Thermocline and zonal advective feedbacks within the equatorial ocean recharge oscillator model for ENSO

Through the dynamical coupling between ocean and atmosphere, the vertical advection of anomalous subsurface temperature by the mean upwelling and the zonal advection of mean sea surface temperature (SST) by anomalous current constitute the so-called the thermocline and zonal advective feedbacks that are essential for El Nino / Southern Oscillation (ENSO) coupled dynamics. In this paper, we demonstrate that these two feedbacks are dynamically linked because of the geostrophic balance between the upper ocean zonal current and the meridional gradient of the thermocline. Both feedbacks thus play important and similar roles in the growth and phase transition of ENSO. We further propose a new version of the conceptual recharge oscillator model for ENSO by including these two feedbacks. The new model retains the simplest possible form of a harmonic oscillator, yet presents a more complete description of slow physics for ENSO. Moreover, it also provides the reconciliation between the biased emphases in the ENSO theories on the thermocline and zonal advective feedbacks.