Quantifying the Dependence of Westerly Wind Bursts on the Large-Scale Tropical Pacific SST

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Abstract
The correlation between parameters characterizing observed westerly wind bursts (WWBs) in the Equatorial Pacic and the large scale SST is analyzed using singular value decomposition. The WWB pa- rameters include the amplitude, location, scale and probability of occurrence for a given SST distribution, rather than the wind stress itself. This approach therefore allows for a nonlinear relationship between the SST and the wind signal of the WWBs. It is found that about half of the variance of the WWBs parameters is explained by only two large scale SST modes. The rst mode represents a developed El Niæo event, while the second mode represents the seasonal cycle. More specically , the central longitude of WWBs, their longitudinal extend and their probability seem to be determined to a signicant degree by ENSO- driven signal. The amplitude of the WWBs is found to be strongly inuenced by the phase of the seasonal cycle. It is concluded that the WWBs, while partially stochastic, seem an inherent part of the large scale deterministic ENSO dynamics. Implications to ENSO predictability and prediction are discussed. óóóóóóñ