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The El Ni(n)o and the Southe Oscillation (ENSO) occurrence can be usually explained by two views of(i) a self-sustained oscillatory mode and (ii) a stable mode interacting with high-frequency forcing such as westerly wind bursts and Madden-Julian Oscillation events.The positive ocean-atmosphere feedback in the tropical Pacific hypothesized by Bjerknes leads the ENSO event to a mature phase.After ENSO event matures,negative feedbacks are needed to cease the ENSO anomaly growth.Four negative feedbacks have been proposed:(i) reflected Kelvin waves at the ocean weste boundary,(ii) a discharge process due to Sverdrup transport,(iii) weste-Pacific wind-forced Kelvin waves and (iv) anomalous zonal advections and wave reflection at the ocean easte boundary.These four ENSO mechanisms are respectively called the delayed oscillator,the recharge-discharge oscillator,the weste-Pacific oscillator and the advective-reflective oscillator.The unified oscillator is developed by including all ENSO mechanisms,i.e.all four ENSO oscillators are special cases of the unified oscillator.The tropical Pacific Ocean and atmosphere interaction can also induce coupled slow westward-and eastward-propagating modes.An advantage of the coupled slow modes is that they can be used to explain the propagating property of interannual anomalies,whereas the oscillatory modes produce a standing oscillation.The research community has recently paid attention to different types of ENSO events by focusing on the central-Pacific El Ni(n)o.All of the ENSO mechanisms may work for the central-Pacific El Ni(n)o events,with an addition that the central-Pacific El Ni(n)o may be related to forcing or processes in the extra-tropical Pacific.