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 • • • • 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?