Niño. It is indeed possible that these studies have all hinted at various truths to the actual physical mechanisms at play. In addition, the problem of ENSO asymmetry is also a controversial issue (Okumura et al. 2011; Cai et al. 2015b; Chen et al. 2016; Levine et al. 2016). An extreme El Niño is characterized by a disproportionately warm maximum SST anomaly in the eastern equatorial Pacific, whereas the anomaly centres of weak El Niño and extreme La Niña events are situated in the central equatorial Pacific (the centre of a weak La Niña is located further towards the east) (Cai, 2015a). These imply that the occurrence mechanism of El Niño differs from that of La Niña, and it is inappropriate to describe these two events with a single dynamical model confined to the equator. Note that, since the adiabatic motion of the water plays a key role in the oceanic circulation and climate (Huang 2015), El Niño and La Niña may be caused by different currents.

In order to get a deeper understanding on ENSO cycle, there is a necessity to restate a fundamental fact: *In a self-sustaining climate system, in addition to the thermal processes related to evaporation 