Tidal Energy Dissipation Research Articles

Landfast Ice Controls on Turbulence in Antarctic Coastal Seas

AbstractKnowledge of the ocean surface layer beneath Antarctic landfast ice is sparse. In this article surface layer turbulent and fine structure are quantified with and without landfast ice at the same West Antarctic Peninsula location. Landfast ice reduced turbulence levels locally to an order of magnitude less than ice‐free values, and near‐inertial energy and sub‐inertial tidal energy levels to less than half their ice‐free values. Vertical turbulent heat and nutrient fluxes were, respectively, 6 and 10 times greater than previously estimated. Under‐ice tidal energy dissipation over the entire Antarctic continental shelf due to seasonal landfast ice cover is estimated to be between 788 MW to ∼6 GW. The total rate of wind‐generated turbulence in the surface ocean is greatly reduced by the presence of seasonal landfast ice to an average of 14% of the ice‐free value, but with large sectoral variations. Counter‐intuitively, however, tides and wind contribute approximately equally to the turbulent kinetic energy budget of the upper ocean between the Antarctic coastline and the maximal landfast ice extent, with large sectoral variations, attributed to geographic variations in the strength of the barotropic tide.

Influence of Energy Dissipation on Spin Pole Precession Trajectories for Synchronous Rotators

Abstract We present an analysis of the influence of tidal energy dissipation on the precessional motion of the spin pole of a synchronously rotating body, whose orbit pole is also precessing. In the absence of dissipation, this problem has been frequently analyzed in a Hamiltonian context. The Cassini states, or fixed points of the motion of the spin pole, correspond to tangent intersections of the Hamiltonian function with the unit sphere. When dissipation is added to the dynamics, the locations of the fixed points change. We present a new geometrical characterization of the nullclines of the dissipative flow, or motion of the spin pole, and use it to find the locations of the dissipative fixed points. Using the Poincaré−Hopf index theorem, we show that in the case where there are four fixed points, one is a saddle, and depending on the sign of the dissipation rate parameter, the other three comprise either two sources and one sink or one source and two sinks. We also examine the domains of attraction of the sinks and present an analysis of their stability to initial conditions and model parameters.

Long-Term Earth-Moon Evolution With High-Level Orbit and Ocean Tide Models.

Tides and Earth‐Moon system evolution are coupled over geological time. Tidal energy dissipation on Earth slows Earth′s rotation rate, increases obliquity, lunar orbit semi‐major axis and eccentricity, and decreases lunar inclination. Tidal and core‐mantle boundary dissipation within the Moon decrease inclination, eccentricity and semi‐major axis. Here we integrate the Earth‐Moon system backwards for 4.5 Ga with orbital dynamics and explicit ocean tide models that are “high‐level” (i.e., not idealized). To account for uncertain plate tectonic histories, we employ Monte Carlo simulations, with tidal energy dissipation rates (normalized relative to astronomical forcing parameters) randomly selected from ocean tide simulations with modern ocean basin geometry and with 55, 116, and 252 Ma reconstructed basin paleogeometries. The normalized dissipation rates depend upon basin geometry and Earth′s rotation rate. Faster Earth rotation generally yields lower normalized dissipation rates. The Monte Carlo results provide a spread of possible early values for the Earth‐Moon system parameters. Of consequence for ocean circulation and climate, absolute (un‐normalized) ocean tidal energy dissipation rates on the early Earth may have exceeded today′s rate due to a closer Moon. Prior to ∼3Ga, evolution of inclination and eccentricity is dominated by tidal and core‐mantle boundary dissipation within the Moon, which yield high lunar orbit inclinations in the early Earth‐Moon system. A drawback for our results is that the semi‐major axis does not collapse to near‐zero values at 4.5 Ga, as indicated by most lunar formation models. Additional processes, missing from our current efforts, are discussed as topics for future investigation.

