Mechanisms of Past Climate Change (16:375:553) Fall 2007 El Niño, La Niña and the Southern Oscillation

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Some History In the early 20 th Century, Sir Gilbert Walker discovered a recurrent pattern in sea level pressure data from the Pacific region. He called this pattern “The Southern Oscillation.”

Mechanisms of Past Climate Change (16:375:553) Fall 2007 The Southern Oscillation Sir Gilbert Walker ( ) Darwin Tahiti

Mechanisms of Past Climate Change (16:375:553) Fall 2007 The Oceanic Connection Jacob Bjerknes ( )

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Ekman Transport Balance between surface wind stress and Coriolis force In the Northern Hemisphere, the Ekman transport is directed to the right of the flow. (To the left in the Southern Hemisphere)

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Equatorial Upwelling

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Coastal Upwelling Motion of surface waters away from coast requires upwelling of water from below to satisfy continuity of mass. Andes Mts. S. Pacific Ocean

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Observed SST Distribution Equatorial Upwelling Coastal Upwelling Winds have a major influence on tropical SST pattern.

Mechanisms of Past Climate Change (16:375:553) Fall 2007 SST and Atmospheric Circulation WarmCold Western Equatorial Pacific Eastern Equatorial Pacific Rising air; clouds and precipitation Sinking air; very little precipitation Walker Circulation

Mechanisms of Past Climate Change (16:375:553) Fall 2007 In The Tropics… Sea surface temperatures are strongly influenced by surface winds. Atmospheric circulation is strongly influenced by the sea surface temperatures. Therefore… Strong air-sea interactions are possible

Mechanisms of Past Climate Change (16:375:553) Fall 2007

Mechanisms of Past Climate Change (16:375:553) Fall 2007

Mechanisms of Past Climate Change (16:375:553) Fall 2007

Mechanisms of Past Climate Change (16:375:553) Fall 2007

Mechanisms of Past Climate Change (16:375:553) Fall 2007 La Niña conditions: Strong cold tongue El Niño conditions: Cold tongue absent

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Recent History of El Niño and La Niña

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Recent History of El Niño and La Niña

Mechanisms of Past Climate Change (16:375:553) Fall 2007 El Niño is Quasiperiodic

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Current SST Anomalies

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Temporal Evolution of El Niño/La Niña

Mechanisms of Past Climate Change (16:375:553) Fall 2007 ENSO Events Can Evolve Differently

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Thermocline Temperatures and Anomalies

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Thermocline Fluctuations Cross-section of temperatures and currents along Equator

Mechanisms of Past Climate Change (16:375:553) Fall 2007 Thermocline and SST Anomalies ugli/enso_anim_jjb2.html

Mechanisms of Past Climate Change (16:375:553) Fall 2007 ENSO and Global Climate

Mechanisms of Past Climate Change (16:375:553) Fall 2007 ENSO and Global Climate

Mechanisms of Past Climate Change (16:375:553) Fall 2007 ENSO and U.S. Climate (Winter Season) Temperature Precipitation El Niño La Niña

Mechanisms of Past Climate Change (16:375:553) Fall 2007 More Information The International Research Institute for Climate Prediction at Columbia University’s Lamont-Doherty Earth Observatory has an excellent web site with information on El Niño.