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1
Popat, Nilesh R. "Steep capillary waves on gravity waves." Thesis, University of Bristol, 1989. http://hdl.handle.net/1983/78695ee9-b923-4374-b70c-6589b4215241.
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The frequent presence of ripples on the free surface of water. on both thin film flows and ponds or lakes motivates this theoretical investigation into the propagation of ripples on gravity waves. These ripples are treated as "slowly-varying" waves in a reference frame where the gravity wave flow is steady. The methods used are those of the averaged Lagrangian (Whitham 1965,1967,1974) and the averaged equations of motion (Phillips 1966) which are shown to be equivalent. The capillary wave modulation is taken to be steady in the reference frame which brings the gravity wave, or gravity driven flow, to rest. Firstly the motion over ponds or lakes is considered. Linear capillary-gravity waves are examined in order to set the scene. Crapper's (1957) exact finite-amplitude waves are examined next to show the actual behaviour of the flow field. The underlying gravity driven flow is that of pure gravity waves over an' "infinite" depth liquid. These gravity waves are modelled with "numerically exact" solutions for periodic plane-waves. The initial studies are inviscid and show that steep gravity waves either "absorb" or "sweep-up" a range of capillary waves or, alternatively, cause them to break in the vicinity of gravity wave crests. Improvements on the theory are made by including viscous dissipation of wave energy. This leads to a number of solutions approaching "stopping velocities" or the "stopped waves solution". In addition to these effects "higher-order dispersion" is introduced for weakly nonlinear waves near linear caustics. This clarifies aspects of the dissipation results and shows that wave reflection sometimes occurs. Secondly, waves on thin film flows are considered. Linear capillary-gravity waves are again examined in order to set the scene. Kinnersley's (1957) exact finite-amplitude waves are examined next to show the actual behaviour of the flow field. The underlying gravity driven flow is given by shallow water gravity waves. No modelling of these is necessary simply because they are included within Whitham's or Phillips' equations ab initio. This study is inviscid and shows the unexpected presence of critical velocities at which pairs of solution branches originate. iii
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Leaman, Nye Abigail. "Scattering of internal gravity waves." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/238679.
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Internal gravity waves play a fundamental role in the dynamics of stably stratified regions of the atmosphere and ocean. In addition to the radiation of momentum and energy remote from generation sites, internal waves drive vertical transport of heat and mass through the ocean by wave breaking and the mixing subsequently produced. Identifying regions where internal gravity waves contribute to ocean mixing and quantifying this mixing are therefore important for accurate climate and weather predictions. Field studies report significantly enhanced measurements of turbulence near 'rough' ocean topography compared with those recorded in the ocean interior or near more gradually varying topography (e.g. Toole et al. 1997, J. Geophys. Res. 102). Such observations suggest that interaction of waves with rough topography may act to skew wave energy spectra to high wavenumbers and hence promote wave breaking and fluid mixing. This thesis examines the high wavenumber scatter and spatial partitioning of wave energy at 'rough' topography containing features that are of similar scales to those characterising incident waves. The research presented here includes laboratory experiments using synthetic schlieren and PIV to visualise two-dimensional wavefields produced by small amplitude oscillations of cylinders within linear salt-water stratifications. Interactions of wavefields with planar slopes and smoothly varying sinusoidal topography are compared with those with square-wave, sawtooth and pseudo knife-edge profiles, which have discontinuous slopes. Far-field structures of scattered wavefields are compared with linear analytical models. Scatter to high wavenumbers is found to be controlled predominantly by the relative slopes and characterising length scales of the incident wavefield and topography, as well as the shape and aspect ratio of the topographic profile. Wave energy becomes highly focused and the spectra skewed to higher wavenumbers by 'critical' regions, where the topographic slope is comparable with the slope of the incident wave energy vector, and at sharp corners, where topographic slope is not defined. Contrary to linear geometric ray tracing predictions (Longuet-Higgins 1969, J. Fluid Mech. 37), a significant back-scattered field can be achieved in near-critical conditions as well as a forward scattered wavefield in supercritical conditions, where the slope of the boundary is steeper than that of the incident wave. Results suggest that interaction with rough benthic topography could efficiently convert wave energy to higher wavenumbers and promote fluid mixing in such ocean regions.
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Halliday, Oliver John. "Atmospheric convection and gravity waves." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/22414/.
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Doherty, Mary Jane. "Focal lengths and gravity waves." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/73280.
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Thesis (M.S.V.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH.
Transferred to 1/2 in VHS videotape from 8 mm film.
Includes bibliographical references (leaves 56-57).
Film is composed of tiny photographs which, when projected, sometimes look very much like people and things in the real world. Film, too, cannot be separated from its tools. Aesthetic criticism was, and still is, weighted towards consideration of the life-like tiny photographs. This thesis traces the evolution of film technology in order to establish the point where non- fiction ideology (aesthetics) lost pace with technical innovation - a derailment, so to speak, with nefarious implications for the present-day filmmaker. The emphasis is on lenses - the provocative "camera eye" - and sound recording equipment - which proved to be the rate-limiter of technical advance. This thesis considers two filmmaking solutions to the present malaise; the Standard TV Documentary, and the single-person shooting methodology of former MIT filmmakers, Jeff Kreines and Joel DeMott - both of which, in turn , will be compared to my own response - in the form of a movie, Gravity, which is about the members of an MIT experimental astrophysics laboratory trying to discover gravity waves. A videotape copy of the movie. is included with the thesis paper.
by Mary Jane Doherty.
