Effects of locally enhanced vertical diffusivity over rough bathymetry on the world ocean circulation

Observations indicate that vertical diffusivity in the deep ocean is consid erably enhanced over rough bathymetry and is very small elsewhere. Here we investigate effects of locally enhanced vertical diffusivity over rough bot tom topography on the world ocean circulation by use of a coarse resolution ocean general circulation model. Vertical diffusivity is enhanced in the m odel, taking into account effects of internal tide breaking, For comparison , two cases of an experiment are carried out, where vertical diffusivity in creases with depth without horizontal inhomogeneity Horizontal distribution of deep upwelling is qualitatively different, depending on whether or not vertical diffusivity is horizontally inhomogeneous. Upwelling: of Circumpol ar Deep Water in the Pacific and Antarctic Bottom Water in the Atlantic is confined where vertical diffusivity is enhanced in the case of horizontally inhomogeneous vertical diffusivity, whereas it is horizontally uniform in the other cases. This difference leads to different three-dimensional struc ture of the deep circulation.