Showing papers on "Waves and shallow water published in 2004"

Internal solitons in the northeastern south China Sea. Part I: sources and deep water propagation

Abstract: A moored array of current, temperature, conductivity, and pressure sensors was deployed across the Chinese continental shelf and slope in support of the Asian Seas International Acoustics Experiment. The goal of the observations was to quantify the water column variability in order to understand the along and across-shore low-frequency acoustic propagation in shallow water. The moorings were deployed from April 21-May 19, 2001 and sampled at 1-5 min intervals to capture the full range of temporal variability without aliasing the internal wave field. The dominant oceanographic signal by far was in fact the highly nonlinear internal waves (or solitons) which were generated near the Batan Islands in the Luzon Strait and propagated 485 km across deep water to the observation region. Dubbed trans-basin waves, to distinguish them from other, smaller nonlinear waves generated locally near the shelf break, these waves had amplitudes ranging from 29 to greater than 140 m and were among the largest such waves ever observed in the world's oceans. The waves arrived at the most offshore mooring in two clusters lasting 7-8 days each separated by five days when no waves were observed. Within each cluster, two types of waves arrived which have been named type-a and type-b. The type-a waves had greater amplitude than the type-b waves and arrived with remarkable regularity at the same time each day, 24 h apart. The type-b waves were weaker than the type-a waves, arrived an hour later each day, and generally consisted of a single soliton growing out of the center of the wave packet. Comparison with modeled barotropic tides from the generation region revealed that: 1) The two clusters were generated around the time of the spring tides in the Luzon strait; and 2) The type-a waves were generated on the strong side of the diurnal inequality while the type-b waves were generated on the weaker beat. The position of the Kuroshio intrusion into the Luzon Strait may modulate the strength of the waves being produced. As the waves shoaled, the huge lead solitons first split into two solitons then merged together into a broad region of thermocline depression at depths less than 120 m. Elevation waves sprang up behind them as they continued to propagate onshore. The elevation waves also grew out of regions where the locally-generated internal tide forced the main thermocline down near the bottom. The "critical point" /spl alpha/ where the upper and lower layers were equal was a good indicator of when the depression or elevation waves would form, however this was not a static point, but rather varied in both space and time according to the presence or absence of the internal tides and the incoming trans-basin waves themselves.

Internal tide and nonlinear internal wave behavior at the continental slope in the northern south China Sea

Abstract: A field program to measure acoustic propagation characteristics and physical oceanography was undertaken in April and May 2001 in the northern South China Sea. Fluctuating ocean properties were measured with 21 moorings in water of 350- to 71-m depth near the continental slope. The sea floor at the site is gradually sloped at depths less than 90 m, but the deeper area is steppy, having gradual slopes over large areas that are near critical for diurnal internal waves and steep steps between those areas that account for much of the depth change. Large-amplitude nonlinear internal gravity waves incident on the site from the east were observed to change amplitude, horizontal length scale, and energy when shoaling. Beginning as relatively narrow solitary waves of depression, these waves continued onto the shelf much broadened in horizontal scale, where they were trailed by numerous waves of elevation (alternatively described as oscillations) that first appeared in the continental slope region. Internal gravity waves of both diurnal and semidiurnal tidal frequencies (internal tides) were also observed to propagate into shallow water from deeper water, with the diurnal waves dominating. The internal tides were at times sufficiently nonlinear to break down into bores and groups of high-frequency nonlinear internal waves.

Extracting coherent wave fronts from acoustic ambient noise in the ocean

Abstract: A method to obtain coherent acoustic wave fronts by measuring the space–time correlation function of ocean noise between two hydrophones is experimentally demonstrated. Though the sources of ocean noise are uncorrelated, the time-averaged noise correlation function exhibits deterministic waveguide arrival structure embedded in the time-domain Green’s function. A theoretical approach is derived for both volume and surface noise sources. Shipping noise is also investigated and simulated results are presented in deep or shallow water configurations. The data of opportunity used to demonstrate the extraction of wave fronts from ocean noise were taken from the synchronized vertical receive arrays used in the frame of the North Pacific Laboratory (NPAL) during time intervals when no source was transmitting.

