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We examine ocean tides in the barotropic version of the Model for Prediction Across Scales (MPAS‐Ocean), the ocean component of the Department of Energy Earth system model. We focus on four factors that affect tidal accuracy: self‐attraction and loading (SAL), model resolution, details of the underlying bathymetry, and parameterized topographic wave drag. The SAL term accounts for the tidal loading of Earth's crust and the self‐gravitation of the ocean and the load‐deformed Earth. A common method for calculating SAL is to decompose mass anomalies into their spherical harmonic constituents. Here, we compare a scalar SAL approximation versus an inline SAL using a fast spherical harmonic transform package. Wave drag accounts for energy lost by breaking internal tides that are produced by barotropic tidal flow over topographic features. We compare a series of successively finer quasi‐uniform resolution meshes (62.9, 31.5, 15.7, and 7.87 km) to a variable resolution (45 to 5 km) configuration. We ran MPAS‐Ocean in a single‐layer barotropic mode forced by five tidal constituents. The 45 to 5 km variable resolution mesh obtained the best total root‐mean‐square error (5.4 cm) for the deep ocean (> $ > $1,000 m) M2 ${\mathrm{M}}_{2}$ tide compared to TPXO8 and ran twice as fast as the quasi‐uniform 8 km mesh, which had an error of 5.8 cm. This error is comparable to those found in other forward (non‐assimilative) ocean tide models. In future work, we plan to use MPAS‐Ocean to study tidal interactions with other Earth system components, and the tidal response to climate change. Plain Language Summary: Over the next century, climate change impacts on coastal regions will include floods, droughts, erosion, and severe weather events. The Department of Energy (DoE) is funding the Integrated Coastal Modeling Project to understand these potential risks better. In this paper, we implement tides in the DoE ocean model. Tides themselves respond to climate change, altering coastal flooding risk assessments. We explore the sensitivity of tides to model resolution (the spacing of model gridpoints), ocean‐floor topography, and the so‐called "self‐attraction and loading" (SAL) effect. Self‐attraction and loading occurs as the mass of water in a location fluctuates, causing a deformation of the Earth's crust and changes in the gravitational potential, which must be accounted for when modeling tides. We present a computationally efficient method of calculating the SAL effects and show that it is more accurate than other commonly used approximations. In future work we will examine interactions of tides with other components of the climate system, including sea ice, floating ice shelves, rivers, and current systems. Key Points: We calculate the full self‐attraction and loading (SAL) term inline, in a barotropic configuration of Model for Prediction Across Scales (MPAS‐Ocean)Inclusion of the inline SAL and higher resolution meshes yield improved tidal accuracy in stand‐alone barotropic MPAS‐Ocean configurationsA 45 to 5‐km variable‐resolution mesh provides reduced tidal errors with better computational performance than a quasi‐uniform 8‐km mesh [ABSTRACT FROM AUTHOR]

The wavenumber spectral slope of sea surface height (SSH) computed within the mesoscale range (70–250 km) from satellite altimetry exhibits a large spatial variability which, until now, has not been reproduced in numerical ocean models. This study documents the impacts of including internal tides, high‐resolution bathymetry, and high‐frequency atmospheric variability on the SSH wavenumber spectra in the Atlantic Ocean, using a series of 1/50° North and equatorial Atlantic simulations with a realistic representation of barotropic/baroclinic tides and mesoscale‐to‐submesoscale variability. The results show that the inclusion of internal tides does increase high frequency SSH variability (with clear peaks near 120 and 70 km) and flattens the spectra slope in the mesoscale range in a good agreement with observations. The surface signature of internal tides, mostly in the equatorial Atlantic but also in subtropical regions in the eastern North Atlantic, is the primary reason behind the observed large spatial variability of the spectral slope in the Atlantic. Internal tides are stronger in the tropical regions when compared to higher latitudes because of the stronger barotropic tides and stronger stratification in the upper layer of the water column. High‐resolution bathymetry does play an important role in the internal tide generation on a local scale, but its impact on the modeled large‐scale SSH variability and SSH wavenumber spectra is quite small. High‐frequency wind variability plays only a minor role on the generation of the simulated high‐frequency SSH variability. Impact of altimetry sampling on the computation of the SSH wavenumber spectra is also discussed. Plain Language Summary: The sea surface height (SSH) wavenumber spectrum is a quantification of the magnitude of SSH variability on different spatial scales. The slope of SSH wavenumber spectra is essential to understanding how kinetic energy is transferred across different scales in the turbulent ocean. The most striking feature of the SSH spectral slope as derived from satellite observations is that it has a wide range of values over different parts of the Atlantic Ocean: from an order of −5 in the western boundary current, to an order of −4 to −3 in the interior of subtropical North Atlantic, and to an order of −1 to −0.5 in the tropical Atlantic. In this study, we reproduced the observed spatial variability of the SSH spectral slope in numerical ocean models, and further documented that internal tide is the main driver behind the scenes. The surface manifestation of internal tides flattens the spectral slope of the SSH. This flattening is most significant in the tropical Atlantic, but also occurs in the subtropical eastern North Atlantic. The impacts from other factors such as high‐resolution bathymetry and high‐frequency atmospheric forcing are relatively small. Key Points: 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 simulationsThe 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 spectraHigh‐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 [ABSTRACT FROM AUTHOR]

