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Abstract:
Changes in the climate system over recent decades have modified the wind stress driving the Southern Ocean circulation, thus modifying the very energetic mesoscale eddy field at the latitudes of the Antarctic Circumpolar Current (ACC). Past studies have mainly focussed on the temporal variations of eddy kinetic energy (EKE). Here, we analyze the regional patterns and temporal evolution of the ACC mesoscale eddy field over the past 60 years, investigating the role of the ocean-atmosphere coupling (in the form of absolute vs. relative winds in the momentum equation). A set of global ocean model experiments containing a nested 0.1 resolution ACC domain is analyzed. The eddy statistics, computed with an eddy detection and tracking algorithm based on the Okubo-Weiss parameter, shows good consistency with satellite-based estimates. The temporal evolution of the eddy statistics is driven to a large extent by the sustained strengthening of the Southern Hemisphere westerly winds, gradually shifting towards smaller and more energetic eddies since the 1970s. The trend in the amplitude is related with the sustained increase in wind work and vertical shear of the ACC, and is correlated to the changes in EKE, both spatially and temporally. Likewise, the more energetic model with absolute winds exhibits smaller and more energetic mesoscale eddies. These results suggest that the ocean-atmosphere coupling and resulting ocean density structure significantly affect the mean and temporal evolution of the mesoscale eddy field properties.
