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Internal tide is generated in the interface of density stratification by some hydrodynamic disturbance. The major mechanisms are borotrophic tidal current oscillated at the edge of the continental shelf, submarine canyons, ridges or sills. The resulting disturbance generated has the same motion cycle of tidal period. There were internal tides reported in the Kaoping Submarine Canyon. The generation sites and mechanisms, however, are not clear. This study analysis four cruises of field observed data using ship mounted ADCP and CTD, and moored temperature strings and current meters. The results showed: (1) The phase of M2 tidal current increase toward the canyon head, with minimum value at the canyon mouth. This result implies that the internal tide was generated near the canyon mouth and propagated up canyon with the thermocline decreasing toward the shallower water. (2) The internal tide generated at the canyon mouth propagated, through some mechanisms, at the upper layer density interface about 150m instead of beaming near the bottom layer where the current and topography interact. (3) The vertical variations of tidal ellipse and phase based on bottom mounted ADCP support the results of ship mounted observations, the internal tidal energy propagates near the interface of 150m below the surface.

Internal waves are vertical displacements of stratified water which can propagate a long distance without much energy dissipation. It plays on important role in conveying nutrient from deep ocean to shallower layers, and promoting biological growth. It also affects acoustics, ocean engineering and submarine navigation. Therefore, in the last few years, many scholars have devoted the research of internal waves, especially their generation and transportation in South China Sea. This research discusses the internal wave source, through the Princeton Ocean Model (POM). There are two simulations, one has bigger grid size 3.6km for the whole Luzon Strait in the region, 118¢XE ~123¢XE 18¢XN ~22¢XN, the other has smaller grid of 1.6km, for 118.5¢XE ~123¢XE and 19.5¢XN ~21.5¢XN. The total simulation period is 25 days, The north and south bomdawes use radiation boundary condition, the east side is driven by tidal calculated from WXTide32 model, the west side also uses radiation boundary condition. Three dimensional flow field during May, 2005, is simulated temperature, baroclinic velocity distribution, baroclinic energy flux, Empirical Orthogonal Functio ns (EOF), Fast Fourior transform (FFT), buoyancy frequency and Froude number are all analyzed, The results show that, when tidal current near the Batan island has the stronger baroclinic flow downward to transmit, after through Heng-Chun ridge the baroclinic energy flux to concenter, extrapolated this time possibly produces for internal tide.

It is generally understood that tidal currents ominated the flow field in many submarine canyons, and internal tide may be an order of magnitude more energetic than that of barotropic. The internal tide can be generated and amplified in a marine environment with the strong vertical density interface. The barotropic tides were known to play the dominant role in driving the internal tides at the topographic relief or shelf break.This research tries to look at the mechanisms of internal tides generation and propagation in the Kaoping Submarine Canyon off southwestern Taiwan, using Princeton Ocean Model (POM) with different settings. The model was tested with bottom topography of flat, a slope and real water depth, with and without vertical stratifications. The model settings are grid size 500m, simulate period days, radiation boundary condition at 4 sides. The model forcings are sea level variations at the west side, both semidiurnal tide (M2) and mixed tide (M2+K1) based on OSU tidal model TPXO 6.2. The results suggest that the offshore M2 tidal forcing can generate large internal tidal currents within the canyon with vertical density stratification. The internal tidal currents at the upper-layer of the canyon lag that of lower-layer 3~5 hours. There is no time lag and no amplification of current in the canyon if there is no stratification. There is a transition zone of minimum flow at depth of about 100-200m. Below the interface, the amplitude of semidiurnal internal tidal current increased with water depth in the canyon. The simulated density contours suggest a 120m amplitude vertical fluctuation center at 150m depth, with 5¢J temperature fluctuation. The computed baroclinic energy flux indicates that the energy in lower layer of the canyon is stronger than that of upper layer. The high energy flux appears at the canyon foot and rim, and propagates along the canyon axis landward.

The internal tide in GPSC¡]Gaoping submarine canyon¡^is the main factor controlling the movement of watermasses. In order to improve our understanding on the compact of suspended sediment exchange in and out GPSC, the data used in this study are collected from four cruises of field observations using research vessel OR3. Instruments deployed include ADCPs¡BEK500¡BCTD and vertical string of temperature loggers. The collected data are analyzed through a variety of time series analysis technique, such as harmonic analysis¡BFFT and EOF. The results show that¡]1¡^the echo intensity recorded by ADCP through calibration could reduce the decay of echo with the distance. The results seem useful to apply in watermass behavior studies.¡]2¡^ Echo intensity with calibration were comparable with signal recorded by EK500 which could be validated to each other. These observations were related to sediment resuspension influenced by internal tide. ¡]3¡^There were two layers of large turbidity, at the depth of canyon edge and near the bottom of canyon, both were fluctuated with two interval tidal frequency.¡]4¡^Another band of echo intensity fluctuations, not directly correlate to sediment resuspension, was likely due to vertical migration, of zooplankton or biology effects.