Responses of hydrodynamics to changes in shoreline and bathymetry in the Pearl River Estuary, China

Numerous estuaries worldwide have been modified in the past decades by human interventions. The shoreline and bathymetry in the Pearl River Estuary (PRE) have changed greatly over the past 40 years due to the influence of land reclamation and waterway dredging, which have resulted in the corresponding adjustment of its hydrodynamics. Utilizing the ROMS numerical model, this paper studies the hydrodynamic responses to changes in shoreline and bathymetry in the PRE from 1971 to 2012. The results show that, on one hand, during neap tide, the change in the shoreline makes the residual current in the West Channel (WC) increase by 0.10 (0.05) m/s at maximum in the surface (near bottom) layer. Therefore, the exchange flow increases by 9.5% and the longitudinal circulation strengthens. The surface isohalines move southward up to 18 km, but the bottom isohalines move northward ∼2 km in the WC and East Channel (EC), which is different from the previous conclusion that the seaward extension of coastlines inhibits saltwater intrusion. The decrease in salinity in the upper layer reduces the upper seaward salt transport, resulting in a larger net landward salt transport from 25.21 × 103 kg/s to 35.44 × 103 kg/s. During spring tide, the changes are relatively weaker, but the direction of salt transport changes to seaward and the net seaward transport also increases. Moreover, the change in shoreline reduces the water area and volume in the PRE by 21.3% and 15.6% respectively, which causes a reduction of 11.3% (17.1%) in tidal prism during spring (neap) tide. The wave celerity is enhanced (>23%) and the amplification of semidiurnal tide is strengthened (>20%) in the WC and West Shoal (WS). The reduction in tidal prism together with the strengthened reflection of tidal waves with a larger phase lag between elevation and velocity of M2 tidal component cause a significant decrease of 19.0% in tidal energy flux entering the PRE. However, the tidal range increases by ∼0.30 m (mainly due to the increase in M2 tidal amplitude) in the EC, which is induced by lower tidal energy dissipation there. On the other hand, during neap tide, the change in bathymetry greatly enhances the bottom landward residual current whose peak value increases by 80% in the WC, thereby increasing approximately 14 km of the intrusion distance of saline water, enhancing the exchange flow by 27.5% and strengthening the longitudinal circulation. The net landward salt transport increases to 38.39 × 103 kg/s. The results during spring tide are similar to those during neap tide but with smaller changes, and the net seaward salt transport decreases. Moreover, the wave celerity is slightly reduced (<8%) and the amplification of semidiurnal tide is also decreased (<10%) in the WC and WS. Meanwhile, the change in bathymetry only decreases the water volume by 4.7%, leading to a relatively smaller effect on the tidal prism, and it strengthens (weakens) the reflection of tidal waves in the West Shoal and Middle Shoal (WC and EC), resulting in a slight reduction in tidal energy flux entering the bay. In the WC, the tidal range is basically unchanged since the increased tidal energy flux is offset by the increased dissipation. The quantitative results obtained in this study may provide some references for the development and protection of the PRE and other estuaries that are subject to strong human interventions.

Enhanced vertical mixing in the glacial ocean inferred from sedimentary carbon isotopes

Reconstructing the circulation, mixing and carbon content of the Last Glacial Maximum ocean remains challenging. Recent hypotheses suggest that a shoaled Atlantic meridional overturning circulation or increased stratification would have reduced vertical mixing, isolated the abyssal ocean and increased carbon storage, thus contributing to lower atmospheric CO2 concentrations. Here, using an ensemble of ocean simulations, we evaluate impacts of changes in tidal energy dissipation due to lower sea levels on ocean mixing, circulation, and carbon isotope distributions. We find that increased tidal mixing strengthens deep ocean flow rates and decreases vertical gradients of radiocarbon and δ13C in the deep Atlantic. Simulations with a shallower overturning circulation and more vigorous mixing fit sediment isotope data best. Our results, which are conservative, provide observational support that vertical mixing in the glacial Atlantic may have been enhanced due to more vigorous tidal dissipation, despite shoaling of the overturning circulation and increases in stratification.

