Dissertations / Theses on the topic 'Earth's rotation'
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Hancock, Craig Matthew. "Degree-2 spherical harmonics of the Earth's gravity field from Earth rotation parameters and SLR measurements to LAGEOS." Thesis, University of Newcastle Upon Tyne, 2012. http://hdl.handle.net/10443/1413.
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The gravity field of the Earth is fundamental to subjects such as geodesy and geophysics. Many observations within geodesy refer directly or indirectly to gravity. Geodetic techniques provide information regarding the Earth and the processes that act on it. Mass and angular momentum are, according to physics, conserved in a closed system. The Earth interacts very little with components outside of it and can be thought of as a closed system. Mass components in one reservoir of the Earth system are exchanged with others. Mass redistribution within the Earth system is caused by geophysical processes. This movement of geophysical fluid (mass) causes variations in the Earth’s rotation, gravity field and geocentre. The improvement of geodetic techniques over the last few decades allows us to measure the effects of these processes on the Earth to an unprecedented accuracy. Earth rotation parameters (ERPs) are excited by variations in the mass distribution on the Earth’s surface and the exchange of angular momentum between the atmosphere and oceans and the solid Earth. The same mass redistribution causes temporal changes in the gravity field coefficients with the second degree harmonics related to the rotational deformation and hence to changes in the Earth’s inertial tensor. If precise models of the atmospheric and oceanic angular momentum are available solution for polar motion and degree-2 Stokes harmonics can be unified. In this study we utilise SLR tracking of LAGEOS to compare (i) degree-2 harmonics from ERPs and gravitation, and (ii) LAGEOS excitation functions and geophysical data (mass + motion). To what extent a unified approach is possible with current models for AM data and gravity mass change estimated from ERP within orbit determinations is investigated. Finally, the ability of SLR to calculate the motion of the Earth’s geocentre is also investigated.
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Winkelnkemper, Timo [Verfasser]. "Ensemble Simulations of Atmospheric Angular Momentum and its Influence on the Earth's Rotation / Timo Winkelnkemper." Bonn : Universitäts- und Landesbibliothek Bonn, 2009. http://d-nb.info/1199009350/34.
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Weis, Philipp. "Ocean tides and the Earth's rotation : results of a high-resolving ocean model forced by the lunisolar tidal potential." Hamburg Max-Planck-Inst. für Meteorologie, 2006. http://www.mpimet.mpg.de/fileadmin/publikationen/Reports/WEBB̲zE3̲6.pdf.
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Watkins, Andrew. "Earth Rotation and Deformation Signals Caused by Deep Earth Processes." Bowling Green State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1510767104519046.
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Howard, P. D. "Very Long Baseline Interferometry and earth rotation parameters." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373809.
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Cotto-Figueroa, Desireé. "The Rotation Rate Distribution of Small Near-Earth Asteroids." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1224698418.
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Klavetter, James Jay. "The observed chaotic rotation of Hyperion." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/54331.
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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989.Includes bibliographical references (leaves 65-68).
by James Jay Klavetter.
Sc.D.
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Chan, Ngai Ham. "Stability of Planetary Rotation." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11684.
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This thesis focuses on the long-term rotational stability of the Earth and terrestrial planets. One important class of perturbation is a reorientation of the solid planet with respect to a rotation pole that remains fixed in an inertial frame. These motions are driven by mass redistribution within or on the surface of the planet (e.g. glaciation, mantle convective flow). Long-term changes in the orientation of the rotation pole are called True Polar Wander (TPW).Earth and Planetary Sciences
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Seyed-Mahmoud, Behnam. "Elliptical instability in rotating ellipsoidal fluid shells applications to the earth's fluid core /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0004/NQ43451.pdf.
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Moore, Terry. "Satellite laser ranging and the determination of earth rotation parameters." Thesis, University of Nottingham, 1986. http://eprints.nottingham.ac.uk/13312/.
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Over recent years considerable advances have taken place in the field of space geodesy, resulting in a number of highly precise global positioning techniques. The increased resolution of many of the scientific products from the new observational techniques has stimulated the interest of not only geodesists but also geophysicists. Furthermore, their potential to determine the orientation of the earth's axis of rotation (polar motion) and the variations of the rate of rotation of the earth about that axis, was recognised by the scientific community. The result was the establishment of Project MERIT, to intercompare these new observational techniques. Satellite Laser Ranging, a method of measuring the distance from a point on the earth's surface to an artificial satellite by means of timing the flight of a short pulse of laser light, is currently the most accurate available means of tracking near earth satellites. However, in order to reach the accuracy requirements of current geodetic applications dedicated satellites, such as the NASA LAser GEOdynamic Satellite (LAGEOS), must be tracked and specialised processing software must be used. This Thesis describes the basic theory behind the analysis of Satellite Laser Ranging Observations, with a special emphasis on the determination of earth rotation parameters (the polar motion and the variations in the rate of rotation). The development and testing, at Nottingham, of the Satellite Orbit Determination and Analysis Package Of Programs, SODAPOP, for the processing of laser range data, is described. The thesis also presents and discusses the results of the analysis of laser range observations the LAGEOS satellite, from the short and main campaigns of project MERIT.
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Symons, Leighton James. "Global GPS networks and the determination of Earth Rotation Parameters." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263465.
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Bergman, Michael I. (Michael Ira). "Magnetohydrodynamics of the Earth's core : 1) steady, rotating magnetoconvection 2) magnetic Rossby waves." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/51501.
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Crawford, Thomas Joseph. "An experimental study of the spread of buoyant water into a rotating environment." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/264526.
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This thesis examines previously unresolved issues regarding the fluid dynamics of the spread of buoyant water into a rotating environment. We focus in particular on the role that finite potential vorticity and background turbulence play in determining the flow properties. When water of an anomalous density enters into an oceanic basin, gravity-driven surface flows can be established as a result of the density difference. These flows are often of a sufficiently large scale that the dynamics are affected by the Coriolis force arising from the rotation of the earth. This causes the formation of a large outflow gyre near to the source which feeds into a propagating gravity current that is confined to the coast. Previous experimental work in this field has sought to simplify the problem through the use of a point source and a quiescent ambient. We extend this work to provide a better representation of the real-world flow by introducing a source of finite depth and background turbulence to the rotating ambient. This study seeks to answer three key questions that are critical to the understanding of the flow behaviour in this scenario. First, what is the effect of the finite potential vorticity of the outflow on the properties of the outflow vortex and the boundary current? Second, what role does the presence of the the outflow vortex play in determining the behaviour of the current? Third, what is the effect of background turbulence on the flow properties? To carry out the investigation, experiments were conducted in the laboratory and compared with a theoretical description of the flow. The currents are generated inside a rotating tank filled with saltwater by the continuous release of buoyant freshwater from a source structure located at the fluid surface. A horizontal source of finite depth is used to introduce finite potential vorticity into the outflow. The impact of background turbulence is examined by introducing an oscillating grid into the rotating tank. We find that the finite potential vorticity of the outflow plays an important role in determining the flow properties for sufficiently low Rossby and Froude number. As the value of these parameters is increased a zero potential vorticity model is able to capture the key elements of the flow behaviour. The outflow vortex is found to act as a time-varying source to the boundary current, with the current velocity fixed by the vortex velocity field. The vortex vorticity is seen to decrease with time, while the vortex radius continues to increase at late times despite the vortex having reached a limiting depth, which enables potential vorticity to be conserved and the current to be supplied with a non-zero velocity. Finally, the structure of the background turbulence is found to be key in determining the effect that it has on the flow properties, with different behaviours observed for three-dimensional and quasi- two-dimensional turbulence.
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Artz, Thomas [Verfasser]. "Determination of Sub-daily Earth Rotation Parameters from VLBI Observations / Thomas Artz. Landwirtschaftliche Fakultät." Bonn : Universitäts- und Landesbibliothek Bonn, 2011. http://d-nb.info/1017217548/34.
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Archinal, Brent Allen. "Determination of earth rotation by the combination of data from different space geodetic systems /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487324944212785.
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Nam, Young-sun. "GPS determination of diurnal and semidiurnal variations in earth rotation parameters and the geocenter /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Osman, Maslan Bin Haji. "Rotating magnetoconvection with ohmic heating." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363534.
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Ning, Zuoli. "Roles of plate locking and block rotation in the tectonics of the Pacific Northwest /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/6833.
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Rogister, Yves. "Modes normaux de modèles de Terre en rotation." Habilitation à diriger des recherches, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00773648.
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The normal-mode spectrum of rotating Earth models is made up of the seismic modes, the rotational modes and the spectrum of the liquid core. The local equations for the infinitesimal elastic-gravitational deformation, based on a Lagrangian perturbation of a spherically-averaged Earth model using the theory of hydrostatic equilibrium, are first established. A comparison is made between this approach and the classical global angular momentum approach to Earth rotation variations. The splitting of the seismic modes by rotation and ellipticity is then computed. Numerical investigation also shows that, by changing the structure of the liquid core, the rotational modes and core spectrum interact to give rise to avoided crossings, which provide a physically plausible mechanism to explain the observed double frequency of the Chandler wobble. The analogy with other oscillatory physical systems allows for a better understanding of the avoided crossing phenomenon.
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Cuccato, Davide. "Modeling, estimation and control of ring laser gyroscopes for the accurate estimation of the earth rotation." Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3423956.
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He − Ne ring lasers gyroscopes are, at present, the most precise devices for absolute angular velocity measurements. Limitations to their performances come from the non-linear dynamics of the laser. Accordingly to the Lamb semi-classical theory of gas lasers, a model can be applied to a He–Ne ring laser gyroscope to estimate and remove the laser dynamics contribution from the rotation measurements.
We find a set of critical parameters affecting the long term stability of the system. We propose a method for estimating the long term drift of the laser parameters, and for filtering out the laser dynamics effects, e.g. the light backscattering. The intensities of the counterpropagating laser beams exiting one cavity mirror are continuously measured, together with the monitor of the laser population inversion. These quantities, once properly calibrated with a dedicated procedure, allow us to estimate cold cavity and active medium parameters of the Lamb theory. Our identification procedure, based on the perturbative solutions of the laser dynamics, allow us for the application of the Kalman Filter theory for the estimation of the angular velocity.
