Analysis of nonlinear internal waves in the New York Bight (original) (raw)
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A Case Study of Internal Solitary Wave Propagation During ASIAEX 2001
IEEE Journal of Oceanic Engineering, 2004
During the recent Asian Seas International Acoustics Experiment (ASIAEX), extensive current meter moorings were deployed around the continental shelf-break area in the northeastern South China Sea. Thirteen RADARSAT SAR images were collected during the field test to integrate with the in situ measurements from the moorings, ship-board sensors, and conductivity/temperatire/depth (CTD) casts. Besides providing a synoptic view of the entire region, satellite imagery is very useful for tracking the internal waves, locating surface fronts, and identifying mesoscale features. During ASIAEX in May 2001, many large internal waves were observed at the test area and were the major oceanic features studied for acoustic volume interaction. Based on the internal wave distribution maps compiled from satellite data, the wave crests can be as long as 200 km with an amplitude of 100 m. Environmental parameters have been calculated based on extensive CTD casts data near the ASIAEX area. Nonlinear internal wave models have been applied to integrate and assimilate both synthetic aperture radar (SAR) and mooring data. Using SAR data in deep water as an initial condition, numerical simulations produced the wave evolution on the continental shelf and compared reasonably well with the mooring measurements at the downstream station. The shoaling, turning, and dissipation of large internal waves at the shelf break have been studied and are very important issues for acoustic propagation.
NONLINEAR INTERNAL WAVE STUDY IN THE SOUTH CHINA SEA
Advances in Engineering Mechanics - Reflections and Outlooks - In Honor of Theodore Y.-T. Wu, 2005
The internal wave distribution map in the northeast part of South China Sea (SCS) has been compiled from hundreds of ERS-1/2, RADARSAT and Space Shuttle Synthetic Aperture Radar (SAR) images. Based on the map compiled from satellite data, the wave crest can be as long as 200 km with amplitude of 100 m. In recent Asian Seas International Acoustics Experiment (ASIAEX), extensive moorings have been deployed around the continental shelf break area in the northeast of South China Sea. Simultaneous RADARSAT SAR images have been collected during the field test to integrate with the in-situ measurements from moorings, ship-board sensors, and CTD casts. Besides it provides synoptic information, satellite imagery is very useful for tracking the internal waves, and locating surface fronts and mesoscale features. Environmental parameters have been calculated based on extensive CTD casts data near the ASIAEX area. Nonlinear internal wave models have been applied to integrate and assimilate both SAR and mooring data. The shoaling, turning, and dissipation of large internal waves on the shelf break, elevation solitons, and wave-wave interaction have been studied.
Simulation of the Transformation of Internal Solitary Waves on Oceanic Shelves
Journal of Physical Oceanography, 2004
Due to the horizontal variability of oceanic hydrology (density and current stratification) and the variable depth over the continental shelf, internal solitary waves transform as they propagate shorewards into the coastal zone. If the background variability is smooth enough, a solitary wave possesses a soliton-like form with varying amplitude and phase. This stage is studied in detail in the framework of the variable-coefficient extended Korteweg-de Vries equation where the variation of the solitary wave parameters can be described analytically through an asymptotic description a slowly-varying solitary wave. Direct numerical simulation of the variablecoefficient extended Korteweg-de Vries equation is performed for several oceanic shelves (North-west Shelf of Australia, Malin Shelf Edge, Arctic Shelf) to demonstrate the applicability of the asymptotic theory. It is shown that the solitary wave may maintain its soliton-like form for large distances (up to 100 km), and this confirms why internal solitons are observed widely in the world's oceans. In some cases the background stratification contains critical points (when the coefficients of the nonlinear terms in the extended Korteweg-de Vries equation change sign), or does not vary sufficiently smoothly; in such cases the solitary wave deforms a group of secondary waves. This stage is studied numerically.
