scholarly journals Acoustic-Gravity Waves Interacting with a Rectangular Trench

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Usama Kadri
Keyword(s):  
Early Detection ◽  
Flow Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Linear Problem ◽  
Two Dimensional ◽  
Bottom Pressure ◽  
Acoustic Gravity Wave ◽  
Mathematical Solution ◽  
Acoustic Gravity Waves

A mathematical solution of the two-dimensional linear problem of an acoustic-gravity wave interacting with a rectangular trench, in a compressible ocean, is presented. Expressions for the flow field on both sides of the trench are derived. The dynamic bottom pressure produced by the acoustic-gravity waves on both sides of the trench is measurable, though on the transmission side it decreases with the trench depth. A successful recording of the bottom pressures could assist in the early detection of tsunami.

scholarly journals On the origin of medium-period ionospheric waves and their possible modelling: a short review

1997 ◽  
Vol 40 (5) ◽  
Author(s):  
P. Dominici ◽  
L. R. Cander ◽  
B. Zolesi
Keyword(s):  
Data Analysis ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Sudden Change ◽  
Short Review ◽  
Acoustic Gravity Wave ◽  
Acoustic Gravity Waves ◽  
Physical Conditions ◽  
Wave Induced ◽  
The Waves

This article introduces the concept of ionospheric waves with periods from about 15 min to about 4 h as one of the acoustic-gravity wave-induced phenomena. The existence of these medium-period ionospheric waves in the various ionospheric layers is supported by the results of a data analysis which has shown remarkable characteristics in occurrence and direction of the waves with a period not longer than about 2 h. The explanation offered is based on the assumption that a unique phenomenon capable to launch acoustic-gravity waves related to such ionospheric waves is the sudden change in physical conditions of the atmosphere due to the passage of the solar terminator.

scholarly journals Beyond the Rigid Lid: Baroclinic Modes in a Structured Atmosphere

2017 ◽  
Vol 74 (11) ◽  
pp. 3551-3566 ◽  
Author(s):  
Jacob P. Edman ◽  
David M. Romps
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Green's Functions ◽  
Green’S Functions ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Mode Decomposition ◽  
Wide Range ◽  
Tropospheric Heating ◽  
Baroclinic Modes

Abstract The baroclinic-mode decomposition is a fixture of the tropical-dynamics literature because of its simplicity and apparent usefulness in understanding a wide range of atmospheric phenomena. However, its derivation relies on the assumption that the tropopause is a rigid lid that artificially restricts the vertical propagation of wave energy. This causes tropospheric buoyancy anomalies of a single vertical mode to remain coherent for all time in the absence of dissipation. Here, the authors derive the Green’s functions for these baroclinic modes in a two-dimensional troposphere (or, equivalently, a three-dimensional troposphere with one translational symmetry) that is overlain by a stratosphere. These Green’s functions quantify the propagation and spreading of gravity waves generated by a horizontally localized heating, and they can be used to reconstruct the evolution of any tropospheric heating. For a first-baroclinic two-dimensional right-moving or left-moving gravity wave with a characteristic width of 100 km, its initial horizontal shape becomes unrecognizable after 4 h, at which point its initial amplitude has also been reduced by a factor of 1/π. After this time, the gravity wave assumes a universal shape that widens linearly in time. For gravity waves on a periodic domain the length of Earth’s circumference, it takes only 10 days for the gravity waves to spread their buoyancy throughout the entire domain.

scholarly journals Acoustic-gravity nonlinear structures

2002 ◽  
Vol 9 (3/4) ◽  
pp. 333-339 ◽  
Author(s):  
D. Jovanović ◽  
L. Stenflo ◽  
P. K. Shukla
Keyword(s):  
Gravity Waves ◽  
Mode Coupling ◽  
Shear Flows ◽  
Vortex Structures ◽  
Coupling Mechanism ◽  
Nonlinear Structures ◽  
Two Dimensional ◽  
Acoustic Gravity Waves ◽  
Nonlinear Generation ◽  
Existence Conditions

Abstract. A catalogue of nonlinear vortex structures associated with acoustic-gravity perturbations in the Earth's atmosphere is presented. Besides the previously known Kelvin-Stewart cat's eyes, dipolar and tripolar structures, new solutions having the form of a row of counter-rotating vortices, and several weakly two-dimensional vortex chains are given. The existence conditions for these nonlinear structures are discussed with respect to the presence of inhomogeneities of the shear flows. The mode-coupling mechanism for the nonlinear generation of shear flows in the presence of linearly unstable acoustic-gravity waves, possibly also leading to intermittency and chaos, is presented.

