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1
Cotto, Amaryllis. « Intermittently Forced Vortex Rossby Waves ». FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/553.
Texte intégralRésumé :
Wavelike spiral asymmetries are an intriguing aspect of Tropical Cyclone dynamics. Previous work hypothesized that some of them are Vortex Rossby Waves propagating on the radial gradient of mean–flow relative vorticity. In the Intermittently Forced Vortex Rossby Wave theory, intermittent convection near the eyewall wind maximum excites them so that they propagate wave energy outward and converge angular momentum inward. The waves’ energy is absorbed as the perturbation vorticity becomes filamented near the outer critical radii where their Doppler–shifted frequencies and radial group velocities approaches zero. This process may initiate outer wind maxima by weakening the mean–flow just inward from the critical radius. The waves are confined to a relatively narrow annular waveguide because of their slow tangential phase velocity and the narrow interval between the Rossby wave cut–off frequency, where the radial wavenumber is locally zero, and the zero frequency, where it is locally infinite.
2
Proehl, Jeffrey A. « Equatorial wave-mean flow interaction : the long Rossby waves / ». Thesis, Connect to this title online ; UW restricted, 1988. http://hdl.handle.net/1773/10960.
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3
Murphy, Darryl Guy. « Rossby waves in the Southern Ocean ». Thesis, University of Exeter, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303178.
Texte intégral
4
Wood, R. G. « Rossby waves in mid-latitude oceans ». Thesis, University of Essex, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379474.
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5
Kovalam, Sujata. « MF radar observations of tides and planetary waves ». Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phk878.pdf.
Texte intégralRésumé :
Copies of previously published articles inserted. Bibliography: p. 185-200. Data obtained from six radar stations covering a wide latitude range has been used to determine the global distribution of planetary waves and tides. In the process a number of data analyses techniques were considered for their characterisation.
6
Fyfe, John. « A barotropic stability study of free and forced planetary waves / ». Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75433.
Texte intégralRésumé :
The stability of free and forced planetary waves in a $ beta$-channel is investigated with a barotropic model. The forced waves at equilibrium result from a constant mean-zonal wind interacting with a finite-amplitude topography.The frequencies of all infinitesimal perturbations to the equilibrium flows are determined numerically as a function of the flow parameters. The results are interpreted using a truncated spectral model and related to those of previous studies with infinite $ beta$-planes. In contrast to some earlier analytical studies we find that unstable long waves $(L sb{x}$ $>$ $L sb{y})$ exist under superresonant conditions. We also report on the existence of an interesting travelling topographic instability.
The linear instability of a weakly non-zonal flow is investigated numerically and analytically (via WKB theory). The theory reproduces the qualitative nature of the numerically-determined fastest-growing mode.
Nonlinear integrations, involving many degrees of freedom, reveal that initially-infinitesimal disturbances may grow explosively to finite-amplitude. The longer-term integrations are interpreted using a statistical mechanical model.
7
Giannitsis, Constantine 1971. « Non-linear saturation of vertically propagating Rossby waves ». Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/53043.
Texte intégralRésumé :
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2001.Includes bibliographical references (p. 203-208).
Linear quasi-geostrophic theory predicts an exponential amplitude increase with height for Rossby waves propagating vertically through a stratified atmosphere, as a result of wave activity density conservation. At the same time layer-wise conservation of potential enstrophy constrains wave amplitudes, given the limited amount of potential enstrophy available in the initial mean flow. A break down of linear theory is thus expected above a certain critical wave amplitude, raising the question of how the non-linear flow reacts to limit the vertical penetration of waves. Keeping in mind the potential importance for the dynamics of the winter stratosphere, where strong wave penetration and amplitude growth are often observed, the issue of wave saturation in a non-linear flow is examined in a generally abstract context, through a variety of simple model studies. We thus consider the cases of a topographically forced barotropic beta plane channel model, of vertical propagation through a three-dimensional beta plane channel model, and of a polar coordinate model with realistic basic state and geometry. In the barotropic model transient wave growth is forced through the use of bottom topography and the deviations of the non-linear flow evolution from the predictions of both a linear and a quasi-linear analytical solution are examined for strong topographic anomalies. The growth of the forced wave is found to decelerate the zonal mean flow which in turn reduces the topographic forcing. Wave-mean flow interactions are thus found to be sufficient in leading to saturation of the eddy amplitudes. Interestingly it is the formation of zonal mean easterlies, rather than the depletion of mean available potential enstrophy, that is found to be the crucial factor in the saturation dynamics. Similar results are obtained for the case of vertical propagation through a three dimensional beta plane channel. The vertical penetration of the forced wave is shown to cause a reduction of the zonal mean winds and mean potential vorticity gradients in the center of the channel, eventually leading to the formation of either a critical line or a refractive index turning surface. In both cases the penetration of the wave to high altitudes is prohibited, thus constraining wave amplitudes. While signs of non-linear behaviour are clear in synoptic maps of potential vorticity, wave-wave interactions are found to play a secondary role in the saturation process. The results of the three-dimensional beta plane channel model are then extended to a more realistic set-up, using a polar coordinate model with a basic state based on the observed winter stratosphere climatology. The basic conclusions of the idealized study are shown to remain unchanged.
by Constantine Giannitsis.
Ph.D.
8
Ash, Ellis R. « Rossby waves and mean currents in the Southern Ocean ». Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/11542.
Texte intégralRésumé :
Dynamics in the Southern Ocean are dominated by the Antarctic Circumpolar Current (ACC), and this large eastward current has an important influence on the earth's climate. Output from the last six years of the Fine Resolution Antarctic Model, where the mean flow is known, is used to develop techniques for quantifying Rossby waves and eddy activity. Some eastward jets in the mean flow are found to act as waveguides for Rossby waves. Phase speeds are found to increase linearly with frequency, but do not vary with the strength of mean flow. The reason for this is demonstrated using the dispersion relation, but it is shown that Rossby waves cannot be used to measure mean flows in the ACC without a further understanding of the theory involved. A property of the time-average eddy activity, known as the eddy orientation angle, is shown to indicate the axes of the prominent eastward jets in the mean flow. This shows that eddies are acting to force these jets. Five yeas of measurements from the TOPEX/POSEIDON satellite mission are used to identify Rossby waves in the real ocean. Coherent Rossby wave propagation is again confined to localised regions, some of which act as waveguides. Phase speeds are measured in these regions, and shown to be consistent with previous measurements of Rossby waves. An improved resolution dataset, combining TOPEX/POSEIDON and ERS altimetry measurements, is used to analyse the time-average eddy activity and associated forcing on the mean flow in unprecedented detail. Current data from cruises of the World Ocean Circulation Experiment are used in conjunction with altimetry data to estimate the mean flow at locations along ship tracks. Using these estimates, and the position of temperature fronts as an indication of prominent jets in the mean flow, the eddy forcing is shown to be different to that observed in FRAM. Instead of forcing the mean flow, eddies are being generated within the jets which are likely to be maintained by topographic forcing.
9
Yang, Gui-Ying. « Propagation of nonstationary Rossby waves and extratropical-tropical interaction ». Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646005.
Texte intégralRésumé :
The propagation of Rossby waves with positive and negative frequency, corresponding to eastward and westward phase speeds respectively, is investigated. The techniques used are theoretical analysis, ray tracing, and initial value problems in barotropic and baroclinic numerical models. It is found that the characteristics of positive and negative frequency Rossby waves can differ significantly from each other andfrom those of stationary, zero frequency Rossby waves. However, general deductions from studies of stationary Rossby waves are still found to be valid. Using an analytic Gill-type model and a dry primitive equation model with only idealised vorticity or thermal forcing, a possible trigger mechanism for the Madden Julian Oscillation (MJO) has been studied. The results show that eastward moving forcing in the subtropics or extratropics can lead to a significant equatorial Kelvin wave response which tends to be a maximum in the African/Indian Ocean sector, and is enhanced by easterly winds in the upper troposphere. It is suggested . that one mechanism for initiating the MJO is for eastward moving extratropical waves to excite a large equatorial response, sufficient to trigger large-scale convection, in the presence of favourable easterly winds in the upper troposphere. The dry primitive equation model is used to study the possible interaction of atmospheric flow in the two hemispheres and the triggering of other equatorial waves. It is found that stationary and westward moving forcing in the Northern Hemisphere extratropics can give a significant Southern Hemisphere response. A westward moving forcing in the subtropics, with a period of several days, can trigger the equatorial mixed Rossby-gravity and n=l Rossby waves. The zonal basic flow is found to have a significant effect on these equatorial wave responses.
10
Jonsson, Eskil. « Modelling the Formation and Propagation of Orographic Rossby Waves ». Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-325188.