M.S.V.S.
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Mantke, Wolfgang. "Spin and gravity." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/27605.
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Gibson-Wilde, Dorothy E. "Atmospheric gravity waves in constituent distributions /." Title page, abstract and contents only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phg4516.pdf.
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Meza, Valle Claudio Alejandro. "Early detection of extreme waves by acoustic gravity-waves." Tesis, Universidad de Chile, 2019. http://repositorio.uchile.cl/handle/2250/171084.
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Tesis para optar al grado de Magíster en Ciencias de la Ingeniería, Mención Matemáticas AplicadasExtreme waves generated in the ocean are of high importance because various maritime structures in the world, including ships, are confronted to this type of wave events, both in deep waters and in coastal areas. Some extreme waves correspond to wave phenomena generated in an atypical way in the ocean, also called monster waves, freak waves, rogue waves, extreme waves, solitons etc., since their generation differs from the common waves generated by wind. Assuming a slightly compressible ocean, the generation and analysis of acoustic-gravity waves (AGW or acoustic waves) in the ocean have been the subject of study for some time, because from them it is possible to obtain some information from the gravity wave, in this case a extreme wave that have generated them, and also to know other kind of phenomena induced by these AGW, as is the case of the bottom pressure. In the present work, a mathematical model has been developed which represents the generation and propagation of an extreme wave represented by a pressure change in the surface of the ocean considering compressible fluid, from which the generation and propagation of acoustic waves is induced. Since sound travels at a speed of 1500 m/s in the ocean, these waves arrive first at any observation point, allowing early detection of the extreme wave from the pressure in the oceanic bottom due to propagation of the acoustic wave. The theoretical development and two-dimensional numerical simulations are presented in the document. The implementation of this methodology and its results is relevant in the field of civil and maritime engineering in Chile since its high potential in coastal zones, due to the fact that for some years, the frequency of extreme wave events has been seen increased, and having an alternative detection system for extreme wave events can become a relevant factor in coastal management and natural disasters services. It is important to mention that this type of work has not been developed previously in Chile.
proyectos Centros de Excelencia Basal Conicyt PIA AFB 170001 CMM & UMI-CNRS 2807 y Fondecyt Regular 1171854
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Horne, Iribarne Ernesto. "Transport properties of internal gravity waves." Thesis, Lyon, École normale supérieure, 2015. http://www.theses.fr/2015ENSL1027/document.
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Les ondes internes sont produites par suite de l’équilibre dynamique entre les forces de flottabilité et la gravité quand une particule de fluide est déplacée verticalement dans un milieu stratifié stable. Les systèmes géophysiques tels que océan et l’atmosphère sont naturellement stratifiés et donc favorables à la propagation des ondes internes. En outre, ces deux environnements stockent une grande quantité de particules tant dans leur intérieur que sur les bords. Par conséquent, les ondes internes et les particules vont inévitablement interagir dans ces systèmes. Au cours de ce travail, des expériences exploratoires sont réalisées pour étudier le transport par érosion des particules, généré par les ondes internes. Afin de déterminer un seuil de transport, les propriétés particulières des réflexions d’ondes internes («réflexion critique ») sont utilisées pour augmenter l’intensité du champ d’ondes à la surface de réflexion. Une méthode a été développée en collaboration avec une équipe de traitement du signal pour améliorer la détermination des composantes de l’onde impliquées dans une réflexion quasi critique. Cela nous a permis de comparer nos résultats expérimentaux avec une théorie de la réflexion critique, montrant un bon accord et permettant d’extrapoler ces résultats à des expériences au-delà de la nôtre et à des conditions océaniques. Nous avons aussi étudié l’interaction des ondes internes avec une colonne de particules en sédimentation. Deux effets principaux ont été observés : la colonne oscille autour d’une position d’équilibre, et elle est déplacée dans son ensemble. La direction du déplacement de la colonne est expliquée par le calcul de l’effet de la dérive Lagrangienne produite pour des ondes. Cet effet pourrait également expliquer la dépendance en fréquence du déplacementInternal waves are produced as a consequence of the dynamic balance between buoyancy and gravity forces when a particle of fluid is vertically displaced in a stably stratified environment. Geophysical systems such as ocean and atmosphere are naturally stratified and therefore suitable for internal waves propagation. Furthermore, these two environments stock a vast amount of particles at their boundaries and in their bulk. Therefore, internal waves and particles will inexorably interact in these systems. In this work, exploratory experiments are performed to study wave generated erosive transport of particles. In order to determine a transport threshold, the peculiar properties of internal waves (“critical reflection”) are employed to increase the intensity of the wave field at the boundaries. A method was developed in collaboration with a signal processing team to improve the determination of the wave components involved in near-critical reflection. This method enabled us to compare our experimental results with a theory of critical reflection, showing good agreement and allowing to extrapolate these results to experiments beyond ours and to oceanic conditions. In addition, we study the interaction of internal waves with a column of particles in sedimentation. Two main effects are observed: the column oscillates around an equilibrium position, and it is displaced as a whole. The direction of the displacement of the column is explained by computing the effect of the Lagrangian drift of the waves. This effect could also explain the frequency dependence of the displacement
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Eckermann, Stephen D. "Atmospheric gravity waves : obsevations and theory /." Title page, table of contents and abstract only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phe1862.pdf.