Oxygen dynamics in permeable sediments with wave-driven pore water exchange

Abstract: The effects of advective pore water exchange driven by shallow water waves on the oxygen distribution in a permeable (k 5 3.3 3 10 212 to 4.9 3 10 211 m 2 ) natural sediment were studied with a planar oxygen optode in a wave tank. Our experiments demonstrate that pore water flow driven by the interaction of sediment topography and oscillating boundary flow changes the spatial and temporal oxygen distribution in the upper sediment layer. Oxygenated water intruding in the ripple troughs and deep anoxic pore water drawn to the surface under the ripple crests create an undulating oxic‐anoxic boundary within the upper sediment layer, mirroring the topographical features of the sediment bed. Anoxic upwelling zones under ripple crests can separate the oxic sediment areas of neighboring ripple troughs with steep horizontal oxygen concentration gradients. The optode showed that migrating wave ripples are trailed by their pore water flow field, alternately exposing sediment volumes to oxic and anoxic pore water, which can be a mechanism for remobilizing particulate oxidized metal precipitates and for promoting coupled nitrification‐denitrification. More rapid ripple migration (experimental threshold;20 cm h 21 ) produces a continuous oxic surface layer that inhibits the release of reduced substances from the bed, which under slowly moving ripples is possible through the anoxic vertical upwelling zones. Swift, dramatic changes in oxygen concentration in the upper layers of permeable seabeds because of surface gravity waves require that sediment-dwelling organisms are tolerant to anoxia or highly mobile and enhance organic matter mineralization. The dominant boundary layer flows in shallow marine environments are those generated by surface gravity waves. This dominance is reflected by the presence of wave ripples structuring large areas of shallow sandy seabeds that are abundant in coastal, estuarine, and shelf environments. Most of these sandy sediments are permeable (k . 10 212 m 2 ) and thus allow interstitial water motion. Pressure differences at the sediment‐water interface might drive interfacial solute transport through the surface layers of these beds. This advective transport can exceed transport by molecular diffusion by several orders of magnitude (Huettel and Webster 2001). In contrast, the major transport mechanisms in fine-grained muddy sediments are molecular diffusion and locally bioturbation (Berner 1980; Aller 1982). Increased fluid exchange between sediment and overlying water affects the oxygen dynamics in permeable sediments and therefore also affects biogeochemical processes. Booij

Vertical mixing schemes in the coastal ocean: Comparison of the level 2.5 Mellor‐Yamada scheme with an enhanced version of the K profile parameterization

Abstract: [1] The performance of two vertical mixing parameterizations in idealized continental shelf settings is analyzed to assess in what aspects and under what conditions they differ. The level 2.5 Mellor-Yamada turbulence closure (M-Y) is compared with an enhanced version of the K profile parameterization (KPP), which has been appended to include a representation of the bottom boundary layer. The two schemes are compared in wind-driven one- and two-dimensional shallow ocean settings to examine differences in (1) the surface boundary layer response, (2) the response when surface and bottom boundary layers are in close proximity, and (3) the response when the horizontal advective effects of a coastal upwelling circulation compete with the vertical mixing processes. The surface boundary layer experiments reveal that M-Y mixes deeper and entrains more than KPP when the pycnocline beneath the wind-mixed layer is highly stratified and mixes less when it is weaker. This is related to the role of vertical diffusion of turbulent kinetic energy in M-Y and the nature of the interior shear mixing parameterization of KPP. In shallow water when surface and bottom boundary layers impinge on each other, the stronger mixing at the interface produced by KPP can lead to much more rapid disintegration of the pycnocline. The two-dimensional upwelling circulation experiments show that the two schemes can produce quite similar or significantly different solutions in the nearshore region dependent on the initial stratification. The differences relate to the stronger suppression of turbulence by M-Y under the restratifying influence of horizontal advection of denser water in the bottom boundary layer.

Underwater acoustic channel characterisation for medium-range shallow water communications

Abstract: The ability to effectively communicate underwater has numerous applications for researchers, marine commercial operators and defence organizations. As electromagnetic waves cannot propagate over long distances in seawater, acoustics provides the most obvious choice of channel. Although acoustics has been used effectively for point-to-point communications in deep-water channels, acoustics has had limited success for horizontal transmissions in shallow water. Time-varying multipath propagation and nonGaussian noise are two of the major factors that limit acoustic communication performance in shallow water. Although it is known that medium-range shallow water propagation is dominated by time-varying multipath arrivals, very few measurements of the variability of the multipath structure are available. In this paper, we present channel measurements made in a shallow water channel (depth 15-20 m) up to a range of 1 km. An analysis of the temporal variability of the arrival structure is presented. Most communication systems make the assumption that the noise is additive and Gaussian. Snapping shrimp dominate the ambient noise spectrum above a few kHz in warm shallow waters. It is known that snapping shrimp noise is impulsive and highly nonGaussian. These noise characteristics need to be taken into account when designing communication systems if robust and near-optimal performance is desired. An analysis of the ambient noise characteristics from some warm shallow water channels is also presented.

