A parameterization of local and remote tidal mixing

<p>Vertical mixing is often regarded as the Achilles&#8217; heel of ocean models. In particular, few models include a comprehensive and energy-constrained parameterization of mixing by internal ocean tides. Here, we present an energy-conserving mixing scheme which accounts for the local breaking of high-mode internal tides and the distant dissipation of low-mode internal tides. The scheme relies on four static two-dimensional maps of internal tide dissipation, constructed using mode-by-mode Lagrangian tracking of energy beams from sources to sinks. Each map is associated with a distinct dissipative process and a corresponding vertical structure. Applied to an observational climatology of stratification, the scheme produces a global three-dimensional map of dissipation which compares well with available microstructure observations and with upper-ocean finestructure mixing estimates. Implemented in the NEMO global ocean model, the scheme improves the representation of deep water-mass transformation and obviates the need for a constant background diffusivity.</p>

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The dissipation of the internal tide inferred from a global ocean model, altimetry, and in-situ observations

10.5194/egusphere-egu2020-12500 ◽

2020 ◽

Author(s):

Maarten Buijsman ◽

Harpreet Kaur ◽

Zhongxiang Zhao ◽

Amy Waterhouse ◽

Caitlin Whalen

Keyword(s):

Correction Factor ◽

Internal Tide ◽

Horizontal Resolution ◽

Ocean Model ◽

Internal Tides ◽

Global Ocean ◽

Flux Divergence ◽

Data Set ◽

Tidal Dissipation ◽

Dissipation Rates

<p>In this presentation we combine several model and observational data sets to better understand the dissipation of the diurnal and semidiurnal internal tide in the global ocean, which is relevant for maintaining the global overturning circulation. We compute depth-integrated internal tide dissipation rates from a realistically-forced global HYbrid Coordinate Ocean Model (HYCOM) simulation with a horizontal resolution of 4 km (1/25 degrees) and 41 layers. We also compute dissipation rates from altimetry in two ways: 1) from the low-mode flux divergence away from topography and 2) by fitting exponential decay curves along low-mode internal tide beams. The internal-tide sea-surface height amplitude is computed with a least-squares harmonic analysis over a 20+ year altimetry data set. Hence, the altimetry-inferred dissipation rates both reflect the tidal dissipation and the energy scattered from the stationary to the nonstationary internal tide. To account for the dissipation of the nonstationary tide, we apply a spatially-varying correction factor to the stationary dissipation inferred from altimetry. &#160;This correction factor is computed from a global 8-km HYCOM simulation with a duration of 6 years, from which the stationary and nonstationary internal tides can be easily isolated. We compare the simulated and the corrected altimetry-inferred dissipation rates with dissipation rates from finescale and microstructure observations. Preliminary results show that the simulated dissipation is up to a factor of two larger than the depth-integrated dissipation rates inferred from finescale methods, but smaller than the dissipation rates from microstructure.</p>

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Accuracy assessment of global internal tide models using satellite altimetry

10.5194/os-2020-57 ◽

2020 ◽

Author(s):

Loren Carrere ◽

Brian K. Arbic ◽

Brian Dushaw ◽

Gary D. Egbert ◽

Svetlana Y. Erofeeva ◽

...

Keyword(s):

Variance Reduction ◽

Accuracy Assessment ◽

Three Dimensional ◽

Internal Tide ◽

Detailed Comparison ◽

Internal Tides ◽

Global Ocean ◽

Ocean Tide ◽

Small Scale ◽

Ocean Topography

Abstract. In order to access the targeted ocean signal, altimeter measurements are corrected for several geophysical parameters among which the ocean tide correction is one of the most critical, but the internal tide signature at the surface are not yet corrected globally. Internal tides can have a signature of several cm at the surface with wavelengths about 50–250 km for the first mode and even smaller scales for higher order modes. The goals of the upcoming Surface Water Ocean Topography (SWOT) mission and other high-resolution ocean measurements make the correction of these small scale signals a challenge, as the separation of all tidal variability from other oceanic signals becomes mandatory. In this context, several scientific teams are working on the development of new internal tide models, taking advantage of the very long altimeter time series now available, which represent an unprecedented and valuable global ocean database. The internal tide models presented here focus on the coherent internal tide signal and they are of three types: empirical models based upon analysis of existing altimeter missions, an assimilative model, and a three-dimensional hydrodynamic model. A detailed comparison and validation of these internal tide models is proposed using existing satellite altimeter databases. The analysis focuses on the four main tidal constituents M2, K1, O1 and S2. The validation process is based on a statistical analysis of multi-mission altimetry including Jason-2 and Cryosphere Satellite-2 data, taking advantage of the long-term altimeter databases available. The results show a significant altimeter variance reduction when using internal tide corrections on all ocean regions where internal tides are generating/propagating. A complementary spectral analysis also gives some estimation of the performance of each model as a function of wavelength, and some insight into the residual non-stationary part of internal tides in the different regions of interest.