The geographical variability, frequency content, and vertical structure of near‐surface oceanic kinetic energy (KE) are important for air‐sea interaction, marine ecosystems, operational oceanography, pollutant tracking, and interpreting remotely sensed velocity measurements. Here, KE in high‐resolution global simulations (HYbrid Coordinate Ocean Model; HYCOM, and Massachusetts Institute of Technology general circulation model; MITgcm), at the sea surface (0 m) and at 15 m, are compared with KE from undrogued and drogued surface drifters, respectively. Global maps and zonal averages are computed for low‐frequency (<0.5 cpd), near‐inertial, diurnal, and semidiurnal bands. Both models exhibit low‐frequency equatorial KE that is low relative to drifter values. HYCOM near‐inertial KE is higher than in MITgcm, and closer to drifter values, probably due to more frequently updated atmospheric forcing. HYCOM semidiurnal KE is lower than in MITgcm, and closer to drifter values, likely due to inclusion of a parameterized topographic internal wave drag. A concurrent tidal harmonic analysis in the diurnal band demonstrates that much of the diurnal flow is nontidal. We compute simple proxies of near‐surface vertical structure—the ratio 0 m KE/(0 m KE + 15 m KE) in model outputs, and the ratio undrogued KE/(undrogued KE + drogued KE) in drifter observations. Over most latitudes and frequency bands, model ratios track the drifter ratios to within error bars. Values of this ratio demonstrate significant vertical structure in all frequency bands except the semidiurnal band. Latitudinal dependence in the ratio is greatest in diurnal and low‐frequency bands. Plain Language Summary: It is important to map and understand ocean surface currents because they affect climate and marine ecosystems. Recent advances in global ocean models include the addition of astronomical tidal forcing alongside atmospheric forcing and the usage of more powerful computers that can resolve finer features. Here, we evaluate ocean surface currents in high‐resolution simulations of two different ocean models through comparison with observations from surface drifting buoys. We examine near‐inertial motions, forced by fast‐changing winds; semidiurnal tides, forced by the astronomical tidal potential; diurnal motions, arising from tidal and other sources; and low‐frequency currents and eddies, forced by atmospheric fields. Global patterns in the models and drifters are broadly consistent. The two models differ in their degree of proximity to drifter measurements in the near‐inertial band, most likely due to different update intervals for atmospheric forcing and in the semidiurnal band, most likely due to different damping schemes. A simple proxy for vertical structure of the currents, measured by differences in drifter flows at the surface versus 15 m depth, is tracked reasonably well by the models. Discrepancies between models and observations motivate future improvements in the models. Key Points: We examine frequency content of ocean kinetic energy (KE) at the sea surface (0 m) and 15 m depth with global drifter data and two modelsNear‐surface near‐inertial and tidal KE in numerical models are sensitive to atmospheric forcing frequency and dampingThe ratio 0 m KE/(0 m KE + 15 m KE) in models lies within error bars of the observational ratios over some latitudes and frequency bands [ABSTRACT FROM AUTHOR]

