Tidal energy redistribution among vertical modes in a fluid with a mid-depth pycnocline

Bordois, Lucie; Auclair, Francis; Paci, Alexandre; Dossmann, Yvan; Gerkema, Theo; Nguyen, Cyril

doi:10.1063/1.4964759

Cited by 7 publications

(1 citation statement)

References 17 publications

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“…They thus induce vertical displacements of the isopycnal levels of several meters to a few tens of meters, observable in the thermocline (Wallace et al, 2008;Xu et al 2020). Denmann and Garett (1983) and Bordois et al (2016) point out that the stratification peak acts as a waveguide for the propagation of IT.…”

Section: Introductionmentioning

confidence: 99%

Internal tides off the Amazon shelf Part I : importance for the structuring of ocean temperature during two contrasted seasons

Assene

Koch-Larrouy

Dadou

et al. 2023

Preprint

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Abstract. Tides and internal tides (IT) in the ocean can significantly affect local to regional ocean temperature, including sea surface temperature (SST), via physical processes such as diffusion (vertical mixing) and advection (vertical and horizontal) of water masses. Offshore of the Amazon River, strong IT have been detected by satellite observations and well modelled ; however, their impact on temperature, SST and the identification of the associated processes have not been studied so far. In this work, we use high resolution (1/36°) numerical simulations with and without the tides from an ocean circulation model (NEMO). This model explicitly resolves the internal tides (IT) and is therefore suitable to assess how they can affect ocean temperature in the studied area. We distinguish the analysis for two contrasted seasons, from April to June (AMJ) and from August to October (ASO), since the seasonal stratification off the Amazon River modulates the IT’s response and their influence in temperature. The generation and the propagation of the IT in the model are in good agreement with observations. The SST reproduced by the simulation including tides is in better agreement with satellite SST data compared to the simulation without tides. During ASO season, stronger meso-scale currents, deeper and weaker pycnocline are observed in contrast to the AMJ season. The observed coastal upwelling during ASO season is better reproduced by the model including tides, whereas the no-tide simulation is too warm by +0.3 °C for the SST. In the subsurface above the thermocline, the tide simulation is cooler by −1.2 °C, and warmer below the thermocline by +1.2 °C compared to the simulation without the tides. The IT induce vertical mixing on their generation site along the shelf break and on their propagation pathways towards the open ocean. This process mainly explains the cooler temperature at the ocean surface and is combined with vertical and horizontal advection to explain the cooling in the subsurface water above the thermocline and a warming in the deeper layers below the thermocline. The surface cooling induced in turn an increase of the net heat flux from the atmosphere to the ocean surface, which could induce significant changes in the local and even for the regional tropical Atlantic atmospheric circulation and precipitation. We therefore demonstrate that IT, via vertical mixing and advection along their propagation pathways, and tides over the continental shelf, can play a role on the temperature structure off the Amazon River mouth, particularly in the coastal cooling enhanced by the IT. Keywords: internal tides, Amazon continental shelf and slope, temperature, modeling, satellite data, mixing, heat flux.

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Section: Introductionmentioning

confidence: 99%

Internal tides off the Amazon shelf Part I : importance for the structuring of ocean temperature during two contrasted seasons

Assene

Koch-Larrouy

Dadou

et al. 2023

Preprint

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Nonlinear processes generated by supercritical tidal flow in shallow straits

et al. 2017

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Numerical experiments have been carried out using a nonhydrostatic and non-Boussinesq regional oceanic circulation model to investigate the nonlinear processes generated by supercritical tidal flow in shallow straits. Our approach relies on idealized direct numerical simulations inspired by oceanic observations. By analyzing a large set of simulations, a regime diagram is proposed for the nonlinear processes generated in the lee of these straits. The results show that the topography shape of the strait plays a crucial role in the formation of internal solitary waves (ISWs) and in the occurrence of local breaking events. Both of these nonlinear processes are important turbulence producing phenomena. The topographic control, observed in mode 1 ISW formation in previous studies [Y. Dossmann, F. Auclair, and A. Paci, “Topographically induced internal solitary waves in a pycnocline: Primary generation and topographic control,” Phys. Fluids 25, 066601 (2013) and Y. Dossmann et al., “Topographically induced internal solitary waves in a pycnocline: Ultrasonic probes and stereo-correlation measurements,” Phys. Fluids 26, 056601 (2014)], is clearly reproducible for mode-2 ISW above shallow straits. Strong plunging breaking events are observed above “narrow” straits (straits with a width less than mode 1 wavelength) when the fluid velocity exceeds the local mode 1 wave speed. These results are a step towards future works on vertical mixing quantification and localization around complex strait areas.

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Transformation of mode-2 internal solitary wave over a pseudo slope-shelf

et al. 2017

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Numerical simulations are performed to investigate the effect of wave amplitude in a numerical wave tank on the evolution of a convex mode-2 internal solitary wave (ISW) propagating over a pseudo slope-shelf. A finite volume method based on a Cartesian grid system is adopted to solve the Navier-Stokes equations using Improved Delayed Detached Eddy Simulation model for the turbulent closure. Numerical results reveal three types of waveform during wave generation on the flat bottom: (1) pseudo vortex shedding in the case of very large initial amplitude; (2) PacMan phenomenon in large amplitude; and (3) smooth mode-2 ISW for small amplitude. During wave propagation on the plateau, the first type of waveform induces a quasi-elevated mode-1 ISW; the second generates chaotic internal waves with significant reduction in amplitude; while the third renders a slightly deformed mode-2 ISW across the plateau. Moreover, the decrease in the magnitude of leading trough is more intense than that in the leading crest due to strong wave-obstacle interaction in the case of very large initial wave amplitude.

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Tidal energy redistribution among vertical modes in a fluid with a mid-depth pycnocline

Cited by 7 publications

References 17 publications

Internal tides off the Amazon shelf Part I : importance for the structuring of ocean temperature during two contrasted seasons

Internal tides off the Amazon shelf Part I : importance for the structuring of ocean temperature during two contrasted seasons

Nonlinear processes generated by supercritical tidal flow in shallow straits

Transformation of mode-2 internal solitary wave over a pseudo slope-shelf

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