The parameter identification and backscattering subtraction procedure has been verified by means of a Monte Carlo studies of the system, and then applied to the experimental data of the ring lasers G-PISA and G-WETTZELL. After the subtraction of laser dynamics effects by Kalman filter, the relative systematic error of G-PISA reduces from 50 to 5 parts in 103, and it can be attributed to the residual uncertainties on geometrical scale factor and orientation of the ring. We also report that after the backscattering subtraction, the relative systematic errors of G-WETTZELL are reduced too.
Conversely, in the last decade an increasing attention was drawn to high precision optical experiments, e.g. ring laser experiments, which combine high sensitivity, accuracy and long term stability. Due to the experimental requirements, position and orientation of optical elements and laser beams formation must be controlled in the field of nano-positioning and ultra-precision instruments. Existing methods for beam direction computing in resonators, e.g. iterative ray tracing or generalized ray transfer matrices, are either computationally expensive or rely on overparametrized models of optical elements.
By exploiting the Fermat’s principle, we develop a novel method to compute the beam directions in resonant optical cavities formed by spherical mirrors, as a function of mirror positions and curvature radii. The proposed procedure is based on the geometric Newton method on matrix manifold, a tool with second order convergence rate that relies on a second order model of the cavity optical length. As we avoid coordinates to parametrize the beam position on mirror surfaces, the computation of the second order model does not involve the second derivatives of the parametrization.
With the help of numerical tests, we show that the convergence properties of our procedure hold for non-planar polygonal cavities, and we assess the effectiveness of the geometric Newton method in determining their configurations with an high degree of accuracy and negligible computational effort.
We also presents a method to account for the (ring laser) cavity deformations due to mirrors displacement, seen as the residual motions of the mirrors centers after the removal of rigid body motions. Having the cavity configuration and the model to account for mirrors movements, the calibration and active control of the optical cavity can be addressed as a control problem. In fact, our results are of some importance not only for the design and simulation of ring laser gyroscopes, but also for the active control of the optical cavities.
In the final part of this work we detail a complete model including the simulation of the physical processes of interest in the operation of a ring laser gyroscope. Simulation results for the application of the model to the ring laser GP2 are presented and discussedI giroscopi laser che sfruttano la tecnologia He − Ne a 632 nm sono attualmente i dispositivi più precisi per la misura accurata della velocità angolare di rotazione. Gli attuali limiti alle loro prestazioni provengono dalla dinamica non lineare del battimento laser. Sfruttando la teoria semi-classica di Lamb viene sviluppato un modello per le dinamica del laser, successivamente applicato per stimare e rimuovere il contributo della dinamica del laser dalle misure di rotazione di un giroscopio. Individuati una serie di parametri critici la cui variazione influenza la stabilità nel tempo della misura, viene proposto un metodo per stimare la deriva dei parametri laser e per filtrare gli effetti della dinamica laser dalle misure acquisite con il giroscopio. Le intensità dei fasci laser contropropaganti che escono da uno specchio della cavità sono acquisite, assieme ad un monitor della inversione di popolazione laser. Questi osservabili, una volta correttamente calibrati con una procedura dedicata, permettono di stimare i parametri dissipativi di cavità fredda e i parametri del mezzo attivo, che determinano la parte principale delle non linearità del sistema. La procedura di identificazione, basata sulle soluzioni perturbative della dinamica del laser, ci consente l’applicazione di un filtro di Kalman per la stima della velocità angolare. La procedura di identificazione dei parametri e sottrazione delle sistematiche laser è stata validata mediante uno studio Monte Carlo del sistema, inoltre i risultati delle analisi su dati sperimentali dei prototipi G-PISA e G-WETTZELL sono mostrati e discussi. Dopo la sottrazione della dinamica del laser mediante filtro di Kalman, l’errore sistematico relativo alla frequenza di rotazione di G-PISA si riduce da 50 a 5 parti in 103, residuo che può essere attribuito alle incertezze residue sul fattore di scala geometrico e sull’orientamento del giroscopio. Anche nel caso dell’analisi dei dati di G-WETTZELL si segnala che l’errore sistematico relativo viene ridotto. Negli ultimi dieci anni, una crescente attenzione è stata attirata da esperimenti ottici di alta precisione, ad esempio, esperimenti basati su giroscopi laser, che combinano alta sensibilità, precisione e stabilità a lungo termine. Per soddisfare a stringenti requisiti sperimentali, la posizione e l’orientamento degli elementi ottici, e la formazione dei fasci laser, devono essere controllati nel campo degli strumenti di nano-posizionamento e ultra-precisione. Metodi esistenti per il calcolo del cammino del fascio laser in risonatori, ad esempio, il ray tracing iterativo o le matrici di trasferimento generalizzate, sono computazionalmente costosi o si basano su modelli ridondanti di elementi ottici. Sfruttando il principio di Fermat, un nuovo metodo per calcolare il cammino ottico in cavità risonanti formate da specchi sferici è sviluppato, in funzione delle posizioni degli specchi e del valore dei rispettivi raggi di curvatura. La procedura proposta si basa sul metodo di Newton geometrico, un algoritmo con tasso di convergenza del secondo ordine che si basa su un modello del secondo ordine della lunghezza ottica della cavità. Evitando di parametrizzare con coordinate la posizione del raggio laser sugli specchi, il calcolo del modello di secondo ordine non coinvolge le derivate seconde della parametrizzazione. Con l’aiuto di simulazioni numeriche, si dimostra che le proprietà di convergenza della nostra procedura valgono per un vasto insieme di cavità poligonali non planari, e viene valutata l’efficacia del metodo di Newton geometrico nella determinazione delle configurazioni delle cavità laser con un alto grado di precisione e sforzo computazionale trascurabile. Viene anche presentato un metodo per tenere conto delle deformazioni della cavità ottica dovute agli spostamenti degli specchi, ovvero gli spostamenti degli specchi che non si traducono in movimenti di corpo rigido della cavità stessa. Conoscendo la configurazione della cavità e avendo un modello per descrivere i movimenti degli specchi, la calibrazione ed il controllo attivo della cavità ottica possono essere studiati. I nostri risultati sono infatti di una certa importanza non solo per la progettazione e la simulazione, ma anche per l’allineamento e in linea di principio anche per il controllo attivo di giroscopi laser ad alta precisione. Nella parte finale di questo lavoro si descrive il modello RLG, un modello multiuso completo comprensivo della simulazione accurata di tutti i processi fisici rilevanti nel funzionamento di un giroscopio laser ad alta risoluzione. I risultati della simulazione dell’applicazione del modello RLG al giroscopio G-PISA vengono presentati e discussi
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Nurul, Huda Ibnu. "Etude des propriétés rhéologiques globales de la Terre à l'aune des observations VLBI." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEO007.
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Depuis le début du vingtième siècle, l’observation des variations de rotation de la Terre par les techniques astro-géodésiques permet de dévoiler les propriétés rhéologiques globales de la Terre. En particulier, les paramètres des modes d'oscillation libre de l'axe de rotation, qui sont aussi des paramètres de résonance - reflètent les défauts d'élasticité de la Terre solide, la réponse de l’océan au forçage externe et les propriétés de la graine fluide, éventuellement du noyau solide. On peut obtenir de meilleures contraintes sur ces paramètres de résonance en confrontant le mouvement terrestre du pôle de rotation observé (mouvement du pôle) – et aussi la nutation en tant que mouvement du pôle en rétrograde diurne - à l’excitation modélisée qui le produit. Les propriétés rhéologiques de la Terre sont d'autant mieux déterminées que le mouvement du pôle (y compris dans la bande diurne) est observé précisément et l’excitation modélisée correctement. A l'heure actuelle, si la précision du mouvement du pôle est légèrement meilleure au delà de 2 jours, la meilleure reconstitution du forçage concerne la bande de nutation (la bande rétrograde diurne), car il est procède alors des marées gravimétriques luni-solaires, lesquelles sont modélisées avec une grande précision). C'est pourquoi notre travail est d'abord consacré à l'ajustement direct des composantes luni-solaires périodiques de la nutation à partir des retards du VLBI, puis à l'estimation des paramètres de résonances dans la fonction de transfert entre ces termes de nutation observés et ceux modélisés pour une terre rigide, lesquels reflètent le forçage luni-solaire. Les résultats obtenus confirme notamment le raccourcissement d’environ 40-50 jours de la période de résonance du mouvement du pôle dans la bande rétrograde diurne. Nous montrons comment cette diminution s'explique par la réponse dynamique des océans à la marée du pôle, laquelle est étudiée à l'aune des modèles de marées océaniques diurnes . Nous prédisons également un changement des paramètres de résonance du mouvement du pôle à proximité de la fréquence de résonance de la nutation libre du noyau; cette modification semble confirmée par la détermination de ces paramètres à partir des termes de nutation. Notre étude des paramètres de résonance s'étend au delà de la bande de nutation. D'une part, nous réexaminons l’estimation des paramètres de résonance du mouvement du pôle dans la bande saisonnière, dominée par l’oscillation de Chandler, en utilisant les derniers modèles hydro-atmosphériques. D'autre part, nous étudions la résonance du mouvement du pôle à la bande prograde diurne, où l’excitation est dominée par la marée océanique. Nous obtenons une période de résonance de l’ordre de 393 jours, corroboré par notre modélisation fondée sur les modèles de marée océanique. L'ensemble des résultats obtenus permet d'apporter des contraintes sur la dépendance en fréquence du nombre de Love et du nombre de Love océanique caractérisant respectivement la réponse de la Terre solide et des océans à un potentiel externe de degré 2Since the beginning of the 20th century, the observation of the Earth rotation variations through astro-geodetic techniques enables to investigate the global rheological properties of the Earth, in particular, the resonance parameters of the free rotation modes reflect the solid Earth anelasticity, the ocean response to an external forcing, and the properties of the fluid inner core, eventually of the solid inner core. Better constraints on these resonance parameters can be obtained by confronting the observed terrestrial motion of the rotation pole (the so-called polar motion) - including nutation as a retrograde diurnal polar motion - to the modelled excitation producing it. The more precise the modelled excitation and the observed polar motion are, the better the Earth rheological properties will be determined. For now, the best precision are reached in the nutation band. So, our work is first dedicated to a direct adjustment of the nutation components from VLBI delays, then the adjustment of the resonance parameters in the transfer function between the observed nutation terms and the corresponding rigid nutation terms that reflects the luni-solar forcing. The obtained resonance parameters confirms in particular the shortening of the polar motion resonance period of about 40 - 50 day in the retrograde diurnal band. Then, we show that the dynamical behaviour of the oceans in the diurnal band is mostly responsible for that. We also predicted a supplementary change of the resonance parameters in the vicinity of the free core nutation resonance, as expected from the solid Earth response, and confirmed by the adjustment of these parameters through the nutation terms. In addition to the nutation band, we revisit the estimation of the polar motion resonance parameters in the seasonal band, dominated by the Chandler wobble, in light of the most recent global circulation models of the hydro-atmospheric layers. Finally, we extend the investigation of polar motion resonance to the prograde diurnal polar motion, where the excitations mostly result from the ocean tides. We obtain a resonance period of about 393 days, and confirmed by our prediction based on the ocean tidal models. These results allow us to impose constraints on the frequency dependence of the body Love number and the Love number oceanic, characterizing respectively the response of the solid Earth and the oceans to an external potential of degree 2
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Collombet, Marielle. "Cinématique et rotation des Alpes Occidentales. Approche paléomagnétique et modélisation analogique." Phd thesis, Université Joseph Fourier (Grenoble), 2001. http://tel.archives-ouvertes.fr/tel-00509762.
