Abstract: Diapycnal mixing by meso-scale eddies in the ocean

 

 

Authors: Carsten Eden

The mean available potential energy released by baroclinic instability into the meso-scale eddy field of the ocean has to be dissipated in some way and Tandon and Garrett (1996)

suggested that this dissipation could ultimately involve irreversible mixing of buoyancy by molecular processes at the small-scale end of the turbulence cascade.

This idea is revisited and it is argued that the presence of dissipation within the thermocline of the ocean automatically requires that a component of the eddy flux associated with meso-scale eddies must be associated with irreversible mixing of buoyancy within the thermocline. A parameterisation is proposed for the implied diapycnal diffusivity based on

(i) the dissipation rate for eddy kinetic energy given by the meso-scale eddy closure of Eden and Greatbatch (2008) and (ii) a fixed mixing efficiency.

The implied eddy-induced diapycnal diffusivity (kappa) is implemented in a coarse resolution model of the North Atlantic. In contrast to the vertical diffusivity given by a standard vertical mixing scheme, large lateral inhomogeneities can be found for kappa in the interior of the ocean.

In general, kappa is large, i.e. up to o(10) cm2/s, near the western boundaries and almost vanishing in the interior of the ocean.