The location of mixing due to internal tides is important for both the ocean circulation as well as local biogeochemical processes. Numerous observations and modeling studies have shown that submarine canyons may be regions of enhanced internal tide‐driven mixing, but there has not yet been a systematic study of all submarine canyons resolved in bathymetric datasets. Here, we parameterize the internal tide‐driven dissipation from a suite of simulations and pair this with a global high‐resolution, internal tide‐resolving model and bathymetric dataset to estimate the internal‐tide‐driven dissipation that occurs in all documented submarine canyons. We find that submarine canyons dissipate a significant fraction of the incoming internal tide's energy, which is consistent with observations. When globally integrated, submarine canyons are responsible for dissipating 30.8–75.3 GW, or 3.2%–7.8% of the energy input into the M2‐frequency internal tides. This percentage of the internal tide energy that is dissipated in submarine canyons is comparable to or larger than previous calculations using extrapolations from observations of single canyons. Plain Language Summary: Internal waves, or waves that propagate in density layers below the surface of the ocean, are responsible for transporting a significant amount of energy throughout the ocean. When these waves break, they deposit their energy in local mixing events. Submarine canyons have been identified as a type of topography that leads to significant internal wave‐driven mixing. In this study, we use a global map of canyons, together with a high‐resolution ocean model, to calculate the percentage of internal wave energy that is lost to mixing in submarine canyons. We find that a significant fraction of the incident internal wave energy is lost within each submarine canyon. We then sum the energy loss for all submarine canyons to calculate the amount of internal wave‐driven mixing that occurs within canyons over the global ocean. We find that approximately 5%, a non‐negligible amount, of the energy in the global M2‐frequency internal wavefield is lost in canyons. This percentage of the internal wave energy that is lost in submarine canyons is comparable to or larger than previous calculations using extrapolations from observations of single canyons. Key Points: We present a framework for estimating the range of global internal tide‐driven dissipation in submarine canyonsSubmarine canyons may dissipate approximately 5% of the energy input into the global internal tidesPrior estimates of canyon‐driven dissipation may be underestimates, as regions of max canyon‐induced mixing have been un‐ or under‐observed [ABSTRACT FROM AUTHOR]

Internal waves generated at the seafloor propagate through the interior of the ocean, driving mixing where they break and dissipate. However, existing theories only describe these waves in two limiting cases. In one limit, the presence of an upper boundary permits bottom-generated waves to reflect from the ocean surface back to the seafloor, and all the energy flux is at discrete wavenumbers corresponding to resonant modes. In the other limit, waves are strongly dissipated such that they do not interact with the upper boundary and the energy flux is continuous over wavenumber. Here, a novel linear theory is developed for internal tides and lee waves that spans the parameter space in between these two limits. The linear theory is compared with a set of numerical simulations of internal tide and lee wave generation at realistic abyssal hill topography. The linear theory is able to replicate the spatially averaged kinetic energy and dissipation of even highly nonlinear wave fields in the numerical simulations via an appropriate choice of the linear dissipation operator, which represents turbulent wave breaking processes. [ABSTRACT FROM AUTHOR]

The flow of tides over rough bathymetry in the deep ocean generates baroclinic motion including internal waves and bottom‐trapped tides. The stresses generated by this motion feedback on the amplitude and phase of the large‐scale tide. Quantifying the stresses associated with tidal flow over abyssal hills is especially important, as this scale of bathymetry is often unresolved in global baroclinic tide models, and the stresses must therefore be parameterized. Here, we extend the previous theoretical work of the authors to determine the amplitude, phasing, and vertical location of the stresses exerted on a flow driven by a time‐periodic body force when it encounters rough bathymetry. The theory compares favorably with a suite of fully nonlinear numerical simulations. It is shown that all topographic stresses are applied directly above the bathymetry, leading to a two‐layer baroclinic flow, with the near‐bottom spatial‐mean flow (the benthic tide) strongly modified by topographic stresses, and the flow at height unperturbed by the presence of topography. Our results provide a framework to improve baroclinic tide models by (i) providing a simple parameterization for the subinertial stress which is currently not included in any models, (ii) establishing that parameterized stresses should be applied in the diffusive boundary layer directly above the topography, independent of where internal tides may dissipate, and (iii) identifying a minimum resolution of ∼10 km for baroclinic tidal models to adequately capture wave resonance effects that can significantly impact the magnitude of the benthic tide. Plain Language Summary: The ocean tide is a periodic motion of the water column at the scale of ocean basins. The amplitude of the ocean tide is determined by a balance between the gravitational attraction of the moon and the forces exerted when the tide flows over the rough seafloor. Much of the roughness in the deep ocean is due to mountains on the seafloor, 10–50 km in width, known as "abyssal hills." In this study, mathematical descriptions are developed for the strength and distribution of the forces exerted on the ocean tide due to its interaction with these hills. These forces always act below the crest of the hills, leading to a sub‐crest or "benthic tide" that differs from the tide above the crest of the hills. Our results provide a framework for improving the representation of tides in numerical ocean models. Key Points: The interaction of the spatial‐mean tide with rough bathymetry generates baroclinic motion including internal tidesThese motions exert stresses on the spatial‐mean tide near the seafloor which modifies the benthic tidal amplitudeThe benthic tidal amplitude may be decreased or increased depending on the nature of the interaction [ABSTRACT FROM AUTHOR]