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Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1990.Copies of author's previously published articles inserted. Includes bibliographical references (leaves 261-288).
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Yan, Xiuping. "Satellite observations of atmospheric gravity waves." Thesis, University of Leicester, 2010. http://hdl.handle.net/2381/7979.
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A new methodology of gravity wave observations has been developed for the HIgh Resolution Dynamics Limb Sounder (HIRDLS). Individual vertical profiles of gravity-wave temperature perturbations that were determined by subtraction of a dynamic 31 day background field and a 1000 km along-track temperature filter were Fourier transformed to estimate the gravity-wave temperature amplitudes and vertical wavelengths (~2 – 16 km) in the stratosphere. Gravity wave activity is highly variable with season and can be highly orographically dependent, especially in the winter extratropics. Investigations of episodes of enhanced gravity waves over the southern Andes, the Cascade Range and the Rockies in the winter months of 2006 indicate that orographic gravity waves propagate downwind from the mountains. By way of contrast, observations of gravity waves around the Himalayas show a strong relationship with the cyclones in that region. HIRDLS observations over the southern Andes during July-September 2006 were compared to the orographic gravity-wave parameterization scheme in the UK Met Office Unified Model®. The results indicate that the observed waves are likely to be orographically excited. The observed wave activity extends large distances (a few thousand kilometres) downwind of the mountains and over the ocean. This downstream wave activity is not represented by the parameterization scheme similar to many schemes, which assume that the waves propagate vertically above the mountains only. Gravity waves over the tropics and tropical South America were compared with the AVHRR Outgoing Longwave Radiation (OLR), TRMM convective rainfall and ECMWF winds for convective sources. The comparisons show that the peak gravity wave temperature amplitudes correspond closely to the OLR ≤ 200 W/m ², in good agreement with the mesoscale cyclones and are above the updrifts, which indicate deep convective generation of the gravity waves. These waves show vertical propagation with higher-frequency and ~ 7.5 km vertical wavelengths in the lower stratosphere.
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Watkins, Christopher Lloyd. "Atmospheric gravity waves on giant planets." Thesis, Queen Mary, University of London, 2012. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8683.
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Internal gravity waves are a common feature of stratified fluids. They facilitate transport of momentum and energy – thus influencing the evolution of the fluid. There is a large body of research addressing the behaviour of gravity waves in the terrestrial atmosphere. This thesis builds and extends the research to giant planets – in particular to close-in extrasolar giant planets and the solar system giant planet, Jupiter. Because the atmospheres of close-in giant planets are expected to be strongly stratified, knowledge of the behaviour of gravity waves in such atmospheres is especially important. Close-in giant planets are thought to have their rotations and orbital period 1:1 synchronised, i.e., they are “tidally locked”. Such planets do not exist in the Solar System. However, many are known from observations of extrasolar systems. Their synchronisation means that they have a permanent day-side and night-side leading to interesting atmospheric dynamics. Modelling these circulations with global circulation models (GCMs) and comparing these models with observations is an active research area. However, many GCMs filter some or all gravity waves removing their effects. This thesis addresses this by explicitly looking at the effects gravity waves can have on the circulation. It is shown that gravity waves provide a mechanism for accelerating, decelerating, and heating the flow. Further, horizontally propagating gravity waves are shown to provide a possible means for coupling the day- and night-sides of tidally locked planets. As well as affecting the dynamics of the atmosphere, gravity wave behaviour is affected by the dynamics of the atmosphere. Therefore, gravity waves can be used to explore atmospheric properties. In this thesis gravity waves observed in Jupiter’s atmosphere, by the Galileo probe, are used to identify features of Jupiter’s atmosphere such as the altitude of the turbopause and the vertical profile of zonal winds at the probe entry site.
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Dobra, Tom. "Nonlinear interactions of internal gravity waves." Thesis, University of Bristol, 2019. http://hdl.handle.net/1983/4a3f99e2-5e73-4c7c-8d3d-e1141fb23dda.
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Internal waves carry more available energy than any other transmission system on Earth: lunar diurnal excitation drives 1 TW of wave power inside the world's oceans. Energy is transmitted over thousands of kilometres and individual waves may be hundreds of metres high. Where they break, they deposit their energy, and, in such regions, they greatly enhance the vertical transport of carbon dioxide, oxygen and heat. Despite their significance, much remains to be understood about internal waves, and this thesis explores some of these questions using a combination of experiments and theory. One way to generate internal waves is by sinusoidally oscillating the boundary of the fluid. A full spectrum of harmonics is generated, whose phases and amplitudes are predicted by perturbation theory. Their origin is identified solely as nonlinear geometric excitation at the boundary; no interactions between the harmonics of the same infinitely wide, monochromatic input are possible within the fluid. However, for narrow wave beams, resonant triadic wave-wave interactions are predicted using a novel numerical implementation of the singular two-dimensional Green's function. To verify the predictions, a new experiment was designed, consisting of an electronically actuated "magic carpet" inserted into the base of a tank. It perturbs the fluid lying above its surface to generate internal waves of almost any shape and size. The carpet is actuated by an array of 100 stepper motors, which are controlled by bespoke software that manages the timing in increments of 30 ns; this ensures precise spatiotemporal control of the waveform. The carpet itself is made of a neoprene-nylon composite, and its bending behaviour is modelled in detail to characterise the waveform imparted on the fluid. The experiments support the theoretical predictions, but also permit strongly nonlinear regimes, such as wave breaking, at amplitudes above the applicable domain of the theory.
