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.

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.

Bekanntlich sind atmosphärische Rossbywellezüge (RWTs) Lösungen der Singular Vector Analyse eines gedämpften, barotropen Modells mit Nordwinter Grundströmen. In den SV Basen der verwendeten 40 DJF Grundströme konnten nur wenige wachsende den Rossbywellenzügen ähnliche (RWT Moden) Singulären Vektoren (SVen) gefunden werden. Die RWT Moden kommen nur in wenigen Gebieten der Erde vor. Die instabilste Mode entwickelt sich in der Region des Nordpazifiks (NPACs) innerhalb von 4 Tagen in jedem der verwendeten beobachteten DJF Grundströme. Alle anderen RWT Moden kommen nur bei Verwendung einiger der Grundströme vor. Ihre Entwicklungspfade sind eindeutig für Entwicklungszeiten bis zu 96 h und streuen für längere Zeiten. Die NPAC Mode erklärt zum Optimierungszeitpunkt 96 h bis zu 60 % der atmosphärischen kinetischen Energie (KE) auf der 300 hPa Fläche in der NPAC Region. Es konnte auch gezeigt werden, daß die Zeitreihe des beobachteten Wachstums der NPAC Mode mit dem berechneten Wachstum (den Eigenwerten) konsistent ist. Interessanterweise zeigt die NPAC-KE zum Optimierungszeitpunkt 96 h auch eine schwach signifikante Korrelation mit dem PNA-Index, die für die Optimierungszeit 144 h nicht mehr existiert. Die Ergebnisse legen die Vermutung nahe, daß die verwendeten Grundströme die Entwicklung der RWT Moden bis zu einer Entwicklungszeit von 4 Tagen dominieren und daß die finite Instabilität maßgeblich zur Entwicklung der beobachteten NPAC Rossbywellenzüge in der Atmosphäre beiträgt. Die Ergebnisse geben Hinweise darauf, daß die NPAC mode auch einen Beitrag zur Entwicklung der PNA leistet.

Este trabalho avalia a importância relativa dosmodos dinâmicos na composição da estrutura vertical do fluxo geostrófico e de suas anomalias em relação à média, com o objetivo de fornecer uma descrição das formas de estratificação predominantes na coluna de água e de identificar prováveis regiões de ocorrência de ondas de Rossby planetárias (OR) dos diversos modos dinâmicos. Raios de deformação internos são estimados para avaliar a possibilidade de interações não-lineares entre OR e as alterações da estratificação local forçadas por sua própria passagem. A análise proposta baseia-se em dados de densidade estimados a partir de perfis verticais de salinidade climatológicos aliados a perfis sintéticos de temperatura. Estes últimos são extrapolados verticalmente a partir de dados orbitais da temperatura da superfície do mar (TSM) e da anomalia da altura da superfície livre (h), segundo um método de reconstrução estatística desenvolvido para este estudo. O primeiro modo baroclínico é dominante tanto no fluxo total quanto em suas anomalias, respondendo em média por 30% da estrutura vertical de velocidade, sendo que este valor descresce aproximadamente por uma razão de três em modos superiores. O segundo modo é significativo ou mesmo dominante em algumas regiões, particularmente em latitudes próximas ao equador. O terceiro é evidente em algumas áreas localizadas, mas não assume papéis importantes em escala de bacia. O modo 0 responde por frações de 6 a 9%, mas é provável que estes resultados sejam subestimados pela metodologia aplicada. Anomalias verticais relacionadas ao primeiro modo coincidem com regiões onde OR longas do primeiro modo tem maior expressão, enquanto o segundo modo parece ser um marcador de OR curtas e ondas de instabilidade tropical. Fenômenos transientes associados ao terceiro modo são observados em áreas restritas dos três oceanos. A magnitude das variações dos raios internos em resposta à fenômenos transientes em algumas regiões implicam em variações significativas na velocidade de fase teórica de OR longas lineares, um indício de que efeitos não-lineares podem ser importantes. Por fim, amplificações da importância do modo barotrópico sobre feições topográficas significativas sugere a existência de mecanismos de transferência de energia entre modos dinâmicos induzidas pela interação com a batimetria. / This study evaluates the relative importance of the dynamical modes in the composition of the geostrophic flow and of its anomalies from the long-term average, respectively seeking to determine the dominant vertical stratification structures of the water column and to identify regions where planetary Rossby waves (RW) of different dynamical modes may most likely occur. The baroclinic Rossby radii of deformation are estimated to evaluate the possibility of nonlinear interactions between RWand changes of the local stratification forced by the wave\'s passing. This analysis is based on density data estimated from climatological salinity profiles and synthetic temperature profiles. The latter are vertically extrapolated for sea surface temperature (SST) and sea surface height anomaly (h) satellite data, using a statistical reconstruction method developed in this study. The first baroclinic mode dominates both the total geostrophic flow and its anomalies, accounting for 30% of the velocity\'s vertical structure on average, where this value decreases approximately by a factor of 3 in subsequent baroclinic orders. The second mode is significant or even dominant in some areas, particularly near the equator. The third mode is evident in some localized regions, but can be ignored at basin-scales. The barotropic mode accounts for 6 to 9% fractions on average, however these values are probably underestimated by the used methods. Vertical anomalies related to the first baroclinic mode coincide with regions where long RWs answers for a significant fraction of local variance, while the second mode highlights zones where short RWs and tropical instability waves are reported. Transient phenomena related with the third mode are observed in comparatively small areas on all three oceans. The magnitude of the baroclinic radii\'s variations in response of the transient variability results in significant changes of the theorethical phase speed for long linear RWs, an evidence that nonlinear effects may be important. Lastly, the greater significance of the barotropic mode over proeminent bottom features suggests the existence of energy transfer mechanisms between dynamical modes triggered by the interaction with the bathymetry.

