Observations of the Low‐Mode Internal Tide and Its Interaction With Mesoscale Flow South of the Azores

Löb, Jonas; Köhler, Janna; Mertens, Christian; Walter, Maren; Zhu-hua, LI; Storch, Jin‐Song von; Zhao, Zhenwei; Rhein, Monika

doi:10.1029/2019jc015879

Cited by 15 publications

(15 citation statements)

References 65 publications

(156 reference statements)

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“…Kerry et al (2014) demonstrated that the location of eddies influenced the spatial pattern of IT propagation near the Luzon Strait. Löb et al (2020) observed a decrease in the energy flux of internal tides by approximately one-third when eddies interacted with internal tides; a decrease in the coherent part of the energy flux in the first two modes supported the hypothesis that wave-eddy interactions increased the incoherent part of the energy flux and transferred energy from low modes into higher modes, consequently leading to increased local dissipation. Huang et al (2018) showed a variety of mode-1 SIT modulations by an anticyclonic eddy and cyclonic eddy pair in the northern South China Sea, such as variations in the propagation speed of mode-1 SIT, leading to wave crest rotations and energy refraction, and an intensified mode-2 SIT was said to be transferred from mode-1 SIT through eddy-wave interactions.…”

Section: Introductionsupporting

confidence: 57%

Vertical structural variability of diurnal internal tides inside a mesoscale anticyclonic eddy based on single virtual-moored Slocum glider observations

Lim

Park

2022

Front. Mar. Sci.

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The vertical structural variability of the diurnal internal tide (DIT) with a mode-1 wavelength of ~420 km inside a mesoscale baroclinic anticyclonic eddy was examined based on observations by a single virtual-moored (VM) Slocum glider. During the glider observational period from 10 to 19 September 2018, the eddy traveled northward at approximately 50 km, allowing the glider to scan a cross section of 50 km wide and 800 m deep inside the eddy. VM observations showed that DIT experienced a noticeable vertical structural variability near the eddy center. In a range of 30 km horizontally from the eddy center (inner center), DIT’s vertical displacements were significantly intensified in the 400–800-m depth below the eddy. In the range of 30–50 km from the eddy center (outer center), DIT was almost uniformly distributed from the surface to 800-m depth. Owing to the spatiotemporally restricted dataset by the glider, the significance of DIT’s modulation observed inside the eddy can be questionable. As a result of comparing DIT’s vertical structural variability in two domains in terms of available potential energy (APE) and horizontal kinetic energy (HKE) using CTDs inside the eddy and ADCPs outside the eddy, DIT’s vertical structure inside the eddy was significantly distinguished from that outside the eddy. The relative vorticity inside the eddy was estimated based on the satellite dataset; it was negatively great in the inner center (approximately 0.35 – 0.25f) and small in the outer center (approximately 0.2 – 0.1f). These observational behaviors indicate a close relationship between them; the vorticity-dependent modulation of the DIT seems to be observationally confirmed inside the eddy. Further, in order to examine the energy transferring behavior in low vertical modes, a wavenumber spectral analysis was performed on the DIT displacements and the lowest four wavenumbers, Kz (1) through Kz (4), showed a similar behavior to those observed in DIT’s vertical structural variability inside of the eddy; the relative power of the sum of Kz (2) ~ Kz (4) with respect to Kz (1) was strong in the inner center and weakened in the outer center. These results seem to support that the wave–eddy interaction is non-uniform inside the eddy and partially depends on the relative vorticity.

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Section: Introductionsupporting

confidence: 57%

Vertical structural variability of diurnal internal tides inside a mesoscale anticyclonic eddy based on single virtual-moored Slocum glider observations

Lim

Park

2022

Front. Mar. Sci.

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“…As low-mode ITs propagate through the ocean, the background mesoscale eddy field can modulate, inhomogenize and scatter the waves. This process by which a tidal wave field can become incoherent due to scattering by balanced flow and the energetics associated with the process has been investigated based on in situ measurements, satellite altimeter datasets and numerical simulations [98,99,[102][103][104][105][106][107][108][109]. These studies reveal that only a small fraction of low mode tidal energy, typically less than 5% wave energy, is lost to higher baroclinic wave modes in the low Rossby number regime as the wave propagates O(100-1000) km.…”

Section: (A) Low Mode Internal Tidesmentioning

confidence: 99%

“…[44,117,[144][145][146]182]. Furthermore, some features of wave-balance interactions, such as trapping of NIWs in anticyclonic mesoscale eddies [132,[134][135][136] and scattering and loss of coherence of ITs by mesoscale eddies [98,99,102,104,106,107] can be obtained from observational datasets. Theoretical and numerical investigations can choose relevant regimes based on observations and can cross check their results qualitatively with some selected features observed in the ocean.…”

Section: Challenges In Quantifying Wave-balance Energy Exchanges From...mentioning

confidence: 99%

Turbulent wave-balance exchanges in the ocean

Thomas

2023

Proc. R. Soc. A.

