Soliton Packets Research Articles

High-frequency internal waves in Lake Geneva

Trains of high-frequency internal waves have been observed in the thermocline of Lake Geneva within a few hours after the passing of disturbances which cause a rapid increase or ‘jump’ in the depth of the thermocline. Three possible mechanisms for the source of the internal waves are proposed and compared with available data, (i) that the waves are a soliton packet following the jump, (ii) that the waves are generated as the jump passes over or around a local region of rough topography, and (iii) that the jump produces a moving disturbance near the shoreline with internal waves forming a wake behind it. The investigation of the last possibility involves the solution of the problem of the form of an internal wave wake in the presence of mean currents which vary in depth both in their strength and direction. The wave pattern of the wake in the observed current distribution and stratification of the lake is described and compared with that in the absence of shear. An expression for the energy of internal waves propagating in a shear flow is also derived, and it is found that the rate of energy loss from the jump to the waves is small. The minimum Richardson number resulting from the co-existence of the mean shear and the internal waves is marginally greater than 1/4, suggesting that the waves may be limited by shear-flow instability. However, none of the mechanisms for their generation and propagation is fully compatible with the available data.

Acoustic mode coupling induced by internal wave fields in shallow water

The problem of the propagation of acoustic waves in a stochastic ocean waveguide, for which the sound-speed variability within the water column is treated explicitly as a random variable, is addressed. The sound speed is composed of a deterministic, time-independent profile and two time-dependent stochastic components representing a (linear) background Garrett–Munk internal wave field and (nonlinear) internal wave soliton packets. A high-angle elastic parabolic equation method is used to compute single-frequency realizations of the pressure field using this representation of the sound-speed fluctuations. Transmission loss and scintillation index measures are estimated for both the full field and its modal decomposition at various ranges from the acoustic source, for different source depths and for both flat and sloping bottoms. These measures are incorporated in the analysis of acoustic modal coupling induced by the internal wave fields as a function of range; results support a recent prediction [D. Creamer, submitted to J. Acoust. Soc. Am.] that the scintillation index increases exponentially with range due to the competition between mode coupling and mode stripping found in shallow water waveguides. a)Permanent address: Forschungsanstalt der Bundeswehr für Wasserschall-und Geophysik, Klausdorfer Weg 2-24, 24148 Kiel, Germany.

Modeling backscatter from a shallow-water soliton: Relationship to the anomalous resonance effect observed in Yellow Sea data

Computer simulations have confirmed that large amplitude shallow-water internal waves (solitons) can effect transmission loss. Zhou etal. [J. Acoust. Soc. Am. 82, 287–292 (1987)] first hypothesized that solitons caused the anomalous transmission loss observed in acoustic data taken in the Yellow Sea. Others [Chin-Bing etal., Math. Model. Sci. Comput. 4, (1994); King etal., Theoret. Comput. Acoust. 2, 793–807 (1994)] confirmed via computer simulations that interactions of acoustic energy with shallow-water solitons resulted in coupling between the lower-order propagation modes and the very lossy, higher-order modes. Furthermore, a single soliton packet could transfer sufficient acoustic energy from lower-order modes to higher-order bottom-attenuated modes to produce the anomalous transmission loss effects observed in the Zhou data. Recently this simulation study has been extended to include a wave-number analysis of the backscattered field from the soliton. Examples of the backscattered field from the soliton will be presented that include the frequency interval where the forward-field acoustic mode conversion (and corresponding anomalous transmission loss) occur. [Work supported by ONR/NRL and by a Federal High Performance Computing DoD grant.]

Soliton coding based on shape invariant interacting soliton packets: the three-soliton case

Proposed is the transmission of optical information by soliton coding based on exact N-soliton solutions of the nonlinear Schrödinger equation whose intensity profile yields N pulses that propagate without significant changes of their relative distance and amplitude. Presented is an example of a three-soliton sequence that may be generated by phase coding three equal amplitude solitons and that stably propagates in a long distance transmission system with bandwidth limited periodic amplification.

Statistical and dynamical analysis of internal waves on the continental shelf of the Middle Atlantic Bight from space shuttle photographs

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 soliton 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 × 10−4 Hz, 3.0 × 10−4, and 6.9 × 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 solitons, 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.

Influence of internal solitons on sound propagation in shallow water with a summer strong thermocline

Analysis of extensive data has shown that the internal waves in the coastal zone exhibit the properties of solitons. Using experimental data and numerical simulation results, this paper shows what happens to sound propagation if internal solitons are present in shallow water with a strong summer thermocline. The experiments were conducted in the Yellow Sea off the China coast during the summer, where strong thermoclines with more than 10 °C temperature difference are often present. In order to provide a clear physical picture on the true problem, a carefully chosen simple ocean model is used to show the resonant interaction of sound waves with internal solitons, including signal frequency, soliton wavelength, and packet length resonances. Then, the numerical model is extended to include the classic characteristic properties of more realistic ocean soliton packets. Under the resonance condition acoustic mode coupling transfers a significant amount of energy from lower modes into higher-order modes that have much larger attenuation rates. This becomes a new attenuation mechanism for shallow water with a strong thermocline. The ‘‘resonancelike’’ behavior predicted by the PE analysis is consistent with mode coupling theory. [Work supported by ONR and IAAS.]

Local generation of internal soliton packets in the central bay of Biscay

Large-amplitude internal solitary waves (solitons) near the shelf break in the Bay of Biscay are now well documented and understood. A similar phenomenon recently has been reported in the central Bay, about 150 km from the nearest shelf topography. By making several transects with the ship's acoustic Doppler current profiler, we present convincing evidence that these solitons, instead of having travelled along the thermocline from the shelf break, are generated locally at about the position where the beam of internal tidal energy, originating from the shelf break, reflects from the ocean surface.

Large-amplitude internal soliton packets in the central Bay of Biscay

In the Bay of Biscay, large-amplitude internal tides result from the interaction of surface tides with steep bottom topography. Near the shelf break, the troughs of the internal tides are associated with packets of large nonlinear internal waves or “solitons”. By using an Acoustic Doppler Current Profiler, we here demonstrate that a similar phenomenon occurred at a considerable distance (150 km) from the shelf break, and make a detailed examination of the dramatic changes in velocity structure which accompanied the passage of the soliton packets. In particular, horizontal and vertical velocities exceeding, respectively, 60 and 16 cm s −1 were observed. A novel mechanism is proposed for the possible local generation of such large-amplitude solitons so far from topography.

A method of soliton analysis taking into account the exciton non-conservation

A method for the analysis of solitons in molecular crystals is proposed that takes into account the effects of exciton non-conservation. In the framework of this method it was possible to assess the influence exerted by the exciton non-conservation on soliton characteristics. It is shown that as a consequence of the exciton non-conservation, the internal soliton energy is increased and the effective mass is decreased. This means that the exciton non-conservation leads to an acceleration of solitons and is responsible for a spread of the soliton wave packet of some 5%.

The Sulu Sea Internal Soliton Experiment

Abstract We present the results of a comprehensive study of large-amplitude internal solitons generated in the Sulu Sea in the Philippines by intense tidal flow over a sharp bathymetric feature. Surface signatures of these waves have been observed in images from the DMSP, Landsat, and Nimbus-7 satellites and the space shuttle SIR-A synthetic aperture radar. A two-week experiment was conducted in the Sulu Sea in May 1980 from R.V. Oceanograher, during which a three-mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source. Seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea. Vertical profiles of density, temperature, and acoustic backscatter, as well as radar and photographic surface signatures, were obtained from the ship. Data from satellites, moorings, and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves, which ha...