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Dans les Alpes Occidentales, la plupart des modèles cinématiques considèrent que depuis la fin du Crétacé, la convergence entre les plaques Adriatique et Européenne a été accomodée par des translations le long de décrochements et de l'épaississement crustal. Les rotations, difficiles à détecter, ont souvent été négligées. Cependant certains modèles les considèrent comme un mécanisme majeur de déformation au cours de l'édification de la chaîne alpine. Afin de tester ces modèles, nous avons mené une étude paléomagnétique sur l'ensemble de la zone briançonnaise de l'Arc Alpin Occidental. Le métamorphisme subi par cette zone durant la fin de l'Eocène et le début de l'Oligocène est responsable d'une réaimantation de l'aimantation rémanente naturelle (ARN). L'analyse de cette aimantation permet donc d'accéder à l'histoire post-métamorphique des zones internes. Près de 350 échantillons, répartis sur 37 sites échelonnés entre le massif du Grand Galibier au Nord et les Alpes Ligure au Sud Est, sont porteurs d'une composante d'aimantation caractéristique stable isolée entre 200° et 450°. Cette composante présente systématiquement une polarité inverse fortement déviée par rapport à la direction Oligocène pour l'Europe stable. Ces déviations augmentent de 47° à 117° du Nord au Sud. Nous les interprétons comme le résultat d'une rotation antihoraire des domaines internes par rapport à l'Europe stable. Cette étude paléomagnétique a été doublée d'une approche plus mécanique basée sur des expériences analogiques simples pour étudier l'influence potentielle de la rotation de la plaque Apulienne sur la mise en place de l'Arc Alpin Occidental. Les structures générées par une plaque tournante basale sous une épaisseur de sable donnée, suggèrent que la rotation antihoraire pourrait être une des conditions aux limites majeure contrôlant l'évolution tardive de l'arc. La complémentarité des deux études permet de proposer un modèle cinématique global pour la mise en place tardive (post-Oligocène) de l'arc Alpin Occidental et apporte des éléments de réponse aux apparentes contradictions qui règnent entre contrainte et déformations actuelles. Les rotations permettraient d'expliquer en particulier pourquoi la chaîne Alpine est toujours active sismiquement alors que les données GPS n'indiquent pas de convergence significative entre Lyon et Turin.
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Grejner-Brzezinska, Dorota A. "Analysis of GPS Data Processing Techniques: In Search of Optimized Strategy of Orbit and Earth Rotation Parameter Recovery /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487929745335624.
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Kramer, Emily Anne. "Rotational lightcurve analysis of binary Asteroid (22) Kalliope/Linus." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/114347.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008.Cataloged from PDF version of thesis.
Includes bibliographical references (page 34).
Binary asteroids have been insightful to scientists in recent years in their quest to better understand the Solar System in its early stage. Observing a mutual event between a primary and its moon can yield the sizes of the objects in units of the semi-major axis a. When the linear dimensions of the orbit can be known, Kepler's Third Law allows for a solution of the mass. As an example, because the absolute linear scale of (22) Kalliope/Linus is known [1], one can determine the component sizes and reduce error bars on the mass and density of this M-type asteroid. Since the bulk composition is known from spectral data, the porosity of the asteroid can be calculated. Knowing the porosity of the asteroid can give scientists a better understanding of its formation and dynamical evolution. Binary object (22) Kalliope/Linus is a classic example of a system for which this technique can yield valuable results. An observing campaign involving five observers resulted in twenty-eight nights of data. The data were used to create rotational lightcurves, which were scanned for signatures of mutual events.
by Emily A. Kramer.
S.B.
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Deutschmann, Tim. "On Modeling Elastic and Inelastic Polarized Radiation Transport in the Earth Atmosphere with Monte Carlo Methods." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-161475.
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The three dimensional Monte Carlo radiation transport model McArtim is extended
to account for the simulation of the propagation of polarized radiation and the inelastic
rotational Raman scattering which is the cause of the so called Ring effect.
From the achieved and now sufficient precision of the calculated Ring effect new opportunities
in optical absorption spectroscopy arise. In the calculation the method of
importance sampling (IS) is applied. Thereby one obtains from an ensemble of
Monte Carlo photon trajectories an intensity accounting for the elastic
aerosol particle-, Cabannes- and the inelastic rotational Raman scattering (RRS) and
simultaneously an intensity, for which Rayleigh scattering is treated as an elastic scattering
process. By combining both intensities one obtains the so called filling-in (FI,
which quantifies the filling-in of Fraunhofer lines) as a measure for the strength of
the Ring effect with the same relative precision as the intensities.
The validation of the polarized radiometric quantities and the Ring effect is made by comparison
with partially published results of other radiation transport models.
Furthermore the concept of discretisation of the optical domain into grid cells is extended
by making grid cells arbitrarily joining into so called clusters, i.e. grid cell aggregates.
Therewith the program is able to calculate derivatives of radiometrically or spectroscopically
accessible quantities, namely the intensities at certain locations in the atmospheric radiation field
and the light path integrals of trace gas concentrations associated thereto, i.e. the product of the DOAS (differential optical absorption spectroscopy) method, with respect to optical
properties of aerosols and gases in connected spatial regions.
The first and second order derivatives are validated through so called self-consistency tests.
These derivatives allow the inversion of three dimensional tracegas and aerosol concentration
profiles and pave the way down to 3D optical scattered light tomography. If such tomographic inversion scheme is based solely on spectral intensitites the available second order derivatives allows the consideration of the curvature in the cost function and therefore allows implementation
of efficient optimisation algorithms.
The influence of the instrument function on the spectra is analysed in order
to mathematically assess the potential of DOAS to a sufficient degree. It turns out
that the detailed knowledge of the instrument function is required for an advanced
spectral analysis.
Concludingly the mathematical separability of narrow band signatures of absorption and
the Ring effect from the relatively broad band influence of the elastic scattering processes
on the spectra is demonstrated which corresponds exactly to the DOAS principle. In that procedure
the differential signal is obtained by approximately 4 orders of magnitude faster
then by the separate modelling with and without narrow band structures.
Thereby the fusion of the separated steps DOAS spectral analysis and subsequent
radiation transport modeling becomes computationally feasible.
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Couhert, Alexandre. "Amélioration des références massiques de la Terre par synergie entre différentes mesures de géodésie spatiale : Application à l'océanographie par altimétrie spatiale." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30242.
Full textAbstract:
Dans le contexte du changement climatique mondial et la nécessité d'étudier les conséquences de l'ampleur de la fonte des glaces continentales sur le niveau des mers ainsi que sur la répartition des masses fluides à l'échelle du globe, notre travail de thèse s'intéresse aux phénomènes à très grande échelle qui modifient la forme de la Terre, son champ de gravité et l'équilibre de sa rotation. Il se focalise sur la stratégie à mettre en place pour observer et modéliser des variations très fines sur des termes géodynamiques (coefficients de bas degrés) qui sont encore aujourd'hui mal connus, et pourtant déterminants dans l'établissement des références terrestres fondamentales. La première partie de la thèse concerne l'observation du mouvement du géocentre par différentes techniques de mesures géodésiques. Ces travaux débouchent, par une meilleure maîtrise des sources d'erreurs, sur une explication des écarts entre les séries de mesures laser du mouvement du géocentre obtenues sur les satellites LAGEOS (référence actuelle pour l'origine du repère international, ITRF) et celles obtenues indépendamment sur le satellite altimétrique Jason-2 à partir d'observations DORIS/laser/GPS. La deuxième partie de la thèse s'intéresse à la détermination cohérente des coefficients de degrés 0 (coefficient gravitationnel GM), 1 (géocentre), et 2 (inertie/orientation) du champ de pesanteur terrestre. Nous utilisons pour cela les mesures de télémétrie laser disponibles depuis les années 1970 (par exemple, Starlette lancé en précurseur par le CNES dès 1975), car ce sont les seules mesures à caractère absolu qui donnent accès à ces trois premiers degrés. Nos analyses menées sur près de 35 ans aboutissent à une nouvelle valeur de la constante gravitationnelle géocentrique et la détection d'une réponse viscoélastique du manteau de notre planète aux échelles de temps décennales, par combinaison des termes de degré 2 et paramètres d'orientation de la Terre avec les équations d'Euler-LiouvilleIn the context of the overall climate change and the need to analyze the implications of the record ice-sheet melting for the sea level and global fluid mass redistribution budgets, our PhD work focuses on large-scale phenomena impacting the shape of the Earth, its gravity field, and the stability of its rotation pole. We explore strategies for the observation and modeling of subtle variations in geodynamic parameters (lowermost degree coefficients), which are still poorly constrained, despite their importance in determining fundamental terrestrial references. The first part of this PhD is dedicated to the observation of the geocenter motion, using different geodetic technics. The outcomes of this work provided explanations, through a correct handling of the dominant error sources, for the discrepancies between the reference laser-based LAGEOS geocenter time series (defining the origin of the international frame, ITRF) and independent solutions using DORIS/laser/GPS observations from the Jason-2 altimeter satellite. The second part of this PhD presents a self-consistent determination of the degrees 0 (gravitational coefficient GM), 1 (geocenter motion), and 2 (Earth's figure axis orientation) of the geopotential. To this end, we use the available laser data since the 1970s (e.g., the first geodetic satellite Starlette launched by CNES in 1975), as they are the only absolute measurements making possible the monitoring of the first three degree terms. Based on 35 years of satellite laser tracking, an updated value of the geocentric gravitational coefficient was obtained, and a viscoelastic behavior of the Earth's mantle manifesting at decadal time scales was exhibited, combining the derived figure axis variations of the Earth and polar motion observations with the Euler-Liouville equations
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Hicks, Stacy Jo. "Characterization of Eight Potentially Hazardous Near Earth Asteroids: Rotation Period Analysis and Structure Modeling Via Light Curve Inversion Techniques." TopSCHOLAR®, 2018. https://digitalcommons.wku.edu/theses/3060.