Life at low Reynolds Number Re-visited: The apparent activation energy of viscous flow in sea water

In a 1976 lecture entitled “Life at low Reynolds Number,” Edward Purcell examined constraints on mobility of small aquatic animals defining the energetic challenge as “to move far enough to beat diffusion.” We show that the essential requirement is the need to do sufficient work to overcome the activation energy of viscous flow. Raman spectroscopy shows that sea water is dominated (78–85%) by the hydrogen bonded forms, primarily as the large (H2O)5 tetrahedral pentamer form. Two hydrogen bonds must be broken to disrupt this structure. The strength of the hydrogen bond in water is ~8.4 kJ/mol and the experimentally determined activation energy of viscous flow (~16.7 kJ/mol) is approximately equal to that required to break two hydrogen bonds in water. For viscous flow to occur a molecular vacancy must form for a flowing molecule to move into; the smaller the vacancy needed the less energy required. The heat created by a small animal swimming breaks hydrogen bonds thus forming a layer of small non-hydrogen bonded H2O molecules around the animal. These “lubricate” the surface yielding far more efficient viscous flow. The activation energy of the viscous flow of water decreases with pressure most likely due to the weaker strength of the hydrogen bond under pressure – lab and field data support this observation. The dissipation of tidal energy as heat, often attributed to “intermolecular forces,” is directly related to the breaking of hydrogen bonds.

Role of tide-induced vertical mixing in the deep Pacific Ocean circulation

We investigate the control mechanisms of the deep Pacific Ocean circulation by introducing updated methods for parameterizing tidal mixing. The column-integrated rates of dissipation in near- and far-fields are derived from the tidal energy conversion and dissipation rates estimated by a high resolution tide model. In the calculation of the far-field mixing, its dependency on stratification is taken into account based on theoretical and observational knowledge. Unlike previous studies that did not take the stratification dependence into account, the far-field mixing does not function to significantly enhance the deep Pacific Ocean circulation. The deep Pacific Ocean circulation is also found to be insensitive to the decay scale height of the near-field mixing. However, these factors affect the reproducibility of the radiocarbon distribution, especially its minimum in the upper deep layer, through their influence on the mixing with the shallower layers.

Bardsey – an island in a strong tidal stream: underestimating coastal tides due to unresolved topography

Abstract. Bardsey Island is located at the western end of the Llŷn Peninsula in northwestern Wales. Separated from the mainland by a channel that is some 3 km wide, it is surrounded by reversing tidal streams of up to 4 m s−1 during spring tides. These local hydrodynamic details and their consequences are unresolved by satellite altimetry and are not represented in regional tidal models. Here we look at the effects of the island on the strong tidal stream in terms of the budgets for tidal energy dissipation and the formation and shedding of eddies. We show, using local observations and a satellite-altimetry-constrained product (TPXO9), that the island has a large impact on the tidal stream and that even in this latest altimetry-constrained product the derived tidal stream is under-represented due to the island not being resolved. The effect of the island leads to an underestimate of the current speed in the TPXO9 data in the channel of up to a factor of 2.5, depending on the timing in the spring–neap cycle, and the average tidal energy resource is underestimated by a factor up to 14. The observed tidal amplitudes are higher at the mainland than at the island, and there is a detectable phase lag in the tide across the island; this effect is not seen in the TPXO9 data. The underestimate of the tide in the TPXO9 data has consequences for tidal dissipation and wake effect computation and shows that local observations are key to correctly estimating tidal energetics around small-scale coastal topography.

High-Resolution Modeling of Semidiurnal Internal Tidal Waves in the Laptev Sea in the Ice-Free Period: Their Dynamics and Energetics

The QUODDY-4 three-dimensional finite-element hydrostatic model has been used to reproduce the spatial distributions of dynamic and energetic characteristics of the internal tidal waves (ITWs) of the Laptev Sea in the ice-free period. It has been shown that one distinctive feature of ITW amplitudes at the pycnocline depth is that the area with relatively high ITW amplitudes is limited. The peak amplitudes reaching at least 5 m have been detected only in the central part of the sea near the continental slope, but the ITW amplitudes in the western and eastern parts of the sea do not exceed 0.2 and 0.1 m, respectively. Like ITW amplitudes, the baroclinic tidal velocities are expressed mainly in the central part of the sea and almost vanish in its western and eastern parts. The presence of a zone of high baroclinic velocities near the northern open border of the sea and an increase in velocities with approaching the coast of the continent at the mouth of the Lena River is noted. The fields of components of the averaged (over a tidal cycle) baroclinic tidal energy budget (integrated by depth) are discussed. The averaged (over the sea area) values of the density of baroclinic tidal energy, as well as the tidal energy conversion and dissipation rates, are $$1.2\,\, \times \,\,{{10}^{3}}$$ J/m2, $$ - 0.3\,\, \times \,\,{{10}^{{ - 3}}}$$ W/m2, and $$7.3\,\, \times \,\,{{10}^{{ - 3}}}$$ W/m2, respectively. The ITW lifetime in the Laptev Sea, defined as the ratio of the average density of baroclinic tidal energy to the dissipation rate, is around 50 h; i.e., the ITW lifetime in the sea is 4 times higher than the tidal cycle length for the M2 tidal harmonic.