Este trabalho avalia a importância relativa dosmodos dinâmicos na composição da estrutura vertical do fluxo geostrófico e de suas anomalias em relação à média, com o objetivo de fornecer uma descrição das formas de estratificação predominantes na coluna de água e de identificar prováveis regiões de ocorrência de ondas de Rossby planetárias (OR) dos diversos modos dinâmicos. Raios de deformação internos são estimados para avaliar a possibilidade de interações não-lineares entre OR e as alterações da estratificação local forçadas por sua própria passagem. A análise proposta baseia-se em dados de densidade estimados a partir de perfis verticais de salinidade climatológicos aliados a perfis sintéticos de temperatura. Estes últimos são extrapolados verticalmente a partir de dados orbitais da temperatura da superfície do mar (TSM) e da anomalia da altura da superfície livre (h), segundo um método de reconstrução estatística desenvolvido para este estudo. O primeiro modo baroclínico é dominante tanto no fluxo total quanto em suas anomalias, respondendo em média por 30% da estrutura vertical de velocidade, sendo que este valor descresce aproximadamente por uma razão de três em modos superiores. O segundo modo é significativo ou mesmo dominante em algumas regiões, particularmente em latitudes próximas ao equador. O terceiro é evidente em algumas áreas localizadas, mas não assume papéis importantes em escala de bacia. O modo 0 responde por frações de 6 a 9%, mas é provável que estes resultados sejam subestimados pela metodologia aplicada. Anomalias verticais relacionadas ao primeiro modo coincidem com regiões onde OR longas do primeiro modo tem maior expressão, enquanto o segundo modo parece ser um marcador de OR curtas e ondas de instabilidade tropical. Fenômenos transientes associados ao terceiro modo são observados em áreas restritas dos três oceanos. A magnitude das variações dos raios internos em resposta à fenômenos transientes em algumas regiões implicam em variações significativas na velocidade de fase teórica de OR longas lineares, um indício de que efeitos não-lineares podem ser importantes. Por fim, amplificações da importância do modo barotrópico sobre feições topográficas significativas sugere a existência de mecanismos de transferência de energia entre modos dinâmicos induzidas pela interação com a batimetria. / This study evaluates the relative importance of the dynamical modes in the composition of the geostrophic flow and of its anomalies from the long-term average, respectively seeking to determine the dominant vertical stratification structures of the water column and to identify regions where planetary Rossby waves (RW) of different dynamical modes may most likely occur. The baroclinic Rossby radii of deformation are estimated to evaluate the possibility of nonlinear interactions between RWand changes of the local stratification forced by the wave\'s passing. This analysis is based on density data estimated from climatological salinity profiles and synthetic temperature profiles. The latter are vertically extrapolated for sea surface temperature (SST) and sea surface height anomaly (h) satellite data, using a statistical reconstruction method developed in this study. The first baroclinic mode dominates both the total geostrophic flow and its anomalies, accounting for 30% of the velocity\'s vertical structure on average, where this value decreases approximately by a factor of 3 in subsequent baroclinic orders. The second mode is significant or even dominant in some areas, particularly near the equator. The third mode is evident in some localized regions, but can be ignored at basin-scales. The barotropic mode accounts for 6 to 9% fractions on average, however these values are probably underestimated by the used methods. Vertical anomalies related to the first baroclinic mode coincide with regions where long RWs answers for a significant fraction of local variance, while the second mode highlights zones where short RWs and tropical instability waves are reported. Transient phenomena related with the third mode are observed in comparatively small areas on all three oceans. The magnitude of the baroclinic radii\'s variations in response of the transient variability results in significant changes of the theorethical phase speed for long linear RWs, an evidence that nonlinear effects may be important. Lastly, the greater significance of the barotropic mode over proeminent bottom features suggests the existence of energy transfer mechanisms between dynamical modes triggered by the interaction with the bathymetry.

