THE EFFECT OF OCEAN CURRENT ON SOUND PROPAGATION

1994 ◽  
Vol 02 (04) ◽  
pp. 441-451 ◽  
Author(s):  
NATALIE S. GRIGORIEVA
Keyword(s):  
Sound Wave ◽  
Gulf Stream ◽  
Sound Speed ◽  
Sound Propagation ◽  
Horizontal Direction ◽  
Ocean Current ◽  
Field Pattern ◽  
Near Surface ◽  
Motion Effect ◽  
A Current

The effect of medium motion on sound propagation in the ocean is investigated. In a moving fluid, the sound propagation is described by a system of seven linear partial differential equations for seven unknown elements of a sound wave. These are the sound pressure, the particle oscillation velocity in a sound wave as well as the changes of medium density, its entropy, and concentration of the salt caused by passage of a sound wave. In the case of stratified moving medium, the point source field is represented in the form of a sum of quasinormal waves. If the ocean perturbed by a current is weakly inhomogeneous along the horizontal direction, the modification of the well-known method of horizontal rays/vertical modes is used. The "effective" sound speed for the model of stratified ocean is introduced. It allows the qualitative estimation of the medium motion effect on sound propagation taking into account the deformation of the initial sound speed profile. A sequence of direct numerical simulations of sound propagation problems has been carried out for the Gulf Stream models. It is shown that a large-scale current may alter the nature of guided wave sound propagation. For example, a current may lead to noticeable strengthening of a near surface waveguide. It results in smoothed field pattern and significant illumination of the shadow zones. Taking account of the medium inhomogeneity along the horizontal direction leads to the shift of the shadow zones and the illuminated domains relative to the source. If a sound path crosses the Gulf Stream ring, the medium motion effect on sound propagation may be ignored.

COMPARISON OF THE EFFECTS OF MEDIUM MOTION AND ITS INHOMOGENEITY ON SOUND PROPAGATION IN THE OCEAN

1996 ◽  
Vol 04 (04) ◽  
pp. 385-397
Author(s):  
NATALIE S. GRIGORIEVA
Keyword(s):  
Sound Wave ◽  
Gulf Stream ◽  
Sound Pressure ◽  
Adiabatic Approximation ◽  
Sound Propagation ◽  
Medium Density ◽  
Normal Waves ◽  
Linear Partial Differential Equations ◽  
Oscillation Velocity ◽  
Moving Fluid

The purpose of this paper is to compare the effects of medium motion and its inhomogeneity on sound propagation in the ocean at frequencies from a few tens to a hundred Hz for the sound paths up to several hundreds kilometers in length. It is considered the acoustic propagation passing through a cyclonic eddy and the Gulf Stream current. In moving fluid, the sound propagation is described by a system of seven linear partial differential equations for seven unknown elements of a sound wave. These are the sound pressure, the particle oscillation velocity in a sound wave as well as the changes in medium density, its entropy and concentration of the salt caused by the passage of a sound wave. All these elements of a sound wave are seek in the form of a sum of the quasi-normal waves using the modification of the method of horizontal rays/vertical modes. The numerical simulations are carried out on the base of formulas taking into account the first correction to the adiabatic approximation.

scholarly journals Intensification of Upper-Ocean Submesoscale Turbulence through Charney Baroclinic Instability

2016 ◽  
Vol 46 (11) ◽  
pp. 3365-3384 ◽  
Author(s):  
Xavier Capet ◽  
Guillaume Roullet ◽  
Patrice Klein ◽  
Guillaume Maze
Keyword(s):  
Kinetic Energy ◽  
Gulf Stream ◽  
Energy Input ◽  
Baroclinic Instability ◽  
Upper Ocean ◽  
Mode Water ◽  
Near Surface ◽  
Turbulent Statistics ◽  
Frontal Activity ◽  
Southern Flank

AbstractThis study focuses on the description of an oceanic variant of the Charney baroclinic instability, arising from the joint presence of (i) an equatorward buoyancy gradient that extends from the surface into the ocean interior and (ii) reduced subsurface stratification, for example, as produced by wintertime convection or subduction. This study analyzes forced dissipative simulations with and without Charney baroclinic instability (C-BCI). In the former, C-BCI strengthens near-surface frontal activity with important consequences in terms of turbulent statistics: increased variance of vertical vorticity and velocity and increased vertical turbulent fluxes. Energetic consequences are explored. Despite the atypical enhancement of submesoscale activity in the simulation subjected to C-BCI, and contrary to several recent studies, the downscale energy flux at the submesoscale en route to dissipation remains modest in the flow energetic equilibration. In particular, it is modest vis à vis the global energy input to the system, the eddy kinetic energy input through conversion of available potential energy, and the classical inverse cascade of kinetic energy. Linear stability analysis suggests that the southern flank of the Gulf Stream may be conducive to oceanic Charney baroclinic instability in spring, following mode water formation and upper-ocean destratification.

scholarly journals Diagnostics for near-surface wind convergence/divergence response to the Gulf Stream in a regional atmospheric model

2011 ◽  
Vol 13 (1) ◽  
pp. 16-21 ◽  
Author(s):  
Kohei Takatama ◽  
Shoshiro Minobe ◽  
Masaru Inatsu ◽  
R. Justin Small
Keyword(s):  
Gulf Stream ◽  
Surface Wind ◽  
Atmospheric Model ◽  
Near Surface ◽  
Regional Atmospheric Model

scholarly journals A Method for Processing Acoustic Doppler Current Profiler Velocity Data from Towed, Undulating Vehicles

