AN EQUATORIAL OCEAN RECHARGE PARADIGM FOR ENSO .1. CONCEPTUAL-MODEL

A new conceptual model for ENSO has been constructed based upon the po sitive feedback of tropical ocean-atmosphere interaction proposed by B jerknes as the growth mechanism and the recharge-discharge of the equa torial heat content as the phase-transition mechanism suggested by Can e and Zebiak and by Wyrtki. This model combines SST dynamics and ocean adjustment dynamics into a coupled basinwide recharge oscillator that relies on the nonequilibrium between the zonal mean equatorial thermo cline depth and wind stress. Over a wide range of the relative couplin g coefficient, this recharge oscillator can be either self-excited or stochastically sustained. Its period is robust in the range of 3-5 yea rs. This recharge oscillator model clearly depicts the slow physics of ENSO and also embodies the delayed oscillator (Schopf and Suarez; Bat tisti and Hirst) without requiring an explicit wave delay. It can also be viewed as a mixed SST-ocean dynamics oscillator due to the fact th at it arises from the merging of two uncoupled modes, a decaying SST m ode and a basinwide ocean adjustment mode, through the tropical ocean- atmosphere coupling. The basic characteristics of this recharge oscill ator, including the relationship between the equatorial western Pacifi c thermocline depth and the eastern Pacific SST anomalies, are in agre ement with those of ENSO variability in the observations and simulatio ns with the Zebiak-Cane model.