A Scale‐Dependent Analysis of the Barotropic Vorticity Budget in a Global Ocean Simulation.

Autor: Khatri, Hemant1,2 (AUTHOR) hkhatri@liverpool.ac.uk, Griffies, Stephen M.2,3 (AUTHOR), Storer, Benjamin A.4 (AUTHOR), Buzzicotti, Michele5 (AUTHOR), Aluie, Hussein4,6 (AUTHOR), Sonnewald, Maike2,3 (AUTHOR), Dussin, Raphael3 (AUTHOR), Shao, Andrew7 (AUTHOR)
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Zdroj: Journal of Advances in Modeling Earth Systems. Jun2024, Vol. 16 Issue 6, p1-29. 29p.
Abstrakt: The climatological mean barotropic vorticity budget is analyzed to investigate the relative importance of surface wind stress, topography, planetary vorticity advection, 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 coarse‐grained. At length‐scales greater than 1,000 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 O(10–100) $\mathcal{O}(10\mbox{--}100)$ km in size, and the associated bottom pressure anomalies in local vorticity balances at length‐scales smaller than 1,000 km. Overall, there is a transition from the Topographic‐Nonlinear regime at scales smaller than 1,000 km to the Topographic‐Sverdrup regime at length‐scales greater than 1,000 km. 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 viscous friction generally peak. Plain Language Summary: Vorticity provides a measure of the local rotation and shear of fluid flow. The analysis of physical processes contributing to ocean vorticity has proven fundamental to our understanding of how those processes drive ocean flows, ranging from large‐scale ocean gyres to boundary currents such as the Gulf Stream, which is tens of km in width. Furthermore, a vorticity analysis can inform us about the relative importance of different physical processes in generating flow structures having different length scales. In the present work, we perform a length‐scale dependent vorticity budget analysis using a coarse‐graining method to remove signals finer than a fixed length scale. We coarse‐grain the climatological mean vorticity budget terms over a range of length scales, and then compare the relative magnitudes to identify the dominant vorticity balances as a function of length scale. We find that the spatial structure of the meridional transport is mainly controlled by atmospheric winds, variations in ocean depth and the momentum transport by ocean currents. However, the relative magnitudes of these factors change drastically at different length scales. We conclude that physical interpretations of the primary vorticity balances are fundamentally dependent on the chosen length scale of the analysis. Key Points: Relative magnitudes of barotropic vorticity budget terms display significant length‐scale dependenceBottom pressure torque and wind stress curl control the depth‐integrated meridional flow at length scales larger than 1,000 kmNonlinear advection and bottom pressure torque dominate the barotropic vorticity budget at smaller length scales [ABSTRACT FROM AUTHOR]
Databáze: GreenFILE
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