens when NAO weakens?

During a negative NAO there is a weakening of both the Icelandic low and Azores high, which act to decrease the pressure gradient across the North Atlantic. This decreased pressure gradient results in a slackening of the westerlies.

What kind of weather results when the NAO is in its positive phase?

Positive NAO During winters when the NAO is in its positive mode, the presence of the strong high-pressure and strong low-pressure systems produces warmer, wetter conditions over northern Europe and most of northeastern North America.

How will climate change affect the NAO?

These unfavorable conditions for Southern Europe may become rarer in future due to global warming as the amount of CO2 and other greenhouse gases in the atmosphere increases considerably. Ensemble analyses of climate model projections indicate that in a warmer climate, the NAO will be more positive.

Is The NAO positive or negative?

The NAO is in a negative phase when both the sub-polar low and the subtropical high are weaker than average.

What effect does the North Atlantic Oscillation have on Europe’s climate?

Weak North Atlantic Oscillation index leads to dry, cold UK winter with wetter Med and weak Trades. Both the phases of the oscillation affect the whole of the North Atlantic and into the Mediterranean as well as into central Europe. In the extremes it will affect the weather into the Middle East and Russia.

What does positive NAO index mean?

The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low. The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track.

How does climate change affect North Atlantic Oscillation?

Over recent decades the boreal winter index of the North Atlantic Oscillation (NAO) has exhibited an upward trend, corresponding to lowered surface pressure over the Arctic and increased surface pressure over the subtropical North Atlantic.

What causes the North Atlantic Oscillation?

Air pressure over two regions drive this oscillation: The high latitudes of the North Atlantic Ocean near Greenland and Iceland generally experience lower air pressure than surrounding regions. This zone of low pressure is called the sub-polar low, or sometimes the Icelandic Low.

What causes Icelandic low?

In winter the ocean is considerably warmer than the continents, and this difference is responsible for the location of the Icelandic low, which dominates the wind circulation over the North Atlantic (see North Atlantic Oscillation).