North Atlantic Oscillation

Joseph Papapietro

Outline

What is NAO? Atmospheric changes. The Atmosphere/Ocean connection. Biological/Ecological Effects

North Atlantic

Oscillation

A decade-scale processes that appears to play a major role in regional and global climate dynamics, resulting in weather changes in North America

and Europe. The oscillation ranges are due to variability in the permanent

pressure system in the sub tropics and in the northern region of the Atlantic.

A positive NAO index occurs when there is a large pressure gradient between the Sub-tropic permanent high pressure

system and North Atlantic Low pressure system. This results in relatively strong westerlies that run across the

Atlantic, carrying warm air from North America to Northern Europe.

A negative NAO index occurs when there is a small pressure difference between the Sub-tropic permanent high pressure system

and North Atlantic Low pressure system. This results in relatively weak westerlies that drop from Iceland and drag cold air to

Northern Europe.

Weather

Positive NAO: Warm in Eastern

North America Cold in Iceland Warm/Wet in Northern

Europe Cool/Dry in

Mediterranean

Negative NAO Cool Eastern North

America [More snow?] Warmer than usual in

Iceland [Ice melt?] Cool/dry in Northern

Europe Warm/Moist in

Mediterranean

cool

warm

cool

warm

Sea Surface Temperature maps for Positive NAO

(top), and Negative NAO (bottom).

Some Biological Effects

relatively Positive NAO for ~40 years The Labrador Sea snow crab have flourished in

cooler sea temperatures. Cod larvae

low tolerance to warm waters of NE Atlantic. NE N. America - positive NAO brings rain and

increased warmth – fresher/nutrient deficient water blocks upwelling of deep salty/nutritious water. Less productivity.

Thank You!

References: - Pearson, Aria; New Scientist; 1/3/2009, Vol. 200 Issue 2688, p32-35, 4p

- http://en.wikipedia.org/wiki/North_Atlantic_oscillation [photos]

- http://www.whoi.edu/page.do?pid=12455&tid=282&cid=10146 [photos]