2008 ◽  
Vol 25 (9) ◽  
pp. 1710-1716 ◽  
Author(s):  
Jiayi Pan ◽  
David A. Jay
Keyword(s):  
Surface Waters ◽  
High Frequency ◽  
Acoustic Doppler Current Profiler ◽  
Small Time ◽  
Ocean Current ◽  
Near Surface ◽  
Vertical Range ◽  
External Reference ◽  
Current Profiler ◽  
Adcp Measurements

Abstract The utility of the acoustic Doppler current profiler (ADCP) for sampling small time and space scales of coastal environments can be enhanced by mounting a high-frequency (1200 kHz) ADCP on an oscillating towed body. This approach requires both an external reference to convert the measured shears to velocities in the earth coordinates and a method to determine the towed body velocities. During the River Influence on the Shelf Ecosystems (RISE) project cruise, a high-frequency (1200 kHz) and narrowbeam ADCP with mode 12 sampling was mounted on a TRIAXUS oscillating towfish, which steers a 3D path behind the ship. This deployment approach extended the vertical range of the ADCP and allowed it to sample near-surface waters outside the ship’s wake. The measurements from a ship-mounted 1200-kHz narrowbeam ADCP are used as references for TRIAXUS ADCP data, and a method of overlapping bins is employed to recover the entire vertical range of the TRIAXUS ADCP. The TRIAXUS vehicle horizontal velocities are obtained by removing the derived ocean current velocity from the TRIAXUS ADCP measurements. The results show that the method is practical.

scholarly journals Effects of climate and spawning stock structure on the spatial distribution of Northeast Arctic cod larvae

2020 ◽  
Author(s):  
Clarissa Akemi Kajiya Endo ◽  
Frode B Vikebø ◽  
Natalia A Yaragina ◽  
Solfrid Sætre Hjøllo ◽  
Leif Christian Stige
Keyword(s):  
Spatial Distribution ◽  
Environmental Variables ◽  
Barents Sea ◽  
Condition Index ◽  
Ocean Current ◽  
Larval Abundance ◽  
Near Surface ◽  
Spawning Stock ◽  
Long Time ◽  
Abundance And Distribution

Abstract The spatial distribution of fish early life stages can impact recruitment at later stages and affect population size and resilience. Northeast Arctic (NEA) cod spawning occurs along the Norwegian coast. Eggs, larvae, and pelagic juveniles drift near-surface towards the Barents Sea nursery area. In this study, a 35-year long time series of NEA cod larvae data was analysed in combination with factors that potentially may affect the distribution of eggs and larvae. These factors included biological aspects of the spawning stock, and environmental variables, such as water temperature, wind, ocean current, and prey abundance. Our aim was to shed light on how these factors influence larval abundance and distribution and how larval abundance and distribution influenced recruitment at age 3. We found that biomass and mean weight of the spawners were positively associated with larval abundance and that a high liver condition index of the spawners was associated with a north-easterly distribution of the larvae. The environmental variables showed generally weak or no correlations with abundance or distribution of larvae. Lastly, we found significant association between larval abundance and year-class abundance at age 3, while the spatial distribution metrics of the larvae, i.e. distribution extent, mean longitude, and mean latitude, showed no significant association with future year-class abundance.

Comparison of Sound Propagation Characteristic between Deep and Shallow Water

2014 ◽  
Vol 577 ◽  
pp. 1198-1201
Author(s):  
Zhang Liang ◽  
Chun Xia Meng ◽  
Hai Tao Xiao
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Sound Speed ◽  
Sound Propagation ◽  
Spherical Wave ◽  
Sound Field ◽  
Propagation Loss ◽  
Speed Profile ◽  
Sound Speed Profile ◽  
Propagation Law

The physical characteristics are compared between shallow and deep water, in physics and acoustics, respectively. There is a specific sound speed profile in deep water, which is different from which in shallow water, resulting in different sound propagation law between them. In this paper, the sound field distributions are simulated under respective typical sound speed profile. The color figures of sound intensity are obtained, in which the horizontal ordinate is distance, and the vertical ordinate is depth. Then we can get some important characteristics of sound propagation. The results show that the seabed boundary is an important influence on sound propagation in shallow water, and sound propagation loss in deep water convergent zone is visibly less than which in spherical wave spreading. We can realize the remote probing using the acoustic phenomenon.

scholarly journals Dynamic-pressure distributions under Stokes waves with and without a current

2017 ◽  
Vol 376 (2111) ◽  
pp. 20170103 ◽  
Author(s):  
Motohiko Umeyama
Keyword(s):  
Water Waves ◽  
Dynamic Pressure ◽  
Water Pressure ◽  
Travelling Waves ◽  
Stokes Wave ◽  
Front Face ◽  
Nonlinear Water Waves ◽  
Near Surface ◽  
Stokes Waves ◽  
A Current

To investigate changes in the instability of Stokes waves prior to wave breaking in shallow water, pressure data were recorded vertically over the entire water depth, except in the near-surface layer (from 0 cm to −3 cm), in a recirculating channel. In addition, we checked the pressure asymmetry under several conditions. The phase-averaged dynamic-pressure values for the wave–current motion appear to increase compared with those for the wave-alone motion; however, they scatter in the experimental range. The measured vertical distributions of the dynamic pressure were plotted over one wave cycle and compared to the corresponding predictions on the basis of third-order Stokes wave theory. The dynamic-pressure pattern was not the same during the acceleration and deceleration periods. Spatially, the dynamic pressure varies according to the faces of the wave, i.e. the pressure on the front face is lower than that on the rear face. The direction of wave propagation with respect to the current directly influences the essential features of the resulting dynamic pressure. The results demonstrate that interactions between travelling waves and a current lead more quickly to asymmetry. This article is part of the theme issue ‘Nonlinear water waves’.

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