Texte intégralRésumé :
Orographic Rossby waves are the main mechanism by which the jet streams meander aroundthe Earth and have possibly far-reaching impacts on weather and climate (chapter 1). Hence,they are of particular importance to study and this project should serve as a starting point inwhat to consider when trying to model these waves. For example, we have to account forpressure gradients, Coriolis effect, orography, potential vorticity conservation and also Earth’scurvature at this scale. These are covered in detail in ch. 2 and adapted to the Shallow WaterEquations. In addition, some entry-level numerical techniques for solving these equations arepresented throughout ch. 2.4 and then implemented for the global-scale Shallow WaterEquations with conserved potential vorticity in ch. 3. The model is validated to work for typicalshallow water flows in a bath tub and passes common tests like the Gaussian curve test (ch.4.1). However, when considering atmospheric flows (ch. 4.2) it becomes evident that ourmodel, as well as our numerical methods are lacking and cannot reproduce Rossby waves ina stable manner. Hence, a heavily modified version of Hogan’s model (Hogan, n.d) isemployed with a simplified numerical scheme. With these corrections, orographic Rossbywaves appear to naturally form at appropriate locations. However, they do not fully exhibit theexpected behaviours discussed in ch. 2.2. Even Hogan’s model appears to have severelimitations as waves propagate in the wrong direction. Hence, this study is not complete andwarrants further development in order to be useful.Orografiska Rossby-vågor är den huvudsakliga mekanismen genom vilken jetströmmarnaslingrar runt jorden och kan ha en omfattande inverkan på väder och klimat (kapitel 1). Därförär de av särskild betydelse att studera och detta projekt bör fungera som en utgångspunkt förvad man måste överväga när man försöker modellera dessa vågor. Till exempel så måste vi tahänsyn till tryckgradienter, Coriolis-effekten, orografi, potentiell vorticitetsbevarande och ävenjordens krökning på denna skala. Dessa beskrivs i detalj i kap. 2 och anpassas tillrörelseekvationerna för grunt vatten (Saint-Venant-ekvationerna). Därefter presenteras någranumeriska tekniker på grundläggande nivå för att lösa dessa ekvationer i kap. 2.4, varvid desedan implementeras för de globala Saint-Venant-ekvationerna med bevarad potentiellvorticitet i kap 3. Modellen är validerad för typiska grunda vattenflöden i ett badkar ochpasserar vanliga numeriska tester så som Gauss-kurvtestet (kap. 4.1) och bore-testet. Mennär vi överväger atmosfäriska flöden (kap. 4.2) blir det tydligt att våra modeller och numeriskametoder är primitiva och inte kan reproducera Rossby-vågor på ett stabilt sätt. Därmed,modifierar vi Hogans modell (Hogan, n.d) för att passa vår modell vilket resulterar orografiskaRossby-vågor. Dock så är dessa förskjutna och stämmer inte riktigt överens med teorin i kap.2.2. Även Hogans modell visar sig ha allvarliga begränsningar då vågorna propagerar i felriktning. Därmed är denna studie ej komplett och kräver ytterligare utveckling för att varaanvändbar.
11
Rivest, Chantal. « Topographically forced waves in a time-dependent flow ». Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63184.
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12
Choboter, Paul F. « Forced Rossby waves in a zero absolute vorticity gradient environment ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ37107.pdf.
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13
Kessler, William S. « Observations of long Rossby waves in the northern tropical Pacific / ». Thesis, Connect to this title online ; UW restricted, 1989. http://hdl.handle.net/1773/10971.
Texte intégral
14
Harlander, Uwe. « Asymptotic and numerical solutions of trapped Rossby waves in high-latitude shear flows with boundaries ». Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-214605.
Texte intégralRésumé :
We consider the amplitudes of coastally trapped Rossby waves in a high-latitude shear flow on a modified ß-plane, where also the effect of the sphericity of the earth (c5-effect) is taken into account. We present a particular analytical solution and also asymptotic and numerical solutions. We find that the asymptotic WKB solutions are accurate compared to the numerical results. We show that the o-effect is most important for shorter waves and leads to an enhanced selection of trapped Rossby wave modesWir betrachten die Amplituden von küstennah gefangenen Rossby-Wellen in einer Scherströmung hoher Breiten. Die Rechnungen werden auf einer modifizierten ß-Ebene durchgeführt, die auch die Spherizität der Erde berücksichtigt (o-Effekt). Wir zeigen eine spezielle analytische Lösung und auch asymptotische und numerische Lösungen. Die asymptotischen WKB-Lösungen erweisen sich als genau, verglichen mit den numerischen Resultaten. Der o-Effekt wirkt sich a stärksten bei den sehr langen und den kurzen Wellen aus und führt zu einer stärkeren Selektion von Moden gefangener Rossby-Wellen
15
Fröhlich, Kristina, Alexander Pogoreltsev et Christoph Jacobi. « Tides, Rossby and Kelvin waves simulated with the COMMA-LIM Model ». Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217759.
Texte intégralRésumé :
A 48-layer version of the COMMA-LIM (Cologne Model of the Middle Atmosphere – Leipzig Institute for Meteorology) three-dimensional global mechanistic model of the Earth\'s atmosphere from 0 km to 135 km with logarithmic pressure height coordinates was developed. The model is capable of reproducing the global structures and propagation of different planetary waves in the middle atmosphere. The contribution of gravity waves, tides, Rossby and Kelvin waves into the zonally averaged momentum budget of the mesosphere / lower thermosphere region has been investigatedEine neue Version des COMMA-LIM (Cologne Model of the Middle Atmosphere – Leipzig Institute for Meteorology) wurde im Zusammenhang mit der Erhöhung der vertikalen Schichtauflösung entwickelt. Das COMMA ist ein dreidimensionales globales mechanistisches Modell der Erdatmosphäre mit einer Ausdehnung von ca. 0 – 135 km in logarithmischen Druckkoordinaten. Damit können globale Eigenschaften der mittleren Atmosphäre sowie die Ausbreitung verschiedener planetarer Wellen nachvollzogen werden. Die Beiträge der Schwerewellen, thermischer Gezeiten, Rossby und Kelvin Wellen zur zonal gemitteltem Impulsbalance der Mesosphäre und unteren Thermosphäre wurden untersucht
16
Fröhlich, Kristina, Alexander Pogoreltsev et Christoph Jacobi. « Tides, Rossby and Kelvin waves simulated with the COMMA-LIM Model ». Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 30 = Meteorologische Arbeiten aus Leipzig ; 8 (2003), S. 149-156, 2003. https://ul.qucosa.de/id/qucosa%3A15248.
Texte intégralRésumé :
A 48-layer version of the COMMA-LIM (Cologne Model of the Middle Atmosphere – Leipzig Institute for Meteorology) three-dimensional global mechanistic model of the Earth\''s atmosphere from 0 km to 135 km with logarithmic pressure height coordinates was developed. The model is capable of reproducing the global structures and propagation of different planetary waves in the middle atmosphere. The contribution of gravity waves, tides, Rossby and Kelvin waves into the zonally averaged momentum budget of the mesosphere / lower thermosphere region has been investigated.Eine neue Version des COMMA-LIM (Cologne Model of the Middle Atmosphere – Leipzig Institute for Meteorology) wurde im Zusammenhang mit der Erhöhung der vertikalen Schichtauflösung entwickelt. Das COMMA ist ein dreidimensionales globales mechanistisches Modell der Erdatmosphäre mit einer Ausdehnung von ca. 0 – 135 km in logarithmischen Druckkoordinaten. Damit können globale Eigenschaften der mittleren Atmosphäre sowie die Ausbreitung verschiedener planetarer Wellen nachvollzogen werden. Die Beiträge der Schwerewellen, thermischer Gezeiten, Rossby und Kelvin Wellen zur zonal gemitteltem Impulsbalance der Mesosphäre und unteren Thermosphäre wurden untersucht.
17
Ravia, Roni. « Excitation and dispersion of a Rossby wave train on the polar jet by an extra-tropical transition of a hurricane ». Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101167.
Texte intégralRésumé :
The enhanced potential vorticity gradients along the polar jet serve as a wave guide for trapped Rossby waves. These tropopause level, synoptic scale Rossby waves are of primary importance for weather development at the surface. In particular, extreme weather events have been linked to the existence of overlying upper level meridionally elongated filaments of stratospheric (high potential vorticity) air which form during the breaking of these waves. Motivated by the desire to understand the conditions under which these waves are formed and to improve their predictability, the current thesis discusses one excitation mechanism---the potential vorticity anomaly associated with a hurricane approaching the extra-tropics.Attention is directed toward the adiabatic interaction of the cyclone with the polar jet before the two features meet. The hurricane's ability to excite Rossby waves is verified from observations of past interactions and theoretical study using a mechanistic model with idealized settings. The nature of the interaction between the cyclone and the polar jet is found to be sensitive to parameters such as the cyclone's radius and PV anomaly. Three different regimes have been identified. It is also concluded that the same parameters have influence on the skill of the Rossby wave prediction. The more intense the cyclone is, the harder it is to accurately predict the response of the polar jet.
18
Chen, Shuiming. « Vertical structure of mesoscale ocean currents in the Indian Ocean observation, numerical modeling and theory / ». Thesis, University of Hawaii at Manoa, 2003. http://proquest.umi.com/pqdweb?index=0&did=765960941&SrchMode=2&sid=8&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1209408688&clientId=23440.
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19
Delk, Tracey Lee. « Intraseasonal, large-scale circulations and tropical cylcome activity over the Western North Pacific during Boreal summer / ». Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FDelk.pdf.
Texte intégralRésumé :
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, June 2004.Thesis advisor(s): Patrick Harr. Includes bibliographical references (p. 73-75). Also available online.
20
Harlander, Uwe. « Some simple solutions of trapped Rossby waves in zonal barotropic multiple-jet flows ». Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-215362.
