Recent El Nino Southern Oscillation
When the Christ child comes a year late March 22, 2016 / IMAU / Although the name El Niño (`little boy/Christ child’) actually refers to the fact that most ENSO (El Niño Southern Oscillation) events peak around Christmas, it also nicely captures a troublesome property of the phenomenon: It behaves as quirkily and unpredictably as a three-year-old child. Next winter’s El Niño can be reasonably well predicted in summer (which basically amounts to diagnosing a developing event), but for longer lead times predictability drops quickly: the `spring predictability barrier’. The basic physics of El Niño are well understood (see figure): under normal (non-ENSO) conditions, the easterly trade winds over the Pacific push warm water to Indonesia. Near Peru this leads to upwelling of cold deep water. If the easterlies weaken, the warm water `sloshes back’ eastwards as an equatorial Kelvin wave. As a result, the water near coastal Peru gets warmer and heats the overlying at...