NONLINEAR INTERNAL WAVES ON SHELF OF THE SEA OF JAPAN
Internal waves are a widespread phenomenon in the oceans and seas, which plays an important role both in geophysical fluid dynamics and underwater acoustics. Internal waves are inherent in the shelf zone, where they manifest themselves in the form of long waves (tidal and inertial) and in the form of packets of soliton-like waves. The paper will give a generalization of the results of experiments on the study of internal waves, we carried out for a long time on the shelf of the Sea of Japan. The experiments were conducted in an area remote 100 km south of Vladivostok, near the research station of Pacific Oceanology Institute, Far East Branch of RAS (Cape Schultz). The first studies began in 1982 and continues to the present. We used different methods in our field experiments. Measurements of internal wave spatial spectra were carried out by using antenna of moored line temperature sensors in the inner shelf. For purpose of investigation dynamics of internal waves we used towed line ...
Journal of Geophysical Research, 1993
By interpreting two space shuttle photographs taken with a Linhof camera on June 8, 1991, a total of 34 internal soliton packets on the continental shelf of the Middle Atlantic Bight are recognized. The internal solitoh field has a three-level structure: packet groups with average wavelength of 17.5 km, packets with average wavelength of 7.9 km, and solitons with average wavelength of 0.6 km. Using the finite-depth theory we derive that the maximum amplitude of solitons is 5.6 m, the phase speed is 0.42 m/s, and the period is 23.8 min. The frequency distribution of solitons is triple-peaked at 1.9 x 10-4 Hz, 3.0 x 10-4 , and 6.9 x 10-4 Hz. Substituting statistical results of number of solitons in a packet into the fission law, we find that the upper and the lower edges of the shelf break are the primary and the secondary generation sources of internal soiltons, respectively. This reveals that the sharp change in the bottom topography is a key condition for the soliton fission or disintegration. Calculations show that the group period of solitons is 12.5 hours coinciding with that of local semidiurnal tides. This fact confirms that the tides are a dominant generation force for internal solitons on the continental shelf. From 1983 to 1985, U.S. astronauts on-board the space shuttle have taken many photographs containing imagery of internal waves over oceanic areas such as the South China Sea
Ocean Science, 2017
Numerical solutions of the Kortewegde Vries (KdV) and extended Korteweg-de Vries (eKdV) equations are used to model the transformation of a sinusoidal internal tide as it propagates across the continental shelf. The ocean is idealized as being a two-layer fluid, justified by the fact that most of the oceanic internal wave signal is contained in the gravest mode. The model accounts for nonlinear and dispersive effects but neglects friction, rotation and mean shear. The KdV model is run for a number of idealized stratifications and unique realistic topographies to study the role of the nonlinear and dispersive effects. In all model solutions the internal tide steepens forming a sharp front from which a packet of nonlinear solitary-like waves evolve. Comparisons between KdV and eKdV solutions are made. The model results for realistic topography and stratification are compared with observations made at moorings off Massachusetts in the Middle Atlantic Bight. Some features of the observations compare well with the model. The leading face of the internal tide steepens to form a shock-like front, while nonlinear high-frequency waves evolve shortly after the appearance of the jump. Although not rank ordered, the wave of maximum amplitude is always close to the jump. Some features of the observations are not found in the model. Nonlinear waves can be very widely spaced and persist over a tidal period.
Nonlinear internal waves on the California continental shelf
Journal of Geophysical Research, 1985
A series of intermittent interval wave events were observed at a single site in 133 m of water on the northern California continental shelf during the Coastal Ocean Dynamics Experiment 1981. Simultaneous time-series observations of temperature and conductivity were used to infer isotherm and isopycnal depths which were combined with current observations to develop a kinematic description of an average internal wave event. The event described consists of a downward displacement of the middepth isopycnals and a corresponding increase of upper-layer minus lower-layer velocity in the ratio R = 105 + 33 s. The observed value of R is in excellent agreement with the prediction of the two-layer internal solitoh theory for which the theoretical value of R, given the hydrographic conditions of the observation site, is 105 s. Predicted values of upper-layer onshore velocity (0.15 m s-X), lower-layer offshore velocity (0.12 m s-x), and time scale (24.6 min) compare well with corresponding observations of 0.14 + 0.02 m s-x, 0.14 + 0.02 m s-x, and 28 + 4 min, respectively, for a 29-m internal wave of depression. Based on these results and similar observations of others, we conclude that internal solitary waves, generated in the region of the continental slope, evolve into packets of solitons as they propagate shoreward before dissipating their energy of about 8.23 x 105 J per meter of wave crest.