The interaction of a barotropic flow with topography generates baroclinic motion that exerts a stress on the barotropic flow. Here, explicit solutions are calculated for the spatial-mean flow (i.e., the barotropic tide) resulting from a spatially uniform but time-varying body force (i.e., astronomical forcing) acting over rough topography. This approach of prescribing the force contrasts with that of previous authors who have prescribed the barotropic flow. It is found that the topographic stress, and thus the impact on the spatial-mean flow, depend on the nature of the baroclinic motion that is generated. Two types of stress are identified: (i) a ''wave drag'' force associated with propagating wave motion, which extracts energy from the spatial-mean flow, and (ii) a topographic ''spring'' force associated with standing motion at the seafloor, including bottom-trapped internal tides and propagating low-mode internal tides, which significantly damps the time-mean kinetic energy of the spatial-mean flow but extracts no energy in the time-mean. The topographic spring force is shown to be analogous to the force exerted by a mechanical spring in a forced-dissipative harmonic oscillator. Expressions for the topographic stresses appropriate for implementation as baroclinic drag parameterizations in global models are presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Scientists and engineers have observed for some time that tidal amplitudes at many locations are shifting considerably due to nonastronomical factors. Here we review comprehensively these important changes in tidal properties, many of which remain poorly understood. Over long geological time scales, tectonic processes drive variations in basin size, depth, and shape and hence the resonant properties of ocean basins. On shorter geological time scales, changes in oceanic tidal properties are dominated by variations in water depth. A growing number of studies have identified widespread, sometimes regionally coherent, positive, and negative trends in tidal constituents and levels during the 19th, 20th, and early 21st centuries. Determining the causes is challenging because a tide measured at a coastal gauge integrates the effects of local, regional, and oceanic changes. Here, we highlight six main factors that can cause changes in measured tidal statistics on local scales and a further eight possible regional/global driving mechanisms. Since only a few studies have combined observations and models, or modeled at a temporal/spatial resolution capable of resolving both ultralocal and large‐scale global changes, the individual contributions from local and regional mechanisms remain uncertain. Nonetheless, modeling studies project that sea level rise and climate change will continue to alter tides over the next several centuries, with regionally coherent modes of change caused by alterations to coastal morphology and ice sheet extent. Hence, a better understanding of the causes and consequences of tidal variations is needed to help assess the implications for coastal defense, risk assessment, and ecological change.Plain Language Summary: Tides are one of the most persistent and dominant forces that shape our planet. The regular and predictable daily, fortnightly, monthly, annual, interannual, and longer‐term changes in tides, driven by astronomical forces, are well understood. However, scientists and engineers have observed for some time that tides at many locations are shifting considerably due to nonastronomical factors. Here, we carry out a review of these important changes in tides, many of which remain poorly understood. We highlight that over long geological time scales, changes in tides are driven by tectonic processes, which alter the size, depth, and shape of the ocean. Over shorter geological time scales, changes in tides are mainly driven by changes in water depth. In recent decades, a growing number of studies have identified widespread, and sometimes regionally coherent, changes in tides during the last 150 years. However, determining exactly what has caused these more recent changes in tides has proven difficult. We discuss the local and regional/global mechanisms that might be responsible for the observed changes. Modeling studies predict that sea level rise and climate change will continue to alter tides over the next several centuries. Therefore, a better understanding of what is causing changes in tides is needed.Key Points: Tidal properties have changed, and continue to evolve, due to nonastronomical factorsAttributing causation remains challengingRegionally coherent increases/decreases in tidal properties are likely to occur over the next centuries [ABSTRACT FROM AUTHOR]