Full textAbstract:
The term “homeland security”, seems to have become synonymous with terrorism in the minds of the general public. However, there are other threats to the security of the United States homeland that can be just as, if not more, devastating than terrorism. Included among these other threats is the potential of an asteroid collision with Earth. Historically, asteroid impact events have been responsible for the devastation of our planet and many of the mass extinction events encountered throughout the geologic record. Knowledge of physical parameters such as structure and rotational dynamics of the asteroid are critical parameters in developing interception and deflection techniques, as well as assessing the risk associated with these bodies and mitigation planning in the event of impact. This thesis encompasses the study of eight potentially hazardous asteroids identified in conjunction with NASA’s OSIRIS REX Mission and observed via the Target Asteroid Project, along with observations from the Robotically Controlled Telescope, and the Asteroid Light Curve Database of Photometry. Photometric data was extracted from all observations. Rotation periods of each target were confirmed using Lomb-Scargle time series analysis, with possible secondary periods indicated in the cases of Hathor (2.2169 hours), Bede (161.1501 hours), and Phaethon (4.5563 hours). Shape models for 2002 FG7, 2004 JN13, and Icarus were produced using light curve inversion techniques These are believed to be the first such models for these asteroids.
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Park, Young-Gyu. "Rotating convection driven by differential bottom heating and its application." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/55050.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.Includes bibliographical references (leaves 133-137).
by Young-Gyu Park.
Ph.D.
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Mound, Jonathan Edwin. "Long-term rotational effects on the shape of the Earth and its oceans." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63753.pdf.
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Robuchon, Guillaume. "Couplage entre dynamique interne et rotation : application à l'évolution de Mercure, Japet et Mars." Phd thesis, Université de Nantes, 2009. http://tel.archives-ouvertes.fr/tel-00461943.
Full textAbstract:
L'évolution de certains corps planétaires fait intervenir de manière couplée la dynamique interne et la dynamique de rotation. La convection solide, qui façonne le champ de température et donc la rhéologie visqueuse, contrôle la dissipation visqueuse du forçage de marée qui intervient sur l'évolution de l'orbite et la période de rotation. En retour, la dissipation de marée induit une composante de chauffage pour l'évolution thermique. A travers l'étude de trois corps, Mercure, Mars et Japet, je montre l'intérêt de cette formulation couplée de l'évolution. La dissipation de marée a joué un rôle important dans les premiers temps de l'évolution de Mercure (contribution au budget de chaleur, ralentissement de la rotation). L'étude couplée indique que l'orientation des escarpements lobés observés à la surface de Mercure peut être héritée de cette interaction. L'évolution du noyau issue de cette étude préserve une partie liquide à l'heure actuelle qui autorise une origine comparable à la dynamo terrestre pour le champ magnétique de Mercure. La différence importante entre les rayons équatorial et polaire de Japet peut être comprise comme une forme fossile héritée d'une époque où la période de rotation fut plus rapide et l'intérieur plus chaud. Ce scénario n'est possible que si les éléments radioactifs abondent dans les premiers instants de l'évolution de Japet. Mars ne présente en revanche aucune interaction de marée notable mais l'influence de la dynamique interne sur l'orientation de la rotation est invoquée pour expliquer les positions relatives du dôme de Tharsis et de la dichotomie hémisphérique. J'introduis un formalisme qui permet de mieux tester cette hypothèse.
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Joseph, Judith Anoushka. "Motion sickness with Earth-horizontal translational and rotational oscillation presented in isolation and in combination." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/63716/.
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Low-frequency Earth-horizontal translational and rotational oscillations can cause motion sickness in transport. Previous studies have found that motion sickness depends on the frequency, magnitude, direction and duration of the motion, however, knowledge of the mechanisms of motion sickness is far from complete. The concept of sensory conflict – that motion sickness arises because of a conflict between sensed and expected sensory information is central to theories of motion sickness, but little is known about how the physical characteristics of motion influence sensed and expected sensory signals. The aim of this research was to advance understanding of the effect on motion sickness of factors which may influence sensed and expected vestibular signals during exposure to low-frequency translational and/or rotational oscillation. The first experiment investigated whether motion sickness depends on the phase between combined lateral acceleration and roll oscillation at 0.2 Hz. The roll oscillation had one of four phases relative to the lateral acceleration: 0° delay, 14.5° delay, 29° delay, and 29° advance. Sickness decreased as the delay in the roll motion increased; less sickness occurred with a phase advance than a phase delay, suggesting that motion sickness cannot be predicted from the acceleration in the plane of the seat. The second experiment investigated how motion sickness varies between four 60-minute exposures of 0.1 Hz combined lateral and roll oscillation which involved different combinations of a high and low magnitude motion: LLLL, HHHH, LHHL and HLHL. The high magnitude motion produced greater sickness than the low magnitude motion. For the two variable motion conditions, there was no significant difference in accumulated illness ratings when the motion sickness dose values were the same. In the third experiment, 0.2 Hz roll and pitch oscillation were studied at three displacements: ±1.83° ±3.66° or ±7.32°. A trend for motion sickness to increase with increasing displacement was observed; similar sickness was caused by roll and pitch oscillation at each magnitude. In the fourth experiment, subject head displacement was measured during 0.2 Hz fore-and-aft oscillation with and without a backrest at three magnitudes: 0.22, 0.44, and 0.89 ms-2 r.m.s. Illness increased systematically with increasing magnitude of oscillation with a backrest, but less systematically without a backrest, suggesting an interaction between the effect of motion magnitude and the influence of a backrest. There were no significant differences in illness with or without a backrest at any of the magnitudes studied. Between subjects, there was little evidence to suggest that greater fore-and-aft and pitch displacement of the head was associated with an increase in motion sickness. Combined findings from the third and fourth experiments suggest that 0.2 Hz fore-and-aft oscillation causes greater sickness than 0.2 Hz pitch oscillation at each of the three magnitudes studied (assuming that pitch motion can be represented by the gravitational component, gSinθ). A motion sickness model is proposed showing how the factors investigated in this thesis affect the sensed and expected semi-circular canal signals which are assumed to be involved in the causation of motion sickness. The model predicts how sensed and expected signals vary according to the phase between motions, the magnitude, direction and duration of motion, the type of motion and the postural support given to subjects. Explanations of how the model predicts motion sickness based on the findings of this study and previous studies are discussed.
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Klinger, Barry Arthur. "Eddy generation at a convex corner by a coastal current in a rotating system." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/59860.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992.Includes bibliographical references (leaves 190-195).
by Barry A. Klinger.
Ph.D.
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Martinsson, Lisbeth. "Barns föreställningar om dag- och nattcykeln : Har eleverna uppnått målen för år 5?" Thesis, Karlstad University, Faculty of Social and Life Sciences, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-862.
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Syftet med detta examensarbete är att ta reda på hur elevers uppfattningar om de rörelser som sker i vårt solsystem stämmer överens med de vetenskapliga fakta som finns. I våra vardagliga situationer refererar vi till det vi med ögats hjälp kan uppfatta i fråga om vad som rör sig eller ej. Hur påverkas eleverna av de dagliga uttryck som de får höra sedan de är mycket små, och har de en möjlighet att med skolans hjälp förändra dessa tankesätt?
Undersökningen genomfördes med hjälp av kvalitativa intervjuer av elever i skolår 1 respektive 5. Detta för att se hur stor skillnaden är mellan de elever som inte har erhållit någon undervisning om solsystemet och de elever som ska ha uppnått de mål för fysik som skolverket har ställt upp.
Eleverna som deltog i studien valdes slumpmässigt ur respektive klasser. De fick besvara 14 frågor, var och en för sig. De besvarade frågorna olika utförligt, vissa var mycket fåordiga. Ibland var jag tvungen att ställa följdfrågor, eftersom jag ville förstå eleverna på ett bra sätt.
Resultatet av undersökningen visar att elevernas kunskaper inom området har en stor variation, även inom samma åldrar. Detta kan härledas till elevernas eget intresse av vårt solsystem. Den slutsats som jag har dragit av undersökningen är att det är viktigt att ta reda på vilka föreställningar som eleverna har inför arbetet med arbetsområdet.
The purpose of this degree project is to find pupils´ understanding about the movements which occur in our solar system and compare them with the scientific facts we know about. In our daily life we refer to what we can see with the help from our eyes whether something moves or not. How do the pupils´ get affected by these daily expressions they hear from early ages, and do they have an opportunity with the help from the school to change these ways of thinking?
The survey was carried out with help of qualitative interviews of pupils´ in class 1 and 5. This because to see how large the difference is between pupils´ who hasn’t received any education about the solar system and the pupils´ who are supposed to have reached the goals compiled by The National Agency for Education.
The pupils´ who took part in this study were chosen by random from both classes. They answered to 14 questions, each and everyone on their own. They answered the questions with various details, some were very taciturn. Sometimes I had to ask resulting questions, since I wanted to understand the pupils´ properly.
The result of the survey shows that the pupils´ knowledge within the area have a large variation, even within the same ages. This can be deduced to the interest of the pupils´ in our solar system. The conclusion I have maid from this survey are that it is important to find out which understandings the pupils´ have before the work with the subject area.
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O'Donnell, J. M. "Rotational nuclear energy levels of deformed nuclei in the light rare-earth region around mass 135." Thesis, University of Bradford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376692.
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Tian, Wei. "Modeling and Data Analysis of Large Ring Laser Gyroscopes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-130967.
