Introduction

There is accumulating evidence, some of it described in Sections 1.9 and 7.5, that rough topography is an important factor in ocean mixing. In many of the theoretical and laboratory investigations of its effect on mixing, topography is represented by very simplified geometry such as a sinusoidal ‘roughness’ or the smooth slopes of Chapter 11. In reality the floor of the ocean in many regions is very irregular, and often not known to the resolution required for prediction of its effect on the dynamics of the overlying flow. It is nevertheless possible to identify some generic features of topography and to characterize the flow in their vicinity. The further step of parametrizing turbulence and its dissipation in terms of some gross measures of topography is incomplete but one receiving considerable attention. For that reason, whilst this chapter will review some of what is known of the effects of topography, it falls well short of describing the consequent turbulence in terms that can be applied to obtain reliable quantitative estimates of dissipation rates in ocean basins.

Headlands, promontories and curved coastlines

Flow past headlands often results in eddies being formed on the lee side. D'Asaro (1988), for example, suggests that of eddy shedding around promontories in the Beaufort Gyre region of the Arctic is a source of sub-mesoscale anticyclonic vortices. Eddy shedding is not, however, inevitable.