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Accuracy assessment of global internal-tide models using satellite altimetry

Ocean Science ◽

10.5194/os-17-147-2021 ◽

2021 ◽

Vol 17 (1) ◽

pp. 147-180

Author(s):

Loren Carrere ◽

Brian K. Arbic ◽

Brian Dushaw ◽

Gary Egbert ◽

Svetlana Erofeeva ◽

...

Keyword(s):

Variance Reduction ◽

Accuracy Assessment ◽

Three Dimensional ◽

Internal Tide ◽

Detailed Comparison ◽

Internal Tides ◽

Global Ocean ◽

Ocean Tide ◽

Small Scale ◽

Ocean Topography

Abstract. Altimeter measurements are corrected for several geophysical parameters in order to access ocean signals of interest, like mesoscale or sub-mesoscale variability. The ocean tide is one of the most critical corrections due to the amplitude of the tidal elevations and to the aliasing phenomena of high-frequency signals into the lower-frequency band, but the internal-tide signatures at the ocean surface are not yet corrected globally. Internal tides can have a signature of several centimeters at the surface with wavelengths of about 50–250 km for the first mode and even smaller scales for higher-order modes. The goals of the upcoming Surface Water Ocean Topography (SWOT) mission and other high-resolution ocean measurements make the correction of these small-scale signals a challenge, as the correction of all tidal variability becomes mandatory to access accurate measurements of other oceanic signals. In this context, several scientific teams are working on the development of new internal-tide models, taking advantage of the very long altimeter time series now available, which represent an unprecedented and valuable global ocean database. The internal-tide models presented here focus on the coherent internal-tide signal and they are of three types: empirical models based upon analysis of existing altimeter missions, an assimilative model and a three-dimensional hydrodynamic model. A detailed comparison and validation of these internal-tide models is proposed using existing satellite altimeter databases. The analysis focuses on the four main tidal constituents: M2, K1, O1 and S2. The validation process is based on a statistical analysis of multi-mission altimetry including Jason-2 and Cryosphere Satellite-2 data. The results show a significant altimeter variance reduction when using internal-tide corrections in all ocean regions where internal tides are generating or propagating. A complementary spectral analysis also gives some estimation of the performance of each model as a function of wavelength and some insight into the residual non-stationary part of internal tides in the different regions of interest. This work led to the implementation of a new internal-tide correction (ZARON'one) in the next geophysical data records version-F (GDR-F) standards.

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Summertime M2 Internal Tides in the Northern Yellow Sea

Frontiers in Marine Science ◽

10.3389/fmars.2021.798504 ◽

2021 ◽

Vol 8 ◽

Author(s):

Fan Lin ◽

Lars Asplin ◽

Hao Wei

Keyword(s):

Yellow Sea ◽

Current Model ◽

Internal Tide ◽

Horizontal Resolution ◽

Ocean Model ◽

Internal Tides ◽

Tidal Mixing ◽

Regional Ocean Model System ◽

Strong Current ◽

Northern Yellow Sea

The summertime M2 internal tide in the northern Yellow Sea is investigated with moored current meter observations and numerical current model results. The hydrodynamic model, which is implemented from the Regional Ocean Model System (ROMS) with 1 km horizontal resolution, is capable of resolving the internal tidal dynamics and the results are validated in a comparison with observations. The vertical pattern of a mode-1, semi-diurnal internal tide is clearly captured by the moored ADCP as well as in the simulation results. Spectral analysis of the current results shows that the M2 internal tide is dominant in the northern Yellow Sea. Analysis of the major M2 internal tide energetics demonstrated a complex spatial pattern. The tidal mixing front along the Korean coast and on the northern shelf provided proper conditions for the generation and propagation of the internal tides. Near the Changshan islands, the M2 internal tide is mainly generated near the local topography anomalies with relatively strong current magnitude, equal to about 30% of the barotropic component, thus modifying the local current field. These local internal tides are short-lived phenomena rapidly being dissipated along the propagation pathway, restricting their influence within a few kilometers around the islands.

