TOPOGRAPHY AND BAROTROPIC TRANSPORT CONTROL BY BOTTOM FRICTION

The problem of the stratified general circulation in the presence of t opography is revisited. The novel effect examined here is that of loca lized, but large-scale, topographic anomalies on the wind-driven circu lation, a problem whose relevance is found in the occurrence of many s uch features in the open ocean. Using the classical methods of homogen ization theory, it is argued that the barotropic transport near topogr aphy can come under the direct control of bottom friction. This result differs substantively from either the well-known Sverdrup constraint (which applies to a flat-bottomed ocean, or to one with a resting deep layer) or its recent extensions that allow for planar bottom topograp hic profiles. Bottom friction emerges as a controlling parameter rough ly in the event that the topography forms closed f/(H - h(b)) contours , where H - h(b) is the total fluid depth, although the theoretical mi nimum requirements are somewhat looser than this. Our analytical predi ctions are supported by numerical experimentation with a multi-layer q uasi-geostrophic model, and we examine some mean flow observations fro m the North and South Atlantic in light of the theory. In particular; the theory can rationalize the 100 Sv transport observed recently arou nd the Zapiola Drift.