Texte intégralRésumé :
This study concerns on trapped Rossby waves and local Rossby wave packets in zonal basic flows with two or more prominent extreme values (so called multiple-jet flows). For simplicity, most of the calculations are performed on the f-plane, but an extension to the ß-plane is also discussed. Under the assumption that the basic fiow is a solution to a special type of second order ordinary differential equation, we show that then the amplitudes of stationary trapped Rossby waves are solutions to an equation of the same type. We investigate the occurrence of trapped modal waves as well as the rays of wave action radiation in a particular multiple-jet flow. Further we consider the development of the local wavenumbers of Rossby wave packets in such a flow, with and without a zonally oriented reflective boundary. lt is found that wave action can propagate in the zonal direction only when the boundary is present. Otherwise the rays of wave action radiation form a closed curveDiese Studie beschäftigt sich mit gefangenen Rossby Wellen und lokalen gefangenen Rossbywellenpaketen in einer zonalen Strömung mit zwei oder mehreren ausgeprägten Extrema (sog. Strömungen mit mehrfachen Jets). Der Einfachheit halber werden die meisten Berechnungen auf der f-Ebene angestellt, eine Erweiterung auf die ß-Ebene wird allerdings auch diskutiert. Wenn man annimmt, dass der Grundstrom die Lösung einer bestimmten gewöhnlichen Differentialgleichung zweiter Ordnung ist, kann man zeigen, dass die Amplituden gefangener Wellen Lösungen des gleichen Gleichungstypes sind. Wir betrachten die Bedingungen für das Auftreten gefangener modaler Wellen, als auch die Pfade der Wellenenergie-Abstrahlung in einer bestimmten Mehrfach-Jet-Strömung. Ferner untersuchen wir die Entwicklung der lokalen Wellenzahlen von Wellenpaketen in einer solchen Strömung, mit und ohne eines zonal orientierten reflektierenden Randes. Wir finden, dass sich Wellenenergie auf der f-Ebene nur dann in zonaler Richtung ausbreiten kann, falls eine solcher Rand vorhanden ist. Anderenfalls ergeben die Strahlen der Wellenenergie Ausbreitung eine geschlossene Kurve
21
Boss, Emmanuel. « Dynamics of potential vorticity fronts / ». Thesis, Connect to this title online ; UW restricted, 1996. http://hdl.handle.net/1773/11031.
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22
Ménard, Richard. « Saturation d'ondes de gravité et balance non-linéaire ». Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65947.
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23
Crick, Andrew Paul Richard. « Rossby waves on shear flows and the noiseless generation of small scales ». Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598147.
Texte intégralRésumé :
The framework of normal modes of a stable flow in a channel is reviewed: two kinds of modes, regular and singular, are found. This framework is then used to study an initial-value problem, with initial conditions consisting of super-positions of singular modes. Theoretical predictions are made concerning the excitation of regular modes in certain special cases. Chapter 3 describes numerical simulations of the relevant equations, which are shown to be in agreement with our predictions. In chapter 4 we review previous studies of non linear critical layers, in particular the asymptotic Stewartson-Warn & Warn (SWW) solution, and the instability analysis by Killworth & McIntyre. We investigate the possibility that small non linearities, inherent in the full asymptotic solution, but suppressed in the SWW solution, could grow and trigger the instability. These non linearities have exponentially small amplitudes, but we present a heuristic scaling argument to show that they could indeed grow fast enough to significantly affect the evolution of the flow. Chapter 5 describes the numerical methods that were used in high-precision simulations that resolve the unstable modes. Finally in chapter 6 we describe the results of these simulations. We use these to extrapolate the asymptotic limit considered by SWW, and show that indeed after a certain time, that we measure, the unstable modes grow to large amplitudes, and that the SWW flow is no longer the correct leading-order solution after this time.
24
Nikulin, Grigory. « Impact of Rossby waves on ozone distribution and dynamics of the stratosphere and troposphere ». Doctoral thesis, Kiruna : Swedish institute of Space Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-596.
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25
Harlander, Uwe. « Asymptotic and numerical solutions of trapped Rossby waves in high-latitude shear flows with boundaries ». Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 12 = Meteorologische Arbeiten aus Leipzig ; 4 (1999), S. 170-176, 1999. https://ul.qucosa.de/id/qucosa%3A15132.
Texte intégralRésumé :
We consider the amplitudes of coastally trapped Rossby waves in a high-latitude shear flow on a modified ß-plane, where also the effect of the sphericity of the earth (c5-effect) is taken into account. We present a particular analytical solution and also asymptotic and numerical solutions. We find that the asymptotic WKB solutions are accurate compared to the numerical results. We show that the o-effect is most important for shorter waves and leads to an enhanced selection of trapped Rossby wave modes.Wir betrachten die Amplituden von küstennah gefangenen Rossby-Wellen in einer Scherströmung hoher Breiten. Die Rechnungen werden auf einer modifizierten ß-Ebene durchgeführt, die auch die Spherizität der Erde berücksichtigt (o-Effekt). Wir zeigen eine spezielle analytische Lösung und auch asymptotische und numerische Lösungen. Die asymptotischen WKB-Lösungen erweisen sich als genau, verglichen mit den numerischen Resultaten. Der o-Effekt wirkt sich a stärksten bei den sehr langen und den kurzen Wellen aus und führt zu einer stärkeren Selektion von Moden gefangener Rossby-Wellen.
26
Hughes, Christopher William. « The effect of topography on ocean flow ». Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:37b3f6b2-ce5f-45b3-b2ed-3325518b06bb.
Texte intégralRésumé :
The rôle which topography plays in constraining ocean flow is investigated in several ways, mostly aimed at application to the Southern Ocean where topography is known to be important. The physics of topographic Rossby waves is discussed in some depth and a description of ocean flow in terms of a sum of topographic normal modes is developed. It is shown that the apparent incompleteness of topographic modes can often be circumvented by including a function which absorbs the nett input of potential vorticity. Some subtle problems with this description are dealt with, and a calculation of topographic modes for the Southern Ocean is presented, which shows that the modes are very localised, making the use of them to describe basin-wide flows difficult. The effect of interactions between stratification and topography is investigated in terms of a quasi-two-dimensional model which deals only with the depth-integrated flow, and the assumptions which go into the model are examined in detail both analytically and by calculating terms of interest from a data set produced by the Fine Resolution Antarctic Model. It is shown that advection of density in the Southern Ocean can be described to a first approximation as being due to a barotropic current with no vertical velocity, the horizontal component of the baroclinic flow producing very little effect. The balance of terms reveals interesting features in the modelled flow in the Southern Ocean, showing the value of this type of analysis. Finally, insight developed in the course of the investigation allows a simple model to be constructed representing the feedback between density advection and forcing due to density gradients. This model is used to provide an explanation for the fact that the FRAM model spins up linearly, where most simple models would predict a component of quadratic behaviour in the spin-up.
27
Harlander, Uwe. « Some simple solutions of trapped Rossby waves in zonal barotropic multiple-jet flows ». Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 17 = Meteorologische Arbeiten aus Leipzig ; 5 (2000), S. 44-60, 2000. https://ul.qucosa.de/id/qucosa%3A15148.
Texte intégralRésumé :
This study concerns on trapped Rossby waves and local Rossby wave packets in zonal basic flows with two or more prominent extreme values (so called multiple-jet flows). For simplicity, most of the calculations are performed on the f-plane, but an extension to the ß-plane is also discussed. Under the assumption that the basic fiow is a solution to a special type of second order ordinary differential equation, we show that then the amplitudes of stationary trapped Rossby waves are solutions to an equation of the same type. We investigate the occurrence of trapped modal waves as well as the rays of wave action radiation in a particular multiple-jet flow. Further we consider the development of the local wavenumbers of Rossby wave packets in such a flow, with and without a zonally oriented reflective boundary. lt is found that wave action can propagate in the zonal direction only when the boundary is present. Otherwise the rays of wave action radiation form a closed curve.Diese Studie beschäftigt sich mit gefangenen Rossby Wellen und lokalen gefangenen Rossbywellenpaketen in einer zonalen Strömung mit zwei oder mehreren ausgeprägten Extrema (sog. Strömungen mit mehrfachen Jets). Der Einfachheit halber werden die meisten Berechnungen auf der f-Ebene angestellt, eine Erweiterung auf die ß-Ebene wird allerdings auch diskutiert. Wenn man annimmt, dass der Grundstrom die Lösung einer bestimmten gewöhnlichen Differentialgleichung zweiter Ordnung ist, kann man zeigen, dass die Amplituden gefangener Wellen Lösungen des gleichen Gleichungstypes sind. Wir betrachten die Bedingungen für das Auftreten gefangener modaler Wellen, als auch die Pfade der Wellenenergie-Abstrahlung in einer bestimmten Mehrfach-Jet-Strömung. Ferner untersuchen wir die Entwicklung der lokalen Wellenzahlen von Wellenpaketen in einer solchen Strömung, mit und ohne eines zonal orientierten reflektierenden Randes. Wir finden, dass sich Wellenenergie auf der f-Ebene nur dann in zonaler Richtung ausbreiten kann, falls eine solcher Rand vorhanden ist. Anderenfalls ergeben die Strahlen der Wellenenergie Ausbreitung eine geschlossene Kurve.
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Ishihara, Takashi, et Yukio Kaneda. « Frequency shifts of Rossby waves in the inertial subranges of β-plane turbulence ». American Institute of Physics, 2001. http://hdl.handle.net/2237/7082.
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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.
Texte intégral
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Watanabe, Wandrey de Bortoli. « Propagação de ondas de Rossby em dois modelos quase-geostróficos ». Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-05092016-162955/.