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M2 tidal dynamics in the Ross Sea

Antarctic Science ◽

10.1017/s0954102003001044 ◽

2003 ◽

Vol 15 (1) ◽

pp. 41-46 ◽

Cited By ~ 13

Author(s):

ROBIN ROBERTSON ◽

AIKE BECKMANN ◽

HARTMUT HELLMER

Keyword(s):

Continental Shelf ◽

Ross Sea ◽

Tidal Energy ◽

Ocean Model ◽

Internal Tides ◽

Global Ocean ◽

Tidal Dynamics ◽

Tidal Elevation ◽

Shelf Slope ◽

Continental Shelf Slope

In certain regions of the Southern Ocean, tidal energy is believed to foster the mixing of different water masses, which eventually contribute to the formation of deep and bottom waters. The Ross Sea is one of the major ventilation sites of the global ocean abyss and a region of sparse tidal observations. We investigated M2 tidal dynamics in the Ross Sea using a three-dimensional sigma coordinate model, the Regional Ocean Model System (ROMS). Realistic topography and hydrography from existing observational data were used with a single tidal constituent, the semi-diurnal M2. The model fields faithfully reproduced the major features of the tidal circulation and had reasonable agreement with ten existing tidal elevation observations and forty-two existing tidal current measurements. The differences were attributed primarily to topographic errors. Internal tides were generated at the continental shelf/slope break and other areas of steep topography. Strong vertical shears in the horizontal velocities occurred under and at the edges of the Ross Ice Shelf and along the continental shelf/slope break. Estimates of lead formation based on divergence of baroclinic velocities were significantly higher than those based on barotrophic velocities, reaching over 10% at the continental shelf/slope break.

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Entrainment and Transport in Idealized Three-Dimensional Gravity Current Simulation

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech1915.1 ◽

2006 ◽

Vol 23 (9) ◽

pp. 1249-1269 ◽

Cited By ~ 14

Author(s):

Yu-Heng Tseng ◽

David E. Dietrich

Keyword(s):

Gravity Current ◽

Vertical Mixing ◽

Three Dimensional ◽

Ocean Model ◽

Numerical Dissipation ◽

Good Convergence ◽

Low Viscosity ◽

Denmark Strait ◽

Dimensional Gravity ◽

Fine Resolution

Abstract A purely z-coordinate Dietrich/Center for Air Sea Technology (DieCAST) ocean model is applied to the Dynamics of Overflow Mixing and Entrainment (DOME) idealized bottom density current problem that is patterned after the Denmark Strait. The numerical results show that the background viscosity plays a more important role than the chosen coordinate system in the entrainment and mixing if the background viscosity is not small enough. Both higher horizontal viscosity and coarser resolution leads to slower along-slope propagation. Reducing vertical mixing parameterization also leads to slower along-slope propagation with thicker plume size vertically. The simulation gives consistent results for the moderate- and fine-resolution runs. At a very coarse grid the dense water descends more slowly and is mainly dominated by diffusion. Time-averaged downstream transport and entrainment are not very sensitive to viscosity after the flow reaches its quasi-steady status. However, more realistic eddies and flow structures are found in low-viscosity runs. The results show good convergence of the resolved flow as expected and clarify the effects of numerical dissipation/mixing on overflow modeling. Larger numerical dissipation is not required nor recommended in z-coordinate models.

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Investigation of the Internal Tides in the Northwest Pacific Ocean Considering the Background Circulation and Stratification

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0177.1 ◽

2020 ◽

Vol 50 (11) ◽

pp. 3165-3188

Author(s):

Pengyang Song ◽

Xueen Chen

Keyword(s):

Pacific Ocean ◽

Ocean Circulation ◽

Conversion Rate ◽

Internal Tide ◽

Internal Tides ◽

Global Ocean ◽

Northwest Pacific ◽

Northwest Pacific Ocean ◽

Baroclinic Tide ◽

The Northwest Pacific Ocean

AbstractA global ocean circulation and tide model with nonuniform resolution is used in this work to resolve the ocean circulation globally as well as mesoscale eddies and internal tides regionally. Focusing on the northwest Pacific Ocean (NWP, 0°–35°N, 105°–150°E), a realistic experiment is conducted to simulate internal tides considering the background circulation and stratification. To investigate the influence of a background field on the generation and propagation of internal tides, idealized cases with horizontally homogeneous stratification and zero surface fluxes are also implemented for comparison. By comparing the realistic cases with idealized ones, the astronomical tidal forcing is found to be the dominant factor influencing the internal tide conversion rate magnitude, whereas the stratification acts as a secondary factor. However, stratification deviations in different areas can lead to an error exceeding 30% in the local internal tide energy conversion rate, indicating the necessity of a realistic stratification setting for simulating the entire NWP. The background shear is found to refract propagating diurnal internal tides by changing the effective Coriolis frequencies and phase speeds, while the Doppler-shifting effect is remarkable for introducing biases to semidiurnal results. In addition, nonlinear baroclinic tide energy equations considering the background circulation and stratification are derived and diagnosed in this work. The mean flow–baroclinic tide interaction and nonlinear energy flux are the most significant nonlinear terms in the derived equations, and nonlinearity is estimated to contribute approximately 5% of the total internal tide energy in the greater Luzon Strait area.