Role of internal tide mixing in keeping the deep Andaman Sea warmer than the Bay of Bengal

Vertical profiles of temperature obtained from various hydrographic datasets show that deep waters (below 1,200 m) in the Andaman Sea are warmer (about 2 °C) than that of the Bay of Bengal. As a result, the biochemical properties in the deep waters also exhibit significant differences between these two basins. Higher temperature in the deep waters of Andaman Sea compared to the BoB had been widely attributed to the enclosed nature of the Andaman Sea. In this study, we show that strong tidal energy dissipation in the Andaman Sea also plays an important role in maintaining the higher temperatures in the deep waters. Dissipation rates inferred from the hydrographic data and internal tide energy budget suggests that the rate of vertical mixing in the Andaman Sea is about two-orders of magnitude larger than that in the Bay of Bengal. This elevated internal tide induced vertical mixing results in the efficient transfer of heat into the deeper layers, which keeps the deep Andaman Sea warm. Numerical experiments conducted using a high-resolution setup of Regional Ocean Modelling System (ROMS) further confirm the effect of tidal mixing in the Andaman Sea.

Influence of Horizontal Nonuniformity of Stratification on Internal Tides and Their Induced Diapycnal Diffusion in the Ice-Free Kara Sea

Abstract—The 3D finite-element hydrostatic model QUODDY-4 is used to study the influence of horizontally nonuniform stratification on internal tides and their induced diapycnal diffusion in the ice-free Kara Sea. This model was used to perform two numerical experiments. In the first stratification is assumed to be horizontally uniform and determined by predicted seawater temperature and salinity values found during solution of the problem. It is shown that when horizontally uniform stratification is replaced by horizontally nonuniform stratification, the amplitudes of internal tides over a bottom uplift are increased, while the amplitudes of baroclinic tidal velocities are decreased. These decreasing amplitudes of baroclinic tidal velocities instead of their increasing values typical for waves studied in a linear approximation are apparently related to wave disintegration (in the region of the critical latitude) into trains of nonlinear short-period internal waves. A similar situation arises with baroclinic tidal energy dissipation: it is either enhanced or attenuated depending on location in the sea. These changes in dissipation and stratification lead to variations in diapycnal diffusion, followed by initiation of tidal changes in the climate of the considered marine system.

Impacts of tidal-channel connectivity on transport asymmetry and sediment exchange with mangrove forests

Mangrove forests provide many valuable services, including wave- and tidal-energy dissipation, sediment accumulation, and substrate stabilization. But, their global extent is rapidly shrinking. Sedimentary research that is needed to inform restoration projects has so far focused on characterizing flow patterns through forests associated with single rivers, nearshore environments, or terminating tidal channels. However, flows within the most extensive mangrove forests tend to be driven through channels that connect to multiple estuaries or other channels with temporally lagged tides. For this study, in-situ observations of water and sediment flux were obtained in two tidal channels near the Amazon River to characterize how connectivity impacts sediment transport in coastal mangrove forests. The low-connectivity channel connects to one estuary whereas the high-connectivity channel connects two estuaries. We conclude that channel connectivity controls the amount of sediment stored in channels that is available to supply mangrove forests. Although phase-duration asymmetry is flood dominant in both channels, velocity asymmetry becomes ebb dominant during tidal cycles when the mangrove flats are inundated. Additionally, tidal elevation and water velocity are not in quadrature for the high-connectivity channel, as they are for the low-connectivity channel. As a result, the high-connectivity channel acts as a conduit for sediment from one estuary to another rather than simply importing and retaining sediment like the low-connectivity channel. High-connectivity channels distribute point-source sediment along coastlines and provide sediment to estuaries and channels that may not have their own direct source. As restoration efforts of mangrove forests continue to grow in response to coastal threats such as sea-level rise and diminished fluvial-sediment delivery, the location of these efforts can benefit from the conclusion that channel connectivity influences spatial dispersal of sediment supply to mangrove forests.

