ISOPYCNIC MIXING AND THE VERONIS EFFECT IN AN OCEAN GENERAL-CIRCULATION MODEL

In this study we have run a number of numerical simulations to examine the 'Veronis effect' in an ocean general circulation model. This effe ct is characterized by anomalous interior downwelling, east of the wes tern boundary current of an ocean basin. The impact of varying the hor izontal diffusivity and the use of an isopycnal mixing parameterizatio n are examined. Several diagnostics are used. The net volume transport far a sector in the southern part of the domain, east of the western boundary is found to be the dearest indicator of the strength of the V eronis effect. This effect is found to depend crucially on the horizon tal diffusivity. The use of an isopycnal mixing parameterization signi ficantly mitigates the interior downwelling problem but is constrained by the required use of a background horizontal diffusivity. Thus, in a geopotential coordinate model an isopycnal mixing parameterization e nables the use of a significantly reduced horizontal diffusivity while emphasizing the mixing along isopycnals.