| Abstrakt: |
Vertical two‐dimensional numerical experiments incorporating Garrett‐Munk (GM) internal waves are conducted to investigate tide‐induced near‐field mixing over a finite‐amplitude sinusoidal seafloor, conventionally attributed to the breaking of high‐wavenumber internal tidal waves. Turbulent mixing is characterized by tidal excursion parameter (Te) and topographic steepness parameter (Sp) measuring tidal current strength and seafloor slope gradient, respectively. Under strong tidal currents (Te > 1), high‐wavenumber internal lee waves propagate upward from the seafloor. Even when Te and Sp are set to produce nearly the same upward energy flux, the vertical profile of mixing hotspots varies with Sp. For Sp≳ $\mathit{\gtrsim }$ 0.2, near‐inertial currents above the seafloor rapidly amplify by absorbing energy of internal lee waves from below, hindering their upward propagation and creating "short mixing hotspots." For Sp < 0.2, these near‐inertial currents diminish, allowing internal lee waves to propagate upward and interact with the GM background internal waves, creating "tall mixing hotspots." Plain Language Summary: We perform numerical experiments to study how tidal currents cause mixing in the ocean near a rough seafloor. By considering the interaction between strong tidal currents and small‐scale rough seafloor features, we find that high‐frequency internal waves, different from those previously thought, propagate rapidly upward from the seafloor and interact with background waves, causing mixing above the seafloor. The pattern of this mixing changes with the steepness of the seafloor slope. If the seafloor slope is steep, the currents near the seafloor quickly absorb the energy of the upward‐propagating waves, creating a mixing region confined to the seafloor (short mixing hotspot). In contrast, if the seafloor slope is gentle, less energy is absorbed, allowing the upward‐propagating waves to travel higher and interact with background waves, creating a mixing region extending from the seafloor (tall mixing hotspot). These mixing processes have been overlooked due to limited knowledge of seafloor details. However, they are crucial because tall mixing hotspots can significantly affect global ocean circulation. Therefore, they deserve more attention in future studies. Key Points: Strong tidal flows over rough seafloors induce internal lee waves that propagate upward while inducing mixing near the seafloorOver steep seafloors, inertial currents inhibit the upward propagation of internal lee waves, creating short mixing hotspotsOver less steep seafloors, the lack of inertial currents allows internal lee waves to propagate upward, creating tall mixing hotspots [ABSTRACT FROM AUTHOR] |
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