Importance of oceanic decadal trends and westerly wind bursts for forecasting El Niño

In the western Pacific, Westerly Wind Bursts (WWB) usually show up in the boreal fall-winter season, depending on the activity of the Madden and Jullian oscillation. It is demonstrated with a coupled ocean-atmosphere model that WWB have an impact on the coupled system in El Nino forecasting that depends on the ocean preconditioning. Sea level data reveal decadal changes of the Ocean Heat Content of the entire tropical Pacific (the OHC), with a minimum in the mid-1980s relative to highs before 1982 and after 1996. Adding the WWB in the forecast system does not degrade the successful predictions when the OHC is low whereas WWB are necessary in winter 1981–82 and 1996–97 to successfully predict the forthcoming warm events. Thus, when the OHC is high in addition to the other traditional conditions being favorable for a warm growth, WWB contribute to having a strong El Nino event the following year.

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