Full textAbstract:
Ringlaser dienen dazu, durch genaue inertiale Messungen Rotationen ohne Bezug auf ein externes Referenzsystem lokal und praktisch in Echtzeit zu bestimmen. Sie wurden in den 1970er Jahren insbesondere für die Navigation von Flugzeugen entwickelt. In den letzten Jahrzehnten wurden Ringlaser dann so weit verbessert, dass sie nun auch als eigenständige Messinstrumente in der Geodäsie Verwendung finden. Aufgrund der erreichbaren Genauigkeit ist es inzwischen möglich, Variationen in der Erdrotation mit der dafür erforderlichen Präzision zu detektieren. Der stabilste unter den Ringlasern, der so genannte Ringlaser "G" der geodätischen Fundamentalstation Wettzell, erreicht eine Sensitivität von 1.2 x 10 -11 nrad. Damit ist dieses Instrument in der Lage, Neigungen von bis zu 1 nrad (dies entspricht einem Signal von 0.2 mas in der Polbewegung, in Änderung der Rotationsgeschwindigkeit der Erde) im täglichen und halb-täglichen Frequenzband zu messen. Motivation dieser Arbeit ist es, der in den letzten Jahren erreichten Verbesserung des Auflösungsvermögens und der Sensorstabilität Rechnung zu tragen und die für die Auswertung von Ringlaserdaten benutzten geophysikalischen Modelle weiter zu verbessern, um dadurch die variable Rotation der Erde noch präziser vermessen zu können. Die dafür relevanten Effekte werden in den einzelnen Kapiteln dieser Arbeit separat behandelt. Nach einer Einführung werden in Kapitel 2 dieser Arbeit drei lokale, topozentrische Koordinatensysteme konstruiert, mit welchen sich das zu beobachtende Sagnac-Signal eines Ringlasers in der ersten post-Newtonischen Näherung der Allgemeinen Relativitätstheorie adäquat beschrieben lässt. In Kapitel 3 wird ein verbessertes Modell für die Orientierung des Ringlasers, basierend auf Ergebnissen von Dehant et al. (1999), entwickelt. Ein in den bislang benutzten Modellen vernachlässigter Neigungsterm konnte dabei identifiziert werden. Ein Modell für die retrograde tägliche Polbewegung der Erde wird in Kapitel 4 entwickelt. Ausgehend von den dynamischen Gleichungen für eine starre Erde werden diese um elastische Effekte und Einflüsse der Mehrschichtigkeit der Erde ergänzt und die entsprechenden Euler-Liouvilleschen Gleichungen und Transfer-Funktionen abgeleitet. Gezeiteneinflüsse des Ozeans, speziell die dadurch hervorgerufene sub-tägliche Variation der Erdrotation und ozeanische Auflasteffekte, werden in Kapitel 5 behandelt. Es wird gezeigt, dass die ozeanischen Signale größer als 10 -9 Δf0 (Δf0 348 Hz für den Ringlaser "G") sind und damit in den Messdaten des Ringlasers "G" nachweisbar sein sollten. Auf Grundlage der in dieser Arbeit entwickelten Modelle wurde eine 168 Tage (30. April 17. Oktober 2010) umfassenden Datenreihe des Ringlasers "G" in Kapitel 6 ausgewertet. Für die Auswertung wurde die Software ETERNA 3.40 genutzt und entsprechend angepasst. Die tägliche retrograde Polbewegung konnte dabei mit einer Genauigkeit von 0.15 mas bestimmt werden. Diese Auswertung beweist ein weiteres Mal die Existenz eines flüssigen Erdkerns. Des weiteren konnte gezeigt werden, dass bestimmte Gezeitenparameter des halb-täglichen Frequenzbandes durch lokale Effekte beeinflusst werden. Lokal gemessene Luftdruckdaten wurden benutzt, um den Einfluss atmosphärischer Auflasteffekte auf den Ringlaser "G" zu untersuchen. Die Ergebnisse dieser Arbeit zeigen, dass sich für diese Effekte kein signifikanter Einfluss nachweisen lässt. Die Arbeit schließt mit einer Zusammenfassung der Resultate, einer Beschreibung der sich ergebenden Schlussfolgerungen und einem Ausblick auf zukünftige Arbeiten auf dem Gebiet der RinglaseranalyseRing laser gyroscopes measure inertial rotations locally and in real-time without the need for an external reference system. Initially, they were developed for aircraft navigation applications in the 1970s. With the improvement of ring laser technology during the last decades large ring laser gyroscopes (RLGs) are nowadays used as independent geodetic instruments. Due to the achievable accuracy more and more geophysical signals become observable in the data. The G-ring located at the Geodetic Observatory Wettzell is reckoned as the most stable one amongst the running large RLGs and reaches a sensitivity of 1.2 x 10 -11 nrad. Therefore, the instrument is able to detect a tilt signal of 1 nrad (equivalent to a signal of 0.2 mas in polar motion or 10 -9 Ω0 in variation of Earth rotation rate) in the diurnal and semi-diurnal band. This motivates us to improve previous geophysical models and estimate associated tilt and Earth rotation signals, which are the focuses of this Thesis. Firstly, we construct three local proper topocentric reference frames and interpret the Sagnac effect observed by large RLGs in the first post-Newtonian (PN) approximation of Einstein's theory of gravity. Secondly, in Chapter 3 we develop an improved orientation model for the Sagnac platform, based on the numerical results of Dehant et al. (1999). A missing tilt term in previous RLG tilt models is found. In Chapter 4, based on the Euler-Liouville equations or nutation transfer functions for a rigid Earth, a purely elastic Earth, a two-layered Earth and a three-layered Earth, five retrograde diurnal polar motion models are computed with the HW95 tidal potential catalogue. Thirdly, ocean tide effects (two aspects: effects on sub-daily variations of Earth rotation and loading effect on tilt) are considered in Chapter 5. We show that the Sagnac signals induced by ocean tides are larger than 10 -9 Δf0 (Δf0 348 Hz for the G-ring) and their influences are visible in the G-ring. Fourthly, based on the above-mentioned improved models and 168 days (from Apr.30 to Oct.17 in 2010) of G-ring data, in the diurnal band, we estimate the retrograde diurnal polar motion signal with an accuracy of 0.15 mas. The Earth tide software ETERNA 3.40 was adopted and modified to analyse this data. Our estimation provides one more evidence for the existence of the Earth's fluid outer core. Furthermore, we found that the tidal parameters for the G-ring are affected by the cavity and topographic effects in the semi-diurnal band. The local air pressure record is used in order to investigate the atmospheric loading effect on the G-ring by a simple regression model. Nevertheless, the preliminary result shows that no significant influence from atmospheric loading on our estimation is found. This Thesis closes with a summary of the obtained results, conclusions and suggestions how the analysis of ring laser data could be improved in future work
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Nelson, Michael Roy. "I. Paleomagnetism and crustal rotations along a shear zone, Las Vegas range, Southern Nevada ; II. Seismotectonics of the Tien Shan, Central Asia." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/54960.
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Mäntele, Simone. "Adipose rhythms and metabolism : the circadian system orchestrates the temporal organization of the physiology in synchronization with the 24 hour rotation on the earth." Thesis, University of Surrey, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551155.
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Energy homeostasis and metabolic processes have been shown to be under 24-hour control. Hormones secreted from adipocytes and about 20% of the genes in white adipose tissue exhibit daily variations. Changes in metabolism are able to influence the clock in adipose tissue and disruption of the clock mechanism has been shown to lead to metabolic consequences. The aims of this PhD are firstly to investigate links between peripheral clocks and metabolism by using in vivo human and in vitro experimental models and secondly to investigate a cell model, which might reflect adipocyte biology better than the currently available cell lines. The influence of overweight and type 2 diabetes mellitus on plasma hormones was investigated in men over a 24-hour time course under highly controlled conditions. /' Significantly higher nocturnal plasma melatonin concentrations were observed in obese compared to lean or diabetic subjects. All participants showed clear diurnal variation in plasma leptin, but there was surprisingly no significant difference between the groups, irrespective of whether the data were plotted relative to external clock time or endogenous melatonin phase. Rhythmicity and phase of the expression of core clock genes and clock controlled genes, in a novel adipocyte model derived from IMMORTO™ mouse pre-adipocyte cells, support the presence of a molecular oscillator in those cells. Rhythms were phase advanced by about 5 hours in adipocytes, compared to the pre-adipocytes. Preliminary results revealed that lipolysis in those cells may be gated by the adipocyte clock. Our results suggest that the timing of the leptin secretion into the blood is not influenced by the metabolic state under well controlled conditions whilst the concentration of plasma melatonin is increased in overweight participants. The in vitro results show for the first time a molecular clock in primary-like murine adipose cells. The IMW AT cells appear to be a better model because of the robust rhythmicity of the clock genes. Moreover, the preliminary lipolysis data suggests circadian gating for lipolysis. The different phasing of gene expression in pre-adipocytes and adipocytes suggests possible differences in the response to entraining stimuli and that the molecular oscillator may be influenced by the metabolic or differentiation state of the cell.
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Audibert, Marc. "Déformation discontinue et rotations de blocs. Méthodes numériques de restauration. application à la Galilée." Phd thesis, Université Rennes 1, 1990. http://tel.archives-ouvertes.fr/tel-00594538.
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La déformation de la partie fragile de la croûte se manifeste dans de nombreux cas par l'apparition de cassures ou failles à grande échelle associées en réseaux (plusieurs familles de failles de directions différentes). Ces derniers individualisent un certain nombre de blocs que l'on peut considérer comme autant d'éléments rigides. Pour un réseau de failles quelconque donné, si la géométrie des éléments supposés rigides mais aussi leurs déplacements le long des failles (sens et rejets) sont connus, il existe une solution géométrique unique au problème de restauration c'est-àdire la recherche des positions des blocs les uns par rapport aux autres avant la déformation. Les études cartographiques et de terrain permettent certes d'obtenir une géométrie des réseaux de failles et le jeu de ces dernières, mais très rarement de connaitre l'ensemble des rejets. Cependant, dans un certain nombre de contextes tectoniques les glissements le long des failles s'accompagnent de rotations des blocs autour d'axes: verticaux pour une déformation dans le plan horizontal, ou horizontaux dans le cas de blocs basculés. Dans ce cas, angles de rotation et rejets sont liés géométriquement et les angles peuvent être connus grâce au paléomagnétisme. Le propos de ce mémoire est le développement d'une méthodologie de restauration d'un ensemble de blocs, à partir des données structurales et paléomagnétiques. Cette méthodologie a permis la mise au point, sur micro-ordinateur, d'un programme automatique, incrémentai et itératif, de calculs des positions relatives des blocs. Ce programme comprend deux principes de calcul (rotation et translation), qui sont appliqués à chaque incrément, les blocs étant considérés rigides. A la fin d'un incrément, quand la stabilité du réseau est atteinte, un principe de calcul de déformation périphérique permet d'accomoder les incompatibilités géométriques locales (vides et recouvrements) persistantes . Pour tester la validité et les limites de la méthode, nous l'avons appliquée à un modèle analogique en sable déformé par cisaillement simple, dont on connaissait les stades anté et finidéformation. Nous avons entrepris ensuite une étude paléomagnétique, dans la Province de Tibériade, afin de voir sur le terrain s'il existait un gradient de rotation entre le centre d'un domaine et sa bordure, comme il est observé dans les modèles analogiques. Enfin une application de la méthode de restauration à l'ensemble de la fracturation du Nord d'Israêl et du Sud Liban, a été effectuée
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ARRIAGADA, César. "Rotations tectoniques et déformation de l'avant-arc des Andes centrales au cours du Cénozoïque." Phd thesis, Université Rennes 1, 2003. http://tel.archives-ouvertes.fr/tel-00006036.
