Climate Variability of the Equatorial Thermocline Inferred from a Two-Moving-Layer Model of the Ventilated Thermocline*
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A two-moving-layer model is used to examine the structure of the equatorial thermocline and its connection with the extratropical thermocline. It is found that cooling (warming) in extratropics generates a low (high) potential vorticity anomaly and induces downward (upward) movement of the thermocline, and the perturbation propagates to the equatorial thermocline, inducing a downward (upward) movement of the thermocline and intensification (weakening) of the undercurrent. Thus, surface cooling in the extratropics can induce warming of the equatorial thermocline. In addition, the total mass flux in the subsurface layer in the extratropics and the equatorial undercurrent is enhanced. Although in the extratropics perturbations generated by localized cooling (warming) are confined within the characteristic cone, defined by the unperturbed trajectories of the thermocline circulation, when these perturbations propagate into the equatorial region they are no longer confined by the characteristic cone in the meridional direction.