Tidal mixing fronts, which represent boundaries between stratified and tidally mixed waters, are locations of enhanced biological activity. They occur in summer shelf seas when, in the presence of strong tidal currents, mixing due to bottom friction balances buoyancy production due to seasonal heat flux. In this paper we examine the occurrence and fidelity of tidal mixing fronts in shelf seas generated within a global 3-dimensional simulation of the HYbrid Coordinate Ocean Model (HYCOM) that is simultaneously forced by atmospheric fields and the astronomical tidal potential. We perform a first order assessment of shelf sea tides in global HYCOM through comparison of sea surface temperature, sea surface tidal elevations, and tidal currents with observations. HYCOM was tuned to minimize errors in M 2 sea surface heights in deep water. Over the global coastal and shelf seas (depths <200 m) the area-weighted root mean square error of the M 2 sea surface amplitude in HYCOM represents 35% of the 50 cm root mean squared M 2 sea surface amplitude when compared to satellite constrained models TPXO8 and FES2014. HYCOM and the altimeter constrained tidal models TPXO8 and FES2014 exhibit similar skill in reproducing barotropic tidal currents estimated from in-situ current meter observations. Through comparison of a global HYCOM simulation with tidal forcing to a global HYCOM simulation with no tides, and also to previous regional studies of tidal mixing fronts in shelf seas, we demonstrate that HYCOM with embedded tides exhibits quite high skill in reproducing known tidal mixing fronts in shelf seas. Our results indicate that the amount of variability in the location of the tidal mixing fronts in HYCOM, estimated using the Simpson-Hunter parameter, is consistent with previous studies when the differences in the net downward heat flux, on a global scale, are taken into account. We also provide evidence of tidal mixing fronts on the North West Australian Shelf for which we have been unable to find references in the existing scientific literature. • We perform a first order assessment of the skill of HYCOM tides in the coastal and shelf seas. • RMSE for tidal heights represents 23–35% of the RMS amplitude in the coastal and shelf seas of global HYCOM. • Inclusion of tides in global HYCOM has a visible impact on SST in coastal and shelf seas. • HYCOM with embedded tides reproduces known seasonal tidal mixing fronts in their expected location. • We provide evidence for the existence of tidal mixing fronts on the North West Australian Shelf. [ABSTRACT FROM AUTHOR]

The jets in the equatorial Pacific Ocean of a realistically forced global circulation model with a horizontal resolution of [ABSTRACT FROM AUTHOR]

The effects of a parameterized linear internal wave drag on the semidiurnal barotropic and baroclinic energetics of a realistically forced, three-dimensional global ocean model are analyzed. Although the main purpose of the parameterization is to improve the surface tides, it also influences the internal tides. The relatively coarse resolution of the model of ~8 km only permits the generation and propagation of the first three vertical modes. Hence, this wave drag parameterization represents the energy conversion to and the subsequent breaking of the unresolved high modes. The total tidal energy input and the spatial distribution of the barotropic energy loss agree with the Ocean Topography Experiment (TOPEX)/Poseidon (TPXO) tidal inversion model. The wave drag overestimates the high-mode conversion at ocean ridges as measured against regional high-resolution models. The wave drag also damps the low-mode internal tides as they propagate away from their generation sites. Hence, it can be considered a scattering parameterization, causing more than 50% of the deep-water dissipation of the internal tides. In the near field, most of the baroclinic dissipation is attributed to viscous and numerical dissipation. The far-field decay of the simulated internal tides is in agreement with satellite altimetry and falls within the broad range of Argo-inferred dissipation rates. In the simulation, about 12% of the semidiurnal internal tide energy generated in deep water reaches the continental margins. [ABSTRACT FROM AUTHOR]

