The El Niño–Southern Oscillation (ENSO) is a complex nonlinear phenomenon. While both intrinsic low-frequency atmosphere–ocean interaction and multiplicative high-frequency processes affect the development of ENSO, the strong nonlinearity has prevented us from separating their relative contributions. Here we propose an online filtering scheme to estimate the role of westerly wind bursts (WWBs), a type of high-frequency atmospheric perturbation over the western-central tropical Pacific, in the genesis of the centennial extreme 1997/98 El Niño using the CESM coupled model. This scheme greatly reduces the uncertainty in ENSO forecast caused by initial error and model nonlinearity, and clearly demonstrates that the strong and long-lasting WWBs in March 1997 were essential for generating the 1997/98 El Niño. Without these WWBs, the intrinsic low-frequency coupling would have only produced a weak warm event in late 1997 similar to the 2014/15 El Niño.

厄尔尼诺,西风爆发,气候模式