Generation of an acoustic-gravity wave by two gravity waves, and their subsequent mutual interaction

2013 ◽  
Vol 735 ◽  
Author(s):  
Usama Kadri ◽  
Michael Stiassnie
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Elliptic Integrals ◽  
Mutual Interaction ◽  
Acoustic Gravity Wave ◽  
Exact Resonance ◽  
Near Resonance

AbstractThe nonlinear triad interaction of two opposing gravity waves with almost identical frequencies and one much longer acoustic-gravity wave is studied for non-resonance, as well as for exact resonance conditions. For non-resonance conditions the previously known results for a ‘bound’ acoustic-gravity wave are recovered. For resonance, or near-resonance conditions, where all three waves are ‘free waves’, the interaction is recurrent and the amplitude of the free acoustic-gravity wave turns out to be much larger than that known for the bound wave. The results for the recurrent evolution are given analytically, in terms of Jacobian elliptic functions and elliptic integrals.

The reflexion of plane gravity waves travelling in water of variable depth

1976 ◽  
Vol 284 (1317) ◽  
pp. 49-89 ◽  
Keyword(s):  
Formal Methods ◽  
Gravity Wave ◽  
Linear Theory ◽  
Gravity Waves ◽  
Velocity Potential ◽  
Two Dimensional ◽  
Variable Depth ◽  
Transition Width ◽  
Asymptotic Results ◽  
Surface Gravity Wave

A two dimensional, irrotational, linear theory is used to investigate the reflexion of an incident surface gravity wave travelling over a region of varying depth. The existence of a unique velocity potential is proved for general bottom profiles in two limiting cases, when the wavelength is either small compared with the depth or large compared with the transition width. The associated asymptotic results justify the approximations obtained by others using formal methods. Also, the class of bottom profiles for which numerical results can be achieved is extended.

scholarly journals Measuring Gravity Wave Parameters from a Nighttime Satellite Low-Light Image Based on Two-Dimensional Stockwell Transform

2019 ◽  
Vol 36 (1) ◽  
pp. 41-51 ◽  
Author(s):  
Shensen Hu ◽  
Shuo Ma ◽  
Wei Yan ◽  
Neil P. Hindley ◽  
Kai Xu ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Two Dimensional ◽  
General Shape ◽  
Low Light ◽  
Wave Parameters ◽  
Moonless Night ◽  
Wave Patterns ◽  
Stockwell Transform ◽  
Atmospheric Gravity

AbstractAtmospheric gravity waves are a kind of mesoscale disturbance, commonly found in the atmospheric system, that plays a key role in a series of mesospheric dynamic processes. When propagating to the upper atmosphere, the gravity waves will disturb the local temperature and density, and then modulate the intensity of the surrounding airglow radiation. As a result, the presence of gravity waves on a moonless night can usually cause the airglow to reveal ripple features in low-light images. In this paper we have applied a two-dimensional Stockwell transform technique (2DST) to airglow measurements from nighttime low-light images of the day–night band on the Suomi National Polar-Orbiting Partnership. To our knowledge this study is the first to measure localized mesospheric gravity wave brightness amplitudes, horizontal wavelengths, and propagation directions using such a method and data. We find that the method can characterize the general shape and amplitude of concentric gravity wave patterns, capturing the dominant features and directions with a good degree of accuracy. The key strength of our 2DST application is that our approach could be tuned and then automated in the future to process tens of thousands of low-light images, globally characterizing gravity wave parameters in this historically poorly studied layer of the atmosphere.