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Powell, Jonathan. "Stochastic modelling of atmospheric gravity waves." Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/15652.
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Internal gravity waves have an important effect on the large-scale circulation of the middle atmosphere, which is conditioned by the deposition of momentum due to their breaking. The propagation of gravity waves is influenced by the properties of the background wind. This thesis examines this influence: it uses stochastic techniques to study gravity wave propagation through a randomly fluctuating background wind. It begins by describing general features of the atmosphere and gravity wave propagation. The basic equations of fluid flow within the atmosphere are derived. These lead via the WKB approximation to a dispersion relation and to ray equations for gravity wave propagation. Propagation equations, such as the ray equations and dispersion relation, are derived in a general context. The notion of a Wigner matrix is introduced, and this is used to derive transport equations for a general Hamiltonian system that may contain random components. These results generalise earlier works by Ryzhik and Guo and Wang. Atmospheric gravity waves are described as an application and the equations derived via the WKB approximation are recovered. The major factor influencing the distribution of gravity waves is the spread of their wavenumber as they propagate through a wind. This is described by the Doppler spreading model. A one-dimensional system with a randomly fluctuating background wind, dependent on altitude only, is considered. The model revisits that of Souprayen by using an Ornstein-Uhlenbeck process to describe the wind. Simple equations for the energy spectrum induced by gravity waves are derived. Analytic forms of the energy spectrum are given and features of the spectrum such as the m-3 spectral tail (where m is the vertical wavenumber), central wavenumber and scaling with the Brunt-Väisälä frequently are found to be consistent with observations. An equation for the force on the background, induced by gravity wave breaking is also derived.
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Geldenhuis, Andre. "The Atmospheric Gravity Wave Transfer Function above Scott Base." Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/3698.
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Gravity waves have a significant dynamic effect in the mesosphere. In particular, they drive the mesospheric circulation and are the reason that the summer polar mesosphere is cooler than the winter polar mesosphere. This thesis examines whether the effects of gravity waves are largely determined by filtering effects which allow only gravity waves with certain properties to propagate into the atmosphere. The filtering of gravity waves above Scott Base, Antarctica is examined using a radiosonde derived gravity wave source function, an MF-radar derived mesospheric gravity wave climatology, and a model derived filtering function. Least squares fitting of the source function and filtering function to the observed mesospheric gravity wave climatology allows us to determine which gravity wave phase velocities and propagation direction are likely to be present in the mesosphere and the relative importance of filtering and sources in this region. It is concluded the blocking of eastward gravity waves is important in winter and westward waves in summer.
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Thomas, Alexandra Elizabeth. "The interaction of an internal solitary wave with surface gravity waves." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/13106.
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Solitary waves are nonlinear, non-oscillatory disturbances of permanent form. Recent advances in synthetic aperture radar imaging and analysis techniques have confirmed in situ observations and measurements that the passage of oceanic internal waves, and in particular internal solitary waves, is associated with modulations in sea surface roughness. It has not only revealed the ubiquity of this phenomenon but also highlighted the global existence of large amplitude, tidally induced, internal solitary waves. It appears, however, that little laboratory-based research has been carried out in this field. This work, therefore, focusses on the study of surface wavetrain modulations resulting from the passage of a single internal solitary wave. Digital Particle Image Velocimetry (DPIV) and Planar Laser Induced Fluorescence (PLIF) were employed to provide two-dimensional instantaneous velocity and density information respectively. Previous studies in this field have been performed with intrusive probe techniques, disturbing the fluid flow during measurement. Preliminary DPIV and PLIF experiments were performed on single internal solitary waves in a two-layer brine - fresh water stratification. To the author’s knowledge, the application of PLIF to the study of these waves had not been done previously. Results from the DPIV measurements concurred with previous research and highlighted the constraints of the DPIV system. The results were also compared to a recently developed and validated fully nonlinear numerical method. From the interaction investigations, both wavelength and amplitude modulations of the surface waves as a function of solitary wave phase were observed. In some cases, the shape of the internal wave was also affected. Velocity profiles were compared to the linear superposition of surface wave linear theory and the fully nonlinear numerical method. In addition, the PLIF analysis showed that, for the wave and stratification parameters investigated, there was no evidence for the compression and expansion of the density interface during the interaction.
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Wang, Shuguang. "Gravity waves from vortex dipoles and jets." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2875.
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Jansen, Arne Kristian. "Asymptotic Approximations of Gravity Waves in Water." Thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9888.
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The governing equations for waves propagating in water are derived by use of conservation laws. The equations are then cast onto dimensionless form and two important parameters are obtained. Approximations by use of asymptotic expansions in one or both of the parameters are then applied on the governing equations and we show that several different completely integrable equations, with different scaling transformations and at different order of approximations, can be derived. More precisely, the Korteweg-de Vries, Kadomtsev-Petviashvili and Boussinesq are obtained at first order, while the Camassa-Holm, Degasperis-Procesi, nonlinear Schrödinger and the Davey-Stewartson equations are obtained at second order. We discuss shortly some of the properties for each of the obtained equations.
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Townsend, William A. "Inertia-gravity waves beyond the inertial latitude." Thesis, Keele University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534319.
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Hölscher, Patric [Verfasser]. "Gravitational Waves in Conformal Gravity / Patric Hölscher." Bielefeld : Universitätsbibliothek Bielefeld, 2019. http://d-nb.info/1200097653/34.
