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A scale-dependent analysis of the barotropic vorticity budget in a global ocean simulation
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  • Hemant Khatri,
  • Stephen M Griffies,
  • Benjamin A Storer,
  • Michele Buzzicotti,
  • Hussein Aluie,
  • Maike Sonnewald,
  • Raphael Dussin,
  • Andrew E. Shao
Hemant Khatri
University of Liverpool

Corresponding Author:[email protected]

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Stephen M Griffies
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Benjamin A Storer
University of Rochester
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Michele Buzzicotti
University of Rome Tor Vergata
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Hussein Aluie
University of Rochester
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Maike Sonnewald
Princeton University
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Raphael Dussin
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Andrew E. Shao
Canadian Centre for Climate Modelling and Analysis
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The climatological mean barotropic vorticity budget is analyzed to investigate the relative importance of surface wind stress, topography and nonlinear advection in dynamical balances in a global ocean simulation. In addition to a pronounced regional variability in vorticity balances, the relative magnitudes of vorticity budget terms strongly depend on the length-scale of interest. To carry out a length-scale dependent vorticity analysis in different ocean basins, vorticity budget terms are spatially filtered by employing the coarse-graining technique. At length-scales greater than 10o (or roughly 1000 km), the dynamics closely follow the Topographic-Sverdrup balance in which bottom pressure torque, surface wind stress curl and planetary vorticity advection terms are in balance. In contrast, when including all length-scales resolved by the model, bottom pressure torque and nonlinear advection terms dominate the vorticity budget (Topographic-Nonlinear balance), which suggests a prominent role of oceanic eddies, which are of Ο(10-100) km in size, and the associated bottom pressure anomalies in local vorticity balances at length-scales smaller than 1000 km. Overall, there is a transition from the Topographic-Nonlinear regime at scales smaller than 10o to the Topographic-Sverdrup regime at length-scales greater than 10o. These dynamical balances hold across all ocean basins; however, interpretations of the dominant vorticity balances depend on the level of spatial filtering or the effective model resolution. On the other hand, the contribution of bottom and lateral friction terms in the barotropic vorticity budget remains small and is significant only near sea-land boundaries, where bottom stress and horizontal friction generally peak.