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Oceanic flows are turbulent and multi-scale in nature, and are composed of fast internal waves and slowly evolving balanced eddies. Contrary to conventional wisdom in physical oceanography, the past two decades of in situ , satellite altimeter and realistically forced global scale ocean model outputs have revealed that internal gravity waves can have comparable or higher energy levels than geostrophically balanced flows at 10–100 km scales in different parts of the world’s oceans. These relatively recent findings have fuelled a wide range of research activities aimed at understanding how fast internal gravity waves interact with slowly evolving balanced flows, particularly with the goal of deducing whether internal waves can form an energy sink for oceanic balanced flows. In this paper, we comprehensively review theoretical, numerical and observational investigations undertaken to study internal wave-balance flow exchanges. Theoretical calculations, inspired by different wave-balance regimes seen in observational and global ocean model outputs, are used to point out that internal waves can affect balanced flow dynamics. The theoretical results are followed up by a detailed discussion of numerical results on wave-balance interactions in a broad set of parameter regimes. The numerical results reveal how different kinds of waves exchange energy with balance flow, affect energy flux across scales of balanced flow and facilitate the generation of small-scale dissipative balanced flow structures. The numerical simulation results and global internal wave energy and balanced energy maps are used to conjecture that out of the 0.8 TW of power going to balanced flow kinetic energy in the ocean, at least 0.1 TW could be dissipated by internal gravity waves. We therefore hypothesize that internal waves can form a non-negligible energy sink for balanced flow in the world’s oceans.

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“…The inclusion of internal tides dramatically increases the high‐frequency variability, particularly in the equatorial region. The increase is quite large off the Amazon shelf (near the equator), where internal tides are generated off the shelf break and propagate northeast and eastward into the open ocean (Jackson, 2004, 2007; Magalhaes et al., 2016), and around several bathymetry features/hot spots of the eastern North Atlantic basin, that is, the Sierra Leone Rise (∼5°N), the Cape Verde islands (∼15°N, Ray & Zaron, 2016), and the Atlantis‐Meteor Seamount Complex/Azores islands (30–36°N) (Löb et al., 2020; Zhao et al., 2016). The variability is also increased in the western boundary current around the New England seamounts chain (NESC).…”

Section: Surface Signature Of High‐frequency Motionsmentioning

confidence: 99%

“…The variability is generally weak in the equatorial region, although still noticeably higher than that in the low-EKE region such as the eastern North Atlantic Ocean (Figures 2a and 2b). (Jackson, 2004(Jackson, , 2007Magalhaes et al, 2016), and around several bathymetry features/hot spots of the eastern North Atlantic basin, that is, the Sierra Leone Rise (∼5°N), the Cape Verde islands (∼15°N, Ray & Zaron, 2016), and the Atlantis-Meteor Seamount Complex/Azores islands (30-36°N) (Löb et al, 2020;Zhao et al, 2016). The variability is also increased in the western boundary current around the New England seamounts chain (NESC).…”

Section: Surface Signature Of High-frequency Motionsmentioning

confidence: 99%

On the Spatial Variability of the Mesoscale Sea Surface Height Wavenumber Spectra in the Atlantic Ocean

Chassignet

Wallcraft

et al. 2022

JGR Oceans

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The slope of the sea surface height (SSH) power spectra as derived from satellite observations exhibits a large spatial variability, which is now reproduced in our numerical simulations • The surface manifestation of internal tides with energy peaks near 120 and 70 km is the main driver for spatial variability in the slope of the SSH power spectra • High-resolution bathymetry plays an important role in the internal tide generation locally but has a relatively small impact on the SSH power spectra on a broader scale

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Observations of the Low‐Mode Internal Tide and Its Interaction With Mesoscale Flow South of the Azores

Cited by 15 publications

References 65 publications

Vertical structural variability of diurnal internal tides inside a mesoscale anticyclonic eddy based on single virtual-moored Slocum glider observations

Vertical structural variability of diurnal internal tides inside a mesoscale anticyclonic eddy based on single virtual-moored Slocum glider observations

Turbulent wave-balance exchanges in the ocean

On the Spatial Variability of the Mesoscale Sea Surface Height Wavenumber Spectra in the Atlantic Ocean

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