Two-dimensional internal gravity wave beam instability

2021 ◽  
Author(s):  
Uwe Harlander ◽  
Michael Kurgansky
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Large Scale ◽  
Wave Beam ◽  
Internal Gravity Wave ◽  
Small Scale ◽  
Breaking Wave ◽  
Beam Model ◽  
Two Dimensional ◽  
Beam Instability

<p>The instability of propagating internal gravity waves is of long-standing interest in geophysical fluid dynamics since breaking gravity waves exchange energy and momentum with the large-scale flow and hence support the large-scale circulation. In this study a low-order gravity wave beam model is used to delineate the linear stability of wave beams and also to study subcritical non-modal transient instability. Assuming that the dissipation of the linearly unstable beam equilibrates with the small-scale turbulence, the model explains the constancy with the height of the amplitude of the wave beam, so that oblique wave beams can reach significant altitudes without disintegrating due to the instability that arises [1]. We further study the robustness of the transient growth when the initial condition for optimal growth is randomly perturbed [2]. It is concluded that for full randomization, in particular, shallow wave beams can show subcritical growth when entering a turbulent background field. Such growing and eventually breaking wave beams might add turbulence to existing background turbulence that originates from other sources of instability.</p><p>[1] Kurgansky and Harlander (2021) Two-dimensional internal gravity wave beam instability. Part I: Linear theory, submitted.</p><p>[2] Harlander and Kurgansky (2021) Two-dimensional internal gravity wave beam instability. Part II: Subcritical instability, submitted.</p>

scholarly journals On the propagation of acoustic–gravity waves under elastic ice sheets

2018 ◽  
Vol 837 ◽  
pp. 640-656 ◽  
Author(s):  
Ali Abdolali ◽  
Usama Kadri ◽  
Wade Parsons ◽  
James T. Kirby
Keyword(s):  
Gravity Waves ◽  
Cutoff Frequency ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Bottom Pressure ◽  
Acoustic Gravity Waves ◽  
Gravitational Forces ◽  
Wave Disturbances ◽  
Different Characteristics ◽  
Elasticity Effects

The propagation of wave disturbances in water of varying depth bounded above by ice sheets is discussed, accounting for gravity, compressibility and elasticity effects. Considering the more realistic scenario of elastic ice sheets reveals a continuous spectrum of acoustic–gravity modes that propagate even below the cutoff frequency of the rigid surface solution where surface (gravity) waves cannot exist. The balance between gravitational forces and oscillations in the ice sheet defines a new dimensionless quantity $\mathfrak{Ka}$. When the ice sheet is relatively thin and the prescribed frequency is relatively low ($\mathfrak{Ka}\ll 1$), the free-surface bottom-pressure solution is retrieved in full. However, thicker ice sheets or propagation of relatively higher frequency modes ($\mathfrak{Ka}\gg 1$) alter the solution fundamentally, which is reflected in an amplified asymmetric signature and different characteristics of the eigenvalues, such that the bottom pressure is amplified when acoustic–gravity waves are transmitted to shallower waters. To analyse these scenarios, an analytical solution and a depth-integrated equation are derived for the cases of constant and varying depths, respectively. Together, these are capable of modelling realistic ocean geometries and an inhomogeneous distribution of ice sheets.

scholarly journals A two-dimensional Stockwell Transform for gravity wave analysis of AIRS measurements

2016 ◽  
Author(s):  
N. P. Hindley ◽  
N. D. Smith ◽  
C. J. Wright ◽  
N. J. Mitchell
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Critical Role ◽  
General Circulation Models ◽  
Two Dimensional ◽  
Wave Analysis ◽  
Stockwell Transform

Abstract. Gravity waves play a critical role in the dynamics of the middle atmosphere due to their ability to transport energy and momentum from their sources to great heights. The accurate parametrization of gravity wave momentum flux is of key importance to general circulation models. For the last decade, the nadir-viewing Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite has made global, two-dimensional (2-D) measurements of stratospheric radiances in which gravity waves can be detected. Current methods for gravity wave analysis of these data can introduce unwanted biases. Here, we present a new analysis method. Our method uses a 2-D Stockwell transform (2DST) to determine gravity wave horizontal wavelengths and directions in both directions simultaneously. We demonstrate that our method can accurately recover horizontal wavelengths and directions from a specified wave field. We show that the use of an elliptical spectral windowing function in the 2DST, in place of a Gaussian, can dramatically improve the recovery of wave amplitude. We measure momentum flux in two granules of AIRS measurements in two regions known to be intense hot spots of gravity wave activity: (i) the Drake Pas- sage/Antarctic Peninsula and (ii) the isolated mountainous island of South Georgia. We show that our 2DST method provides improved spatial localisation of key gravity wave properties over current methods. The added flexibility offered by alternative spectral windowing functions and scaling parameters presented here extend the usefulness of our 2DST method to other areas of geophysical data analysis.

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