Ocean Internal Waves as Sources of Small-Scale Patchiness in Seabird Distribution on the Blake Plateau

The Auk ◽  
1987 ◽  
Vol 104 (1) ◽  
pp. 129-133 ◽  
Author(s):  
J. Christopher Haney
Keyword(s):  
Internal Waves ◽  
Small Scale

scholarly journals Strong Modulation of Short Wind Waves and Ka-Band Radar Return Due to Internal Waves in the Presence of Surface Films. Theory and Experiment

2021 ◽  
Vol 13 (13) ◽  
pp. 2462
Author(s):  
Stanislav A. Ermakov ◽  
Irina A. Sergievskaya ◽  
Ivan A. Kapustin
Keyword(s):  
Phase Velocity ◽  
Internal Waves ◽  
Wind Waves ◽  
Strong Increase ◽  
Small Scale ◽  
Surface Films ◽  
Ka Band ◽  
Steady Current ◽  
Backscatter Modulation ◽  
Resonance Surface

Strong variability of Ka-band radar backscattering from short wind waves on the surface of water covered with surfactant films in the presence of internal waves (IW) was studied in wave tank experiments. It has been demonstrated that modulation of Ka-band radar return due to IW strongly depends on the relationship between the phase velocity of IW and the velocity of drifting surfactant films. An effect of the strong increase in surfactant concentration was revealed in convergent zones, associated with IW orbital velocities in the presence of a “resonance” surface steady current, the velocity of which was close to the IW phase velocity. A phenomenological model of suppression and modulations in the spectrum of small-scale wind waves due to films and IW was elaborated. It has been shown that backscatter modulation could not be explained by the modulation of free (linear) millimeter-scale Bragg waves, but was associated with the modulation of bound (parasitic) capillary ripples generated by longer, cm–dm-scale waves—a “cascade” modulation mechanism. Theoretical analysis based on the developed model was found to be consistent with experiments. Field observations which qualitatively illustrated the effect of strong modulation of Ka-band radar backscatter due to IW in the presence of resonance drift of surfactant films are presented.

Wavenumber transport: scattering of small-scale internal waves by large-scale wavepackets

1995 ◽  
Vol 289 ◽  
pp. 379-405 ◽  
Author(s):  
David L. Bruhwiler ◽  
Tasso J. Kaper
Keyword(s):  
Internal Waves ◽  
High Frequency ◽  
Large Scale ◽  
Wave Interaction ◽  
Initial Distribution ◽  
Small Scale ◽  
Theoretic Model ◽  
Frequency Interval ◽  
Crossing Theory ◽  
Invariance Theory

In this work, we treat the problem of small-scale, small-amplitude, internal waves interacting nonlinearly with a vigorous, large-scale, undulating shear. The amplitude of the background shear can be arbitrarily large, with a general profile, but our analysis requires that the amplitude vary on a length scale longer than the wavelength of the undulations. In order to illustrate the method, we consider the ray-theoretic model due to Broutman & Young (1986) of high-frequency oceanic internal waves that trap and detrap in a near-inertial wavepacket as a prototype problem. The near-inertial wavepacket tends to transport the high-frequency test waves from larger to smaller wavenumber, and hence to higher frequency. We identify the essential physical mechanisms of this wavenumber transport, and we quantify it. We also show that, for an initial ensemble of test waves with frequencies between the inertial and buoyancy frequencies and in which the number of test waves per frequency interval is proportional to the inverse square of the frequency, a single nonlinear wave–wave interaction fundamentally alters this initial distribution. After the interaction, the slope on a log-log plot is nearly flat, whereas initially it was -2. Our analysis captures this change in slope. The main techniques employed are classical adiabatic invariance theory and adiabatic separatrix crossing theory.

scholarly journals The Impact of a Variable Mixing Efficiency on the Abyssal Overturning