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Une étude paléomagnétique et structurale au nord du Chili met en évidence que le remplissage sédimentaire du bassin d'Atacama s'est accumulé dans un contexte compressif depuis le Crétacé Supérieur. Les données paléomagnétiques montrent des rotations horaires et suggèrent qu'une zone de cisaillement transpressif dextre NE-NNE a contrôlé les rotations pendant le Paléogène. Une étude de restauration en carte de la déformation des Andes Centrales indique que la formation de l'orocline est principalement associée à la déformation de la Cordillère Orientale. La variabilité spatiale et la grande quantité des rotations dans la marge chilienne suggèrent deux épisodes de rotation, un épisode de rotation dans l'avant arc au cours du Paléogène et une rotation globale de toute la marge pendant la déformation de la Cordillère Orientale. En conclusion les résultats de cette étude démontrent que la déformation compressive et les rotations tectoniques sont des éléments clef de la déformation Andine.
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Schaeffer, Nathanaël. "Instabilités, turbulence et dynamo dans une couche de fluide cisaillée en rotation rapide : importance de l'aspect ondulatoire." Phd thesis, Université Joseph Fourier (Grenoble), 2004. http://tel.archives-ouvertes.fr/tel-00009743.
Full textAbstract:
Nous développons un modèle quasi-géostrophique (QG) amélioré en moyennant l'équation de Navier-Stokes le long de l'axe de rotation. Il permet de modéliser des fluides barotropes en rotation rapide dans un récipient axisymétrique de pente finie. Ce modèle QG est utilisé pour étudier les instabilités d'une couche de cisaillement (couche de Stewartson). Nous montrons que la pente est le paramètre clé de l'instabilité, qui prend la forme d'ondes de Rossby. En plus de la viscosité, nous avons implémenté une friction d'Ekman réaliste (à partir de la formule de Greenspan) à notre modèle QG. Ceci nous permet d'atteindre des régimes d'écoulement tournants très turbulents, avec une dissipation réaliste à toutes les échelles. Nous observons des des spectres très raides (loi puissance -5, correspondant à la turbulence d'ondes de Rossby) et des régimes stationnaires. Ces écoulements sont des dynamos qui sont relativement faciles à démarrer, pour des nombres de Prandtl magnétiques (Pm) modérés à très faibles. l'action dynamo semble s'étendre pour Pm arbitrairement petit, avec un nombre de Reynolds magnétique critique (Rm) approximativement constant. L'aspect ondulatoire de l'écoulement est ici indispensable pour obtenir une dynamo. Enfin, nous essayons d'ajouter la force de Lorentz à notre modèle de dynamo QG. Nous trouvons que la nature ondulatoire de l'écoulement turbulent ne permet pas d'utiliser une approximation diffusive aux petites échelles.
41
Bourda, Géraldine. "Rotation terrestre et Variations du champ de gravité : Etude et apport des missions CHAMP et GRACE." Phd thesis, Observatoire de Paris, 2004. http://tel.archives-ouvertes.fr/tel-00008286.
Full textAbstract:
La distribution des masses à l'intérieur de la Terre régit la vitesse de rotation terrestre, ainsi que le comportement de l'axe de rotation terrestre dans la Terre, et dans l'espace. Ces distributions de masses peuvent être mesurées depuis l'espace grâce aux satellites artificiels, dont l'orbitographie donne accès à la détermination du champ de gravité terrestre. Par conséquent, les variations temporelles du champ de gravité peuvent être reliées aux variations des paramètres d'orientation terrestre (via le tenseur d'inertie). Des progrès considérables ont été effectués ces dernières années dans la modélisation des effets des couches fluides. Et de nos jours, les mesures d'orientation terrestre dans l'espace obtenues par Interférométrie à très Longue Base (VLBI) ont une exactitude meilleure qu'une milliseconde de degré. Ceci permet de progresser dans la connaissance de la dynamique globale de la Terre. Mon travail de thèse a eu pour but d'utiliser la mesure du champ de gravité et de ses variations comme outil pour compléter la modélisation de la rotation terrestre. D'une part, en vue de l'utilisation des mesures du satellite GRACE, d'une grande précision, nous avons effectué des comparaisons précises des méthodes numériques d'intégration d'orbite de Cowell et d'Encke dans le logiciel GINS du GRGS. D'autre part, nous avons établi les liens théoriques entre les Paramètres d'Orientation Terrestres (EOP) et les variations des coefficients du champ de gravité. Ainsi, nous avons utilisé les données de variations temporelles des coefficients de degré 2 du géopotentiel pour en déduire leur influence sur la longueur du jour, le mouvement du pôle et la précession de l'équateur.
42
Hufford, Gwyneth Ellin. "Parameterization of convection in a rotating stratified ocean : comparison of numerical and laboratory experiments with theory." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/59632.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and Woods Hole Oceanographic Institution, 1995.Includes bibliographical references (leaves 70-73).
by Gwyneth Ellin Hufford.
M.S.
43
Fraser, Neil James. "Mechanisms for wintertime fjord-shelf heat exchange in Greenland and Svalbard." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31289.
Full textAbstract:
No region has felt the effects of global climate change more acutely than the cryosphere, which has changed at an unprecedented rate in the past two decades. The scientific consensus is that these changes are driven largely by increasing ocean heat content at high latitudes. In southeast Greenland, acceleration and retreat of the marine-terminating glaciers contributes significantly towards global sea level rise. Circulation in the fjords which accommodate these glaciers is thought to be driven both by freshwater input and by barrier wind-driven shelf exchange. Due to a scarcity of data, particularly from winter, the balance between these two mechanisms is not fully understood. In Svalbard, increasing water temperature has decimated sea ice cover in many of the fjords, and had substantial implications for the local ecosystem. While there is a relatively comprehensive literature on shelf exchange mechanisms in Svalbard fjords, questions remain over how the internal circulation interacts with exchange mechanisms. The region shares a similar underwater topography and oceanographic setting with southeast Greenland, with marine-terminating glaciers in close proximity to warm Atlantic waters, and results from Svalbard can hence be used to inform studies of high-latitude fjord-shelf exchange in a broader context. A realistic numerical model was constructed with the aim of better understanding the interaction between Kangerdlugssuaq Fjord and the adjacent continental shelf, and quantifying heat exchange during winter. The model was initially run in an idealised configuration with winter climatological forcing fields, incorporating a parameterisation for melting at the terminus, and used to test the impact of barrier wind events. The Earth's rotation played a crucial role in the nature of the circulation and exchange in the fjord, with inflow on the right (looking up-fjord) and outflow on the left. While the heat delivered into the fjord-mouth was smaller than that observed in summer, the background internal circulation was found to efficiently distribute waters through the fjord without external forcing, and the heat delivered to the glacier terminus was comparable to summer values. Barrier winds were found to excite coastally-trapped internal waves which propagated into the fjord along the right-hand side. The process was capable of doubling the heat delivery. The process also enhanced the background circulation, likely via Stokes' Drift. The model was then adapted to simulate winter 2007-08 under historical forcing conditions. Time series of glacial melt rate, as well as the heat flux through fjord cross-sections, were constructed and compared to the variability in wind forcing. Long periods of moderate wind stress were found to induce greatly enhanced heat flux towards the ice sheet, while short, strong gusts were found to have little influence, suggesting that the timescale over which the shelf wind field varies is a key parameter in dictating wintertime heat delivery from the ocean to the Greenland Ice Sheet. An underwater glider was deployed to Isfjorden, a large fjord system in Svalbard, to measure the temperature, salinity and depth-averaged currents over the course of November 2014. Like in Kangerdlugssuaq, the circulation in Isfjorden was found to be heavily influenced by the Earth's rotation and by wind activity both locally and on the shelf. The combination of hydrography and high-resolution velocity data provided new insights, suggesting that the approach will be useful for studying high-latitude fjords in the future.
44
Pisani, Anna Rita <1973>. "A comprehensive study of the 26th December 2004 Sumatra earthquake: possible implications on Earth rotation and investigations on the coseismic and postseismic stress diffusion associated with the seismic rupture." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/864/1/Tesi_Pisani_Anna_Rita.pdf.
Full textAbstract:
In this work a multidisciplinary study of the December 26th, 2004 Sumatra
earthquake has been carried out. We have investigated both the effect of the
earthquake on the Earth rotation and the stress field variations associated
with the seismic event.
In the first part of the work we have quantified the effects of a water
mass redistribution associated with the propagation of a tsunami wave on the
Earth’s pole path and on the length-of-day (LOD) and applied our modeling
results to the tsunami following the 2004 giant Sumatra earthquake. We
compared the result of our simulations on the instantaneous rotational axis
variations with some preliminary instrumental evidences on the pole path
perturbation (which has not been confirmed yet) registered just after the
occurrence of the earthquake, which showed a step-like discontinuity that
cannot be attributed to the effect of a seismic dislocation.
Our results show that the perturbation induced by the tsunami on the
instantaneous rotational pole is characterized by a step-like discontinuity,
which is compatible with the observations but its magnitude turns out to be
almost one hundred times smaller than the detected one. The LOD variation
induced by the water mass redistribution turns out to be not significant because the total effect is smaller than current measurements uncertainties.
In the second part of this work of thesis we modeled the coseismic and
postseismic stress evolution following the Sumatra earthquake. By means of
a semi-analytical, viscoelastic, spherical model of global postseismic deformation
and a numerical finite-element approach, we performed an analysis
of the stress diffusion following the earthquake in the near and far field of
the mainshock source. We evaluated the stress changes due to the Sumatra
earthquake by projecting the Coulomb stress over the sequence of aftershocks
taken from various catalogues in a time window spanning about two years
and finally analyzed the spatio-temporal pattern.