The barotropic tide dissipates a well established estimate of 2.5 TW of energy at the M2 frequency. Bottom topography is responsible for part of this dissipation, and the generation of the internal tide is also partly responsible. The fate of this energy is largely described by a cascade from large scales to small scales by non-linear wave-wave interactions where it gets dissipated. This thesis aims to investigate how the presence of mesoscale eddies (vortices) in the ocean affect the internal tide. Previous work has looked at the interaction of the barotropic tide with eddies. Krauss (1999) found that the interaction can produce a modulated internal tide, however a scaling analysis suggests that the effect may not be as strong as reported. The MITgcm is used to simulate internal wave generation by barotropic flow over topography and comparisons are made with Dr. Lamb's IGW model. Baroclinic eddies are analytically prescribed and then geostrophically adjusted also using the MITgcm. Finally, the two are combined, and the internal tide field is analysed with and without the presence of eddies of various magnitude and length scales. The results of this investigation do not find a strong transfer of energy between modes; the modal distribution of energy in the internal tide remains the same when an eddy is added. However, focusing and shadow beams of internal waves are produced in the wake of an eddy as the internal waves pass through it. The beams show very strong variations in intensity, vertically integrated energy flux can reduce almost to zero in the shadow regions and increase more than double in the focusing regions. Modal decomposition of the horizontal flow field reveals that mode 2 and 3 waves are most strongly affected by the eddies and contribute strongly to the formation of the beams. Mode 1 appears to be less affected by the eddy. The larger wavelength and faster group velocity of mode 1 supports the notion that the eddy interacts with it less.

The barotropic tide dissipates a well established estimate of 2.5 TW of energy at the M2 frequency. Bottom topography is responsible for part of this dissipation, and the generation of the internal tide is also partly responsible. The fate of this energy is largely described by a cascade from large scales to small scales by non-linear wave-wave interactions where it gets dissipated. This thesis aims to investigate how the presence of mesoscale eddies (vortices) in the ocean affect the internal tide. Previous work has looked at the interaction of the barotropic tide with eddies. Krauss (1999) found that the interaction can produce a modulated internal tide, however a scaling analysis suggests that the effect may not be as strong as reported. The MITgcm is used to simulate internal wave generation by barotropic flow over topography and comparisons are made with Dr. Lamb's IGW model. Baroclinic eddies are analytically prescribed and then geostrophically adjusted also using the MITgcm. Finally, the two are combined, and the internal tide field is analysed with and without the presence of eddies of various magnitude and length scales. The results of this investigation do not find a strong transfer of energy between modes; the modal distribution of energy in the internal tide remains the same when an eddy is added. However, focusing and shadow beams of internal waves are produced in the wake of an eddy as the internal waves pass through it. The beams show very strong variations in intensity, vertically integrated energy flux can reduce almost to zero in the shadow regions and increase more than double in the focusing regions. Modal decomposition of the horizontal flow field reveals that mode 2 and 3 waves are most strongly affected by the eddies and contribute strongly to the formation of the beams. Mode 1 appears to be less affected by the eddy. The larger wavelength and faster group velocity of mode 1 supports the notion that the eddy interacts with it less.

Full-depth profile data reveal semidiurnal internal waves radiating from Mendocino Escarpment. Energy- and momentum-fluxes are lost between stations bracketing the first surface reflection to the north. A plausible interpretation is that wave energy is dissipated as a consequence of superposition of incident and reflected waves. Because there are no profiler data in the superposition region, a theoretical approach is used to bridge the gap. Assuming zonal independence, constant stratification and linear decay in the dissipation region, the forcing on the mean equations is evaluated with parameters consistent with Mendocino Escarpment data. Both superposition and dissipation cause momentum-flux divergence forcing. An Ekman-like balance is anticipated with predicted mean zonal flows u~O(1-2 cm/s), comparable to surface wind-forced Ekman currents.