Texte intégralRésumé :
As ondas de Rossby são o mecanismo de ajuste às perturbações de grande escala dos fluidos geofísicos. Elas podem ser geradas localmente, forçadas pelo rotacional da tensão de cisalhamento do vento, ou remotamente, devido às perturbações na altura da picnoclina na borda leste. Medidas altimétricas da anomalia da altura do mar tem fornecido evidências robustas da existência destas ondas. Estudos recentes mostram que vórtices não lineares de mesoescala são responsáveis por uma grande parte da variabilidade dos registros altimétricos, tendo sido observados propagando juntamente com as ondas de Rossby. Os objetivos deste estudo são identificar (1) as regiões onde as ondas de Rossby longas lineares explicam as observações, (2) qual mecanismo de geração é dominante e (3) se as ondas propagam-se de forma contínua em condições de não linearidade. Um modelo linear de 1½ camada de ondas de Rossby forçado por dados de tensão de cisalhamento do vento de escaterômetros é utilizado para reproduzir as anomalia da altura do mar. As correlações entre os resultados do modelo linear e os dados altimétricos são de até 0,88. Os resultados sugerem que a dinâmica linear de ondas de Rossby longas explica uma parte significativa da variabilidade anual da anomalia da altura do mar nas regiões tropicais. A oscilação da picnoclina na borda leste é o principal mecanismo gerador de ondas de Rossby nos oceanos Atlântico e Índico, enquanto no Pacífico a fonte dominante das ondas é a forçante atmosférica local. Um modelo quase-geostrófico não linear é utilizado para analisar como as ondas de Rossby geradas na borda leste propagam-se e dissipam-se em condições idealizadas. Em latitudes mais baixas que 32°S, as ondas atravessam toda a bacia oceânica até adentrar a região de meandramento da corrente de borda oeste. Nesta região, a energia é espalhada em todas as bandas de frequência. As ondas de Rossby que estão na latitude crítica tem um papel intermediário na cascata de energia. Em latitudes mais altas que 32°S, as ondas de Rossby não cruzam a totalidade da bacia oceânica, tendo sua energia transferida para outros períodos em uma distância de pelo menos 1000 km da borda oeste.Rossby waves are the large scale mechanism of adjustment to perturbations of geophysical fluids. They can be generated locally, due to forcing by wind stress curl, or remotely, due to perturbations in the pycnocline level at the eastern boundary. Altimetric measurements of sea level anomaly have been providing sturdy evidences of the existence of these waves. Recent studies argue that mesoscale eddies are responsible for a substantial amount of the variability of the altimeter records. Eddies have been shown to propagate along with Rossby waves. The purposes of this study are (1) to identify the regions where linear long Rossby waves explain the observations, (2) to determine which generation mechanism is dominant, and (3) to verify if these waves can continuously propagate in nonlinearity conditions. A linear 1½ layer model forced by scatterometer wind stress data has been used to reproduce the sea level anomaly. Correlations between the results of the linear model and the altimetric data are up to 0.88. Results suggest that the linear long Rossby wave dynamics explain a significant part of the sea level anomaly annual variability in the tropical oceans. The pycnocline fluctuations at the eastern boundary are the main mechanism of generation of Rossby waves in the Atlantic and Indian oceans. The local atmospheric forcing is the principal source of the waves in the Pacific Ocean. A quasi-geostrophic nonlinear model has been used to analyze how the Rossby waves generated at the eastern boundary propagate and dissipate in idealized conditions. In latitudes lower than 32°S, the waves cross all the ocean basin until entering the region where the western boundary current meanders. In this region, energy is scattered throughout the spectrum. The Rossby waves that are in their critical latitude have an intermediate role in the energy cascade. In latitudes higher than 32°S, the Rossby waves fail to completely cross the ocean basin. Their energy is transfered to other periods in a distance of at least 1000 km from the western boundary.
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Richet, Oceane Tess. « Impact of ocean waves on deep waters mixing and large-scale circulation ». Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX104/document.
Texte intégralRésumé :
Les différents projets présentés dans cette thèse contribuent à la compréhension de plusieurs aspects clés de la circulation océanique. Le premier aspect que nous étudions porte sur les processus physiques à l'origine du mélange lié à la marée; deux processus ont été mis en évidence. Depuis la latitude critique vers l'équateur, la marée interne transfert son énergie à des ondes plus petite échelle via des instabilités triadiques résonnantes impliquant les ondes proche inertielles. Depuis la latitude critique vers le pôle, les ondes de marée interne continuent de transférer leur énergie à des ondes plus petite échelle, mais étonnamment ce transfert se fait entre la marée interne et des ondes évanescentes.Dans la deuxième étude, nous étudions l'effet d'un courant moyen sur la propagation et la dissipation des ondes de marée interne, générées à la topographie dans des simulations haute résolution. Dans ce cas, la dépendance en latitude de la dissipation de la marée interne est plus lisse et plus proche d'une constante. Ce changement de la dépendance en latitude peut être lié au décalage des fréquences des ondes de marée interne par effet Doppler, ce qui induit la génération d'ondes secondaires plus petite échelle.Dans la troisième étude, nous étudions l'effet d'une perturbation générée en amont sur la circulation dans le bassin amont dû à l'interaction entre la perturbation et un seuil hydrauliquement contrôlé. Les ondes de Kelvin et topographiques de Rossby, générées par une variation de l'afflux d'eau dans le bassin amont, perturbent l'écoulement au dessus du seuil et ainsi l'export d'eau. Cette perturbation est due à la réfraction des ondes sur le seuil à chaque passage, une fois qu'elles ont fait le tour du bassin amontThe various projects presented in this thesis contribute to our understanding of various key aspects of the oceanic circulation. The first aspect that we investigate is the physical processes responsible for this tidal mixing, and we identify two processes. Equatorward of the critical latitude, internal tides transfer their energy to smaller-scale waves via triadic resonant instabilities involving near-inertial waves. Poleward of the critical latitude, internal tides still transfer energy to smaller-scale waves, but surprisingly this transfer takes place between the internal tide and evanescent waves.In the second study, we investigate the effect of a mean current on the propagation and the dissipation of internal tides generated at the topography in high-resolution simulations. In that case, the latitudinal dependence of the tidal energy dissipation is found to be smoother and closer to a constant. This change in the latitudinal dependence can be linked to the Doppler shift of the frequency of the internal tides, which impacts the generation of smaller-scale secondary waves.In the third study, we study the effect of an upstream disturbance on the upstream circulation by interaction with a hydraulically controlled sill. The Kelvin and topographic Rossby waves, generated by a change in the upstream inflow, perturb the flow through the channel and hence the water export. This perturbation is due to the refraction of the waves at the sill at each passage, once they go around the upstream basin
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Corry, R. A. « Modelling the seasonal variation of the Florida current ». Thesis, University of Oxford, 1985. http://ora.ox.ac.uk/objects/uuid:644edc47-15b5-491f-a2a3-a2c25c864791.
Texte intégralRésumé :
The linear response of a two layer ocean model to a periodic wind stress curl in the presence of bottom topography has been investigated. For periods much less than the time taken for the wind generated baroclinic Rossby waves to pass over the topography (i.e. 'short' periods), the ocean response is primarily that for a homogeneous ocean and thus strongly modified by topography. For periods much longer than this time (i.e. 'long' periods), the Rossby waves compensate for the effect of topography and the non-topographic Sverdrup balance holds. For the Atlantic at 25°N, the long period limit is of the order of years to decades, so at annual period the non-topographic Sverdrup balance is not applicable. Variations in transport can be forced by a wind stress over varying topography, and by the passage of a coastal baroclinic Kelvin wave over varying topography. The relative importance of the above dynamical considerations for the Florida Current can only be determined from a model calculation involving realistic winds, topography and geography. Such a model calculation has been done with observed Bunker wind stress over a two layer ocean. The predicted variation has a Summer maximum and a Fall minimum, in agreement with the measurements of Niiler and Richardson [1973] and more recent STACS data. The one layer model has been forced by monthly means of ATOLL wind stress for the years 1981-1984. The predicted variation was found not to be in agreement with concurrent STACS measurements. A comparison was made between the Bunker winds and the ATOLL winds via various diagnostics. It was found that the meridional component of the wind, which is crucial to the overall Bunker Summer maximum, is of much reduced importance for the ATOLL winds. This could account for the lack of predicted Summer maxima.
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Delk, Tracey Lee. « Intraseasonal, large-scale circulations and tropical cyclcone activity over the Western North Pacific during Boreal summer ». Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1168.
Texte intégralRésumé :
Approved for public release; distribution is unlimited.Large-scale circulations in the 15-25 day period over the western North Pacific during northern summer were determined using the leading modes of a Singular Value Decomposition of 850 hPa winds and outgoing longwave radiation. Composites were constructed to define the wave patterns' structural characteristics. Their evolution is characterized by alternating cyclonic and anticyclonic equatorial anomalies that are linked to anomalous convective activity. Mid-latitude perturbations appear to contribute to the growth of new equatorial disturbances. Variability within the cycle is examined relative to variations in the basic state vertical wind shear and zonal wind convergence or divergence in the region equator-10ðN, 140ðE-160ðE. For the 50 cases in a basic state with easterly vertical wind shear and convergence, westward-moving waves propagate farther northwestward, wavelength contraction is greater, their orientation changes from east-west to southwest-northeast, and waves appear to be coupled with a Southern Hemisphere mid-latitude wave train. For the zonal wind divergence set, wave activity occurs farther eastward, circulations maintain a longer wavelength and more zonal orientation, and linkage with the Southern Hemisphere mid-latitudes is minimal. A statistically-significant relationship exists between the 15-25 day wave phase and tropical cyclone activity. Formation frequency and preferred locations are modulated by the 15-25 day wave.