The analysis performed with the semi-analytical and the finite-element
modeling gives a complex picture of the stress diffusion, in the area under
study, after the Sumatra earthquake. We believe that the results obtained
with the analytical method suffer heavily for the restrictions imposed, on the
hypocentral depths of the aftershocks, in order to obtain the convergence of
the harmonic series of the stress components. On the contrary we imposed no
constraints on the numerical method so we expect that the results obtained
give a more realistic description of the stress variations pattern.
45
Pisani, Anna Rita <1973>. "A comprehensive study of the 26th December 2004 Sumatra earthquake: possible implications on Earth rotation and investigations on the coseismic and postseismic stress diffusion associated with the seismic rupture." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/864/.
Full textAbstract:
In this work a multidisciplinary study of the December 26th, 2004 Sumatra
earthquake has been carried out. We have investigated both the effect of the
earthquake on the Earth rotation and the stress field variations associated
with the seismic event.
In the first part of the work we have quantified the effects of a water
mass redistribution associated with the propagation of a tsunami wave on the
Earth’s pole path and on the length-of-day (LOD) and applied our modeling
results to the tsunami following the 2004 giant Sumatra earthquake. We
compared the result of our simulations on the instantaneous rotational axis
variations with some preliminary instrumental evidences on the pole path
perturbation (which has not been confirmed yet) registered just after the
occurrence of the earthquake, which showed a step-like discontinuity that
cannot be attributed to the effect of a seismic dislocation.
Our results show that the perturbation induced by the tsunami on the
instantaneous rotational pole is characterized by a step-like discontinuity,
which is compatible with the observations but its magnitude turns out to be
almost one hundred times smaller than the detected one. The LOD variation
induced by the water mass redistribution turns out to be not significant because the total effect is smaller than current measurements uncertainties.
In the second part of this work of thesis we modeled the coseismic and
postseismic stress evolution following the Sumatra earthquake. By means of
a semi-analytical, viscoelastic, spherical model of global postseismic deformation
and a numerical finite-element approach, we performed an analysis
of the stress diffusion following the earthquake in the near and far field of
the mainshock source. We evaluated the stress changes due to the Sumatra
earthquake by projecting the Coulomb stress over the sequence of aftershocks
taken from various catalogues in a time window spanning about two years
and finally analyzed the spatio-temporal pattern.
The analysis performed with the semi-analytical and the finite-element
modeling gives a complex picture of the stress diffusion, in the area under
study, after the Sumatra earthquake. We believe that the results obtained
with the analytical method suffer heavily for the restrictions imposed, on the
hypocentral depths of the aftershocks, in order to obtain the convergence of
the harmonic series of the stress components. On the contrary we imposed no
constraints on the numerical method so we expect that the results obtained
give a more realistic description of the stress variations pattern.
46
Guervilly, Céline. "Dynamos numériques planétaires générées par cisaillement en surface ou chauffage interne." Phd thesis, Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00576177.
Full textAbstract:
Dans la première partie de cette thèse, nous développons un code numérique hybride basé sur un modèle quasi-géostrophique des écoulements dans les noyaux planétaires forcés par un chauffage interne. Le champ de vitesse est calculé dans le plan équatorial ; la température et le champ magnétique sont implémentés en trois dimensions dans la sphère. Cette approche hybride nous permet de modéliser des écoulements convectifs turbulents (grands nombres de Reynolds, Re>10000) sous une forte influence de la rotation (petits nombres d'Ekman) pour des petits nombres de Prandtl, P = 0.1−0.01. Une caractéristique robuste de ces écoulements est la présence d'une circulation géostrophique zonale de grande amplitude et stable dans le temps. La taille et l'amplitude du mouvement zonal sont controlées par le mélange de vorticité potentielle et la friction aux bords. On identifie la présence d'ondes de Rossby de grande taille se propageant dans la zone de convection vigoureuse. Ces écoulements produisent des dynamos cinématiques au champ poloïdal de petite échelle et au champ toroïdal dominé par le mode axisymétrique. Les nombres de Reynolds magnétiques critiques sont de l'ordre de 1000. Nous montrons que l'impact du vent thermique agéostrophique sur le seuil dynamo n'est pas significatif. Dans la deuxième partie de cette thèse, nous étudions les dynamos générées par un cisaillement en surface. Un écoulement de Couette sphérique (écoulement entre deux sphères en rotation différentielle) produit des dynamos aux nombres de Reynolds magnétiques critiques élevés. La brisure de symétrie axiale de l'écoulement par l'instabilité en cisaillement (prenant la forme d'une onde) est cruciale. Le champ magnétique toroïdal est de grande amplitude par rapport au champ poloïdal impliquant le rôle de l'effet omega dans le processus. Nous étudions ensuite la dynamique et l'effet dynamo produits par des jets zonaux, i.e., des mouvements de rotation différentielle alternativement est-ouest en latitude. Les jets zonaux imposés en surface sont modifiés par des ondes de Rossby qui provoquent un élargissement des jets et une diminution de leur amplitude. Le mécanisme dynamo est basé sur la propagation des ondes de Rossby. On a relié l'amplitude du champ magnétique poloïdal axisymétrique au nombre d'onde du mode de Rossby à travers sa vitesse de phase. Le nombre d'onde du mode de Rossby étant lié à l'épaisseur des jets, on établit un lien entre production de champ poloïdal axisymétrique et épaisseur des jets zonaux.
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Macedo, Sanchez Orlando. "Etude paléomagnetique des formations crétacées et tertiaires des Andes centrales du Pérou. Rôle des rotations dans la formation des déflexions andines." Phd thesis, Université Paris Sud - Paris XI, 1993. http://tel.archives-ouvertes.fr/tel-00833381.
Full textAbstract:
La déflexion majeure d'Arica, située entre 19-22° S et qui dévie l'orientation générale des structures des Andes Centrales depuis une direction péruvienne N W-SE jusqu'à une direction chilienne presque NS, est une des caractéristiques importantes de la chaîne andine. Aussi à cette latitude la croûte sud-américaine atteint une épaisseur double de la normale (-70 km). Cet épaississement crustal est à l'origine du développement de l'Altiplano, vaste plateau situé à une altitude moyenne proche de 4000 m. Pour déterminer et expliquer les mécanismes à l'origine de cet épaississement crustal et de la haute altitude de la chaîne que lui est associé plusieurs modèles ont été proposés, les uns privilégiant des processus magmatiques les autres des processus tectoniques. Le but de cette étude est d'apporter des contraintes à ces différents modèles et en particulier d'évaluer la contribution des processus tectoniques dans le soulèvement andin par l'obtention des données paléomagnétiques couvrant à la fois une vaste étendue géographique (Cordillère Occidentale du Centre et du Sud du Pérou) ainsi qu'une importante tranche d'âge (les derniers 110 Ma, qui englobe l'ensemble de l'orgenèse andine) . L'ensemble d'es résultats obtenus montre de manière claire que la marge péruvienne a subi dans son ensemble et pendant le Cénozoïque une rotation antihoraire d'environ 20°, qui se serait déroulée de manière progressive. Nos résultats montrent également l'absence de rotation de la marge péruvienne durant le Crétacé, ainsi que l'absence de rotation relative entre le Centre et le Sud du Pérou lors de la formation de la déflexion mineure d'Abancay (située vers 14° S). L'absence de grands accidents décrochants et la remarquable cohérence des résultats paléomagnétiques indiquent que les rotations antihoraires observées dans le Centre ett le Sud du Pérou correspondent à une rotation d'ensemble de la marge péruvienne depuis le Paléocène pour s'achever au Miocène supérieur. Cette rotation, dont le pivot peut être placé à la latitude de Huancabamba (vers 5° S), s'accorde avec les données géologiques qui indiquent un gradient latitudinal croissant des racourcissements du nord au sud du Pérou. Les nouvelles données paléomagnétiques que nous avons obtenues sont alors en accord avec le modèle tectonique de surrection des Andes Centrales proposé par Isacks (1988), qui fait appel à des rotations de sens opposés des marges péruvienne et nord-chilienne pour former la deflexion d'Arica actuelle. Le soulèvement des Andes Centrales peut être expliqué simplement par ces processus tectoniques sans faire appel à une contribution magmatique importante.
48
Ohiwa, Mitchihiro 1977. "An experimental study on mixing induced by gravity currents on a sloping bottom in a rotating fluid." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/55068.
Full textAbstract:
Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2002.Includes bibliographical references (p. 75-77).
Mixing induced by gravity currents on a sloping bottom was studied through laboratory experiments in a rotating fluid. The dense fluid on the sloping bottom formed a gravity current that could be in regimes where the flow was laminar or had waves. The mixing on a sloping bottom for gravity currents in the laminar and wave regimes was studied both qualitatively and quantitatively. The laboratory experiments were conducted on rotating tables in a tank with homogeneous ambient fluid. The slope angle, rotation rate, reduced gravity, and flow rate of the dense source water were changed for the experiments. The mixing was quantized by measuring the density of the ambient fluid, dense source water, and the bottom water collected at the end of the bottom slope and calculating the ratio of the source water in the bottom water. Comparing the mixing in the laminar regime and the wave regime by changing the slope angle and rotation rate showed that the waves in the gravity current increased the mixing due to the waves. Analysis of the ratio of source water based on the internal Froude number, the Ekman number, and the timescale of the experiments showed that diffusion was not the main mechanism for mixing. The Ekman layer solution was validated by the observation of a streak left by a grain of dye in the dense water layer. The values for the entrainment parameter for the laboratory experiments bracketed those calculated for the Denmark Strait overflow and the Mediterranean outflow, and the values based on observations in the ocean and those from the laboratory were similar for a nondimensional parameter defined using variables used in the laboratory experiments. This shows that the results from the experiments could be used to discuss the mixing in the ocean due to gravity currents along a slope in the ocean and that the waves observed in the laboratory might also be observed in the ocean.
by Mitchihiro Ohiwa.
S.M.
49
Wischnewski, Juliane. "Reconstructing climate variability on the Tibetan Plateau : comparing aquatic and terrestrial signals." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5245/.
Full textAbstract:
Spatial and temporal temperature and moisture patterns across the Tibetan Plateau are very complex. The onset and magnitude of the Holocene climate optimum in the Asian monsoon realm, in particular, is a subject of considerable debate as this time period is often used as an analogue for recent global warming. In the light of contradictory inferences regarding past climate and environmental change on the Tibetan Plateau, I have attempted to explain mismatches in the timing and magnitude of change.