Nonlinear Shallow Water Theories for Coastal Waves

Abstract: Ocean waves entering the near-shore zone undergo nonlinear and dispersive processes. This paper reviews nonlinear models, focusing on the so-called Serre equations. Techniques to overcome their limitations with respect to the phase speed are presented. Nonlinear behaviours are compared with theoretical results concerning the properties of Stokes waves. In addition, the models are tested against experiments concerning periodic wave transformation over a bar topography and of the shoaling of solitary waves on a beach.

Shallow-Water Acoustics

Abstract: Extracting a signal from noise can be complicated, especially along a coastline filled with marine life, shipping lanes, undersea waves, shelves, and fronts that scatter sound.

Wave breaking for a shallow water equation

Abstract: In this paper, we establish sufficient conditions on the initial data to guarantee ware breakings for a shallow water equation.

Estimating the depth and shape of subglacial Lake Vostok's water cavity from aerogravity data

Abstract: [1] We use aerogravity data to estimate the water depth of subglacial Lake Vostok in East Antarctica. The inversion produces the first bathymetry map covering the entire lake. Lake Vostok consists of two sub-basins separated by a ridge with very shallow water depths. The deeper southern sub-basin is approximately double the spatial area of the smaller northern sub-basin. The close correlation between the pattern of basal melting and freezing and the bathymetric structure has important ramifications for the water circulation and the sediment deposition. We estimate the lake volume to be 5400 ± 1600 km3.

A new two-dimensional shallow water model including pressure effects and slow varying bottom topography

Abstract: The motion of an incompressible fluid confined to a shallow basin with a slightly varying bottom topography is considered. Coriolis force, surface wind and pressure stresses, together with bottom and lateral friction stresses are taken into account. We introduce appropriate scalings into a three-dimensional anisotropic eddy viscosity model; after averaging on the vertical direction and considering some asymptotic assumptions, we obtain a two-dimensional model, which approximates the three-dimensional model at the second order with respect to the ratio between the vertical scale and the longitudinal scale. The derived model is shown to be symmetrizable through a suitable change of variables. Finally, we propose some numerical tests with the aim to validate the proposed model.

Parameterization of ocean self‐attraction and loading in numerical models of the ocean circulation

Abstract: [1] The effect of ocean self-attraction and loading (SAL) is considered in a global, barotropic ocean model forced by atmospheric wind stress, atmospheric pressure, and tidal forcing. Periods shorter than 7 days are considered. The model is integrated with a proper calculation of these effects in terms of a (very expensive) Green's function convolution at each time step. SAL effects produce a perturbation of typically about 10% of the computed ocean bottom pressure, but much more in places, for both tidal and atmospherically forced motions. An investigation into simple parameterizations of these effects by means of a term proportional to local bottom pressure reveals the following results: For tides, the best coefficient is systematically dependent on depth, ranging from less than 0.08 in shallow water to about 0.12 in the deepest water, and incorporating this effect improves the parameterization. For atmospherically forced motions, there is still some effect of depth but more an effect of latitude (increasingly so for longer periods), regional variation is greater, and correlation between the SAL effect and bottom pressure is weaker. Parameterization with a constant coefficient of 0.1 reduces errors due to failing to include SAL by about 30%. To do better than this, a proper scale-dependent representation of SAL must be used.

Antarctic shallow-water mega-epibenthos: shaped by circumpolar dispersion or local conditions?

Abstract: The mega-epibenthos of two different geographic areas, the Antarctic Peninsula and the high Antarctic (eastern Weddell Sea), were investigated using underwater video. The distribution of the marine fauna at shallow depths between 55 and 160 m in these two areas was investigated to determine whether there are any zoogeographic differences at the community level. A total of 237 taxa represented by 85,538 individuals was identified. Multivariate analyses revealed significant faunal differences between northern Marguerite Bay (western Antarctic Peninsula) and the stations from the Weddell Sea, Atka Bay and Four-Seasons Bank. Echinoderms, especially ophiuroids, dominated Marguerite Bay, bryozoans and ascidians were abundant at Atka Bay, and hydroids and gorgonians were well represented at Four-Seasons Bank. These clear differences can mainly be explained by the influence of local environmental conditions that are probably the primary feature responsible in shaping the Antarctic shallow-water epifauna and not an intensive exchange with larger depths or a limited dispersion due to scarce and isolated shallow areas. In addition, modes of reproduction and characteristics of the early life history (e.g. brooding, viviparity or budding) of key taxa may also shape patterns of species distribution in shallow benthic Antarctic communities.

