Surface reflection of bottom generated oceanic lee waves

Baker, Lois; Mashayek, Ali

doi:10.1017/jfm.2021.627

Cited by 19 publications

(43 citation statements)

References 59 publications

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“…Mean flows in this region are unlikely to be barotropic as some deep flows are believed to be driven by bottom trapped Rossby waves. Mean flows shear in the deep ocean can have an impact on the wave radiation and dissipation (Baker & Mashayek, 2021; Kunze & Lien, 2019), and hence potentially influence the horizontal extent of the advected internal waves and turbulence. Finally, as discussed above, our numerical simulations have no barotropic tides and hence no internal tide generation that can lead to additional wave energy and hence stronger high‐frequency flow response in this region.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Tides have also been shown to suppress lee wave generation (Shakespeare, 2020). Among these mechanisms, idealized numerical simulations and theory (Baker & Mashayek, 2021; Shakespeare et al., 2021; K. Zheng & Nikurashin, 2019) show that lee wave energy generated at rough topography may not only propagate upward and dissipate locally within the water column above topography, but also get swept downstream by the background flow, reflect from the upper boundary, and dissipate remotely. K. Zheng and Nikurashin (2019) estimate that more than 50% of the generated energy is advected downstream and dissipates 20–30 km away from the wave generation site.…”

Section: Introductionmentioning

confidence: 99%

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Non‐Local Energy Dissipation of Lee Waves and Turbulence in the South China Sea

2022

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Breaking of internal lee waves has been shown to drive enhanced turbulence and mixing in regions where strong bottom flows interact with rough topography. However, theoretical predictions for the energy conversion from the bottom flows into lee waves differ from the corresponding turbulent energy dissipation rates observed locally at the wave generation sites. Recent idealized numerical simulations suggest that the discrepancy may be attributed to non‐local wave breaking and dissipation effects: when a mean flow impinges on rough topography and generates lee waves and turbulence, a significant fraction of the generated energy gets advected downstream of the generation site and dissipates remotely. Here, we present a case study for the non‐local lee wave energy dissipation in the South China Sea by using a combination of in situ mooring observations of the bottom flow interacting with two topographic features and corresponding numerical simulations. The results show that most of the near‐inertial and high‐frequency response observed at the mooring site is not locally generated, but rather is produced by the interaction of the subinertial flow with the topographic feature upstream. The wave and turbulent energy detected at the mooring site can be enhanced by an order of magnitude compared to the energy of the locally generated motions. The simulations confirm that up to 70% of the enhanced energy is advected into the region by the subinertial flow, while the rest is radiated into the region as waves. Implication of our results for mixing observations and ocean model parameterizations are discussed.

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Section: Summary and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Non‐Local Energy Dissipation of Lee Waves and Turbulence in the South China Sea

2022

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“…In interpreting our results, caution is advised as turbulent mixing is not only caused by breaking lee waves; for example, downward‐propagating near‐inertial internal waves breaking near the pycnocline can also enhance turbulent dissipation (Meyer et al., 2015). Also, waves generated upstream can travel horizontally (Baker & Mashayek, 2021) or can be advected by the geostrophic flow (Waterman et al., 2014, 2021) and dissipate downstream of topography (Zheng & Nikurashin, 2019), therefore breaking the assumption that lee‐wave energy dissipates locally. Advection by the flow and remote dissipation are more likely to occur in and north of the Polar Front where the strongest flows are found.…”

Section: A Simple Energy Budgetmentioning

confidence: 99%

Turbulent Mixing and Lee‐Wave Radiation in Drake Passage: Sensitivity to Topography

et al. 2022

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Radiation and breaking of internal lee waves are thought to play a significant role in the energy and heat budget of the Southern Ocean. Open questions remain, however, regarding the amount of energy converted from the deep flows of the Antarctic Circumpolar Current (ACC) into lee waves and how much of this energy dissipates locally. This study estimated the linear lee‐wave energy radiation using a unique 4‐year time series of stratification and near‐bottom currents from an array of Current and Pressure measuring Inverted Echo Sounders (CPIES) spanning Drake Passage. Lee‐wave energy was calculated from two 2D anisotropic and one 1D isotropic abyssal hill topographies. Lee‐wave energy radiation from all three topographies was largest in the Polar Front Zone associated with strong deep meandering of the ACC fronts. Both baroclinic and barotropic instabilities appeared to modulate the conversion to lee waves in the Polar Front Zone. Fine structure temperature, salinity, and velocity profiles at the CPIES locations were used to estimate turbulent dissipation due to breaking internal waves by employing a finescale parameterization. High dissipation near the bottom was consistent with upward‐propagating, high‐frequency lee waves as found by earlier studies. In contrast to idealized numerical predictions of 50% local dissipation of lee‐wave energy, this study found less than 10% dissipated locally similar to some other studies. Improving the representation of the abyssal hills by accounting for anisotropy did not reduce the discrepancy between radiated lee‐wave energy and local dissipation. Instead, alternative fates must be considered for the excess radiated lee‐wave energy.

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“…Their model reproduced the surface signature of the waves and was in qualitative agreement with satellite observations. Baker and Mashayek (2021) show a comparable striped vertical velocity pattern around the Drake Passage that motivates the development of a linear theory focused on lee wave generation. The structures observed in their simulations agree qualitatively with their theoretical predictions, although the simplifications made in their theory limit the applicability of their results to the real ocean, where the interaction of lee waves with other processes (e.g., internal tides) has shown to be relevant (Shakespeare, 2020).…”

Section: Summary and Discussionmentioning

confidence: 90%

“…This is a common process in strong currents flowing along sharp bathymetric slopes and interacting with a topographic obstacle. In addition to the generation of lee gravity waves (Baker & Mashayek, 2021; De Marez et al., 2020), barotropic and centrifugal instabilities develop, generating submesoscale vortices and turbulence (Wenegrat & Thomas, 2020). The subsequent current separation leads to offshore injection of potential vorticity generated by enhanced horizontal shear against the slope.…”

Section: Introductionmentioning

confidence: 99%

Coherent Lagrangian Pathways Near an East Alboran Front

Capó

McWilliams

2022

JGR Oceans

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In the eastern Alboran Sea, frontogenesis (FG) is a dominant process for fronts extending from the Spanish coast toward the basin interior, promoting large vertical displacements that connect the surface mixed layer with the oceanic interior. Using a realistic, high‐resolution model simulation for this region, we conduct the offline advection of virtual water parcels released near the surface during a 2‐day episode of intense FG. Three‐dimensional trajectories exhibit high variability depending on the release location, and some large, rapid vertical displacements are induced by different coherent submesoscale flow patterns and by interactions among them: Ageostrophic secondary circulation associated with strain‐ and mixing‐induced FG and internal waves generated by currents over topography. These deep displacements mostly are irreversible, at least on a short time scale, because of the rapidly changing flow patterns. Significant diapycnal mixing and density changes occur along trajectories as they pass through the surface and bottom boundary layers. While we expect these processes to be typical for this region, the computational expense of such a Lagrangian analysis and the complexity of its outcome present a considerable challenge for more comprehensive assessments.

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Surface reflection of bottom generated oceanic lee waves

Abstract: Abstract

Cited by 19 publications

References 59 publications

Non‐Local Energy Dissipation of Lee Waves and Turbulence in the South China Sea

Non‐Local Energy Dissipation of Lee Waves and Turbulence in the South China Sea

Turbulent Mixing and Lee‐Wave Radiation in Drake Passage: Sensitivity to Topography

Coherent Lagrangian Pathways Near an East Alboran Front

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