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Impact of Channel Geometry and Rotation on the Trapping of Internal Tides

Journal of Physical Oceanography ◽

10.1175/2007jpo3586.1 ◽

2007 ◽

Vol 37 (11) ◽

pp. 2740-2763 ◽

Cited By ~ 21

Author(s):

Sybren Drijfhout ◽

Leo R. M. Maas

Keyword(s):

Continental Slope ◽

Three Dimensional ◽

Tidal Energy ◽

Ocean Model ◽

Internal Tides ◽

Open Boundary ◽

Kelvin Wave ◽

Channel Geometry ◽

Channel Slope ◽

The Cross

Abstract The generation and propagation of internal tides has been studied with an isopycnic three-dimensional ocean model. The response of a uniformly stratified sea in a channel, which is forced by a barotropic tide on its open boundary, is considered. The tide progresses into the channel and forces internal tides over a continental slope at the other end. The channel has a length of 1200 km and a width of 191.25 km. The bottom profile has been varied. In a series of four experiments it is shown how the cross-channel geometry affects the propagation and trapping of internal tides, and the penetration scale of wave energy, away from the continental slope, is discussed. In particular it is found that a cross-channel bottom slope constrains the penetration of the internal tidal energy. Most internal waves refract toward a cross-channel plane where they are trapped. The exception is formed by edge waves that carry part of the energy away from the continental slope. In the case of rotation near the continental slope, the Poincaré waves that arise in the absence of a cross-channel slope no longer bear the characteristics of the wave attractor predicted by 2D theory, but are almost completely arrested, while the right-bound Kelvin wave preserves the 2D attractor in the cross-channel plane, which is present in the nonrotating case. The reflected, barotropic right-bound Kelvin wave acts as a secondary internal wave generator along the cross-channel slope.

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Internal-Wave-Driven Mixing: Global Geography and Budgets

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0141.1 ◽

2017 ◽

Vol 47 (6) ◽

pp. 1325-1345 ◽

Cited By ~ 56

Author(s):

Eric Kunze

Keyword(s):

Internal Wave ◽

Internal Tide ◽

Internal Tides ◽

Tidal Mixing ◽

Linear Wave ◽

Power Sources ◽

The North ◽

Dissipation Rates ◽

Thickness Variability ◽

Significant Pathway

AbstractInternal-wave-driven dissipation rates ε and diapycnal diffusivities K are inferred globally using a finescale parameterization based on vertical strain applied to ~30 000 hydrographic casts. Global dissipations are 2.0 ± 0.6 TW, consistent with internal wave power sources of 2.1 ± 0.7 TW from tides and wind. Vertically integrated dissipation rates vary by three to four orders of magnitude with elevated values over abrupt topography in the western Indian and Pacific as well as midocean slow spreading ridges, consistent with internal tide sources. But dependence on bottom forcing is much weaker than linear wave generation theory, pointing to horizontal dispersion by internal waves and relatively little local dissipation when forcing is strong. Stratified turbulent bottom boundary layer thickness variability is not consistent with OGCM parameterizations of tidal mixing. Average diffusivities K = (0.3–0.4) × 10−4 m2 s−1 depend only weakly on depth, indicating that ε = KN2/γ scales as N2 such that the bulk of the dissipation is in the pycnocline and less than 0.08-TW dissipation below 2000-m depth. Average diffusivities K approach 10−4 m2 s−1 in the bottom 500 meters above bottom (mab) in height above bottom coordinates with a 2000-m e-folding scale. Average dissipation rates ε are 10−9 W kg−1 within 500 mab then diminish to background deep values of 0.15 × 10−9 W kg−1 by 1000 mab. No incontrovertible support is found for high dissipation rates in Antarctic Circumpolar Currents or parametric subharmonic instability being a significant pathway to elevated dissipation rates for semidiurnal or diurnal internal tides equatorward of 28° and 14° latitudes, respectively, although elevated K is found about 30° latitude in the North and South Pacific.

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