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Abu, Samah Azizan B. Hj. "Observations of gravity waves at atmospheric fronts." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276732.
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Horlacher, Volker. "Gravity waves and turbulent flow over orography." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400955.
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Holmes, Damian J. "Gravity waves in uniform windflow over topography." Thesis, University of Surrey, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336449.
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Ghaemsaidi, Sasan John. "Interference and resonance of internal gravity waves." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101532.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 91-96).
Internal waves are propagating disturbances within stratified fluids, arising from a balance of gravity, buoyancy, and rotation. As well as being of fundamental scientific interest, they are ubiquitous in a variety of forms in the Earth's oceans, where they are responsible for driving vertical mixing. And it is the rule, rather than the exception, that internal waves propagate through a varying background density stratification. We begin by theoretically studying internal waves that are harmonically forced at a horizontal level above a semi-infinite, non-uniform density stratification. Starting with a two-layer model, we identify the existence of resonance peaks and diminution troughs in the wave transmission spectra, and provide physical insight through the application of ray theory. Thereafter, we proceed to consider smoothly varying stratifications, demonstrating that these resonance and diminution features persist beyond simple models. We conclude by considering the relevance of the results to geophysical settings. As an example, we demonstrate that an ocean stratification is inherently tuned to transmit internal wave energy to the deep ocean at specific combinations of wavelength and frequency. Subsequently, we perform a laboratory experimental study of an internal wave field generated by harmonic, spatially-periodic surface forcing of a strongly-stratified, thin upper layer sitting atop a weakly-stratified, deep lower layer. In linear regimes, the energy flux associated with relatively high frequency internal waves is prevented from entering the lower layer by virtue of evanescent decay. In the experiments, however, we find that the development of parametric subharmonic instability (PSI) in the upper layer transfers energy from the forced primary wave into a pair of subharmonic daughter waves, each capable of penetrating the weakly-stratified lower layer. We find that around 10% of the primary wave energy penetrates into the lower layer via this nonlinear wave-wave interaction for the regime we study. With an emphasis on assessing the role of interference in tuning wave transmission, we perform a series of laboratory experiments in order to measure resonance and diminution in the aforementioned non-uniform stratification. We find that the occurrence of destructive interference in the upper stratification layer naturally yields diminution of the transmitted wave. Conversely, constructive interference results in a notable amplification of the wave field over time scales on the order of the forcing period; the development of nonlinear wave-wave interactions due to wave amplification is observed over longer time scales. Good agreement is obtained between the experimental results and a weakly viscous, long wave model of our system within the linear regime. Given the ubiquity of layering in environmental stratifications, an interesting example being double-diffusive staircase structures in the Arctic water column, we furthermore present the results of a joint theoretical and laboratory experimental study investigating the impact of multiple layering on internal wave propagation. We first present results for a simplified model that demonstrates the nontrivial impact of multiple layering. Incident waves of particular length and time scales can experience constructive interference taking place within the alternating stratified and mixed layers, which in turn appreciably enhances wave transmission. Thereafter, utilizing a weakly viscous, linear model that can handle arbitrary vertical stratifications, we perform a comparison of theory with experiments finding excellent qualitative and quantitative agreement. We conclude by applying this model to a case study of a staircase stratification profile obtained from the Arctic Ocean, finding a rich landscape of transmission behavior.
by Sasan John Ghaemsaidi.
Ph. D.
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Zink, Florian. "Gravity waves and turbulence in the lower atmosphere /." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phz778.pdf.
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Miranda, Pedro Manuel Alberto de. "Gravity waves and wave drag in flow past three-dimensional isolated mountains." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280560.
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Law, Owen Yi Kei. "Experiments on evolution of surface gravity waves from deep to shallow waters /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?MECH%202004%20LAW.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 57-59). Also available in electronic version. Access restricted to campus users.
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De, Deuge Maria. "Optical observations of gravity waves in the high-latitude thermosphere /." Title page, abstract and contents only, 1990. http://web4.library.adelaide.edu.au/theses/09SM/09smd485.pdf.
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Aspden, Jonathan Maclean. "Inertia-gravity wave generation : a WKB approach." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/33317.
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The dynamics of the atmosphere and ocean are dominated by slowly evolving, large-scale motions. However, fast, small-scale motions in the form of inertia-gravity waves are ubiquitous. These waves are of great importance for the circulation of the atmosphere and oceans, mainly because of the momentum and energy they transport and because of the mixing they create upon breaking. So far the study of inertia-gravity waves has answered a number of questions about their propagation and dissipation, but many aspects of their generation remain poorly understood. The interactions that take place between the slow motion, termed balanced or vortical motion, and the fast inertia-gravity wave modes provide mechanisms for inertia-gravity wave generation. One of these is the instability of balanced flows to gravity-wave-like perturbations; another is the so-called spontaneous generation in which a slowly evolving solution has a small gravity-wave component intrinsically coupled to it. In this thesis, we derive and study a simple model of inertia-gravity wave generation which considers the evolution of a small-scale, small amplitude perturbation superimposed on a large-scale, possibly time-dependent °ow. The assumed spatial-scale separation makes it possible to apply a WKB approach which models the perturbation to the flow as a wavepacket. The evolution of this wavepacket is governed by a set of ordinary differential equations for its position, wavevector and its three amplitudes. In the case of a uniform flow (and only in this case) the three amplitudes can be identifed with the amplitudes of the vortical mode and the two inertia-gravity wave modes. The approach makes no assumption on the Rossby number, which measures the time-scale separation between the balanced motion and the inertia-gravity waves. The model that we derive is first used to examine simple time-independent flows, then flows that are generated by point vortices, including a point-vortex dipole and more complicated flows generated by several point vortices. Particular attention is also paid to a flow with uniform vorticity and elliptical streamlines which is the standard model of elliptic instability. In this case, the amplitude of the perturbation obeys a Hill equation. We solve the corresponding Floquet problem asymptotically in the limit of small Rossby number and conclude that the inertia-gravity wave perturbation grows with a growth rate that is exponentially small in the Rossby number. Finally, we apply the WKB approach to a flow obtained in a baroclinic lifecycle simulation. The analysis highlights the importance of the Lagrangian time dependence for inertia-gravity wave generation: rapid changes in the strain field experienced along wavepacket trajectories (which coincide with fluid-particle trajectories in our model) are shown to lead to substantial wave generation.