The rate of planet–star coalescences due to tides and stellar evolution

ABSTRACT Orbits of close-in planets can shrink significantly due to dissipation of tidal energy in a host star. This process can result in star–planet coalescence within the Galactic lifetime. In some cases, such events can be accompanied by an optical or/and UV/X-ray transient. Potentially, these outbursts can be observed in near future with new facilities such as LSST from distances about few Mpc. We use a population synthesis model to study this process and derive the rate of star–planet mergers of different types. Mostly, planets are absorbed by red giants. However, these events, happening with the rate about 3 per year, mostly do not produce detectable transients. The rate of mergers with main sequence stars depends on the effectiveness of tidal dissipation; for reasonable values of stellar tidal quality factor, such events happen in a Milky Way-like galaxy approximately once in 70 yr or more rarely. This rate is dominated by planets with low masses. Such events do not produce bright transients having maximum luminosities ≲ 1036.5 erg s−1. Brighter events, related to massive planets, with maximum luminosity ∼1037.5–1038 erg s−1, have the rate nearly five times smaller.

Oscillations around tidal pseudo-synchronous solutions for circumbinary planets

AbstractTidal evolution of low-eccentric circumbinary planets is expected to drive the rotational evolution toward a pseudo-synchronous solution. In this work, we present a study of the oscillation amplitudes around this state by considering that the two central stars exert creep tides on the planet. These amplitudes are computed by direct numerical integrations of the creep equations and also by means of the calculation of the coefficients of the periodic terms in this stationary solution. As in the two-body-problem, the planetary spin and lag-angle are observed to have maximum oscillation amplitudes for stiff bodies and almost null oscillation for the gaseous regime, while the opposite behaviour is observed in the equatorial and polar flattenings. Our analytical approximation shows to be very accurate and specially necessary for very-low eccentric planets. However, the magnitudes of the oscillation amplitudes around the pseudo-synchronous solution in the circumbinary problem appears to be very small respect to the mean value. Thus, considering these oscillation in the computation of the tidal energy dissipation may not have a substantial contribution in the results, at least compared to the case in which only the mean values are taken into account.

The tidal effect on the climatic characteristics of the Kara Sea in the ice-free period

Using a high-resolution version of the QUODDY-4 three-dimensional finite-element hydrostatic model, we have carried out two series of numerical experiments. The first estimates tidal changes characterizing the role of tides in the formation of climatic characteristics of the Kara Sea in the ice-free period (the magnitude and directions of velocity of permanent surface currents, temperature, and salinity at the pycnocline base and level of the free sea surface). The second series checks the adequacy of the indirect description of tidal changes in terms of tide-induced baroclinic tidal-energy dissipation and diapycnal diffusion when compared to the explicit method and obtains a quantitative measure that can be used for their comparison. The modeling results indicate, first, that the tidal changes are a significant, if not key, factor; second, that the indirect description of tidal changes is adequate when compared to the explicit method; third, that it is unjustified to disregard these changes (this is common in predicting and computing the climates of marine systems); and, finally, that the correlation averaged over the sea surface area can be taken as a quantitative measure of the similarity of the fields of climatic characteristics obtained for the total (wind + thermohaline + tidal) forcing, on the one hand, and the combined (wind + thermohaline) forcing coupled with the indirect method for the description of tidal changes, on the other.