• We explore the behavior of tides in the mid-Archean era through simulations. • Mid-Archean ocean tides may have been larger than modern tides. • Tidal sea surface elevations impact photosynthetic processes on shelves. • Tidal currents impact sediment transport on shelves. • Tidal mixing fronts impact marine productivity on shelves. A variety of different controls have been proposed for Precambrian marine productivity ranging from environmental factors such as temperature to the flux rate of nutrients (e.g., phosphorus) derived from the continents. In addition to other first-order differences in the Earth system such as a less luminous young Sun, the Earth and Moon were substantially closer together, which would have resulted in a greater tidal forcing. The potential biogeochemical implications of this enhanced forcing have been little explored. Here we use idealized bathymetries and continental configurations to examine mid-Archean ocean tides. We find that, even in the absence of realistic coastal geometries, mid-Archean tidal velocities, sea-surface height, and mixing equaled or exceeded modern values, and that there would have been higher frequency of extreme values. We use a modern tidal model with accurate coastal geometry (HYbrid Coordinate Ocean Model; HYCOM) to scale the idealized results. We propose that mid-Archean water parcel velocities would have been at least 4.5 times greater than at present, that sea-surface height would have been at least 2.5 times greater than at present, and that tidal mixing fronts would have been more common. Each of these factors would result in greater flux and distribution of nutrients, both due to exposure of the sea beds/nascent continents and enhanced onshore-offshore transport, potentially strongly influencing marine productivity even in the absence of substantial permanently exposed subaerial continental landmass. [ABSTRACT FROM AUTHOR]

• We review global ocean models with simultaneous tidal and atmospheric forcing. • Tidal interactions with other earth system components can be studied in such models. • Global internal wave models are used to plan field and satellite missions. • Global internal wave models are used in operational oceanography. • Global internal wave models are used to provide boundary forcing for regional models. Until recently, high-resolution global modeling of tides has been done separately from high-resolution global modeling of the atmospherically-forced oceanic general circulation. Here we review the emerging class of high-resolution global models that are simultaneously forced by both atmospheric fields and the astronomical tidal potential. Such models simulate barotropic (surface) tides, internal tides, near-inertial motions, the eddying general oceanic circulation, and a partially resolved internal gravity wave (IGW) continuum spectrum (Garrett-Munk spectrum) simultaneously. We review the technical aspects of such global models and their myriad applications, for example, in satellite oceanography, operational oceanography, boundary forcing of regional models, tidal-cryosphere interactions, and assessment of future coastal flooding hazards in a changing climate with altered tides. [ABSTRACT FROM AUTHOR]

The resonance of diurnal tidal elevations is investigated with a forward ocean tide model run in a realistic near-global domain and a synthesis of free oscillations (normal modes) computed for realistic global ocean geometries and ocean physics. As a prelude to performing the forward ocean tide simulations, the topographic wave drag, which is now commonly employed in forward ocean tide models, is tuned specifically for diurnal tides. The synthesis of global free oscillations predicts reasonably well the forward ocean diurnal tide model sensitivity to changes in the frequency, zonal structure, and meridional structure of the astronomical diurnal tidal forcing. Three global free oscillations that are important for understanding diurnal tides as a superposition of forced-damped, resonant, free oscillations are identified. An admittance analysis of the frequency sweep experiments demonstrates that some coastal locations such as the Sea of Okhotsk are resonant to diurnal tidal forcing. As in earlier work done with semidiurnal tides, a series of simulations are performed in which regions possessing significant coastal diurnal tides are blocked out. The largest perturbations to the open-ocean diurnal tides take place in Blocked Sea of Okhotsk experiments. Lesser but still significant perturbations also arise from the blocking out of other regions of large diurnal tidal elevations or dissipation. Interpretation of the results is made more complex, however, by the fact that substantial perturbations also arise from blocking out regions where neither tidal elevations nor dissipation are large. The "blocking" experiments are relevant to understanding tides of the ice age, during which lower sea levels entail a reduced area of continental shelves. [ABSTRACT FROM AUTHOR]