Observations are presented of nonlinear internal waves on the outer New England continental shelf during the summer Shelfbreak Primer study conducted between July 26 and August 5, 1996. Current and temperature measurements were made with an upward looking acoustic Doppler current profiler (ADCP) located on the 147 m isobath near the shelfbreak and three vertical thermistor moorings located upshelf. Data from the ADCP and two nearby thermistor chains show energetic internal tides propagating at roughly 0.9 m s Ϫ1 to the north-northwest, nearly perpendicular to the local topography with 10 -15 cm s Ϫ1 horizontal currents and 15-30 m vertical displacements. These waves evolve rapidly within a 5.8 km range into an undular internal tidal bore. Cross-isobath barotropic tidal currents, responsible for generating the internal tides are in the 5-12 cm s Ϫ1 range. The bore formation is highly variable. There is evidence of a correlation between internal tide steepening and a shelfbreak front jet orientation that is oppositely directed to the internal tide propagation. There is no correlation between steepening and the jet's vertical shear. Statistics of the undular bores show rms travel time fluctuations from 0.8 to 1.7 hours and average tidal bore durations from 12 to 9 hours. The average undular bore speed is 0.9 m s Ϫ1 , with an rms fluctuation of 0.4 m s Ϫ1 . The number of high-frequency waves in the bore varies from 0 to 8 near the shelfbreak and increases to 30 waves 26.7 km upshelf. The observed distribution function of temporal spacing between high-frequency internal waves is spread between 4 and 20 min.
Intense short-period internal waves in the ocean
Journal of Marine Research, 2005
Trains of quasi-periodic high-frequency internal waves (IWs) of large amplitude are common in the upper thermocline of the ocean. Sources for these waves may be different ones but it is not always possible to experimentally establish them for certain. We analyzed results of many IW experiments carried out in different representative regions of the World Ocean, including continental margins in the Mid-Atlantic Bight, in the northwestern Pacific at Kamchatka, the Seyshelles-Mascarene bottom rise, and some regions of the open ocean where the intense short-period IWs occur. Comparative analysis of the intense IWs observed in the Mid-Atlantic Bight and at Kamchatka revealed similarity and difference in the IW field in these regions differing by their bottom topography. Most of the observed trains in the Mid-Atlantic Bight propagate shoreward from the shelf break in the form of soliton packets or solibores and do not occur seaward from the shelf. The soliton trains in the northwestern Pacific at Kamchatka are common not only at the shelf edge but also in deep water where they propagate in various directions that seem to be related to the supercritical steepness and complicated form of the continental slope. Observation of generation and evolution of the IW trains at the Seyshelles-Mascarene bottom rise where huge internal solitons have been encountered has shown that the undular bore generated at the lee side of the bottom rise gradually evolves in a train of solitons with the trailing linear waves. Large solitons are generated also in deep water as a result of ray propagation of the internal tide emanated from the rise as happens in the Bay of Biscay. Certain consequences of the IW interaction with the background current leading to intensification of the high-frequency waves were observed in several regions of the open ocean. Revealed dependency of the intense wave propagation direction on the current direction, and closeness of the wave frequency to the frequency at which the waveguide steeply tapers may be regarded as clear evidences for the important role which currents play in the IW intensification.
Statistics of Nonlinear Internal Waves during the Shallow Water 2006 Experiment
Journal of Atmospheric and Oceanic Technology
During the Shallow Water Acoustic Experiment 2006 (SW06) conducted on the New Jersey continental shelf in the summer of 2006, detailed measurements of the ocean environment were made along a fixed reference track that was parallel to the continental shelf. The time-varying environment induced by nonlinear internal waves (NLIWs) was recorded by an array of moored thermistor chains and by X-band radars from the attending research vessels. Using a mapping technique, the three-dimensional (3D) temperature field for over a month of NLIW events is reconstructed and analyzed to provide a statistical summary of important NLIW parameters, such as the NLIW propagation speed, direction, and amplitude. The results in this paper can be used as a database for studying the NLIW generation, propagation, and fidelity of nonlinear internal wave models.