Jet-topography Effects on Horizontal Eddy Mixing in the Southern Ocean

Thursday, 18 December 2014
Alice Barthel1, Stephanie Waterman1,2 and Andrew Hogg3, (1)University of New South Wales, Climate Change Research Centre & ARC Centre of Excellence for Climate System Science, Sydney, Australia, (2)University of British Columbia, Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, (3)Research School of Earth Sciences & ARC Centre of Excellence for Climate System Science, Australian National University, Canberra, Australia
The Southern Ocean is a region of strong eastward jet flows and intense eddy activity. Studies suggest that topography plays an important role in steering these jets and setting the location of enhanced eddy activity, which has important implications for the meridional transport of tracers such as heat and nutrients across the jets. We have yet to identify the dominant processes and factors that set the intensity and distribution of eddy activity and the horizontal eddy mixing in the vicinity of topography. Understanding the physical processes governing these eddy effects will reveal the dependence of eddy mixing on key parameters, allowing prediction of future changes and development of physically-based eddy parameterizations.

We report on a theoretical study that investigates the effects of jet-topography interactions on jet-eddy dynamics and the mixing of tracers. We use a quasigeostrophic model of a zonally-evolving unstable jet impinging on topography in a configuration relevant to an Antarctic Circumpolar Current frontal jet. We examine the spatial patterns of surface eddy kinetic energy and irreversible mixing of tracers relative to the topography and the zonally-evolving jet structure. We explore their dependence on system parameters such as topography height, stratification and inflowing jet stability.

This study highlights the changes in eddy effects caused by the introduction of topography, with a particular focus on the along-stream variations. It also suggests the influence of topography is not necessarily limited to the downstream region. This study will help improve our understanding of the mechanisms underlying jet-eddy-topography interactions and their representation in ocean models.