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Wright, Corwin. "Detection of stratospheric gravity waves using HIRDLS data." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:ef4aa65d-67c1-43ac-90de-1b5bda6c8230.
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Temperature measurements from the HIRDLS instrument on NASA's Aura satellite are analysed for the purposes of detecting and studying internal gravity waves in the terrestrial stratosphere. A detailed description of the methodology used to obtain these data is given, including details of the instrument correction processes used to compensate for errors introduced by a blockage in the instrument optics. A short precis of the relevant theoretical considerations related to atmospheric gravity waves is then outlined. The thesis then discusses the use of the Stockwell (time-frequency) Transform for the detection of gravity waves in HIRDLS data, together with a detailed analysis of the limitations of this method, and the results obtained from this analysis are analysed by comparison to other instruments and climatology. It is concluded that the Stockwell Transform is an appropriate method for the analysis of the HIRDLS dataset, and that the results obtained are robust. We apply these results to analyse stratospheric gravity wave activity during the 2005/06 Arctic sudden stratospheric warming. By comparing the magnitude and form of the gravity wave results to local wind data obtained from ECMWF operational analyses, we conclude that a heavily deformed stratopause observed during this period by other instruments was most probably due to wind-based filtering of the gravity wave spectrum during this period.
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Steinhagen, Ulrich. "Synthesizing nonlinear transient gravity waves in random seas." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963498436.
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Griffiths, R. M. "The interaction between vorticity and internal gravity waves." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599729.
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Our dissertation investigates the interaction between a localised region of vorticity and internal gravity waves, using only analytical methods. We aim to understand further the mechanism by which internal gravity waves radiate vorticity and to address the validity of applying an analogy of Lighthill's sound generation theory to the generation of internal gravity waves. We consider an initial value problem for a two-dimensional incompressible density-stratified fluid. The buoyancy frequency is taken to be constant and the Boussinesq approximation is imposed. To make the analysis as general as possible, and more importantly to assess the importance of nonlinear mechanisms in the generation of internal gravity waves, we include nonlinear terms in the equations of motion. To make further analytical progress we consider the case of a large internal Froude number Fr, which is more often realised in physical scenarios. We attempt solutions to the equations of motion via asymptotic expansions in the small parameter ε = 1/Fr2. We consider the main results of the dissertation to be twofold. First we see the appearance of distinct regions in space-time where different dominant balances occur in the equations of motion. In particular we have an inner region, a far field and a wave region, and we have been able to perform an asymptotic matching of the different solutions in these regions successfully. The magnitude of these regions is characterised by the small parameter ε. It is hoped that the existence of such regions could be confirmed experimentally. Such space-time regions do not occur in the linear analysis of this problem, but are only evident when nonlinear terms are retained in the equations of motion. The second part of our analysis that we consider to be important arises through the study of the dynamics of vorticity transfer in our problem. The introduction of stratification destroys conservation of vorticity; the non-conservation of vorticity is observed in the inner region and the far field.
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Robinson, Tristan Oliver. "Gravity currents in the presence of water waves." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1445076/.
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This thesis describes a laboratory study on the effect of free surface progressive waves on high Reynolds number gravity currents generated by instantaneous release of finite volumes of dense homogeneous fluid. The waves and gravity currents are studied as two-dimensional and the flows across the width of the flume are assumed to be constant. The engineering applications of this investigation will provide an insight into the processes by which dredging plumes are dispersed and flows propagate into estuaries at the coastline. This investigation examines the process at a fundamental level and gives a summary of the key characteristics and trends of the gravity current in the marine environment. This work has been carried out in the wave current flume at UCL using a number of advanced flow measuring techniques such as Laser Doppler Velocimetry to measure the orbital velocities of the waves and Particle Image Velocimetry to measure the internal dynamics of the gravity current. The position and density profiles of the gravity current were measured using digital images. In a static environment a gravity current spreading in two directions has symmetry in shape and distance from the point of release. In the presence of waves, the gravity current fronts propagate with and against the wave direction. The wave motion induces an asymmetry in the shape and rate of propagation of the gravity current fronts. Under certain wave conditions the overall length of the gravity current is found to be unchanged by the presence of the waves and the characteristics of the gravity current are similar to the case in static ambient water. However, in some cases the overall distance is severely modified by the wave motion. In addition to modifying the propagation rate of the gravity current the wave-induced mean flow modifies the profile of the gravity current head. The direction of the gravity current relative to the wave motion is vital in determining the rate of dispersion and the height of the density current.
