and precipitation, there should be a dynamical ring, as depicted in* . To refer to the work given by Huang (2015) again, this ring dominates the whole system. For example, during the initiation of El Niño, a positive SST anomaly may form in response to a change in the flow field, and its evolution should, in turn, gradually cause a change in the SLP field and a corresponding adjustment of the wind. Any objective ENSO model should follow this rule. In fact, by and large, researchers have automatically obeyed this rule. The diversity of their models lies in different hypotheses and simplifying. To keep it in mind, we re-understand the previous three classical ENSO theories as follows:

\(1) In the positive Bjerknes feedback mechanism, which involves Walker circulation, the ENSO cycle is described by an SST anomaly in the EP, an east-west SST gradient and a wind anomaly in the EP. Under the hypothesis that all the adjustments are along the equator, the SST gradient results in air-pressure differences which, in turn, affect the Walker circulation (its lower segment in the EP is actually a westward wind). The current anomaly along the equator is taken as a default response to 