Acoustic Visualization of Nonlinear Internal Gravity Waves Using an Improved High Frequency Sonar System

2006 ◽  
Vol 40 (1) ◽  
pp. 97-102
Author(s):  
Michael T. McCord ◽  
Earl W. Carey
Keyword(s):  
Fine Structure ◽  
Gravity Waves ◽  
High Frequency ◽  
High Sensitivity ◽  
Internal Gravity Waves ◽  
Horizontal Resolution ◽  
Naval Research ◽  
Sonar System ◽  
Industry Applications ◽  
Sonar Systems

High frequency sonar systems have been used by the Naval Research Laboratory to study nonlinear internal gravity waves and define the fine structure of ocean temperature and salinity layers that are found in coastal waters, usually within 130 meters of the surface. Of particular interest is the fine structure of these waves, which are being investigated using high sensitivity sonar systems that provide 1 m horizontal resolution and less than 8 cm vertical resolution. This article describes the integration of commercial and custom-designed components, including a recently patented transmitter-receiver switch. The significance of this T-R switch is that it improves the sensitivity of short-range sonar systems, enables a more refined measurement of nonlinear internal gravity waves, and could have broad industry applications.

Numerical Investigation of Mechanisms Underlying Oceanic Internal Gravity Wave Power-Law Spectra

2020 ◽  
Vol 50 (9) ◽  
pp. 2713-2733
Author(s):  
Yulin Pan ◽  
Brian K. Arbic ◽  
Arin D. Nelson ◽  
Dimitris Menemenlis ◽  
W. R. Peltier ◽  
...  
Keyword(s):  
Power Law ◽  
Gravity Waves ◽  
High Frequency ◽  
Internal Gravity Wave ◽  
Numerical Data ◽  
Field Measurements ◽  
Internal Gravity Waves ◽  
Collision Integral ◽  
Turbulence Theory ◽  
Nonlinear Interactions

AbstractWe consider the power-law spectra of internal gravity waves in a rotating and stratified ocean. Field measurements have shown considerable variability of spectral slopes compared to the high-wavenumber, high-frequency portion of the Garrett–Munk (GM) spectrum. Theoretical explanations have been developed through wave turbulence theory (WTT), where different power-law solutions of the kinetic equation can be found depending on the mechanisms underlying the nonlinear interactions. Mathematically, these are reflected by the convergence properties of the so-called collision integral (CL) at low- and high-frequency limits. In this work, we study the mechanisms in the formation of the power-law spectra of internal gravity waves, utilizing numerical data from the high-resolution modeling of internal waves (HRMIW) in a region northwest of Hawaii. The model captures the power-law spectra in broad ranges of space and time scales, with scalings ω−2.05±0.2 in frequency and m−2.58±0.4 in vertical wavenumber. The latter clearly deviates from the GM76 spectrum but is closer to a family of induced-diffusion-dominated solutions predicted by WTT. Our analysis of nonlinear interactions is performed directly on these model outputs, which is fundamentally different from previous work assuming a GM76 spectrum. By applying a bicoherence analysis and evaluations of modal energy transfer, we show that the CL is dominated by nonlocal interactions between modes in the power-law range and low-frequency inertial motions. We further identify induced diffusion and the near-resonances at its spectral vicinity as dominating the formation of power-law spectrum.

scholarly journals Parameters of internal gravity waves in the mesosphere-lower thermosphere region derived from meteor radar wind measurements

2005 ◽  
Vol 23 (11) ◽  
pp. 3431-3437 ◽  
Author(s):  
A. N. Oleynikov ◽  
Ch. Jacobi ◽  
D. M. Sosnovchik
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Lower Thermosphere ◽  
Radar Data ◽  
Internal Gravity Waves ◽  
Meteor Radar ◽  
Energy Propagation ◽  
Data Set ◽  
Wind Measurements ◽  
Phase Progression

Abstract. A procedure of revealing parameters of internal gravity waves from meteor radar wind measurements is presented. The method is based on dividing the measuring volume into different parts and, using wavelet analysis, calculating the phase progression of frequency peaks in the vertical and horizontal direction. Thus, the distribution of vertical and horizontal wavelengths and directions of IGW energy propagation, using meteor radar data, has been obtained. The method was applied to a 4-month data set obtained in July and August, 1998 and 1999. As expected, the majority of waves have been found to propagate upwards, although a considerable number seem to propagate downwards as well. High-frequency (intrinsic periods T* of less than 2 h) waves are dominating. The distribution of waves over the course of an average day is only weakly structured, with weak maxima in the morning and evening.