Therefore, I analysed the temporal variation of fossil pollen and diatom spectra and the geochemical record from palaeo-ecological records covering different time scales (late Quaternary and the last 200 years) from two core regions in the NE and SE Tibetan Plateau. For interpretation purposes I combined my data with other available palaeo-ecological data to set up corresponding aquatic and terrestrial proxy data sets of two lake pairs and two sets of sites. I focused on the direct comparison of proxies representing lacustrine response to climate signals (e.g., diatoms, ostracods, geochemical record) and proxies representing changes in the terrestrial environment (i.e., terrestrial pollen), in order to asses whether the lake and its catchments respond at similar times and magnitudes to environmental changes. Therefore, I introduced the established numerical technique procrustes rotation as a new approach in palaeoecology to quantitatively compare raw data of any two sedimentary records of interest in order to assess their degree of concordance.
Focusing on the late Quaternary, sediment cores from two lakes (Kuhai Lake 35.3°N; 99.2°E; 4150 m asl; and Koucha Lake 34.0°N; 97.2°E; 4540 m asl) on the semi-arid northeastern Tibetan Plateau were analysed to identify post-glacial vegetation and environmental changes, and to investigate the responses of lake ecosystems to such changes. Based on the pollen record, five major vegetation and climate changes could be identified: (1) A shift from alpine desert to alpine steppe indicates a change from cold, dry conditions to warmer and more moist conditions at 14.8 cal. ka BP, (2) alpine steppe with tundra elements points to conditions of higher effective moisture and a stepwise warming climate at 13.6 cal. ka BP, (3) the appearance of high-alpine meadow vegetation indicates a further change towards increased moisture, but with colder temperatures, at 7.0 cal. ka BP, (4) the reoccurrence of alpine steppe with desert elements suggests a return to a significantly colder and drier phase at 6.3 cal. ka BP, and (5) the establishment of alpine steppe-meadow vegetation indicates a change back to relatively moist conditions at 2.2 cal. ka BP. To place the reconstructed climate inferences from the NE Tibetan Plateau into the context of Holocene moisture evolution across the Tibetan Plateau, I applied a five-scale moisture index and average link clustering to all available continuous pollen and non-pollen palaeoclimate records from the Tibetan Plateau, in an attempt to detect coherent regional and temporal patterns of moisture evolution on the Plateau. However, no common temporal or spatial pattern of moisture evolution during the Holocene could be detected, which can be assigned to the complex responses of different proxies to environmental changes in an already very heterogeneous mountain landscape, where minor differences in elevation can result in marked variations in microenvironments.
Focusing on the past 200 years, I analysed the sedimentary records (LC6 Lake 29.5°N, 94.3°E, 4132 m asl; and Wuxu Lake 29.9°N, 101.1°E, 3705 m asl) from the southeastern Tibetan Plateau. I found that despite presumed significant temperature increases over that period, pollen and diatom records from the SE Tibetan Plateau reveal only very subtle changes throughout their profiles. The compositional species turnover investigated over the last 200 years appears relatively low in comparison to the species reorganisations during the Holocene. The results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem. Forest clearances and reforestation have not caused forest decline in our study area, but a conversion of natural forests to semi-natural secondary forests.
The results from the numerical proxy comparison of the two sets of two pairs of Tibetan lakes indicate that the use of different proxies and the work with palaeo-ecological records from different lake types can cause deviant stories of inferred change. Irrespective of the timescale (Holocene or last 200 years) or region (SE or NE Tibetan Plateau) analysed, the agreement in terms of the direction, timing, and magnitude of change between the corresponding terrestrial data sets is generally better than the match between the corresponding lacustrine data sets, suggesting that lacustrine proxies may partly be influenced by in-lake or local catchment processes whereas the terrestrial proxy reflects a more regional climatic signal. The current disaccord on coherent temporal and spatial climate patterns on the Tibetan Plateau can partly be ascribed to the complexity of proxy response and lake systems on the Tibetan Plateau. Therefore, a multi-proxy, multi-site approach is important in order to gain a reliable climate interpretation for the complex mountain landscape of the Tibetan Plateau.Die räumlichen und zeitlichen Temperatur- und Feuchtigkeitsmuster auf dem Tibet-Plateau sind sehr komplex. Im Einzugsbereich der asiatischen Monsune sind insbesondere der Beginn und das Ausmaß des Klimaoptimums während des Holozäns von wissenschaftlichem Interesse, da diese Periode oft als Analogie für die derzeitige globale Klimaerwärmung herangezogen wird. In Hinblick auf sich teilweise widersprechende Paläoklima- und Umweltrekonstruktionen für das Tibet-Plateau, ist es mein Ziel, die bestehenden Unstimmigkeiten bezüglich des Zeitpunktes und des Ausmaßes des Umweltwandels zu erklären. Dafür wurden von mir zeitliche Variationen fossiler Pollen- und Diatomeenspektren und geochemische Untersuchungen an Seesedimenten unterschiedlicher Zeitskalen (Spätquartär und die letzten 200 Jahre) aus zwei Kernregionen auf dem NO und SO Tibet-Plateau analysiert. Zur Unterstützung der Interpretation wurden die hier erhobenen Daten mit bereits vorhandenen paläoökologischen Aufzeichnungen der Lokalitäten kombiniert, um Datensätze der entsprechenden aquatischen und terrestrischen Proxy-Daten (Stellvertreterdaten) zweier Seenpaare aus den beiden Regionen gegenüberstellen zu können. Hierbei konzentrierte ich mich auf den direkten Vergleich von Proxies, die die Seenentwicklung reflektieren (z.B. Diatomeen, Ostracoden, geochemische Eigenschaften), mit Proxies, die Veränderungen der terrestrischen Umgebung des Sees beschreiben (terrestrische Pollen). Durch diesen Vergleich lässt sich beurteilen, ob Veränderungen im See selbst mit Umweltveränderungen in dem jeweiligen Einzugsgebiet zeitlich übereinstimmen. Dafür habe ich die bereits etablierte numerische Methode Procrustes-Rotation als neuen Ansatz in der Paläoökologie eingeführt. Damit ist ein quantitativer Vergleich von Rohdaten zweier beliebiger sedimentärer Datensätze möglich, um den Grad der Übereinstimmung zu prüfen. Um die in dieser Arbeit rekonstruierten Umwelt- und Klimaereignisse des nordöstlichen Tibet-Plateaus in einen größeren Zusammenhang hinsichtlich holozäner Klimaentwicklung des gesamten Plateaus setzen zu können, und um schlüssige zeitliche und räumliche Klimatrends auf dem Plateau erkennen zu können, habe ich auf alle vorhandenen Paläoklimadatensätze einen Fünf-Skalen Feuchtigkeitsindex und eine Clusteranalyse angewandt. Es konnten jedoch keine einheitlichen zeitlichen und räumlichen Trends der holozänen Klimaentwicklung nachgewiesen werden, was meiner Analyse entsprechend, auf die komplexen Reaktionen verschiedener Proxies auf Umweltveränderungen in einer ohnehin sehr heterogen Berglandschaft, zurückgeführt werden kann. Die Ergebnisse des numerischen Proxy-Vergleichs beider Seenpaare zeigen, dass die Verwendung von verschiedenen Proxies und die Arbeit mit paläo-ökologischen Datensätzen unterschiedlicher See-Typen zu abweichenden Klimaableitungen führen können. Unabhängig vom untersuchten Zeitraum (Holozän oder die letzten 200 Jahren) oder der Region (SO oder NO Tibet-Plateau), ist die Übereinstimmung zweier Datensätze hinsichtlich der Richtung, des Zeitpunktes und des Ausmaßes der abgeleiteten Paläo-Umweltverhältnisse in der Regel zwischen den entsprechenden terrestrischen Datensätzen besser als zwischen den entsprechenden lakustrinen Datensätzen. Die derzeitige Uneinigkeit über stimmige zeitliche und räumliche Klimatrends auf dem Tibet-Plateau kann daher teilweise der Komplexität der verschieden Proxies und ihrer individuellen Empfindlichkeiten gegenüber Umweltveränderungen sowie der unterschiedlichen Reaktionsweise verschiedenartiger See-Systeme auf dem Plateau zugeschrieben werden. Meine Ergebnisse zeigen, dass ein „Multi-Proxy-Multi-Site-Ansatz“ für zuverlässige Paläoklimaableitungen für das Tibet-Plateau von zentraler Bedeutung ist.
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Wells, Judith R. (Judith Roberta). "A laboratory study of localized boundary mixing in a rotating stratified fluid." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/58062.
Full textAbstract:
Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and the Woods Hole Oceanographic Institution), 2003.Includes bibliographical references (p. 145-148).
Oceanic observations indicate that abyssal mixing is localized in regions of rough topography. How locally mixed fluid interacts with the ambient fluid is an open question. Laboratory experiments explore the interaction of mechanically induced boundary mixing and an interior body of linearly stratified rotating fluid. Turbulence is generated by a vertically oscillating horizontal bar, located at middepth along the tank wall. The turbulence forms a region of mixed fluid which quickly reaches a steady state height and collapses into the interior. The mixed layer thickness ... is independent of the Coriolis frequency f. N is the buoyancy frequency, co is the bar frequency, and the constant, Y=1 cm, is empirically determined by bar mechanics. In initial experiments, the bar is exposed on three sides. Mixed fluid intrudes directly into the interior as a radial front of uniform height, rather than as a boundary current. Mixed fluid volume grows linearly with time ... The circulation patterns suggest a model of unmixed fluid being laterally entrained with velocity, e Nhm, into the sides of a turbulent zone with height hm and width Lf ... where Lf is an equilibrium scale associated with rotational control of bar-generated turbulence. In accord with the model, outflux is constant, independent of stratification and restricted by rotation ... Later experiments investigate the role of lateral entrainment by confining the sides of the mixing bar between two walls, forming a channel open to the basin at one end. A small percentage of exported fluid enters a boundary current, but the bulk forms a cyclonic circulation in front of the bar. As the recirculation region expands to fill the channel, it restricts horizontal entrainment into the turbulent zone. The flux of mixed fluid decays with time.
(cont.) ... The production of mixed fluid depends on the size of the mixing zone as well as on the balance between turbulence, rotation and stratification. As horizontal entrainment is shut down, longterm production of mixed fluid may be determined through much weaker vertical entrainment. Ultimately, the export of mixed fluid from the channel is restricted to the weak boundary current.
by Judith R. Wells.
Ph.D.