Energetics of Deep-Decoupling Oscillations

Abstract

A number of single-hemisphere ocean models, when forced with steady mixed boundary conditions, have produced self-sustaining oscillations with century to millennial scale periods. Here the energetics of these deep-decoupling oscillations are explored. It is found that in the deep-decoupled phase of the oscillation (when deep overturning and convection are absent) the sinks of potential energy (convection and conversion to kinetic energy) shut down, and potential energy is stored in the form of a basin warming. This potential energy becomes available when deep convection renews to begin the deep-coupled phase. During the deep-coupled phase the stored energy is drawn down as the potential energy sinks become larger than the diffusive source. This encourages one to consider the deep-coupled phase as a response to a pool of energy that grows in the absence of deep ventilation rather than a result of the specific mechanisms that are involved in breaking down the halocline in particular oscillations.