The Influence of Potential Vorticity Sheet at Mixed Layer Base on the Surface Transfer Function
ID：161
Oral Presentation
2027-01-13 09:30 （China Standard Time）
Session：Session 38 - Oceanic (Sub)mesoscale Processes and Their Climate Impacts
Abstract
At the base of the mixed layer (MLB), a sharp stratification jump gives rise to a potential vorticity (PV) sheet. In this study, we theoretically investigate how the flow induced by this PV sheet modifies the total transfer function (a kernel that maps sea surface buoyancy to streamfunction) with the surface quasi-geostrophic (SQG) flow. We construct an idealized stratification profile that captures key features of the real ocean: a constant stratification in the mixed layer overlying an exponentially decaying stratification in the interior. Using this configuration, we derive the transfer functions of both the SQG and MLB PV sheets, and examine their sensitivity to stratification parameters. When both contributions are considered, the MLB-induced flow opposes the SQG flow, weakening the magnitude and flattening the spectral slope of the transfer function. This effect is scale-dependent and weakens towards smaller scales. The scale-dependent vertical structures of both flow components are further examined. Finally, we validate our theoretical predictions using realistic ocean reanalysis data, confirming that incorporating the MLB PV sheet significantly improves the reconstruction of the sea-surface transfer function. These results highlight the dynamical importance of the MLB PV sheet in upper‑ocean flows and provide a useful extension to classical SQG theory for reconstructing surface currents.
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Jan 12–15
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