Tidal studies have shown that there exists a resonance of the semi-diurnal tide in the Hudson Bay-Hudson Strait system. The resonant response is particularly strong within Hudson Strait and Ungava Bay. It is shown here that the semi-diurnal tide in Hudson Strait has characteristics that are similar to those of a half-wavelength open channel resonance. A simple analytical model is developed to account for the salient aspects of the semi-diurnal response in the strait. Non-dimensional parameters that govern the response are identified and evaluated based on the physical dimensions of the region and results from a numerical tidal model. Taking account of the mechanical impedance presented to the channel by Hudson Bay, the results suggest that a channel mode is resonant near semi-diurnal periodicities, in general agreement with observations and more complex tidal models of the region. The possibility that Ungava Bay may have a separate quarter-wavelength resonance driven at the entrance to the continental shelf is also briefly explored.[Traduit par la rédaction] Des études sur les marées ont montré qu'il existe une résonance de la marée semi-diurne dans le système baie d'Hudson - détroit d'Hudson. La réponse résonante est particulièrement forte dans le détroit d'Hudson et la baie d'Ungava. Nous démontrons ici que la marée semi-diurne dans le détroit d'Hudson a des caractéristiques semblables à celles d'une résonance de demi-longueur d'onde dans un canal à écoulement libre. Nous proposons un modèle analytique simple reproduisant les principaux aspects de la réponse semi-diurne dans le détroit. Nous identifions et évaluons les paramètres non dimensionnels auxquels la réponse est liée d'après les dimensions physiques de la région et les résultats d'un modèle numérique de marée. En prenant en compte l'impédance mécanique produite par la baie d'Hudson dans le canal, les résultats suggèrent qu'il existe un mode de canal présentant une résonance proche des périodicités semi-diurnes, ce qui s'accorde approximativement avec les observations et les modèles de marées plus complexes de la région. Nous explorons rapidement, aussi, la possibilité qu'il existe dans la baie d'Ungava une résonance distincte de quart de longueur d'onde générée à l'entrée de la plate-forme continentale. [ABSTRACT FROM AUTHOR]

Abstract: The resonances of tides in the coupled open ocean and shelf are modeled by a mechanical analogue consisting of a damped driven larger mass and spring (the open-ocean) connected to a damped smaller mass and spring (the shelf). When both masses are near resonance, the addition of even a very small mass can significantly affect the oscillations of the larger mass. The influence of the shelf is largest if the shelf is resonant with weak friction. In particular, an increase of friction on a near-resonant shelf can, perhaps surprisingly, lead to an increase in ocean tides. On the other hand, a shelf with large friction has little effect on ocean tides. Comparison of the model predictions with results from numerical models of tides during the ice ages, when lower sea levels led to a much reduced areal extent of shelves, suggests that the predicted larger tidal dissipation then is related to the ocean basins being close to resonance. New numerical simulations with a forward global tide model are used to test expectations from the mechanical analogue. Setting friction to unrealistically large values in Hudson Strait yields larger North Atlantic amplitudes, very similar to those seen in a simulation with the Hudson Strait blocked off. Thus, as anticipated, a shelf with very large friction is nearly equivalent in its effect on the open ocean to the removal of the shelf altogether. Setting friction in shallow waters throughout the globe to unrealistically large values yields even larger open ocean tidal amplitudes, similar to those found in simulations of ice-age tides. It thus appears that larger modeled tides during the ice ages can be a consequence of enhanced friction in shallower water on the shelf in glacial times as well as a reduced shelf area then. Single oscillator and coupled oscillator models for global tides show that the maximum extractable power for human use is a fraction of the present dissipation rate, which is itself a fraction of global human power consumption. [Copyright &y& Elsevier]

Abstract: This paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents. Both one-layer and two-layer simulations are performed. As far as the authors are aware, the two-layer simulations and the simulations in a companion paper (Deep-Sea Research II, 51 (2004) 3043) represent the first published global numerical solutions for baroclinic tides. Self-consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self-attraction and loading term. Energies are too large, and elevation accuracies are poor, unless substantial abyssal drag is present. Reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag or horizontal viscosity , but only if these are inordinately large. More plausible schemes concentrate drag over rough topography. The topographic drag scheme used here is based on an exact analytical solution for arbitrary small-amplitude terrain, and supplemented by dimensional analysis to account for drag due to flow-splitting and low-level turbulence as well as that due to breaking of radiating waves. The scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the TOPEX/POSEIDON (T/P)-constrained GOT99.2 model. The multiplicative factor may account for undersampled small spatial scales in bathymetric datasets. An optimally tuned multi-constituent one-layer simulation has an RMS elevation discrepancy of 9.54cm with respect to GOT99.2, in waters deeper than 1000m and over latitudes covered by T/P (66N to 66S). The surface elevation discrepancy decreases to 8.90cm (92 percent of the height variance captured) in the optimally tuned two-layer solution. The improvement in accuracy is not due to the direct surface elevation signature of internal tides, which is of small amplitude, but to a shift in the barotropic tide induced by baroclinicity. Elevations are also more accurate in the two-layer model when pelagic tide gauges are used as the benchmark, and when the T/P-constrained TPXO6.2 model is used as a benchmark in deep waters south of 66S. For Antarctic diurnal tides, the improvement in forward model elevation accuracy with baroclinicity is substantial. The optimal multiplicative factor in the two-layer case is nearly the same as in the one-layer case, against initial expectations that the explicit resolution of low-mode conversion would allow less parameterized drag. In the optimally tuned two-layer solution, local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10. [Copyright &y& Elsevier]