The Tidal Effect on Climatic Characteristics of the Kara Sea in the Ice-Free Period

Using a high-resolution version of the QUODDY-4 three-dimensional finite-element hydrostatic model, we have carried out two series of numerical experiments. The first estimates tidal changes characterizing the role of tides in the formation of climatic characteristics of the Kara Sea in the ice-free period (the magnitude and directions of velocity of permanent surface currents, temperature, and salinity at the pycnocline base and level of the free sea surface). The second series checks the adequacy of the indirect description of tidal changes in terms of tide-induced baroclinic tidal-energy dissipation and diapycnal diffusion when compared to the explicit method and obtains a quantitative measure that can be used for their comparison. The modeling results indicate, first, that the tidal changes are a significant, if not key, factor; second, that the indirect description of tidal changes is adequate when compared to the explicit method; third, that it is unjustified to disregard these changes (this is common in predicting and computing the climates of marine systems); and, finally, that the correlation averaged over the sea surface area can be taken as a quantitative measure of the similarity of the fields of climatic characteristics obtained for the total (wind + thermohaline + tidal) forcing, on the one hand, and the combined (wind + thermohaline) forcing coupled with the indirect method for the description of tidal changes, on the other.

German Bight estuaries: An inter-comparison on the basis of numerical modeling

The Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), which is an unstructured-grid model, was coupled with a 3D sediment model and established for the German Bight and its estuaries. The horizontal resolution of the model ranges from ~10 m in the estuaries to ~400 m in most of the open sea. Validation against tidal gauge data, fixed station data, and FerryBox data demonstrated that the model adequately simulated tidal dynamics in the entire area as well as the salinity fronts and estuarine turbidity maxima in the Ems, Weser and Elbe estuaries. Comparisons of model output with that of experiments with constant density allowed to estimate the role of density control, which appeared to be strongest in the landward reaches of salinity front. The increase of tidal range caused by density effects was most prominent in the Weser and Elbe estuaries, and relatively small in the Ems, where the runoff was also small. The magnitude of the density effect on the sea level oscillations was comparable to that of the M4 tide amplitude, demonstrating its importance in shaping the tidal asymmetry in the estuaries. Density effects not only reduced the dissipation of tidal energy; density stratification suppressed also the resuspension of sediment and contributed to a displacement of the position of the estuarine turbidity maximum upstream compared to the case of an homogeneous estuary. In the case of hyper-turbid Ems Estuary, density effects on stratification caused by high sediment concentrations resulted in a suppression of turbulence and further increase of concentration of suspended matter at the bottom. Although the three estuaries, which are only ~100 km apart, were driven by similar tidal and atmospheric forcings, they exhibited different extensions of both fronts and vertical stratification, mainly due to different river runoff conditions. At intra-tidal time scales, the dependencies between sea surface height and sea surface salinity varied considerably from estuary to estuary, and the largest flood asymmetry appeared in the Elbe Estuary. Wind acted as the dominant factor driving the longer-term estuarine variability; the correlation between zonal wind magnitude and sea surface height appeared to be very strong. The simulated suspended particulate matter dynamics and position of the estuarine turbidity maxima (ETM) were in agreement with observations. Secondary ETM appeared at different locations depending on the grain size, providing an illustration of sediment sorting.

Strong tidal energy dissipation in Saturn at Titan’s frequency as an explanation for Iapetus orbit

Context. Natural satellite systems present a large variety of orbital configurations in the solar system. While some are clearly the result of known processes, others still have largely unexplained eccentricity and inclination values. Iapetus, the furthest of Saturn’s main satellites, has a still unexplained 3% orbital eccentricity and its orbital plane is tilted with respect to its local Laplace plane (8° of free inclination). On the other hand, astrometric measurements of saturnian moons have revealed high tidal migration rates, corresponding to a quality factor Q of Saturn of around 1600 for the mid-sized icy moons. Aims. We show how a past crossing of the 5:1 mean motion resonance between Titan and Iapetus may be a plausible scenario to explain Iapetus’ orbit. Methods. We have carried out numerical simulations of the resonance crossing using an N-body code as well as using averaged equations of motion. A large span of migration rates were explored for Titan and Iapetus was started on its local Laplace plane (15° with respect to the equatorial plane) with a circular orbit. Results. The resonance crossing can trigger a chaotic evolution of the eccentricity and the inclination of Iapetus. The outcome of the resonance is highly dependent on the migration rate (or equivalently on Q). For a quality factor Q of over around 2000, the chaotic evolution of Iapetus in the resonance leads in most cases to its ejection, while simulations with a quality factor between 100 and 2000 show a departure from the resonance with post-resonant eccentricities spanning from 0 up to 15%, and free inclinations capable of reaching 11°. Usually high inclinations come with high eccentricities but some simulations (less than 1%) show elements compatible with Iapetus’ current orbit Conclusions. In the context of high tidal energy dissipation in Saturn, a quality factor between 100 and 2000 at the frequency of Titan would bring Titan and Iapetus into a 5:1 resonance, which would perturb Iapetus’ eccentricity and inclination to values observed today. Such rapid tidal migration would have avoided Iapetus’ ejection around 40–800 million years ago.