2016 ◽  
Vol 46 (2) ◽  
pp. 663-681 ◽  
Author(s):  
Casimir de Lavergne ◽  
Gurvan Madec ◽  
Julien Le Sommer ◽  
A. J. George Nurser ◽  
Alberto C. Naveira Garabato
Keyword(s):  
Potential Energy ◽  
Internal Waves ◽  
Bottom Water ◽  
Internal Tides ◽  
Mixing Efficiency ◽  
Small Scale ◽  
Antarctic Bottom Water ◽  
Energy Fraction ◽  
Geothermal Heating ◽  
The Impact

AbstractIn studies of ocean mixing, it is generally assumed that small-scale turbulent overturns lose 15%–20% of their energy in eroding the background stratification. Accumulating evidence that this energy fraction, or mixing efficiency Rf, significantly varies depending on flow properties challenges this assumption, however. Here, the authors examine the implications of a varying mixing efficiency for ocean energetics and deep-water mass transformation. Combining current parameterizations of internal wave-driven mixing with a recent model expressing Rf as a function of a turbulence intensity parameter Reb = εν/νN2, the ratio of dissipation εν to stratification N2 and molecular viscosity ν, it is shown that accounting for reduced mixing efficiencies in regions of weak stratification or energetic turbulence (high Reb) strongly limits the ability of breaking internal waves to supply oceanic potential energy and drive abyssal upwelling. Moving from a fixed Rf = 1/6 to a variable efficiency Rf(Reb) causes Antarctic Bottom Water upwelling induced by locally dissipating internal tides and lee waves to fall from 9 to 4 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) and the corresponding potential energy source to plunge from 97 to 44 GW. When adding the contribution of remotely dissipating internal tides under idealized distributions of energy dissipation, the total rate of Antarctic Bottom Water upwelling is reduced by about a factor of 2, reaching 5–15 Sv, compared to 10–33 Sv for a fixed efficiency. The results suggest that distributed mixing, overflow-related boundary processes, and geothermal heating are more effective in consuming abyssal waters than topographically enhanced mixing by breaking internal waves. These calculations also point to the importance of accurately constraining Rf(Reb) and including the effect in ocean models.

scholarly journals Ocean feature models − their use and effectiveness in ocean acoustic forecasting

1997 ◽  
Vol 15 (1) ◽  
pp. 101-112 ◽  
Author(s):  
J. Small ◽  
L. Shackleford ◽  
G. Pavey
Keyword(s):  
Internal Waves ◽  
Environmental Variability ◽  
High Amplitude ◽  
Propagation Loss ◽  
Feature Model ◽  
Acoustic Properties ◽  
Small Scale ◽  
Feature Models ◽  
Independent Field ◽  
Rms Errors

Abstract. The aim of this paper is to test the effectiveness of feature models in ocean acoustic forecasting. Feature models are simple mathematical representations of the horizontal and vertical structures of ocean features (such as fronts and eddies), and have been used primarily for assimilating new observations into forecasts and for compressing data. In this paper we describe the results of experiments in which the models have been tested in acoustic terms in eddy and frontal environments in the Iceland Faeroes region. Propagation-loss values were obtained with a 2D parabolic-equation (PE) model, for the observed fields, and compared to PE results from the corresponding feature models and horizontally uniform (range-independent) fields. The feature models were found to represent the smoothed observed propagation-loss field to within an rms error of 5 dB for the eddy and 7 dB for the front, compared to 10–15-dB rms errors obtained with the range-independent field. Some of the errors in the feature-model propagation loss were found to be due to high-amplitude 'oceanographic noise' in the field. The main conclusion is that the feature models represent the main acoustic properties of the ocean but do not show the significant effects of small-scale internal waves and fine-structure. It is recommended that feature models be used in conjunction with stochastic models of the internal waves, to represent the complete environmental variability.