The oscillating wave surge converter

Abstract: The Oscillating Wave Surge Converter (OWSC) is a novel shoreline or near-shore wave energy converter. The concept has developed from an analysis of the performance of the LIMPET shoreline oscillating water column. This analysis showed that the hydrodynamics of shoreline wave energy converters are highly non-linear and that they have a qualitatively different response to similar devices that are sited in deeper water. In particular, the water particle motion in shallow water is predominantly horizontal, with elongated wave troughs and heightened wave peaks. The OWSC is designed to couple strongly with the horizontal particle motion, permitting large amplitudes of motion of the working surface whilst minimising energy losses in associated water particle motions. The OWSC consists of a paddle rotating about a horizontal axis above the water surface and perpendicular to the direction of wave propagation. The paddle hangs at the mouth of a gully, effectively forming a 'water column' between the paddle and gully back wall. Thus, the OWSC is similar to the Japanese 'Pendulor' system; however the OWSC uses resonance of the water column rather than harbour resonance as its operating principle. A limited study of geometric parameters using a two-dimensional wave-tank model has been performed. Results from these experiments have shown that the 'water column' has an effect on the paddle dynamics and OWSC performance, with the OWSC having a higher power capture than both a shoreline oscillating water column (OWC) and Pendulor in shallow water. The potential for the OWSC in the shoreline and near-shore regions is also discussed, with implications for construction costs and the price for electricity generated by the OWSC. Potential control strategies for the OWSC are also discussed, together with their likely effect on operation and performance.

Modelling of dispersant application to oil spills in shallow coastal waters

Abstract: Application of dispersants in shallow water remains an issue of debate within the spill response community. An experimental oil spill to evaluate potential environmental impacts and benefits of applying dispersants to spills in shallow water has therefore been under consideration. One site being considered was Matagorda Bay, on the Texas coast. Coupled three-dimensional oil spill and hydrodynamic models were used to assist in the design of such an experiment. The purpose of the modeling work was to map hydrocarbon concentration contours in the water column and on the seafloor as a function of time following dispersant application. These results could assist in determining the potential environmental impact of the experiment, as well as guiding the water column sampling activities during the experiment itself. Eight potential experimental oil spill scenarios, each of 10 bbl in volume, were evaluated: 4 release points, each under two alternate wind conditions. All scenarios included application of chemical dispersants to the slick shortly after release. Slick lifetimes were under 5 h. Due to the shallow depths, some fraction (2–7%) of the released hydrocarbons became associated with bottom sediments. The algorithms used for the oil droplet—sediment interactions are theoretical, and have not been verified or tested against experimental data, so the mass balances computed here must be considered tentative. Currents computed by the hydrodynamic model are consistent with previous observations: the circulation is largely tidally driven, especially near the ship channel entrance. In the center of the bay, the circulation appears relatively weak. The use of water column drifters with surface markers during the experiment would augment model results in assisting activities to monitor concentrations. These simulations suggest that the eventual behavior of an oil droplet cloud in the middle of the bay will be relatively insensitive to release point or time in the tidal cycle. A limited analysis was run to evaluate model sensitivity to the oil-sediment sorption coefficient. Increasing this coefficient by a factor of 10 results in an approximately linear increase in the fraction of oil in the sediments. Sensitivity of estimated time-to-zero-volume for the 0.1-ppm concentration contour demonstrated that the model prediction of 3.5 days was associated with an uncertainty of ±12 h for a release of 10 barrels. This time estimate is also a function of the oil-sediment interaction rate, since more oil in the sediments means less oil in the water column.

