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The Ekman Streamfunction: a wind-derived metric to quantify the Southern Ocean overturning circulation
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  • Kial Douglas Stewart,
  • Andrew McC. Hogg,
  • Matthew H. England,
  • Darryn W. Waugh,
  • Andrew E. Kiss
Kial Douglas Stewart
Australian National University

Corresponding Author:[email protected]

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Andrew McC. Hogg
Australian National University
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Matthew H. England
University of New South Wales
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Darryn W. Waugh
Johns Hopkins University
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Andrew E. Kiss
The Australian National University
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Abstract

We introduce a novel wind-derived metric to quantify variability in the Southern Ocean overturning circulation. This metric, which we call the Ekman streamfunction, integrates the Ekman pumping vertical velocity zonally and northwards from the Antarctic coastline to a given latitude. To evaluate the relationship between the Ekman streamfunction and Southern Ocean overturning circulation, we use a global 0.1 ocean–sea-ice model driven with interannual forcing (1958-2018). Throughout much of the Southern Ocean, strong correlations (r>0.9) exist between the Ekman streamfunction and the Southern Ocean overturning circulation on monthly and annual timescales. A regression analysis identifies regions where Ekman streamfunction variability coincides with >4Sv changes in the overturning; one such location is where the wind stress curl changes sign and the Ekman pumping velocity is highly variable. This study offers a new approach to infer recent changes in the Southern Ocean overturning circulation from existing datasets of wind stress.