ENSO:
El Niño Southern Oscillation
Background, Dynamics,
Regional Impacts,
and Future Outlook
Josh Gellers
Luis Poza
EESC W4400
ENSO:Background Information
• Coupled ocean-atmosphere instability in the
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equatorial Pacific
Two distinct phases, El Nino and La Nina,
occurring every 2-10 years
Sir Gilbert Walker recognized teleconnections in
1920s (i.e. sea-level pressure differences)
Name coined by Peruvian fishermen
Paleoclimate record indicates impacts as far back
as 130,000 years ago
ENSO: Dynamics
•Normally, temperature gradient
between western and eastern
equatorial Pacific due to equatorial
upwelling and presence of easterlies.
•During El Nino, Walker Cell is
disrupted, meaning more convection
over eastern Pacific.
•Easterly winds weaken or reverse and the
eastern Pacific experiences a warm SST
anomaly.
•During El Nino, thermocline deepens in
east and shoals in west.
•Leading to…
ENSO: Regional Impacts
El Niño:
Increased likelihood of:
-Above normal rainfall anomaly in
Peru, Ecuador, Western US
-Depleted fishery stocks in eastern
Pacific
-Drought in northeast Brazil,
eastern Australia, Indonesia and
southeast Asia, southeastern
Africa
-Weakened Indian monsoon
ENSO: The Future
• Effects of warming
and GHG increase
uncertain
-ENSO neutral state more like current La Niña
-More frequent and intense El Niño events
-No change at all?