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Krishnamurthy, Venkataramanaiah. "The slow manifold and the persisting gravity waves." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/54304.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985.Microfiche copy available in Archives and Science.
Bibliography: leaves 144-146.
by Venkataramanaiah Krishnamurthy.
Ph.D.
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Calvo, David C. (David Christopher). "Dynamics and stability of gravity-capillary solitary waves." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/88871.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (leaves 137-143).
Over the past several years, it has been recognized that a new class of solitary waves can propagate in nonlinear dispersive wave systems if the phase speed of linear waves attains a local extremum at some finite wavenumber. Near such a point, solitary waves in the form of small-amplitude wavepackets can be obtained for which the phase speed of the carrier oscillations matches the group speed of their envelope. Such an extremum is found in the analysis of water waves when the restoring forces of both gravity and surface tension are taken into account, and certain kinds of these gravity-capillary solitary waves have been observed in experiments. While past theoretical studies have focussed mainly on determining steady solitary wave profiles, very little work has been done on examining their stability properties which is the thrust of this thesis. Beginning in the weakly nonlinear regime, an asymptotic analysis of linear stability is presented and comparison is made with numerical computations. Contrary to predictions of the nonlinear Schrbdinger (NLS) equation, some free solitary wave types are found to be unstable owing to exponentially effects terms that lie beyond standard two-scale perturba- tion theory. Moreover, numerical simulations show that unstable gravity-capillary solitary waves may decompose into stable solitary waves that have soliton properties. Stability results are then extended to the fully nonlinear regime to treat both free and forced situa- tions using numerical techniques to solve the full hydrodynamic equations in steady form. A dramatic difference is found between the linear stability of free and forced waves in both weakly and fully nonlinear cases, and results obtained here are compared with laboratory experiments.
(cont.) The analysis followed in the free-surface problem is then generalized to examine the dynamics of gravity-capillary interfacial solitary waves in a layered two-fluid system. Here, the linear stability and limiting wave forms of free solitary waves are determined over a range of system parameters using the full hydrodynamic equations. Finally, a related problem of gravity-capillary envelope solitons is considered under the general situation of unequal phase and group speeds. By asymptotic and numerical techniques it is found that envelope solitons are generally nonlocal-tails are radiated owing to a resonance mechanism that is beyond the NLS equation.
by David C. Calvo.
Ph.D.
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Lange, Martin, and Christoph Jacobi. "Analysis of gravity waves from radio occultation measurements." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217072.
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In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crestsAtmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist
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Lange, Martin, and Christoph Jacobi. "Analysis of gravity waves from radio occultation measurements." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 26 = Meteorologische Arbeiten aus Leipzig ; 7 (2002), S. 101-108, 2002. https://ul.qucosa.de/id/qucosa%3A15225.
Full textAbstract:
In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in
the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crests.Atmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist.
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Wu, Lichuan. "Introducing Surface Gravity Waves into Earth System Models." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-314760.
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Surface gravity waves alter the turbulence of the bottom atmosphere and the upper ocean. Accordingly, they can affect momentum flux, heat fluxes, gas exchange and atmospheric mixing. However, in most state-of-the-art Earth System Models (ESMs), surface wave influences are not fully considered or even included. Here, applying surface wave influences into ESMs is investigated from different aspects. Tuning parameterisations for including instantaneous wave influences has difficulties to capture wave influences. Increasing the horizontal resolution of models intensifies storm simulations for both atmosphere-wave coupled (considering the influence of instantaneous wave-induced stress) and stand-alone atmospheric models. However, coupled models are more sensitive to the horizontal resolution than stand-alone atmospheric models. Under high winds, wave states have a big impact on the sea spray generation. Introducing a wave-state-dependent sea spray generation function and Charnock coefficient into a wind stress parameterisation improves the model performance concerning wind speed (intensifies storms). Adding sea spray impact on heat fluxes improves the simulation results of air temperature. Adding sea spray impact both on the wind stress and heat fluxes results in better model performance on wind speed and air temperature while compared to adding only one wave influence. Swell impact on atmospheric turbulence closure schemes should be taken into account through three terms: the atmospheric mixing length scale, the swell-induced momentum flux at the surface, and the profile of swell-induced momentum flux. Introducing the swell impact on the three terms into turbulence closure schemes shows a better performance than introducing only one of the influences. Considering all surface wave impacts on the upper-ocean turbulence (wave breaking, Stokes drift interaction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves), rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir circulation are the most important terms when considering the impact of waves on upper-ocean mixing. Accurate climate simulations from ESMs are very important references for social and biological systems to adapt the climate change. Comparing simulation results with measurements shows that adding surface wave influences improves model performance. Thus, an accurate description of all important wave impact processes should be correctly represented in ESMs, which are important tools to describe climate and weather. Reducing the uncertainties of simulation results from ESMs through introducing surface gravity wave influences is necessary.
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Yamamoto, Mamoru. "Radar observations of gravity waves in the mesosphere." Kyoto University, 1987. http://hdl.handle.net/2433/74712.
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Kim, Yunho. "Quadratic Gravity with Black Holes and Gravitational Waves." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/26707.
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This thesis investigates black holes and gravitational waves in the framework of quadratic gravity. These subjects are introduced by first examining the current state of general relativity and how it is realised. The discussion then addresses the quantitative aspects of black holes, gravitational waves, and quadratic gravity. This is then followed by the exploration of the three main research topics.