Lieutenant, United States Navy
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Khanyile, Bhekumuzi Sfundo. « An investigation of the atmospheric wave dynamics in the polar region using ground based instruments ». Thesis, University of Fort Hare, 2011. http://hdl.handle.net/10353/447.
Texte intégralRésumé :
Abstract This study presents the characteristics of small-scale gravity waves in the mesosphere region as derived from the imaging riometer data at high altitude (~90 km) over SANAE (72˚S, 3˚W). Wavelet analysis and FFT (Fast Fourier transform) have been applied to extract short period gravity wave parameters for the year 2000. The horizontal wavelength, phase speed and observed period of gravity waves are typically 10-100 km, 5-60 m.s-1 and 3-60 minutes, respectively. The horizontal propagation direction is north-eastward throughout the year. This could probably be due to selective filtering by the zonal wind. Zonal and meridional winds in the region of the MLT (mesosphere and lower thermosphere) have been measured using HF radars at high latitudes in the southern hemisphere. Data from January 2000 to December 2003 have been used with the aim of investigating the characteristics of planetary wave activity at ~90 km. For SANAE and Halley stations, 2-, 5-, 10-, 16- and 20-day planetary waves are dominant in summer and winter. The results show the seasonal variations of the mean winds, which are caused by the internal variability of the quasi stationary planetary waves. Planetary wave coupling processes between UKMO assimilated and mesospheric data have also been investigated. The cross wavelet results show a strong coupling during winter months. The results suggest that planetary waves are generated at lower atmospheric heights and propagate upwards into mesospheric heights. However, not all observed disturbances in mesospheric heights can be explained by the propagation of planetary waves from lower atmospheric heights.
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Krieger, Sebastian. « Estudo da variabilidade na distribuição espectral das ondas de Rossby baroclínicas no Altântico e em particular na região do arquipélago de Abrolhos ». Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-30062009-151822/.
Texte intégralRésumé :
Um conjunto de 15 anos de dados de anomalia da altura da superfície do mar (h) dos altímetros TOPEX/Poseidon e Jason-1 interpolado por um método de médias ponderadas pelos coeficientes de autocorrelação é utilizado para verificar as variações espectrais de ondas de Rossby do primeiro modo baroclínico no Oceano Atlântico. O método de interpolação é inovador e foi desenvolvido especificamente para esta finalidade. Médias, tendência e climatologias mensais são calculadas para todo o globo. As tendências globais mostram regiões com tendência de aumento do nível do mar que podem superar a marca de 10mmano1 e algumas regiões com tendência de rebaixamento de mesma ordem de grandeza. Uma metodologia de análise com base em ondaletas bidimensionais foi desenvolvida inteiramente no curso deste trabalho e é aplicada de forma inédita aos dados altimétricos. Através do filtro de ondaletas bidimensional, diagramas zonais temporais de h são decompostos para obter-se a variação do ciclo sazonal e o sinal propagante associado a estas ondas em determinadas latitudes. A metodologia é inicialmente aplicada no Oceano Pacífico a 28,5±N para validar os resultados com a literatura disponível e em seguida ao Oceano Atlântico e detalhada nas latitudes 32,5±N e 17,5±S. As velocidades de fase calculadas para o Atlântico variam de 20kmdia1 em latitudes de 10± e 2kmdia1 em latitudes de 38±. A variação espectral de ondas de Rossby é analisada em três localidades: 28,5±N 134,3±E, 32,5±N 73,5±W e 17,5±S 35,2±E. Em todos os casos é observada variação espectral no tempo, nas bandas anual, semestral e trimestral tanto de intensidade quanto de persistência. Além disso, através da análise da distribuição zonal-temporal da potência espectral em várias bandas, nota-se variabilidade espacial no espectro das ondas de Rossby.Fifteen years of sea surface height anomaly (SSHA) from merged TOPEX/Poseidon and Jason-1 datasets gridded using an autocorrelation-based interpolation method are used to test the spectral variability of first mode baroclinic Rossby waves in the Atlantic Ocean. The gridding method is innovative and was specifically developed for this purpose. Mean SSHA, trends and monthly climatologies were determined globally. The global SSHA trends show regions of rising sea level of more than 10mmyr1 and some regions of sinking the same order of magnitude. A two-dimentional wavelet analisys-based methodology was entirely developed for the purpose of this study and is unprecedently applied to the altimetry data. SSHA longitude-time diagrams are filtered through the twodimentional wavelet filter and decomposed to obtain at certain latitudes the variation of the seasonal cycle and of the propagating signal linked to these waves. The methodology is first applied to the Pacific Ocean at 28,5±N to validate the results with the available literature and then applied to the Atlantic Ocean with detail at the latitudes 32,5±N and 17,5±S. The calculated phase velocities for the Atlantic range from 20kmday1 at 10± latitude to 2kmday1 at 38± latitude. The spectral variability of Rossby waves is analysed at three locations: 28,5±N 134,3±E, 32,5±N 73,5±W and 17,5±S 35,2±E. In all cases spectral change is observed in time, at the annual, semi-annual and quarterly spectral bands both in intensity and in persistence. Furthermore, through the longitude-time spectral power distribution analysis in various spectral bands, there is spatial variability in the Rossby wave spectrum.
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Wilford, Graeme W. « The numerical solution of atmospheric models describing the interactions of inertio-gravity and Rossby waves ». Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/843580/.
Texte intégralRésumé :
This thesis documents three years of work involved in the numerical solution of atmospheric wave models. Derivation of these models is established whilst introducing the basic physical laws governing fluid motion. Numerical techniques axe investigated with particular reference to the solution of parabolic and elliptic partial differential equations. Parallel computer systems are discussed and basic concepts introduced with the emphasis placed on distributed virtual parallelism. The role of inertio-gravity waves under the influence of cyclonic Rossby waves is investigated with respect to the production of atmospheric turbulence. Results from evolving numerical systems bound by various conditions are presented. It is discovered that the wave interaction is not the sole cause of atmospheric blocking as was previously thought. The use of a loosely coupled parallel environment is discussed in relation to potential increases in speed or size of the numerical model. A solution technique is modified to enable such an implementation. The full nonlinear Barre de Saint-Venant model of fluid motion is solved using a combination of finite difference and spectral methods. Preliminary results are presented and further avenues of investigation are discussed.
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Nakamura, Mototaka. « Characteristics of potential vorticity mixing by breaking Rossby waves in the vicinity of a jet ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11730.
Texte intégralRésumé :
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.Includes bibliographical references (p. 248-253).
by Mototaka Nakamura.
Sc.D.
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Atherton, Juli. « Linear and nonlinear Rossby waves in basins both with and without a thin meridional barrier ». Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/53129.
Texte intégralRésumé :
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 (leaf 119).
The linear and nonlinear Rossby wave solutions are examined in homogeneous square basins on the [beta]-plane both with and without a thin meridional barrier. In the presence of the meridional barrier the basin is almost partitioned into two; only two small gaps of equal width, d, to the north and south of the barrier allow communication between the eastern and western sub-basins. Solutions are forced by a steady periodic wind forcing applied over a meridional strip near the eastern side. Bottom friction is present to allow the solutions to reach equilibrium. The linear solution for the basin containing the barrier is determined analytically and the nonlinear solutions for both basins are found numerically. In the linear solution with the barrier present, particular attention was paid to the resonant solutions. We examined the effects of varying the symmetry of the forcing about the mid-latitude, the frequency of the periodic forcing and the strength of the bottom friction. For each solution we focus on how the no net circulation condition, which is central to any solution in a barrier basin, is satisfied. The nonlinear solutions were studied for both basin configurations. In each case the transition from the weakly nonlinear solution to the turbulent solution was examined, as the forcing frequency and forcing strength were varied. Only integer multiples of the forcing frequency are present in the weakly nonlinear solutions. The turbulent solutions were accompanied by the appearance of many other frequencies whose exact origins are unknown, but are probably the result of instabilities. A hysteresis was found for the turbulent solutions of both the barrier-free and barrier basins. In the weakly nonlinear solutions of the barrier basin it was predicted and confirmed that there is never a steady net flow from sub-basin to sub-basin. It was also shown that with a symmetric forcing all modes oscillating with an odd multiple of the forcing frequency are symmetric and all modes oscillating with even multiples of the forcing frequency are antisymmetric.
by Juli Atherton.
S.M.
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Wiegand, Lars. « Equatorwards-breaking Rossby waves in the North Atlantic storm track : forecast quality, predictability and dynamics ». Thesis, University of Leeds, 2011. http://etheses.whiterose.ac.uk/3359/.
