Lateral and isopycnal mixing of passive and active tracers in an ocean general circulation model

The parameterization of isopycnal mixing is examined in an ocean general circulation model. The results are compared to those obtained with lateral mixing.In the equilibrium experiments, the isopycnal case has more gyre kinetic energy, a less intense thermohaline circulation, and less interior downwelling than the lateral case. Convection is replaced by enhanced vertical diffusion in the isopycnal case.In the time dependent passive tracer experiments, the isopycnal case has smaller depth penetration of a surface released tracer. This is likely due to induced recirculation rather than numerical limitations.The active tracer experiments examine the long term asymmetric behaviour of warm and cold surface anomalies introduced in an abrupt and gradual fashion for the lateral and isopycnal models. The thermal anomalies produce asymmetric transient responses. The abrupt and gradual changes produce the same equilibrium but different transient responses. The isopycnal case responds more rapidly and energetically than the lateral case