Statistics of Nonlinear Internal Waves during the Shallow Water 2006 Experiment (original) (raw)
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Time-varying three-dimensional mapping of internal waves during the Shallow Water 2006 experiment
The Journal of the Acoustical Society of America, 2013
Detailed knowledge of sound speed profiles and the sound speed profile's spatial and temporal variability resulting from internal waves (IWs) are indispensable to investigating significant acoustic field fluctuations in shallow water. A strategy to obtain a time-varying, threedimensional (3D) IW temperature field is presented. It uses two types of simultaneous measurements: dense observations from a farm of thermistor strings and IW surface expressions from a ship-based radar. Using data from the Shallow Water 2006 experiment, the temperature field, over multiple kilometers in range, was reconstructed and, fed to a 3D acoustic model to demonstrate IW impacts on acoustic propagation.
Features of the nonlinear internal wave spectrum in the coastal zone
Geophysical Research Letters, 2005
This paper studies two examples of internal wave band temperature fluctuation spectra from moored instruments on the central Mexican Pacific Shelf and the western shelf of the Japan/East Sea. It is observed that for band f (w (N, where N is the buoyancy frequency and f is the inertial frequency, the spectral falloff rate with frequency w tends to w À3. These features of spectra are simulated by the model spectrum of nonlinear internal waves in the shallow sea. It is shown that nonlinear internal waves with frequencies f (w (N are governed by the modified simple wave equation. This equation underlie of the model spectrum of nonlinear internal waves on the shelf. The model spectrum shows w À3 falloff rate with frequency in contrast with model spectrum proposed with Garrett and Munk, which shows w À2 falloff rate.
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.
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 ...
On a spectrum of nonlinear internal waves in the oceanic coastal zone
Nonlinear Processes in Geophysics, 2007
This paper studies the internal wave band of temperature fluctuation spectra in the coastal zone of Pacific ocean. It is observed that on the central Mexican Pacific Shelf in the high-frequency band of temperature spectra the spectral exponent tends to ∼ω −1 at the time of spring tide and ω −2 at the time of neap tide. On the western shelf of the Japan/East Sea, in the ≪ω≪N * range, where N * is the representative buoyancy frequency and is the inertial frequency, the rate tends to ∼ω −3. These features of spectra are simulated by the model spectrum of nonlinear internal waves in the shallow water. Interaction of high-frequency internal waves with an internal wave of semidiurnal frequency is considered. It is shown that as a result of the interaction the spectrum of high-frequency internal waves take the universal form and the spectral exponent tends to ∼ω −1 .
Analysis of nonlinear internal waves in the New York Bight
Journal of Geophysical Research, 1988
This paper presents the results on internal wave analysis of the current meter mooring data in the New York Bight from the SAR Internal Wave Signature Experiment (SARSEX). Selective sets of current and temperature measurements are analyzed for a parametric study of internal wave characteristics and shear effects on wave parameters are studied based on the limited data from moorings. The solitary wave theory has been extended for the wave evolution on a continental shelf by including dissipation and shoaling effects; a series of numerical simulations are performed to demonstrate the relative importance of dissipation and shoaling effects. From an observed initial wave packet at the upstream mooring, the numerical evolution simulation compares reasonably well with the measurements at the distant mooring for the leading two large solitons. 1.
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.
Shallow Water Internal Waves and Associated Acoustic Intensity Fluctuations
Defence Science Journal, 2006
Physical oceanographic and acoustic data were simultaneously collected from the coastal waters of the Arabian Sea. Acoustic transmissions were carried out from an anchored vessel using 620 Hz transducer and received by an array of hydrophones moored at ~5 km away from the anchorage. Thermal structure in this region was characterised by a tri-layer structure, ie, a strong thermocline (> 0.4 o C/m) sandwiched between an upper (< 10 m) and bottom (> 25 m) homogeneous layer. High-resolution (sampled at 10 s interval) temperature data from moored sensors revealed intense internal wave activity. The maximum value of Brunt-Vaisala frequency, which is the maximum frequency limit of internal waves in the thermocline, suggests that the upper frequency limit of the internal wave, which can be generated during this period, is 23 cph (2.6 min). High and low frequency waves caused variations of ~3 o C and ~5 o C respectively in the temperature field. But the low frequency internal waves were found to contain maximum energy compared to the high frequency waves. Fluctuations of 8-12 dB were noticed in the measured acoustic intensity values in the presence of low frequency internal waves. Simulation studies carried out using parabolic equation model using 620 Hz source indicated well-defined ducted propagation with minimum transmission loss, when the source was kept within the homogeneous layer. The presence of tri-layer thermal structure, ie, a strong gradient layer sandwiched between an upper and bottom homogeneous layer, caused surface and bottom channel propagation in this region.