Transformation of the Indonesian Throughflow Water by Vertical Mixing and Its Relation to Tidally Generated Internal Waves

Abstract: Numerical experiments with two-dimensional nonhydrostatic model have been performed to investigate tidally generated internal waves at the Dewakang sill at the southern Makassar Strait where two large-amplitude “bumps” of relatively shallow water exist. We investigate the effect of these features on vertical mixing, with emphasis on the transformation of the Indonesian throughflow (ITF) water properties. The result shows that large-amplitude internal waves are generated at both bumps by the predominant M2 tidal flow, even though the condition of the critical Froude number and the critical slope are not satisfied. The internal waves induce such vigorous vertical mixing in the sill region that the vertical diffusivity attains a maximum value of 6 × 10−3 m2s−1 and the salinity maximum and minimum core layers characterizing the ITF thermocline water are considerably weakened. Close examination reveals that bottom-intensified currents produced mainly by the joint effect of barotropic M2 flow and internal tides generated in the concave region surrounding both bumps can excite unsteady lee waves (Nakamura et al., 2000) on the inside slopes of the bumps, which tend to be trapped at the generation region and grow into large-amplitude waves. Such generation of unsteady lee waves does not occur in case of one bump alone. Trapping and amplification of the waves in the sill region induce large vertical displacements (∼60 m) of water parcels during one tidal period, leading to strong vertical mixing there. Since the K1 tidal currents are relatively weak, large-amplitude internal waves causing intense vertical mixing are not generated.

Downward channeling of dense water in topographic corrugations

Abstract: Dense ocean water is formed primarily at high latitudes, but also in certain marginal seas in warmer areas. The main pathways of this dense water as it moves along the continental slopes is the topic addressed here. An analytical model describing how a geostrophic flow, with the aid of bottom friction, may lean on topographic irregularities and descend downhill toward the deep sea is presented. It is suggested that along-slope variation of the topography is a key element controlling the downward transport of dense bottom water. Deep corrugations can channel more water than shallow, but the transport also depends on their width. On gently sloping topography a maximum downward flow is induced by rather wide canyons (tens of km across), but in steeper regions the most active canyons are only a few km wide. The theory is applied to the continental slope east of Greenland, and it is shown that the transport capacity of this slope is sufficient to redistribute the Denmark Strait Outflow water from the level of 400 m (at the Strait) down to below 2000 m (at the southern tip of Greenland), which is consistent with observations. Application of the theory to the Faroe-Bank Channel (downstream of the sill) is consistent with observations from that region.

Resistance and wash measurements on a series of high speed displacement monohull and catamaran forms in shallow water

Abstract: The paper summarises an experimental investigation into the resistance and wash waves of high speed displacement monohulls and catamarans in shallow water. Measurements of total resistance, running trim, sinkage and multiple longitudinal wave cuts were carried out for three round bilge hulls derived from the NPL series and one from Series 64. Parametric changes included length/displacement ratios of 7.4, 8.5 and 9.5, and hull separation/length ratios of 0.2, 0.4 and infinity. The tests were carried out in two depths of shallow water over a length Froude Number range of 0.25 to 1.0 and a depth Froude Number range of 0.5 to 3.0. The wave resistance was derived using wave pattern analysis and the principal particulars of the generated wave system are presented as maximum wave height, period, distribution of energy and direction of wave propagation. The results of the investigation provide a better understanding of the performance of high speed displacement monohulls and catamarans in shallow water, including the influences of speed, water depth, hull separation and length/displacement ratio. The data derived are very suitable for design applications and for the validation of theoretical analyses of ship wave resistance and wash waves.

Facies and depositional sequence evolution controlled by high-frequency sea-level changes in a shallow-water carbonate ramp (late Kimmeridgian, NE Spain)

Abstract: The outcrops of the Sierra de Albarracin (NE Spain) allow a precise reconstruction of the shallow sedimentary domains of a late Kimmeridgian carbonate ramp, developed in western marginal areas of the Iberian Basin. The sedimentary record shows a hierarchical sequence stratigraphic organization, which implies sea-level changes of different frequencies. The studied succession is arranged in a long-term transgressive–regressive sequence, which is likely to reflect local variation in the subsidence rates. This sequence includes four higher-order sequences A to D, which have variable thickness (from 3 to 21 m). The similar sedimentary evolution observed in distant localities suggests the existence of high-frequency sea-level fluctuations controlling the sequence development. The average amplitude of these cycles would range from 5 to 10 m. The precise estimation of their duration (some few hundreds of kyr) and their possible assignment to any of the long-term orbital cycles (the 100 or the 400 kyr eccentricity cycles) is uncertain. Sequences A and B, formed during the long-term transgressive interval, are relatively thin (from 3 to 9 m) give-up sequences that were never subaerially exposed. These sequences are locally formed by five shallowing-upward elementary sequences. Sequences C and D are catch-down sequences with evidence of emersion of subtidal facies. Sequence C, formed during the stage of maximum gain of long-term accommodation, is the thickest sequence (from 13 to 21 m) and includes coral–microbial reefs (pinnacles up to 16 m in height). The increased production rates were able to fill part of the accommodation created during the early stage of high-frequency sea-level rise and the shallow platform was eventually exposed to subaereal erosion and meteoric cementation.