Texte intégralRésumé :
Upper-level disturbances (ULDs) penetrating from the extratropics into low lati- tudes are a frequent feature of the synoptic-scale circulation over the North Atlantic and can be involved in significant weather events such as heavy precipitation over the western and northern parts of Africa, or Saharan dust outbreaks. The present project is the first to systematically explore the huge dynamical information content of long-term data from the European Centre for Medium-Range Weather Forecasts operational ensemble prediction system (EPS) and from the recently established THORPEX Interactive Grand Global Ensemble (TIGGE) for that particular at- mospheric feature. It investigates the dynamics, forecast quality and predictability of this atmospheric phenomenon exploring a wide range of verification and analysis tools based on potential vorticity (PV). The main conclusions from this work are: (i) The EPSs shows a generally underdispersive behaviour in the ULD region. (ii) Forecast errors are reduced by about 50% if each TIGGE centre's own analysis is used instead of the ECMWF analysis, particularly in regions of large PV gradients. (iii) There is a tendency of too weak Rossby wave breaking and therefore a north- ward shift of the PV streamers in the forecasts. (iv) Ensemble-mean multi-model forecasts of a four-day accumulated precipitation event appear accurate enough for a successful severe-weather warning in contrast to some single-model EPSs. (v) Diabatic processes upstream early in the forecasts appear to be more impor- tant than blocking downstream for strengthening the PV streamers in the medium range. The results and the analysis tools developed in this project have improved the understanding of such ULDs and their impacts and has advanced the verifica- tion of EPSs, which can both contribute to an improvement of numerical weather forecasting in the long term.
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Phillips, A. « Dynamics of the Antarctic mesosphere and lower thermosphere / ». Title page, contents and abstract only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09php5583.pdf.
Texte intégralRésumé :
Thesis (Ph. D.)--University of Adelaide, Mawson Institute for Antarctic Research, 1990.Copies of author's previously published articles inserted. Includes bibliographical references (leaves 219-226).
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Yamashita, Márcio Katsumi. « Análise da influência vertical de ondas de Rossby longas no Atlântico Sul ». Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-11122012-160207/.
Texte intégralRésumé :
Ondas de Rossby longas são ondas de larga escala que se propagam para o oeste com escala espacial de algumas centenas a vários milhares de quilômetros e desempenham um papel crítico na regulação da circulação do oceano. Sua propagação promove deslocamentos verticais da termoclina, muitas vezes da ordem de dezenas de metros, e causa variações de altura da superfície do mar que podem ser observadas através de dados de satélites altimétricos. A hipótese deste estudo é que existe uma fração significativa da variabilidade da velocidade geostrófica na superfície, associada a sinais propagantes para oeste. Para testá-la avaliamos a variabilidade da velocidade geostrófica meridional na superfície induzida pela passagem dessas ondas. Filtros digitais são necessários para distinguir sinais propagantes dos não-propagantes e permitiu a seleção da componente propagante para oeste com período aproximado de 12 meses. Velocidade de fase cp, período P, comprimento de onda λ, amplitude quadrática média A e o percentual de variância explicada σ2 desta componente foram estimados nos locais onde identificamos ondas de Rossby longas do primeiro modo baroclínico. Selecionamos perfis Argo posicionados em diferentes fases da mesma onda para averiguar a influência da sua propagação nos campos de temperatura, salinidade e densidade. Os resultados revelaram que a onda de Rossby anual de 237 mm de altura pode alterar o campo de densidade com valores de até 0,3 kg m-3 numa faixa de 240 m ao nível picnoclina. A variância explicada da componente meridional da velocidade geostrófica propagante para oeste em relação ao sinal original revelou que de 40% a 71% do sinal se propaga para oeste, corroborando a hipótese.Long Rossby waves are large-scale waves which propagate westward with spatial scale ranging from a few hundred to several thousand kilometers. These waves play a critical role in the adjustment of ocean circulation. Their propagation cause vertical displacements of the thermocline, often of tens meters, and cause variations of sea surface height that can be observed on satellite altimeters data. The hypothesis of this study is that there is a significant fraction of surface geostrophic velocity variability associated with westward propagating signals. To test it, we assessed the variability of the meridional geostrophic velocity at the surface induced by the passage of these waves. Digital filters are necessary to distinguish the propagating from non-propagating signals and allowed for the selection of the westward propagating component with an approximate period of about 12 months. Phase speed cp, period P, wavelength λ, mean square amplitude A and percentage of explained variance σ2 of this component were estimated where long Rossby waves from the first baroclinic mode were identified. We selected Argo profiles data positioned at different phases of the same wave to verify the influence of its propagation on temperature, salinity and density fields. The results showed that the annual Rossby wave of 237 mm height can change the density field with values up to 0.3 kg m-3 about 240 m at pycnoclin level. The explained variance of the westward meridional component of geostrophic velocity relative to the original signal revealed that 40% to 71% of the signal propagates westward, supporting the hypothesis.
42
Cardona, Orozco Yuley Mildrey. « Enhanced vertical mixing within mesoscale eddies due to high frequency winds in the south China sea ». Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44917.
Texte intégralRésumé :
The South China Sea is a marginal basin with a complex circulation influenced by the East Asian Monsoon, river discharge and intricate bathymetry. As a result, both the mesoscale eddy field and the near-inertial energy distribution display large spatial variability and they strongly influence the oceanic transport and mixing.
With an ensemble of numerical integrations using a regional ocean model, this work investigates how the temporal resolution of the atmospheric forcing fields modifies the horizontal and vertical velocity patterns and impacts the transport properties in the basin. The response of the mesoscale circulation in the South China Sea is investigated under three different forcing conditions: monthly, daily and six-hourly momentum and heat fluxes. While the horizontal circulation does not display significant differences, the representation of the vertical velocity field displays high sensitivity to the frequency of the wind forcing. If the wind field contains energy at the inertial frequency or higher (daily and six-hourly cases), then Vortex Rossby waves and near inertial waves are excited as ageostrophic expression of the vigorous eddy field. Those waves dominate the vertical velocity field in the mixed layer (vortex Rossby waves) and below the first hundred meters (near inertial waves) and they are responsible for the differences in the vertical transport properties under the various forcing fields as quantified by frequency spectra, vertical velocity profiles and vertical dispersion of Lagrangian tracers.
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Montezuma, Patrick Degret de. « Caracterização do acoplamento físico-biológico causado por ondas de Rossby baroclínicas ». Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-24092009-162736/.
Texte intégralRésumé :
Ondas de Rossby do primeiro modo baroclínico em médias latitudes foram observadas em dados de anomalia da altura da superfície do mar dos radares altimétrico TOPEX/Jason-1 na última década. Entretanto, sinais similares são observados em dados de concentração de clorofila a obtidos através de dados na faixa espectral visível através do sensor SeaWiFs. Anomalias na concentração de clorofila que se propagam para oeste com períodos e comprimentos de onda característicos de ondas de Rossby, indicam que estas ondas induzem parte da variabilidade da produtividade primária em oceano aberto. O foco deste trabalho é o mecanismo de acoplamento físico-biológico causado pela passagem de ondas de Rossby e evidenciado pelos padrões regulares de aumento e diminuição de algas clorofiladas. Levamos em conta dois mecanismos principais: advecção vertical de nutrientes e/ou clorofila a e advecção horizontal de gradientes meridionais de clorofila a. No presente trabalho, nós investigamos esta influência através da correlação entre a anomalia da altura da superfície do mar (AASM) e do logaritmo da concentração de clorofila a (CChl). Foram estimados também a amplitude e a relação de fase entre ambos conjuntos de dados. Para tal, os dois conjuntos de dados foram interpolados numa grade regular de 1° X 1° X 9.9156 dias e selecionados com base numa máscara de continentes que exclui a presença de regiões com menos de 1000 metros de profundidade, ilhas e mares zonalmente fechados para permitir o uso de filtros digitais. Os mapas globais de ambas variáveis foram reorganizados em diagramas zonais-temporais (ou de Hovmöller) para cada grau de latitude. A cada um destes diagramas foi aplicada uma série de filtros bidimensionais de resposta impulsiva finita (FIR-2D). Estes decompõem o sinal de cada variável em bandas espectrais associadas a ondas de Rossby de período aproximado de 24, 12 e 6 meses. A estimativa da velocidade de fase (cp) é baseada no método da transformada Radon; a do período (T) e do comprimento de onda (L) é baseada no ajuste de mínimos quadrados de uma função senoidal. Correlação, fase e amplitude foram obtidas ao longo da extensão zonal das três principais bacias oceânicas (Atlântico, Índico e Pacífico) para cada grau de latitude. As latitudes selecionadas para análise apresentam diferenças nas estimativas de cp24, cp12 e cp6 baseadas na AASM e CChl estatísticamente similares com um intervalo de confiança de 95%. Foram escolhidas latitudes entre os giros subpolar e subtropical e na região central do giro subtropical em ambos hemisférios. Os resultados indicam que nas regiões entre giros oceânicos o processo de advecção horizontal de gradientes meridionais de clorofila predomina em relação ao de advecção vertical de nutrientes e/ou clorofila. Nas regiões centrais dos giros subtropicais a advecção vertical é mais propensa a acontecer em detrimento da advecção horizontal. Os resultados aqui apresentados indicam que as ondas de Rossby do primeiro modo baroclínico tem influência sobre a biomassa fitoplanctônica. Esta influência se dá por advecção horizontal ou vertical, dependendo da região oceânica.Rossby waves of first baroclinic mode in midlatitudes were observed in sea surface height anomaly data from the TOPEX/Jason-1 radar altimeter in the past decade. Nevertheless, similar signals are observed in clorophyll a concentration estimates based on the visible part of the spectrum collected by the SeaWiFS satellite sensor. Westward propagating anomalies with periods and wavelengths characteristic of first mode baroclinic Rossby waves are evident in satellite--borne chlorophyll a concentration data and suggest that these waves are partially responsible for the primary productivity variability in open ocean. The focus of this study is the physical-biological coupling caused by the passage of Rossby waves, evident in the regular patterns of increase and decrease of chlorophyll--rich algae. We took into account two main mechanisms: vertical advection of nutrients and/or chlorophyll a and horizontal advection of the background gradient of meridional chlorophyll concentration. In this work, these mechanisms were investigated through the correlation between sea surface height anomaly (AASM) and the logarithm of the chlorophyll a concentration (CChl). The amplitude and phase relation between data sets were estimated. To this end, both data sets were gridded to a 1° X 1° X 9.9156 days mesh. A continental maks that excludes areas less than 1000 meters deep, islands, and zonally enclosed seas was applied to allow the use of digital filters. The global maps of both variables were rearranged into zonal-temporal (or Hovmöller) diagrams for each degree of latitude. To each one of these diagrams a series of bidimensional finite impulsive response filters (FIR-2D) was applied. These decompose the signal of each variable in spectral bands associated with Rossby waves with periods of approximately 24, 12 and 6 months. Phase speeds (cp) were estimated based on the Radon transform method; periods (T) and wavelengths (L) were obtained by least squares fit of a sinusoidal function. Correlation, phase and amplitude were obtained along the zonal extension of the three basins (Atlantic, Indian and Pacific) at each degree of latitude. The analyzed latitudes present cp24, cp12 and cp6 estimates based on AASM and CChl that are within the 95% confidence interval of each other. Latitudes between the subtropical and subpolar gyres and in the central region of the subtropical gyre were chosen for further analysis in both hemispheres. Results indicate that the horizontal advection of background meridional gradient of chlorophyll concentration prevails in relation to vertical advection of nutrients and/or chlorophyll a in regions between oceanic gyres. In the central regions of the subtropical gyres the vertical advection prevails over the horizontal advection. The results presented in this study indicate that the first mode baroclinic Rossby waves have influence over the phytoplanktonic biomass. This influence operates through horizontal or vertical advection, depending on the oceanic region.