Effects of Radial Sand Ridges on tidal process in the South Yellow Sea

The South Yellow Sea continental shelf, with a wide area of shallow waters, is located at the intersection of the rotating tidal wave system in the west of the South Yellow Sea and the tidal wave system in the East China Sea. The South Yellow Sea has a unique radiation sandbar terrain, and there are large currents of sand ridges and current channels. Most of the current researches focus on the development and evolution mechanisms of Radial Sand Ridges. However, there are few studies on the influence of tidal waves on terrain in this region. In this paper, the three-dimensional numerical model FVCOM (Finite Volume Coastal Ocean Model) was used to simulate the tidal propagation in the South Yellow Sea and was verified with measurements. This paper compares the changes in the tidal wave of the South Yellow Sea with and without the effect of Radial Sand Ridges to analyze the topographic effect. The changes of tidal wave shape, tidal current velocity, the redistribution of tidal energy and the distribution of tidal mixed zone were analyzed. This research has important implications for the prediction of tides, the development of fisheries and the maintenance of the ecological environment of the South Yellow Sea. The results show that the shape of tidal wave is distorted by the radial sand ridges: mainly, the duration of tidal ebbing is longer than that of tidal flooding. The distortion becomes distinct as the tidal wave approaches the shore, implying that the closer the tidal wave gets to the shore, the greater the nonlinear effect will be. The presence of the Radial Sand Ridges makes the flow rate of the radial inlet larger than 1 m/s, and the flow rate of both the rising tide and the ebbing tide is greater than that of the Waste Yellow River Estuary and the South Yangtze Estuary. At the same time, the existence of the special terrain enlarges the tidal energy flux, speeds up the tidal energy dissipation, and also makes the critical values of the tidal mixing front closer to the shore, namely the tidal mixing zone becoming shoreward. The Radial Sand Ridges also turns down the value of nearshore-stratification parameter. The sea-water blending is more severe in this area, compared to an idealized case with a flat shelf covering the South Yellow Sea. The range of influence of Radial Sand Ridges on tidal current velocity, tidal energy flux, tidal energy dissipation and tidal front position is relatively uniform. It has affected from the eastern part of the Shandong peninsula (around 122°E) across the Radial Sand Ridges to the southern Yangtze River estuary.

Internal Tide Dissipation at Topography: Triadic Resonant Instability Equatorward and Evanescent Waves Poleward of the Critical Latitude

AbstractSeveral studies have shown the existence of a critical latitude where the dissipation of internal tides is strongly enhanced. Internal tides are internal waves generated by barotropic tidal currents impinging rough topography at the seafloor. Their dissipation and concomitant diapycnal mixing are believed to be important for water masses and the large‐scale ocean circulation. The purpose of this study is to clarify the physical processes at the origin of this strong latitudinal dependence of tidal energy dissipation. We find that different mechanisms are involved equatorward and poleward of the critical latitude. Triadic resonant instabilities are responsible for the dissipation of internal tides equatorward of the critical latitude. In particular, a dominant triad involving the primary internal tide and near‐inertial waves is key. At the critical latitude, the peak of energy dissipation is explained by both increased instability growth rates, and smaller scales of secondary waves thus more prone to break and dissipate their energy. Surprisingly, poleward of the critical latitude, the generation of evanescent waves appears to be crucial. Triadic instabilities have been widely studied, but the transfer of energy to evanescent waves has received comparatively little attention. Our work suggests that the nonlinear transfer of energy from the internal tide to evanescent waves (corresponding to the 2f‐pump mechanism described by Young et al., 2008, https://doi.org/10.1017/S0022112008001742) is an efficient mechanism to dissipate internal tide energy near and poleward of the critical latitude. The theoretical results are confirmed in idealized high‐resolution numerical simulations of a barotropic M2 tide impinging sinusoidal topography in a linearly stratified fluid.