Bibliography : p. 333-342. / xiii, 342 p. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1994?

The relationship between the outgoing long-wave radiation (OLR) field over the tropical Pacific and wintertime monthly precipitation for the western U. S. is investigated, using the mid-latitude upper-air circulation as an intermediary. Principal components (PC's) of the 500mb monthly averaged height field over the NE Pacific and western North America are compared with those of the monthly tropical Pacific OLR field. It is found that, of the first 6 PC's of the height field, five are correlated significantly with the first 3 OLR field PC's at lags of between two and six months. Canonical correlations between the two sets of PC's are greatest at a lag of four months and are highly significant. When stratified by different levels of the OLR field PC's, the separations between means of the height field PC's are highly significant as well. Differing distributions of the height field PC ensemble are also found to be associated with different OLR field PC levels. The relationship between the 500mb height field and concurrent western district precipitation is examined. Using a hybrid model including both linear statistical and non-linear physical components it is found that considerably more of the variance in the precipitation can be explained by that of the height field alone than when the precipitation is inferred directly from a linear statistical model. A set of reconstructed height field PC's is predicted from OLR values based on the height field/OLR stratification associations compiled for a period separate from that of the forecast. Applied to the precipitation model, this results in predicted western district precipitation which is better correlated with the observations than is the equivalent precipitation forecast from the linear statistical relationship of precipitation to the Southern Oscillation Index. / Graduation date: 1995

The Coriolis force has a subtle, but significant impact on the dynamics of geophysical and astrophysical flows. The Rossby number, Ro, is the nondimensional parameter measuring the relative strength of the Coriolis term to the nonlinear advection terms in the equations of motion. When the rotation is strong, Ro goes to zero and three-dimensional flows are observed to two-dimensionalize. The broad aim of this work is to examine the effect of the strength of rotation on the nonlinear dynamics of turbulent homogeneous flows. Our approach is to decompose the rotating turbulent flow modes into two classes: the zero-frequency 2-dimensional (2D) modes; and the high-frequency inertial waves (3D). / First, using numerical simulations of decaying turbulence over a large range of Ro we identified three regimes. The large Ro regime is similar to non-rotating, isotropic turbulence. The intermediate Ro regime shows strong 3D-to-2D energy transfers and asymmetry between cyclones (corotating) and anticyclones (couter-rotating), whereas at small Ro regime these features are much reduced. / We then studied discreteness effects and constructed a kinematic model to quantify the threshold of nonlinear broadening below which the 2D-3D interactions critical to the intermediate Ro regime are not captured. These results allow for the improvement of numerical studies of rotating turbulence and refine the comparison between results obtained in finite domains and theoretical results derived in unbounded domains. / Using equilibrium statistical mechanics, we examined the hypothesis of decoupling predicted in the small Ro regime. We identified a threshold time, t☆ = 2/Ro2, after which the asymptotic decoupling regime is no longer valid. Beyond t ☆, we show that the quasi-invariants of the decoupled model continue to constrain the system on the short timescales. / We found that the intermediate Ro regime is also present in forced turbulence and that interactions responsible for it are nonlocal. We explain a steep slope obtained in the 2D energy spectrum by a downscale enstrophy transfer. The energy of the 2D modes is observed to accumulate in the largest scales of the domain in the long-time limit. This is reminiscent of the "condensation" observed in classical forced 2D flows and magnetohydrodynamics.

No description available.