scholarly journals Internal Waves and Mixing near the Kerguelen Plateau

2015 ◽  
Vol 46 (2) ◽  
pp. 417-437 ◽  
Author(s):  
Amelie Meyer ◽  
Kurt L. Polzin ◽  
Bernadette M. Sloyan ◽  
Helen E. Phillips
Keyword(s):  
Internal Wave ◽  
Wave Field ◽  
Internal Waves ◽  
Large Scale ◽  
Polar Front ◽  
Frontal Region ◽  
Small Scale ◽  
Kerguelen Plateau ◽  
Flow Strength ◽  
Internal Wave Field

AbstractIn the stratified ocean, turbulent mixing is primarily attributed to the breaking of internal waves. As such, internal waves provide a link between large-scale forcing and small-scale mixing. The internal wave field north of the Kerguelen Plateau is characterized using 914 high-resolution hydrographic profiles from novel Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats. Altogether, 46 coherent features are identified in the EM-APEX velocity profiles and interpreted in terms of internal wave kinematics. The large number of internal waves analyzed provides a quantitative framework for characterizing spatial variations in the internal wave field and for resolving generation versus propagation dynamics. Internal waves observed near the Kerguelen Plateau have a mean vertical wavelength of 200 m, a mean horizontal wavelength of 15 km, a mean period of 16 h, and a mean horizontal group velocity of 3 cm s−1. The internal wave characteristics are dependent on regional dynamics, suggesting that different generation mechanisms of internal waves dominate in different dynamical zones. The wave fields in the Subantarctic/Subtropical Front and the Polar Front Zone are influenced by the local small-scale topography and flow strength. The eddy-wave field is influenced by the large-scale flow structure, while the internal wave field in the Subantarctic Zone is controlled by atmospheric forcing. More importantly, the local generation of internal waves not only drives large-scale dissipation in the frontal region but also downstream from the plateau. Some internal waves in the frontal region are advected away from the plateau, contributing to mixing and stratification budgets elsewhere.

ON COASTAL - OPEN SEA DYNAMIC INTERACTIONS DEFINING PRODUCTIVITY AND ECOLOGY OF SHELF AND ADJACENT TO SHELF WATERS

2017 ◽  
Author(s):  
Vadim Navrotsky ◽  
Vadim Navrotsky
Keyword(s):  
Boundary Layers ◽  
Internal Waves ◽  
Stratified Medium ◽  
Shelf Zone ◽  
Small Scale ◽  
The Sea Of Japan ◽  
Bottom Boundary ◽  
Open Sea ◽  
Bottom Boundary Layers ◽  
Near Shore

It is known that considerable part of living matter in the ocean falls out of biological cycle irretrievably by way of sedimentation. It means that quasi-stationary state of oceanic ecosystems is possible only with supply of mineral and organic matter from land. That supply, which includes also contaminating matter, takes place mainly in near-shore regions, concentrates in bottom boundary layers, and is transferred to the open sea via shelves by means of horizontal and vertical mixing. Effective mixing in shelves is carried out by small-scale processes, which are considerably fed by energy of large-scale processes from out-of-shelf regions. The main objective of our paper is to identify mechanisms of energy transfer from large to small-scale motions and from open sea to near-shore areas. Our experiments and observations in the shelf zone of the Sea of Japan revealed important specific features in stratified bottom boundary layers: 1) Temporal intermittence of internal waves (IW) in near-bottom layers and their transformation into sequences of stratified boluses moving in non-stratified medium. 2) Extremely high horizontal and vertical velocities in the near-bottom layers. 3) Considerable power fluctuations caused by correlated fluctuations of near-bottom pressure and velocity. 4) Non-monotonic vertical structure of temperature and velocity leading to possibility of simultaneous existing of IW breaking and secondary generation of high-frequency IW by turbulence in layers with high curvature of velocity profiles. Taking into account satellite observations of high correlation between chlorophyll-a concentration in coastal and in out-of-shelf waters, as well as dispersion relations for different types of internal waves and results of our field experiments we suggest that interconnection of biological parameters in coastal and in open sea waters is exercised substantially by gravitational and inertial internal waves generated by tides and eddies in the region of continental slope near the shelf boundary.

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