Wind-Driven Flow over Topography in a Zonal β-Plane Channel: A Quasi-geostrophic Model of the Antarctic Circumpolar Current

Abstract

The paper gives a detailed account of the dynamical balance of a wind-driven zonally unbounded flow over topography. The problem is investigated with a quasi-geostrophic β-plane channel with two layers and eddy resolution. The channel has a width of 1500 km and a zonal periodicity of 4000 km. Apart from the dimensions, the model structure is similar to the one used by McWilliams et al. The experiments with this model address the problem of the relative role of transient and standing eddies as well as bottom friction and topographic form stress in the balance of a current driven by a steady surface windstress. The response of the system is investigated for different values of the friction parameter and various locations of topographic obstacles in the bottom layer of the channel. The principal momentum balance emerging from these experiments supports the concept of Munk and Palmén for the dynamics of the Antarctic Circumpolar Current, which proposes that the momentum input by windstress is transferred to the deep ocean—where it leaves the system activity—where it leaves the system by topographic form stress. Frictional effects in the balance of the circumpolar flow may thus be of minor importance. This concept of the momentum balance is confirmed in simulations over more complex topographies. Here we have taken two differently scaled versions of the highly resolved bottom relief in the Macquarie Ridge area. The flow in these simulations is virtually frictionless in the momentum balance. The flow pattern reflects some features of the Circumpolar Current in this areas.