Les océans de la Terre sont stratifiés en densité par les gradients de température et de salinité.L'interaction des courants de marée avec la topographie du fond océanique entraîne donc le rayonnement des ondes de gravité interne dans l'intérieur de l'océan. Ces ondes sont appelées marées internes et leur dissipation due à le déferlement des ondes nonlinéaires joue un rôle important dans le mélange de l'océan abyssal, et donc dans la circulation océanique à la grande échelle.Dans ce contexte, nous étudions la génération des ondes internes par l’oscillation d’objet de différentes géométries simplifiées afin de modéliser le marée barotropique sur la topographie océanique et considérons les effets linéaires et nonlinéaires sur ces ondes résultant d’interactions avec l'objet et entre ces ondes.La contribution relativement nouvelle de cette thèse est l'étude des aspects de flux tridimensionnels qui étaient accessibles avec notre approche expérimentale, et sont généralement difficiles à étudier par modélisation numérique et analytique.Nous étudions d'abord la structure des ondes fundamentale et des harmoniques supérieur pour un sphéroïde oscillant, émettant des ondes divergentes. Les harmoniques supérieures sont générées par l'instabilité non linéaire à la surface de l'objet avec des effets nonlinéaires dans la zone d'intersection des faisceaux fundamentales. Ils peuvent se croiser et se concentrer, donc augmenter d'énergie, et devenir dominant sur les ondes fundamentales. On détermine les structures horizontales des ondes fundamentale et des harmoniques supérieures.Subséquemment, nous considérons les ondes générées par un tore oscillant, qui convergent vers un point focal. En dehors de cette région focale, les résultats expérimentaux et les prédictions théoriques sont en bon accord, mais dans la région focale, l'amplitude de l'onde est deux fois plus grande que près du tore, conduisant à une amplification locale nonlinéaire et à un déferlement des onde pour les grandes amplitudes d'oscillations. En conséquence, la propagation des ondes fundamentales se trouve entravée dans la région focale. L'onde stationnaire se forme alors que de nouvelles ondes sont générées et émises de cette région focale.Un tore plus grand a été testé sur la plate-forme Coriolis pour comparer la focalisation des ondes de gravité internes, inertie-gravité et des ondes inertielles dans un régime faiblement visqueux. En raison de la complexité de la zone focale, une seconde harmonique est observée même quand l'amplitude d'oscillation est faible. Le champ de vorticité verticale des ondes de gravité interne présente une structure dipolaire dans la zone focale, qui se transforme dans le cas tournant en une structure de vortex "Yin-Yang". La structure globale des faisceaux des ondes inertiels est proche de celle pour des ondes de gravité internes, bien q'elle est relativement plus intense. / The Earth's oceans are stratified in density by temperature and salinity gradients.The interaction of tidal currents with ocean bottom topography results therefore in the radiation of internal gravity waves into the ocean interior. These waves are called internal tides and their dissipation owing to nonlinear wave breaking plays an important role in the mixing of the abyssal ocean, and hence in the large-scale ocean circulation.In this context we investigate the generation of internal waves by oscillating objects of different idealized geometries as a model of barotropic flow over ocean topography, and consider linear as well as nonlinear effects on these waves resulting from interactions with the object and from wave--wave interactions.The relatively novel contribution of this thesis is the investigation of three-dimensional flow aspects that were accessible with our experimental approach, and are generally difficult to investigate by numerical and analytical modelling.First we investigate the wave structure of the first and higher harmonics for an oscillating spheroid, emitting diverging waves. Higher harmonics are generated by nonlinear instability at the surface of the object together with nonlinear effects in the zone of intersection of the primary beams. They may intersect and focus, therefore increase in energy, and become dominant over the first harmonic. The horizontal structures of both, first and higher harmonics are determined.We then consider waves generated by an oscillating torus, that are converging to a focal point. Outside this focal region experimental results and theoretical predictions are in good agreement, but in the focal region the wave amplitude is twice as large as it is close to the torus, leading to local nonlinear wave amplification and incipient wave breaking for large oscillation amplitudes. As a result, the propagation of the first harmonic waves is found to be hindered in the focal region. A standing pattern forms, while new waves are generated and emitted away from this focal region.A larger torus has been tested at the Coriolis platform to compare the focusing of internal gravity, inertia--gravity and inertial waves in a low viscous regime. Owing to the complexity of the focal region, a second harmonic is observed even at low oscillation amplitude. The vertical vorticity field of internal gravity waves exhibits a dipolar structure in the focal zone, which transforms in the rotating case into a ``Yin--Yang-shaped'' monopolar vortex structure. The overall structure of the inertial wave beams is close to that for internal gravity waves, though relatively more intense.