Internal Tidal Modal Ray Refraction and Energy Ducting in Baroclinic Gulf Stream Currents

Duda, Timothy F.; Lin, Ying‐Tsong; Buijsman, Maarten C.; Newhall, Arthur E.

doi:10.1175/jpo-d-18-0031.1

Cited by 40 publications

(43 citation statements)

References 74 publications

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“…The ITW' generation is impacted by the stratification changes due to radiative forcing or ocean circulation changes and by the variability of the barotropic tidal forcing. The ITs' propagation pathway is also impacted by such stratification modifications as well as circulation processes such as geostrophic currents (e.i Pereira et al, 2007 for realistic approach ; e.i Chuang and Wang, 1981 for idealized approach) and eddies (e.i Duda et al, 2018 for realistic approach ; e.i Ponte and Klein, 2015 for idealized approach) that directly interact with the ITs. With the increase in the altimetric time series, global maps of the stationary ITs' surface elevation amplitude become more precise (Carrere et al, 2004;Ray and Zaron, 2016;Zaron, 2019;Zhao et al, 2019;Carrere et al, 2021).…”

Section: Internal Tides Issues For Altimetrymentioning

confidence: 99%

The dependency of internal tides on background stratification variability: a case study on the Amazon shelf and the Bay of Biscay

Barbot

Lyard

Tchilibou

et al. 2021

Preprint

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Abstract. The forthcoming SWOT altimetric mission aims to access the smaller mesoscale oceanic circulation with an unprecedented spatial resolution and swath. The repetitivity of the mission orbit implies that high frequency processes, such as the internal tides (ITs), are under-sampled in time and their full temporal evolution is not observed. They are therefore aliased onto lower frequencies and possibly mixed into the mesoscale signals. As with the barotropic tides, the ITs must be corrected from the altimetric observations in order to access to the smaller mesoscales. But unlike barotropic tides, ITs are not completely stationary and have significant temporal variability due to their interactions with the ocean circulation and the stratification variability. ITs prediction, correction and error calculation requires a precise understanding of the ITs' surface elevation signature and its temporal variability. Stratification changes impact both on the generation and the propagation of ITs. This present study proposes to quantify the impacts of the background stratification variations alone with a classification of the observed stratification and an idealized modelling of the ITs. A single methodology is developed to handle a very broad range of stratification variability. The classification is made using clustering methods and the modelling uses the frequency domain model T-UGO. The methodology is successfully tested on the Amazon shelf and in the Bay of Biscay. For the Amazon shelf, the pycnocline depth linearly impacts on the amplitudes and wavelengths of the ITs first two modes. An increase of the pycnocline depth increases the total ITs' amplitude but also transfers the energy from the mode 2 to the mode 1. An increase of the pycnocline depth also increases the wavelengths of both modes 1 and 2. In the Bay of Biscay we found no such proxy to describe the changes in ITs' characteristics so a seasonal climatology is explored. The seasonality of the stratification strongly affects the amplitudes of modes 2 and 3 and significantly impacts on the surface elevation of ITs. Whereas the wavelengths of all modes and the amplitude of mode 1 are only weakly affected by the stratification seasonality. The amplitude variability of modes 2 and 3 also modifies the ratio between the modes in presence and makes the horizontal scales of ITs variable. The significance of the ITs wavelength modifications with stratification changes suggests that a more accurate ITs' surface elevation correction for SWOT measurements should take into account this stratification variability.

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Section: Internal Tides Issues For Altimetrymentioning

confidence: 99%

The dependency of internal tides on background stratification variability: a case study on the Amazon shelf and the Bay of Biscay

Barbot

Lyard

Tchilibou

et al. 2021

Preprint

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“…Rainville & Pinkel 2006; Duda et al. 2018), mooring observations (e.g. Huang et al.…”

Section: Introductionmentioning

confidence: 99%

Interactions of internal tides with a heterogeneous and rotational ocean

2021

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“…Interactions between internal tides and slowly evolving (i.e., quasigeostrophic) background flows can dephase internal tides from the equilibrium tide, and the estimated global distribution of nonstationary tides suggests this process is important. Mesoscale eddies can alter the propagation of low-mode internal waves (Rainville and Pinkel 2006;Park and Watts 2006;Dunphy and Lamb 2014;Ponte et al 2015;Dunphy et al 2017;Duda et al 2018) and semidiurnal tides are largely nonstationary along the equator and in western boundary currents (Buijsman et al 2017;Zaron 2017;Savage et al 2017a). While several studies have examined the temporal variability of tidal nonstationarity (Zaron and Egbert 2014;Buijsman et al 2017) and the local correlation between tidal nonstationarity and the strength of the mesoscale field (Pickering et al 2015), little is known about the dominant horizontal scales of the background flows in these interactions, or whether these interactions merely redirect/refract the internal tides, or actively dissipate and/or scatter them to higher modes.…”

Section: Introductionmentioning

confidence: 99%

Internal Tide Nonstationarity and Wave–Mesoscale Interactions in the Tasman Sea

Savage

Waterhouse

Kelly

2020

Journal of Physical Oceanography

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Internal tides, generated by barotropic tides flowing over rough topography, are a primary source of energy into the internal wavefield. As internal tides propagate away from generation sites, they can dephase from the equilibrium tide, becoming nonstationary. Here, we examine how low-frequency quasigeostrophic background flows scatter and dephase internal tides in the Tasman Sea. We demonstrate that a semi-idealized internal-tide model (the Coupled-mode Shallow Water Model; CSW) must include two background-flow effects to replicate the in-situ internal-tide energy fluxes observed during the Tasmanian Internal-Tide Beam Experiment (TBeam). The first effect is internal-tide advection by the background flow, which strongly depends on the spatial scale of the background flow, and is largest at the smaller scales resolved in the background-flow model (i.e., 50-400 km). Internal-tide advection is also shown to scatter internal-tides from vertical mode-1 to mode-2 at a rate of about 1 mW m−2. The second effect is internal-tide refraction due to background-flow perturbations to the mode-1 eigenspeed. This effect primarily dephases the internal-tide, attenuating stationary energy at a rate of up to 5 mW m−2. Detailed analysis of the stationary internal-tide momentum and energy balances indicate that background-flow effects on the stationary internal tide can be accurately parameterized using an eddy diffusivity derived from a 1D random walk model. In summary, the results identify an efficient way to model the stationary internal tide and quantify its loss of stationarity.

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Internal Tidal Modal Ray Refraction and Energy Ducting in Baroclinic Gulf Stream Currents

Cited by 40 publications

References 74 publications

The dependency of internal tides on background stratification variability: a case study on the Amazon shelf and the Bay of Biscay

The dependency of internal tides on background stratification variability: a case study on the Amazon shelf and the Bay of Biscay

Interactions of internal tides with a heterogeneous and rotational ocean

Internal Tide Nonstationarity and Wave–Mesoscale Interactions in the Tasman Sea

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