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Reason, Christopher James Charles. « Generation of annual period Rossby waves in the South Atlantic Ocean by the wind stress curl ». Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26030.
Texte intégralRésumé :
A theoretical study is presented of generation of first mode annual period baroclinic Rossby waves by the observed wind stress curl in the South Atlantic and South West Indian Oceans. The forcing wind field for the area 15 S to 51 S, 45 W to 41 E was obtained from an harmonic analysis at the annual period of the monthly mean wind stress curl values derived from Hellerman and Rosenstein's 1983 data.
The annual harmonic of the wind stress curl was then used to drive a linear, reduced gravity model of the South Atlantic and South West Indian Oceans bounded by the latitudes 15 S and 51 S and by longitudes 46 W and 50 E. Boundary geometries and oceans are represented to 1.0 and 0.2 degree accuracy, respectively, by a finite difference grid in spherical polar co-ordinates. Successive over-relaxation and a leap frog time differencing scheme are used to solve the two dimensional Rossby wave equation which includes relative vorticity and a Rossby radius that varies with latitude. By assuming quasi-geostrophy, the steady state model response is restricted to first mode baroclinic Rossby waves.
In the model South Atlantic Ocean, the response consists of long Rossby waves which generally propagate south westwards across the ocean and which exhibit refraction of wave energy towards the equator as in the theory of Schopf et al (1981). Short Rossby waves with eastward energy propagation are generated in the small area of the Indian Ocean included in the model domain. However, since the model grid has a resolution of approximately 22 km these waves may not be sufficiently accurately represented in the study. Medium to long waves generated to the south east of Africa may reflect their energy off this landmass into the Indian Ocean.
Slowness curve theory and wavenumber computations along wave rays in the South Atlantic are applied to match the model wave trains with probable sources. It is found that wind stress curl maxima off the Namibian coast near 25 S,10 E, near the Agulhas Plateau at 38 S,25 E and in the South Atlantic Ocean interior near 38 S,10 W are the most efficient wave generators. The results of the study are generally consistent with earlier theoretical studies of the North Pacific by White and Saur (1981) and by Cummins et al (1986) and of the North Atlantic by Krauss and Wuebber (1982).Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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McCrystall, Michelle Roisin. « The impact of tropical sea surface temperature perturbations on atmospheric circulation over north Canada and Greenland ». Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/276908.
Texte intégralRésumé :
Identifying the drivers of Arctic climate variability is essential for understanding the recent rapid changes in local climate and determining the mechanisms that cause them. Remote tropical sea surface temperatures (SST) have been identified in previous studies as having contributed to the recent positive trends in surface temperature and geopotential height at 200 hPa over north Canada and Greenland (1979-2012) through poleward propagating Rossby waves. However, the source and direction of wave propagation on to north Canada and Greenland (NCG) differs across climate datasets indicating that there are still uncertainties surrounding the mechanisms for how the tropics influence the NCG climate. This thesis aims to further investigate the robustness of the trends over NCG and understand how circulation in this region responds to imposed tropical SST perturbations. The eddy 200 hPa geopotential height (Z200) trends over NCG are assessed in a number of different datasets and compared to the response of eddy Z200 over NCG to imposed tropical SST perturbations in a number of sensitivity studies using the HadGEM3 atmosphere-only model. These model experiments are forced with observed differences in SSTs from the beginning and end of the satellite record (1979-1988 and 2003-2012), with spatial perturbations for [i] the entire tropics, [ii] global SSTs, [iii] the tropical Pacific only, [iv] the tropical Atlantic SST only, [v] the tropical Indian Ocean only. The positive spatial trends of eddy Z200 over NCG from ERA-Interim reanalysis is largely captured in ensemble means of two available climate datasets, UPSCALE and AMIP, indicating that this is a robust climate pattern, however, these trends appear to be stronger in the latter part of the record specifically over the UPSCALE period (1985 to 2011). The model sensitivity studies show that a negative eddy Z200 anomaly over NCG was found in response to all imposed tropical SST perturbations (2003-2012) relative to a background state (1979-1988). This was due a stationary trough over the region that was able to intensify in response to a lack of a strong anomalous wave forcing from changes in mid-tropospheric temperature and zonal winds. The forcing from the tropical Atlantic, relative to the other tropical ocean basins, resulted in the largest eddy Z200 response over NCG, indicating its dominance in forcing the large scale tropical signal. The influence of extratropical SST perturbations relative to tropical SST perturbations were also investigated and it was demonstrated that this negative anomaly is largely driven by the change in tropical sea surface temperatures.
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Osychny, Vladimir. « Analysis of the Gulf Stream path and Rossby waves in the North Atlantic based on satellite data / ». View online ; access limited to URI, 2006. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3248239.
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Norton, Andrew David. « Analysis of Ionospheric Data Sets to Identify Periodic Signatures Matching Atmospheric Planetary Waves ». Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/101791.
Texte intégralRésumé :
Atmospheric planetary waves play a role in introducing variability to the low-latitude ionosphere. To better understand this coupling, this study investigates times when oscillations seen in both atmospheric planetary waves and ionospheric data-sets have similar periodicity. The planetary wave data-set used are temperature observations made by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). These highlight periods during which 2-Day westward propagating wave-number 3 waves are evident in the mesosphere and lower thermosphere. The ionospheric data-set is Total Electron Content (TEC), which is used to identify periods during which the ionosphere appears to respond to the planetary waves. Data from KP and F10.7 indices are used to determine events that may be of external origin. A 17-year time-span from 2002 to 2018 is used for this analysis so that both times of solar minimum and maximum can be studied. To extract the periods of this collection of data a Morlet Wavelet analysis is used, along with thresholding to indicate events when similar periods are seen in each data-set. Trends are then determined, which can lead to verification of previous assumptions and new discoveries.Master of Science
The thermosphere and ionosphere are impacted by many sources. The sun and the magnetosphere externally impact this system. Planetary waves, which originate in the lower atmosphere, internally impact this system. This interaction leads to periodic signatures in the ionosphere that reflect periodic signatures seen in the lower atmosphere, the sun and the magnetosphere. This study identifies these times of similar oscillations in the neutral atmosphere, the ionosphere, and the sun, in order to characterize these interactions. Events are cataloged through wavelet analysis and thresholding techniques. Using a time-span of 17 years, trends are identified using histograms and percentages. From these trends, the characteristics of this coupling can be concluded. This study is meant to confirm the theory and provide new insights that will hopefully lead to further investigation through modeling. The goal of this study is to gain a better understanding of the role that planetary waves have on the interaction of the atmosphere and the ionosphere.
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Oliveira, Fabricio Sanguinetti Cruz de. « Sinais propagantes para oeste no oceano Atlântico : vórtices ou ondas de Rossby ? » Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-19102010-164840/.