Visualization and measurement of internal waves by ‘synthetic schlieren’. Part 1. Vertically oscillating cylinder

1999 ◽  
Vol 390 ◽  
pp. 93-126 ◽  
Author(s):  
BRUCE R. SUTHERLAND ◽  
STUART B. DALZIEL ◽  
GRAHAM O. HUGHES ◽  
P. F. LINDEN
Keyword(s):  
Density Gradient ◽  
Gravity Waves ◽  
Wave Attenuation ◽  
Time Derivative ◽  
Low Frequency ◽  
High Sensitivity ◽  
Internal Gravity Waves ◽  
Quantitative Agreement ◽  
Gradient Field ◽  
Displacement Distribution

We present measurements of the density and velocity fields produced when an oscillating circular cylinder excites internal gravity waves in a stratified fluid. These measurements are obtained using a novel, non-intrusive optical technique suitable for determining the density fluctuation field in temporally evolving flows which are nominally two-dimensional. Although using the same basic principles as conventional methods, the technique uses digital image processing in lieu of large and expensive parabolic mirrors, thus allowing more flexibility and providing high sensitivity: perturbations of the order of 1% of the ambient density gradient may be detected. From the density gradient field and its time derivative it is possible to construct the perturbation fields of density and horizontal and vertical velocity. Thus, in principle, momentum and energy fluxes can be determined.In this paper we examine the structure and amplitude of internal gravity waves generated by a cylinder oscillating vertically at different frequencies and amplitudes, paying particular attention to the role of viscosity in determining the evolution of the waves. In qualitative agreement with theory, it is found that wave motions characterized by a bimodal displacement distribution close to the source are attenuated by viscosity and eventually undergo a transition to a unimodal displacement distribution further from the source. Close quantitative agreement is found when comparing our results with the theoretical ones of Hurley & Keady (1997). This demonstrates that the new experimental technique is capable of making accurate measurements and also lends support to analytic theories. However, theory predicts that the wave beams are narrower than observed, and the amplitude is significantly under-predicted for low-frequency waves. The discrepancy occurs in part because the theory neglects the presence of the viscous boundary layers surrounding the cylinder, and because it does not take into account the effects of wave attenuation resulting from nonlinear wave–wave interactions between the upward and downward propagating waves near the source.

OBSERVATIONS UPON CLEAR-AIR STRATIFICATION IN THE LOWER TROPOSPHERE

1964 ◽  
Vol 42 (2) ◽  
pp. 273-286
Author(s):  
M. B. Bell ◽  
D. R. Hay ◽  
R. W. Johnston
Keyword(s):  
Life History ◽  
Fine Structure ◽  
Gravity Waves ◽  
Lower Troposphere ◽  
Eddy Diffusion ◽  
Internal Gravity Waves ◽  
Special Design ◽  
Regular Distribution ◽  
Total Incidence ◽  
Clear Weather

A study of the fine structure of air refractivity in the lower troposphere has been continued through the spring and summer of 1962 by the observation of weak radio reflections from clear air (radar angels), with a vertically directed radar of special design operating at 6770 Mc/s. These observations have been limited to the layer of frictional influence, within 1500 meters of the surface. The interpretation suggests that the reflecting centers are broad strata whose refractivity contrasts weakly with that of their environment, whose vertical depths are no more than a few centimeters, and which are either flat over horizontal distances of at least several meters or concave downwards with radii of curvature somewhat less than their height above ground. The incidence of transitory reflections generally follows a regular distribution in the vertical, with a maximum at 300 meters; the form of this distribution is modified by the intrusion of weather fronts, thermals, and other clear-weather structures. The transitory reflecting stratum is cut off from its generating source early in its life history, to be dispersed into its environment by molecular or eddy diffusion. The total incidence of transitory angels fluctuates quasi-periodically in time, with a period of about 10 minutes; it is suggested that this periodicity is due to the influence of internal gravity waves in the atmosphere. In contrast, persistent reflections are associated with a more stable environment; the maximum incidence is at the lowest heights observed, with a gradual decrease towards higher levels. Their relationship to clear-weather structure is less certain than for the transitory reflections. The persistent reflecting stratum must be replenished continuously by the generating source during its lifetime to offset diffusion into the environment.

Spatial and temporal analysis of high-frequency internal gravity wave signatures in brightness temperature satellite images

2021 ◽  
Author(s):  
Robert Vicari
Keyword(s):  
Water Vapor ◽  
Brightness Temperature ◽  
Gravity Wave ◽  
Gravity Waves ◽  
High Frequency ◽  
Satellite Images ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Small Scale ◽  
Wave Patterns

<p>Highly idealized model studies suggest that convectively generated internal gravity waves in the troposphere with horizontal wavelengths on the order of a few kilometers may affect the lifetime, spacing, and depth of clouds and convection. To answer whether such a convection-wave coupling occurs in the real atmosphere, one needs to find corresponding events in observations. In general, the study of high-frequency internal gravity wave-related phenomena in the troposphere is a challenging task because they are usually small-scale and intermittent. To overcome case-by-case studies, it is desirable to have an automatic method to analyze as much data as possible and provide enough independent and diverse evidence.<br>Here, we focus on brightness temperature satellite images, in particular so-called satellite water vapor channels. These channels measure the radiation at wavelengths corresponding to the energy emitted by water vapor and provide cloud-independent observations of internal gravity waves, in contrast to visible and other infrared satellite channels where one relies on the wave impacts on clouds. In addition, since these water vapor channels are sensitive to certain vertical layers in the troposphere, combining the images also reveals some vertical structure of the observed waves.<br>We propose an algorithm based on local Fourier analyses to extract information about high-frequency wave patterns in given brightness temperature images. This method allows automatic detection and analysis of many wave patterns in a given domain at once, resulting in a climatology that provides an initial observational basis for further research. Using data from the instrument ABI on board the satellite GOES-16 during the field campaign EUREC<sup>4</sup>A, we demonstrate the capabilities and limitations of the method. Furthermore, we present the respective climatology of the detected waves and discuss approaches based on this to address the initial question.</p>