Climate varied enormously over the most recent ice age-for example, large pulses of ice-rafted debris, originating mainly from the Labrador Sea, were deposited into the North Atlantic at roughly 7,000-year intervals, with global climatic implications. Here we show that ocean tides within the Labrador Sea were exceptionally large over the period spanning these huge, abrupt ice movements, which are known as Heinrich events. We propose that tides played a catalytic role in liberating iceberg armadas during that time. [ABSTRACT FROM AUTHOR]

Abstract: The energy flux out of barotropic tides and into internal waves (“conversion”) is computed using a global domain multi-layer numerical model. The solution is highly baroclinic and reveals a global field of internal waves radiating way from generation sites of rough topography. A small number of sites where intense internal wave generation occurs accounts for most of the globally integrated work done on the barotropic tide and dominates sites such as the Mid-Atlantic ridge. The globally integrated conversion of the barotropic tide is 891 Gigawatts and the globally integrated rate of working of the ocean by astronomical forcing is 2.94 Terawatts. Both of these estimates are close to accepted values derived from independent methods. Regional estimates of conversion are also similar to previous inferences, lending additional confidence that the solution has captured the essential physics of low-mode internal wave generation and that numerical prediction of conversion has skill in regions where no previous estimates are available. [Copyright &y& Elsevier]

In global ocean simulations, forward (non-data-assimilative) tide models generally feature large sea-surface-height errors near Hudson Strait in the North Atlantic Ocean with respect to altimetry-constrained tidal solutions. These errors may be associated with tidal resonances that are not well resolved by the complex coastal-shelf bathymetry in low-resolution simulations. An online two-way nesting framework has been implemented to improve global surface tides in the HYbrid Coordinate Ocean Model (HYCOM). In this framework, a high-resolution child domain, covering Hudson Strait, is coupled with a relatively low-resolution parent domain for computational efficiency. Data such as barotropic pressure and velocity are exchanged between the child and parent domains with the external coupler OASIS3-MCT. The developed nesting framework is validated with semi-idealized basin-scale model simulations. The M 2 sea-surface heights show very good accuracy in the one-way and two-way nesting simulations in Hudson Strait, where large tidal elevations are observed. In addition, the mass and tidal energy flux are not adversely impacted at the nesting boundaries in the semi-idealized simulations. In a next step, the nesting framework is applied to a realistic global tide simulation. In this simulation, the resolution of the child domain (1/75°) is three times as fine as that of the parent domain (1/25°). The M 2 sea-surface-height root-mean-square errors with tide gauge data and the altimetry-constrained global FES2014 and TPXO9-atlas tidal solutions are evaluated for the nesting and no-nesting solutions. The better resolved coastal bathymetry and the finer grid in the child domain improve the local tides in Hudson Strait and Bay, and the back-effect of the coastal tides induces an improvement of the barotropic tides in the open ocean of the Atlantic. • A two-way nesting framework has been developed to improve surface tidal accuracy in a global ocean model (HYCOM). • Data are exchanged between a parent and a child domain with an external coupler (OASIS3-MCT). • The developed nesting framework is validated with semi-idealized experiments and applied to a realistic global case. • The two-way nesting results are compared to tide gauge data, and the FES2014 and TPXO9-atals tidal solutions. • The open-ocean surface tide (1/25°) is improved through two-way nesting with the 1/75° coastal-shelf domain. [ABSTRACT FROM AUTHOR]