A PRIMITIVE EQUATION OCEAN CIRCULATION MODEL USING A GENERAL VERTICAL COORDINATE TRANSFORMATION .2. APPLICATION TO AN OVERFLOW PROBLEM

The version of the ocean general circulation model of the Geophysical Fluid Dynamics Laboratory with a generalized vertical coordinate transformation introduced in part 1 is used to study the overflow of a zonal ridge in a coarse-resolution grid typical for climate applications. The configuration roughly resembles the Greenland-Scotland Ridge with respect to scale, latitude, and height of the ridge. Reasonable qualitative agreement with observed conditions over the Iceland-Faroe section has been achieved, especially when a deeper passage was included at the eastern end of the idealized model ridge. Upwelling of deep water occurs at the eastern boundary, where friction and, more importantly, diapycnal diffusion accomplish the necessary changes in potential vorticity. The overflow consists of intermediate water when the renewal time for the deep water is made much larger than that for intermediate water. The meridional mass transport is most sensitive to geometric factors like the height of the ridge. Frictional and diapycnal processes are crucial for the potential vorticity conversion at the ridge and have a strong effect on the water mass distribution. Bottom friction increases the near-bottom flow across f/H lines, resulting in a large amount of northern basin deep water south of the ridge. This effect can be represented only when the frictional bottom boundary layer is adequately resolved by the numerical grid.