The first research topic investigates the induced charging of a black hole due to a topological term in quadratic gravity. The second research topic focuses on the approximate analytic non-Schwarzschild black hole solutions in quadratic gravity. Finally, gravitational waves generated by binary systems within quadratic gravity are studied, with a focus on the corrections produced by the massive scalar field and the massive spin-2 field.
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Woithe, Jonathan Mark. "Optical studies of the mesospheric region." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phw847.pdf.
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Includes copies of articles co-authored by the author during the preparation of this thesis. Includes bibliographical references (leaves 233-245). A three-field photometer was employed at the University of Adelaide's Buckland Park field site to collect optical observations of the 557.7nm OI and 730nm OH airglow emissions on an almost continuous basis since May 1995 to May 2000, with observations made whenever the moon was not up.
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Brunnhofer, Harald Michael. "Forced Capillary-Gravity Waves in a 2D Rectangular Basin." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/27270.
Full textAbstract:
This dissertation concerns capillary-gravity surface waves in a two-dimensional rectangular basin that is partially filled with water. To generate the surface waves, a harmonic forcing is applied to the vertical side walls of the basin. The dissertation consists of four parts which work with different assumptions on the frequencies of the forcing.
The first part discusses the linearized model with Hockingâ s edge condition and gives an eigenvalue equation and an asymptotic expansion for the eigenvalues. Then, for the nonlinear problem, it is assumed that the frequency of the forcing is close to an eigenfrequency and the solution has an asymptotic expansion using a two time-scales approach. Under an edge condition, the first- and second-order approximations of the solution and a solvability condition from the third-order equations yield an ordinary differential equation for the amplitude of the solution.
In part two, it is assumed that the frequency of the forcing applied to the boundary is close to the sum of two eigenfrequencies. In this case, the solvability conditions give a system of two differential equations for the complex valued amplitudes of the two eigenmodes. The system can be reduced to one real-valued differential equation. Its solutions yield the solutions of the original system and their properties. A condition for the existence of homoclinic orbits connecting the trivial equilibrium is obtained. These results are confirmed by numerical experiments.
The third part is based on the results in the second part. Here, one of the eigenfrequencies is chosen to be much larger than the other one, and different orders of the amplitudes of the eigenmodes are assumed. The orders of the coefficients of the system found in the second part are obtained, and the resulting special case is discussed in detail. In particular, numerical examples of orbits that can be associated with homoclinic orbits connecting nontrivial equilibria are given. The behavior of solutions close to those orbits is demonstrated.
In the fourth part, an additional frequency for the forcing terms given in parts two and three is introduced. In each situation, the modified systems are presented and discussed.Ph. D.
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黃元華 and Yuen-wah Wong. "A study of atomospheric gravity waves in East Asia by investigation oftheir effects upon the ionosphere." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1991. http://hub.hku.hk/bib/B31232875.
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Wong, Yuen-wah. "A study of atomospheric gravity waves in East Asia by investigation of their effects upon the ionosphere /." [Hong Kong : University of Hong Kong], 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13148424.
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Buehler, Oliver. "Waves and balanced mean flows in the atmosphere." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264502.
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Smith, Robert K. "The contour-advective semi-Lagrangian hybrid algorithm approach to weather forecasting and freely propagating inertia-gravity waves in the shallow-water system." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/716.
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Winters, Kraig B. "Intensification and instability of internal gravity waves at caustics and critical levels /." Thesis, Connect to this title online; UW restricted, 1989. http://hdl.handle.net/1773/6792.
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O'Reilly, Rachel Ann. "Gravitational waves from unstable, eccentric and inspiralling compact binary systems." Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247959.
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Piovano, Gabriel Andres. "Dark radiation and observable gravity waves from string inflation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13514/.
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In this thesis we work on a model of string inflation called fibre inflation. We investigate whether this inflationary model can predict a tensor-to-scalar-ratio of order 0.01 which might be detectable in the near future. The main constraint comes from the amount of axionic dark radiation produced from the inflaton decay at reheating. Very light axions are a generic feature of 4D string models and behave as extra neutrino species.
We first analyze the inflationary dynamics and derive the predictions for the spectral index and the tensor-to-scalar ratio r as a function of the number of e-foldings under the requirement of generating the correct measured amplitude of the density perturbations. We then focus on reheating. We start by computing the inflaton couplings to all particles in our model: MSSM fields in the visible sector and light axions belonging to the hidden sector.
This computation allows us to derive the dominant inflaton decay channels which are into Higgses, gauge bosons and light axions. In turn, these decay rates lead to a clear prediction for the amount of dark radiation in terms of extra neutrino species of about 0.5-0.6.
These values require approximately 57 e-foldings which can allow for a spectral index almost 1.000 and a tensor-to-scalar-ratio around 0.01 in agreement with Planck observations in the presence of extra dark radiation. We finally point out that, due to the high inflationary scale , the supersymmetry breaking scale turns out to be too high to yield a correct Higgs mass around 125 GeV. This tension can be easily overcome if the visible sector is a simple extension of the MSSM like the NMSSM.
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Yagi, Kent. "Probing Alternative Theories of Gravity with Binary Gravitational Waves." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157775.
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Skopovi, Ivan 1976. "A model for nonlinear gravity waves in stratified flows." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/91372.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, September 2002."August 2002."
Includes bibliographical references (leaves 77-78).
by Ivan Skopovi.
S.M.