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El Niño, La Niña and the Southern Oscillation

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Presentation on theme: "El Niño, La Niña and the Southern Oscillation"— Presentation transcript:

1 El Niño, La Niña and the Southern Oscillation
Spring 2013

2 Some History In the early 20th Century, Sir Gilbert Walker discovered a recurrent pattern in sea level pressure data from the Pacific region. He called this pattern “The Southern Oscillation.” Spring 2013

3 The Southern Oscillation
Sir Gilbert Walker ( ) Tahiti Darwin Spring 2013

4 The Oceanic Connection
Jacob Bjerknes ( ) Spring 2013

5 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) Spring 2013

6 Equatorial Upwelling Spring 2013

7 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 Spring 2013

8 Observed SST Distribution
Winds have a major influence on tropical SST pattern. Equatorial Upwelling Coastal Upwelling Spring 2013

9 SST and Atmospheric Circulation
Rising air; clouds and precipitation Sinking air; very little precipitation Walker Circulation Warm Cold Western Equatorial Pacific Eastern Equatorial Pacific Spring 2013

10 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 Spring 2013

11 Spring 2013

12 Spring 2013

13 Spring 2013

14 Spring 2013

15 La Niña conditions: Strong cold tongue
El Niño conditions: Cold tongue absent Spring 2013

16 Recent History of El Niño and La Niña
Spring 2013

17 Recent History of El Niño and La Niña
Spring 2013

18 El Niño is Quasiperiodic
Spring 2013

19 Current SST Anomalies Spring 2013

20 El Niño’s Life Cycle Initiation Peak Decay Source: IRI

21 Temporal Evolution of El Niño/La Niña
Spring 2013

22 ENSO Events Can Evolve Differently
Spring 2013

23 Thermocline Temperatures and Anomalies
Spring 2013

24 Thermocline Fluctuations
Cross-section of temperatures and currents along Equator Spring 2013

25 Subsurface Structure Source: NASA Goddard Space Flight Center

26 The delayed oscillator
The leading theoretical model is the delayed oscillator [see Battisti and Hirst, 1989]: Here, Ts is the temperature in the East Pacific, b and c are positive constants, and  is a time-lag determined by equatorial oceanic adjustment. • The first term on the RHS can be thought of a representing a positive feedback associated with the atmosphere, e.g., the large-scale Darwin-Tahiti pressure difference (the SOI). • The second term represents a negative feedback associated with thermocline adjustment via equatorial waves. • The time delay is the time required for Rossby waves to propagate westward, reflect at the boundary, and return to the region of origin.

27 Equatorial Kelvin & Rossby Waves
Surface currents (l) and thermocline displacements (r) for a Gaussian perturbation 2-layer oceanic SWE model Kelvin wave: Non-dispersive, eastward propagating (~2 m/s for H = 150 m) Rossby waves: Dispersive, westward propagating (fastest is 1/3 of Kelvin wave group velocity)

28 Propagating equatorial waves

29 ENSO and Global Climate
Spring 2013

30 ENSO Teleconnections ENSO 500mb Geopotential Pattern
PNA 300mb Geopotential Pattern

31 ENSO and Global Climate
Spring 2013

32 ENSO and U.S. Climate (Winter Season)
El Niño La Niña Temperature Precipitation Spring 2013

33 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. Spring 2013

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