EO Study: Searching for Atlantic Rhythms: Winter Weather and the North Atlantic Oscillation

Searching for Atlantic Rhythms

A new version of Searching for Atlantic Rhythms was posted on July 11, 2003. It includes new information about the causes of the North Atlantic Oscillation.

Over the past fifteen years, our society has come to view the El Niño/La Niña phenomenona less as a climate anomaly and more as an invisible spirit that is responsible for nearly every weather-related adversity out there. We blame it for our dead car batteries in January, for the high price of oranges in the summer, and for those cold snaps that hit us in early October. In their zeal to tap into and sell this belief, the public media have fed us a long stream of stories on El Niño-related events. However, they’ve ignored those other climate anomalies outside of the Pacific Basin that drive the weather. Probably the biggest and most powerful of these climate phenomena is the aptly named North Atlantic Oscillation (NAO). While the North Atlantic Oscillation doesn't generate the catastrophic floods, climate changes, and carnage associated with El Niño, its effects are much more consistent and nearly as widespread.

Climate Oscillations:
Introduction: El Niño’s Extended Family

Searching for Atlantic Rhythms

Reverberations of the Pacific Warm Pool

Coming Soon:
Intertropical Convergence Zone

Sweden and Washington, DC
The NAO is the relationship between a high-pressure system over the Azores Islands and a low-pressure system over Iceland. Both of these systems are present on average year round. For most of the spring, summer, and fall these systems remain weak and ineffectual. However, throughout the course of the winter, the NAO comes alive as both the high and the low intensify and fluctuate in pressure relative to one another, creating dramatic variations over the Atlantic Ocean and the surrounding continents. When the pressure difference between the two systems is large, they bring higher temperatures to northern Europe, cause droughts in the Middle East, and push up the mercury in the northeastern United States. When the pressure difference between the two systems is small, they push wet weather toward those countries surrounding the Mediterranean, send Scandinavia into a deep freeze, and decrease the temperature along the East Coast.

A strong North Atlantic Oscillation (large difference in pressure between the mid-latitude and tropical North Atlantic) tends to produce more severe weather in the North Atlantic, increased snowfall in Sweden (left), and an early spring in Washington, DC (right) [Photographs copyright Mark Schoeberl (left) & Barbara Summey (right)]

France and Spain
Despite the lack of publicity the NAO receives, teams of scientists at NASA and other institutions around the world have been studying it for many decades. They found that, much like El Niño, the NAO varies in a rhythmic pattern from decade to decade. Ever since the 1960s, the difference in pressure between the Azores high and the Icelandic low has repeatedly grown on average for three to five years and then has waned and decreased on average for another three to five years. Though the researchers have not had much luck in predicting the anomaly's behavior, many believe that its multi-year variations may be linked to currents in the sea or the formation of sea ice. Their hope is that by studying the NAO and building models mimicking its behavior, they may someday understand what drives these variations. From there they may even be able to predict its behavior.
The Highs and Lows of the NAO
The data used in this study are available in one or more of NASA's Earth Science Data Centers.
Typical weather caused by a negative NAO (small pressure difference between the mid-latitude and tropical North Atlantic) is fewer storms overall, clear skies over the Normandy coast of France (left,) and rain in Spain (right). (Photographs copyright Eric Simmon)

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	A new version of Searching for Atlantic Rhythms was posted on July 11, 2003. It includes new information about the causes of the North Atlantic Oscillation.
	Over the past fifteen years, our society has come to view the El Niño/La Niña phenomenona less as a climate anomaly and more as an invisible spirit that is responsible for nearly every weather-related adversity out there. We blame it for our dead car batteries in January, for the high price of oranges in the summer, and for those cold snaps that hit us in early October. In their zeal to tap into and sell this belief, the public media have fed us a long stream of stories on El Niño-related events. However, they’ve ignored those other climate anomalies outside of the Pacific Basin that drive the weather. Probably the biggest and most powerful of these climate phenomena is the aptly named North Atlantic Oscillation (NAO). While the North Atlantic Oscillation doesn't generate the catastrophic floods, climate changes, and carnage associated with El Niño, its effects are much more consistent and nearly as widespread.		Climate Oscillations: Introduction: El Niño’s Extended Family Searching for Atlantic Rhythms Reverberations of the Pacific Warm Pool Coming Soon: Intertropical Convergence Zone
	The NAO is the relationship between a high-pressure system over the Azores Islands and a low-pressure system over Iceland. Both of these systems are present on average year round. For most of the spring, summer, and fall these systems remain weak and ineffectual. However, throughout the course of the winter, the NAO comes alive as both the high and the low intensify and fluctuate in pressure relative to one another, creating dramatic variations over the Atlantic Ocean and the surrounding continents. When the pressure difference between the two systems is large, they bring higher temperatures to northern Europe, cause droughts in the Middle East, and push up the mercury in the northeastern United States. When the pressure difference between the two systems is small, they push wet weather toward those countries surrounding the Mediterranean, send Scandinavia into a deep freeze, and decrease the temperature along the East Coast.		A strong North Atlantic Oscillation (large difference in pressure between the mid-latitude and tropical North Atlantic) tends to produce more severe weather in the North Atlantic, increased snowfall in Sweden (left), and an early spring in Washington, DC (right) [Photographs copyright Mark Schoeberl (left) & Barbara Summey (right)]
	Despite the lack of publicity the NAO receives, teams of scientists at NASA and other institutions around the world have been studying it for many decades. They found that, much like El Niño, the NAO varies in a rhythmic pattern from decade to decade. Ever since the 1960s, the difference in pressure between the Azores high and the Icelandic low has repeatedly grown on average for three to five years and then has waned and decreased on average for another three to five years. Though the researchers have not had much luck in predicting the anomaly's behavior, many believe that its multi-year variations may be linked to currents in the sea or the formation of sea ice. Their hope is that by studying the NAO and building models mimicking its behavior, they may someday understand what drives these variations. From there they may even be able to predict its behavior. The Highs and Lows of the NAO The data used in this study are available in one or more of NASA's Earth Science Data Centers.		Typical weather caused by a negative NAO (small pressure difference between the mid-latitude and tropical North Atlantic) is fewer storms overall, clear skies over the Normandy coast of France (left,) and rain in Spain (right). (Photographs copyright Eric Simmon)