Texte intégralRésumé :
A maior parte do sinal propagante para oeste nos oceanos é explicada pelas ondas de Rossby baroclínicas. Porém, vórtices de mesoescala podem interferir na identificação dessas ondas. A maior adversidade em se distinguir o sinal dessas feições é que os vórtices parecem propagar-se com uma velocidade aproximada à velocidade de fase das ondas. Um dos objetivos do presente trabalho é caracterizar os sinais propagantes para oeste em termos da sua velocidade de fase no Atlântico. A análise se baseia em de dados das anomalias da altura da superfície do mar (ASM) e da temperatura de superfície do mar (TSM) derivados dos altímetros TOPEX/Poseidon e Jason-1 e radiômetro TRMM/TMI. As anomalias de ASM e TSM foram filtradas por um conjunto de filtros de resposta impulsiva finita (FIR) para eliminar o sinais sazonais, interanuais e sinais de alta frequência. A análise de correlação cruzada entre as matrizes zonais-temporais de ASM e TSM foi feita para limitar as conclusões aos sinais presentes simultaneamente em ambas as bases de dados. A velocidade de fase das ondas de Rossby foi estimada via transformada de Radon aplicada às matrizes de correlação cruzada. Um máximo local solitário sobre a origem foi observado nos diagramas de correlação e associado à presença de vórtices de mesoescala. Porém este máximo se alonga com a mesma inclinação correspondente à velocidade de fase das ondas de Rossby. Isto sugere que estes vórtices podem propagar-se sobrepostos às ondas. As velocidades de propagação dos vórtices são estimadas através do ajuste de uma função de decaimento exponencial no tempo e na distância zonal. Análises preliminares da transformada de Fourier mostraram que os sinais propagantes para oeste são predominantemente anuais, embora picos de frequências semi-anuais são observadas nestes espectros. Em decorrência da evidência de que os sinais propagantes para oeste são compostos simultaneamente por vórtices e ondas de Rossby, um filtro baseado na transformada de Radon e sua inversa foi desenvolvido para separar o sinal de feições com simetria circular. O filtro de vórtice circular foi aplicado em três áreas onde se localizam a Corrente das Agulhas, Confluências Brasil-Malvinas e Corrente do Golfo. Com base na análise visual pode-se afirmar que o filtro identificou com sucesso vórtices circulares nas três áreas estudadas, tanto nos dados de ASM como nos de TSM. As velocidades de fase das ondas de Rossby foram ligeiramente mais rápidas, em média, que as velocidades dos vórtices em todas as três áreas, cerca de 10% na ASM e 13% na TSM. As velocidades calculadas após a aplicação do filtro de vórtice circular apresentaram um viés positivo em relação as obtidas via correlações cruzadas. A maior diferença na estimativa das velocidades dos vórtices foi de 21% e nas ondas 25%, ambas na região da Corrente das Agulhas. Baseado nas evidências apresentadas é possível afirmar que vórtices podem se propagar com velocidades semelhantes à velocidade das ondas de Rossby do primeiro modo baroclínico. O lag das correlações cruzadas indicaram que o processo físico que relaciona a variabilidade nos dados de ASM à dos TSM é a advecção causada pela passagem de uma onda planet´aria do primeiro modo baroclínico. Esta advecção pode ser horizontal ou vertical dependendo do processo dominante que ocorre numa dada região.In the oceans, most of the westward propagating signal is explained by baroclinic Rossby waves. However, mesoscale vortices can interfere in the identification of these waves. The main observational issue is to distinguish eddies from the wave-like propagating signals, since the former propagates with a speed that approximately matches the phase speed of baroclinic Rossby waves. The objective of the present study is to characterize the westward propagating signals in terms of their propagation speeds in the Atlantic. The analysis is based on satellite derived sea surface height (SSH) and sea surface temperature (SST) anomalies from the TOPEX/Poseidon and Jason-1 altimeters and TRMM/TMI radiometer records. The SSH and SST anomaly maps were filtered with a set of finite impulse response filters to eliminate the seasonal and interannual cycles and high frequency signals. The cross-correlation analysis between SSH and SST longitude-time matrices was performed to limit the conclusions to the features that appear simultaneously in both datasets. The of Rossby wave phase speed was estimated via Radon transform applied to the longitude-time cross-correlation matrices. A single local maximum was was observed at the origin of the cross-correlation diagrams and associated to mesoscale vortices. However, this maximum spreads along the same slope that characterizes the the westward Rossby wave phase speed. This suggests that vortices propagate superimposed to Rossby waves. The propagating speed of the vortices is estimated from the linear fit of an exponential decay function. A preliminary Fourier analysis show that the westward propagating signals are predominantly annual, yet peaks in the semiannual frequencies are observed. The evidence that the westward propagating signals are composed simultaneously of vortices and Rossby waves motivated the development of a filter based in the Radon transform and its inverse, to isolate the signal associated to circularly symmetric features. This circular vortex filter was applied in three areas that portray the Agulhas Current, the Brazil-Malvinas Confluence, and the Gulf Stream. Based on visual analysis one can affirm that the circular filter sucessfully identified vortices in three areas, both in the SSH and in the SST data. The phase speeds of Rossby waves were, on average, slightly faster than vortices speeds in the three areas, approximately 10% in SSH and 13% in SST. The speeds calculated after the circular vortex filter was applied presented a positive bias in relation to those obtain from cross correlations. The largest difference in the vortices speeds was 21% and in the wave speeds 25%, both in Agulhas Current region. Based on the present evidences it is possible to state that vortices can propagate with speeds similar to those of first-mode baroclinic Rossby waves. The cross-correlation lag suggests that the physical process that links the variability of the SSH to that of the SST is the advection generated by the passage of a first-mode baroclinic planetary wave. This advection can be horizontal or vertical depending of the dominant process in a given region.
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Baldasso, Patricia. « Análise comparativa da dinâmica das ondas de Rossby a partir de anomalias da altura da superfície do mar obtidas por satélite e modelos numéricos ». Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-12052016-112017/.
Texte intégralRésumé :
Dados de altura da superfície do mar medidos a partir de satélites altimétricos e saídas de dois modelos de circulação geral dos oceanos (OGCM for the Earth Simulator - OFES e Community Earth System Model - CESM) foram utilizados com o objetivo de verificar se modelos numéricos climáticos reproduzem ondas de Rossby de forma similar à observada em dados altimétricos no Atlântico Sul. Os modelos diferem quanto à forçante, o modelo OFES é forçado com dados do NECP-NCAR enquanto que o modelo CESM é acoplado com modelo atmosférico, de gelo e terrestre. Uma vez que essas ondas dependem da estrutura interna de densidade e da forçante do vento, podemos fazer inferências sobre a adequação desses dois fatores nos modelos à realidade observada pelo altímetro. Uma série de filtros de resposta impulsiva finita 2D (FIR-2D) foi aplicada aos dados de anomalia da altura da superfície do mar com o propósito de detectar as ondas de Rossby e as componentes de onda encontradas nos dados dos modelos foram comparadas com as do altímetro. Os dois modelos são capazes de reproduzir ondas de Rossby e apresentam melhores resultados em baixas latitudes. Porém o modelo OFES apresentou mais dificuldades para reproduzir os parâmetros de onda encontrados no altímetro apresentando diferenças médias de até 68% para a amplitude, 34% para o comprimento de onda e 38% para a velocidade de fase. Em contrapartida as maiores diferenças médias entre os parâmetros de onda calculados a partir dos dados altimétricos e do modelo CESM foram de 32% para a amplitude, 20% para o comprimento de onda e 20% para a velocidade de fase. Além disso, o modelo CESM foi capaz de reproduzir o sinal sazonal com uma correlação média de aproximadamente 0,7 com o sinal sazonal encontrado pelo altímetro em toda a bacia do oceano Atlântico Sul enquanto que o sinal sazonal do modelo OFES apresentou uma correlação média de 0,4 com o sinal encontrado pelo satélite. Estes resultados mostram que os dois modelos reproduzem o fenômeno satisfatoriamente, sendo o CESM melhor que o OFES. A diferença dos resultados deve estar ligada aos aspectos supracitados, especificamente à forçante atmosférica e estrutura de densidade na coluna d\'água nas latitudes ao sul de 20ºS.Sea surface height data measured from altimetry satellites and outputs of two ocean general circulation models (OGCM for the Earth Simulator - OFES and Community Earth System Model - CESM) were used to determine whether climate numerical models reproduce the Rossby waves in a manner similar to those observed in altimetry record in the South Atlantic. The models differs in the forcing, OFES is forced with NCEP-NCAR data while CESM is coupled with atmospheric model, ice and land model. Because these waves depend on the internal density structure and wind forcing, we can make inferences about the suitability of these two factors in the models in comparison with the altimetry data used as a reference. A series of finite impulse response band-pass filters (FIR-2D) was applied to isolate the westward propagating signals corresponding to Rossby waves in the altimeter. Both models are able to reproduce Rossby waves and show better results in low latitudes. However, the OFES model presented more difficulty to reproduce the wave parameters found in altimeter with differences of up to 68% for amplitude, 34% for the wavelength and 38% for phase velocity. By contrast the greatest differences between the wave parameters computed from the altimeter data and the CESM model were 32% for amplitude, 20% for the wavelength and 20% for phase velocity. Furthermore, the CESM model was capable of reproducing the seasonal signal correlation with an average of approximately 0.7 with altimeter\'s seasonal signal found throughout the South Atlantic basin, while the OFES\'s seasonal signal showed an average correlation 0.4 with the signal found by the satellite. These results indicate that both models can reproduce the phenomenon satisfactorily, the CESM better than OFES. The difference between the results should be related with the aspects cited above, specifically with the atmospheric forcing and the density structure in the water column in latitudes southern then 20ºS.
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Zhang, Zheen [Verfasser]. « Regionalization of a Global Climate Change Scenario for the Bay of Bengal under Special Consideration of Rossby Waves and Coastal Kelvin Waves : Regionalisierung eines globalen Klimawandel-Szenarios für den Golf von Bengalen unter spezieller Berücksichtigung von Rossby- und Küsten-Kelvinwellen / Zheen Zhang ». Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/1221084194/34.
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