Water mass stability reconstructions from greenhouse (Eocene) to icehouse (Oligocene) for the northern Gulf Coast continental shelf (USA)

Abstract: [1] Shallow water mass characteristics such as temperature and density profile play a critical role in the climate system We have developed a new method by which to reconstruct the ancient shallow water mass stability on the continental shelf using oxygen isotope variation within mollusc shells and fish otoliths and applied the method to an important interval in Earth history, the most recent transition from Greenhouse (Eocene) to Icehouse (Oligocene) climate modes We define the slope of summer temperature (density) versus the seasonal range in temperature (density) as an indicator of water mass stability In addition, extrapolation of the regression to zero seasonality is a proxy for temperature at the bottom of the seasonal thermocline (TBST) During the greenhouse world (the early Eocene and middle Eocene) the water mass plot shows an unstable water mass, agreeing with previous planktonic foraminiferal studies showing that temperature gradients at this time were much smaller than at present During the middle to late Eocene transition, a substantial increase in water mass stability occurred Significant cooling (� 5� C) of the TBST at this transition indicates that the greater cooling of deeper water relative to surface water caused the increase in water mass stability The changes in water column structure at this transition were the most likely cause of a major extinction of planktonic foraminifera from warm to cold water taxa The late Eocene T-DT profile is very similar to modern profiles, suggesting that shallow water mass structure became similar to that of the modern Gulf Coastal shelf by the late Eocene At the Eocene/ Oligocene (E/O) boundary, no major change in water mass structure is identified This agrees with the observation that no major extinction of planktonic foraminifera is found at the E/O boundary INDEX TERMS: 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 1040 Geochemistry: Isotopic composition/chemistry; 4294 Oceanography: General: Instruments and techniques; KEYWORDS: Eocene, paleoclimate, greenhouse

Generation of internal solitary waves in the Sulu Sea and their refraction by bottom topography studied by ERS SAR imagery and a numerical model

Abstract: ERS-2 SAR images acquired over the Sulu Sea reveal that there are at least three areas where internal solitary waves are generated: (1) at the sill between Dok Kan Island and Pearl Bank; (2) at the sill between Pearl Bank and Talantam Shoal; and (3) at the sill between Talantam Shoal and Sentry Bank It is observed that the internal solitary waves generated at different source regions merge into a single solitary wave system When the solitary waves propagate into shallow water, the distance between the solitary waves in a wave packet decreases Furthermore, when the water depth decreases in the direction of the soliton's crest line, the crest line is bent towards the shallow water region These observational facts are explained by a wave refraction model which is based on the Korteweg–de Vries equation which is also valid for large amplitude internal solitary waves provided the pycnocline is sufficiently broad

Long-range propagation of finite-amplitude acoustic waves in an ocean waveguide

Abstract: A hybrid method coupling nonlinear and linear propagation codes is used to study the nonlinear signature of long-range acoustic propagation for high-amplitude sources in an ocean waveguide. The differences between linear and nonlinear propagation are investigated in deep and shallow water environments. The spectral reshaping that occurs in nonlinear propagation induces two main effects: in shallow water, an unusual arrival time structure in the lowest order modes is observed, and in both shallow and deep water environments, there is a tendency to have acoustic energy more uniformly distributed across modes. Further, parametric low-frequency generation in deep water is a candidate for the coupling between water and sediments for T-wave formation.

ENPAC 2003: a tidal constituent database for Eastern North Pacific Ocean

Abstract: : This report describes the development of the Eastern North Pacific (ENPAC) 2003 tidal database of elevations and velocity components for eight major tidal constituents. This database was developed using the two-dimensional, depth-integrated form of the coastal hydrodynamic model, ADCIRC, which solves the shallow-water equations in the generalized wave continuity equation form. The final ENPAC 2003 incorporates the most accurate bathymetric data available. The resolution of the unstructured finite element mesh was designed to provide a high level of resolution along the continental slope and throughout the coastal waters to resolve the nonlinear hydrodynamics that dominate this area. The domain of this model extends beyond the continental shelf into deep ocean waters, but does not include any amphidromes located in the Pacific Ocean. At the open boundary, the forcing conditions are extracted from global ocean models, in the area where these models are most accurate. The results of the ENPAC 2003 model approach the error levels found in the station data that were used for model validation. (6 tables, 187 figures, 36 refs.)