Planetary waves are known to play an important role in determining the annual variability in the severity of Antarctic ozone depletion. In this thesis, data obtained from the TOMS experiment on board the Nimbus-7 satellite are used to create global maps of total column ozone for each day from 1979 to 1992. Planetary wave morphology within these distributions is examined using spatial spectral analysis. The wave powers obtained are compared with a measure of the depth and area of the Antarctic ozone hole. A theoretical overview is given of middle atmosphere dynamics and how it influences the global distribution of ozone. Planetary waves play a predominant role in this dynamical distribution as they are responsible for the eddy transport of heat, momentum and long-lived tracers. A discussion of the equations of motion governing planetary wave propagation and their physical interpretation is given. The use of derived meteorological parameters, such as potential vorticity, in the study of planetary waves is developed. The theoretical tools, together with the equations of motion, are used to examine the excitation mechanisms for planetary waves. This theoretical analysis is also used to show that the strength of the westerly jet within the polar vortex determines which planetary wave modes can be expected in the geopotential height fields. In general only wavenumber 1 and 2 propagate during the Southern Hemisphere winter and the strength of these waves strongly modulates the severity of the Antarctic ozone depletion. Furthermore, the timing of the breakdown of the polar vortex is connected with the temporal variation of planetary wave power. A review of the current research in the field of planetary waves and the global distribution of ozone is given. To quantify planetary wave activity, spatial spectral analysis (Fourier Transforms) of midlatitude zonal profiles of total column ozone are used to calculate wave powers in the ozone distribution. Powers at wavenumber 1 to 6 are calculated for each day from 1979 to 1992 for both the Northern and Southern Hemispheres. The powers are seen to decrease with wavenumber throughout the year and the amplitude of wave modes 3 and higher is suppressed during the winter in accordance with the theoretical discussion. Southern Hemisphere wave powers are compared with a daily depleted mass of ozone over the Antarctic from 1979 to 1992. It is found that during years of high (low) planetary wave activity Antarctic ozone depletion is very weak (severe). Finally, the planetary wave morphology observed in the Southern Hemisphere total column ozone distribution is compared with geopotential height waves reported in the literature. Comparison of Northern Hemisphere wave powers and Arctic ozone depletion shows little or no correlation. To examine whether planetary waves may effect the interannual variability in Antarctic vortex temperatures, winter averaged 100 hPa upper air temperatures from SANAE (70°18' S, 2°21' W) are compared with derived planetary wave powers. It is found that during years of high (low) planetary wave activity the SANAE 100 hPa temperatures are above (below) the mean. Analysis of daily total column ozone and upper air temperatures at SANAE, during the winters of 1987 and 1988, shows that wave 1 forcing can significantly influence the day-to-day variation in these quantities. A statistical model of total ozone variation over the entire globe, from 1979 to 1992, has been developed. This model incorporates a long-term linear trend, an annual variation, a quasi-biennial oscillation, a solar cycle variation and a semiannual variation. Since monthly average total column ozone data are used in this model, short term planetary wave influences are masked, and the variations in global ozone are determined primarily by the 5 signals discussed above. However, analysis of the model coefficients indicates that planetary wave activity may significantly contribute to zonal asymmetry in global total ozone trends. Differences between model results and measured data are compared with planetary wave activity. The timing of the breakdown of the Antarctic circumpolar vortex causes large interannual differences in monthly average total column ozone for the months of October and November in the Southern Hemisphere. This analysis is made more specific for South Africa by examining the variation in monthly average total column ozone over the five South African cities of Pretoria, Bloemfontein, Durban, Port Elizabeth and Cape Town for the years 1979 to 1992. A model of surface erythemal irradiance as a function of total column ozone, time of the year and other meteorological parameters is developed. Total ozone data for the 5 cities, used within the context of the statistical model and the DV irradiance model, allows the prediction of future DV levels over South Africa to the year 2000. Planetary wave motion owes its existence to the conservation of potential vor-ticity. However, to make use of this conservation principle as a diagnostic for planetary wave propagation, it is necessary to know the conditions under which it is conserved. A formalism developed by Plumb and Ko (1992) has been used to suggest a technique whereby the 'lifetime' of potential vorticity may be determined. Use was made of data from the NCAR CCM2 model to test this hypothesis. The concentrations of long-lived tracers (CH4 and NzO) extracted from the CCM2 also show the effects of planetary wave breaking on the meridional distribution of these species. This study has important implications for airborne polar chemistry campaigns. / Thesis (Ph.D.)-University of Natal, 1994.