Abstract
AbstractThe contribution of small‐scale abyssal hill topography to the topographic form stress and local dynamics of the Southern Ocean is investigated using a high‐resolution model of the sector of the Southern Ocean south of Tasmania and New Zealand. The results of two simulations, with and without small, O(1–100 km), scale topography, confirm that the effects of small‐scale topography are exerted through the generation of strong topographic form stress leading to transient eddy dissipation and changes in flow meanders. Small‐scale topographic form stress is comparable in magnitude to that generated by large‐scale topography, but with a pairwise distribution of positive and negative stress values upstream and downstream of the Macquarie Ridge, consistent with the meandering of the flow. In the experiment without small‐scale topography, the bottom mean flow speed increases, while the surface mean speed slightly decreases, making the mean flow more barotropic. Eddy kinetic energy also greatly enhances throughout the water column after removing small‐scale topography. Our results suggest that small‐scale topography has strong impact on transient eddies and plays an important role for setting the vertical structure of the flow and the equilibration and position of flow meanders.
Highlights
The absence of the latitudinal boundaries and vigorous westerly winds in the Southern Ocean allow the formation of the Antarctic Circumpolar Current (ACC)
O(1–100 km), scale abyssal hill topography has been suggested by theoretical studies and idealized numerical models to play an important role in the dynamical balance of the ACC and the ocean circulation through the generation of internal waves, topographic wakes, and other low‐level nonlinear motions
We carry out fine‐resolution regional simulations, and our results show that small‐scale topography makes a significant contribution to the topographic form stress (TFS) and impacts both time‐mean and time‐varying flows in the Southern Ocean
Summary
The absence of the latitudinal boundaries and vigorous westerly winds in the Southern Ocean allow the formation of the Antarctic Circumpolar Current (ACC). It is pivotal in the ocean circulation, providing an inter‐basin connection between the major oceans and permitting the advent of a global overturning circulation. McWilliams et al (1978) found that the transport of the ACC decreased to a value comparable with observations when the two‐layer quasi‐geostrophic model they used included topographic obstacles This revealed that instead of friction near the bottom, it is the TFS that removes the momentum input by wind, confirming the validity of the momentum balance mechanism proposed by Munk and Palmén (1951). Similar results were later obtained by other numerical experiments including quasi‐geostrophic models (Marshall et al, 1993; Wolff et al, 1991) and the Fine Resolution Antarctic Model (FRAM) (Ivchenko & Stevens, 1995; Ivchenko et al, 1996; Killworth & Nanneh, 1994)
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