The Effect of Westerly Wind Bursts on ENSO Diversity: An Oceanic Perspective

The relationship between westerly wind bursts (WWBs) and the El Niño-Southern Oscillation (ENSO) diversity has drawn widespread attention. However, the effect of WWBs on the oceanic intraseasonal Kelvin waves in the context of ENSO diversity formation remains largely unexplored owing to limited observational data and theoretical analysis. To explore ENSO diversity mechanisms, we employ a combination of 20–90–day bandpass filtering, complex empirical orthogonal function analysis and composite analysis to investigate to what extent the oceanic Kelvin waves are influenced by WWBs. From filtered sea level anomalies in the equatorial Pacific Ocean (150°E−100°W, 2°S–2°N) between 1993 and 2023, we identified 149 downwelling and 119 upwelling Kelvin waves. During eastern-Pacific (EP) El Niño years, the WWBs have a further east active center, stronger intensity, a larger zonal extent and longer duration compared to central-Pacific (CP) El Niño years. Similarly, Kelvin waves have stronger intensity, broader extension, and zonal distribution along the equator in EP El Niño years than in CP El Niño years. Statistical and composite analysis reveal a consistent relationship between the zonal range, center location, duration, strength of WWBs and the corresponding response of Kelvin waves (center location, speed, duration, amplitude) across CP and EP El Niño years. The finding implies that WWBs may act as a precursor to ENSO diversity from an oceanic perspective, playing a key role in both the theoretical framework and prediction of ENSO diversity.