scholarly journals Energetic Submesoscale Dynamics in the Ocean Interior

2020 ◽  
Vol 50 (3) ◽  
pp. 727-749 ◽  
Author(s):  
Lia Siegelman
Keyword(s):  
Mixed Layer ◽  
Gravity Waves ◽  
Gulf Stream ◽  
Antarctic Circumpolar Current ◽  
Internal Gravity Waves ◽  
Horizontal Resolution ◽  
Heat Fluxes ◽  
Surface Mixed Layer ◽  
Circumpolar Current ◽  
The Antarctic

AbstractSubmesoscale ocean processes, characterized by order-1 Rossby and Richardson numbers, are currently thought to be mainly confined to the ocean surface mixed layer, whereas the ocean interior is commonly assumed to be in quasigeostrophic equilibrium. Here, a realistic numerical simulation in the Antarctic Circumpolar Current, with a 1/48° horizontal resolution and tidal forcing, is used to demonstrate that the ocean interior departs from the quasigeostrophic regime down to depths of 900 m, that is, well below the mixed layer. Results highlight that, contrary to the classical paradigm, the ocean interior is strongly ageostrophic, with a pronounced cyclone–anticyclone asymmetry and a dominance of frontogenesis over frontolysis. Numerous vortices and filaments, from the surface down to 900 m, are characterized by large Rossby and low Richardson numbers, strong lateral gradients of buoyancy, and vigorous ageostrophic frontogenesis. These deep submesoscales fronts are only weakly affected by internal gravity waves and drive intense upward vertical heat fluxes, consistent with recent observations in the Antarctic Circumpolar Current and the Gulf Stream. As such, deep submesoscale fronts are an efficient pathway for the transport of heat from the ocean interior to the surface, suggesting the presence of an intensified oceanic restratification at depth.

scholarly journals Особенности высокочастотной составляющей фоновых внутренних гравитационных волн на шельфе Японского моря

2020 ◽  
Vol 43 (2) ◽  
Author(s):  
ALEXANDRA KOSHELEVA ◽  
IGOR YAROSHCHUK ◽  
ALEKSEY SHVYREV ◽  
ALEXANDER SAMCHENKO ◽  
ALEXANDER PIVOVAROV ◽  
...  
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Spectral Representation ◽  
Peter The Great Bay ◽  
Internal Gravity Waves ◽  
The Sea Of Japan ◽  
Direct And Inverse Problems ◽  
Experimental Data Processing ◽  
The Past ◽  
Peter The Great

Для решения прямых и обратных задач практической гидроакустики необходимо иметь наборы статистических феноменологических моделей пространственно-временных вариаций скорости звука. Как правило, такие возмущения определяются внутренними гравитационными волнами (ВГВ), что делает актуальной проблему разработки их адекватных статистических моделей. В данной работе на основе результатов обработки экспериментальных данных проанализированы характеристики высокочастотной (превышающей 2,5 цикл/ч) составляющей фоновых ВГВ. Натурные наблюдения проводились авторами на шельфе в юго-западной части залива Петра Великого Японского моря в весенний, летний и осенний сезоны на протяжении последнего десятка лет. Проделанный анализ наиболее интенсивных изотерм демонстрирует, что с достаточной точностью флуктуации температуры можно считать гауссовыми. Это позволило авторам разработать и применить методику рандомизации спектрального представления случайного поля (ковариационной матрицы ВГВ) для построения статистической рандомизированной модели, из которой можно выбирать отдельные статистические реализации поля ВГВ для решения конкретных прикладных задач гидроакустики, связанных в том числе и с разработкой судовой аппаратуры для подводной связи, навигации и обнаружения подводных и надводных источников звука. To solve both direct and inverse problems of practical hydroacoustics, one needs a set of statistical phenomenological models of spatiotemporal variations of sound speed. As a rule, such variations are determined by internal gravity waves (IGW), which makes the problem of developing adequate statistical models of IGW a pending issue. In this paper, based on results of the experimental data processing, the characteristics of high-frequency (exceeding 2.5 cycles/h) component of the background IGW are analyzed. Field observations were carried out by the authors on the shelf in the southwestern part of Peter the Great Bay of the Sea of Japan in spring, summer, and autumn seasons over the past ten years. Analysis of the most intense isotherms demonstrates that the temperature variations can be considered Gaussian with sufficient accuracy. This fact allowed the authors to develop and apply a randomization technique for the spectral representation of a random field (the IGW covariance matrix) to construct a randomized statistical model from which it is possible to select some statistical implementations of the IGW field for solving specific applied problems of hydroacoustics.

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