Dissertations / Theses on the topic 'Equatorial waves'
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King, B. A. "Loquency waves in equatorial oceans." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373656.
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Li, Xiaoqing. "Equatorial waves in planetary atmospheres." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335062.
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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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Pezzi, Luciano Ponzi. "Equatorial Pacific dynamics : lateral mixing and tropical instability waves." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274585.
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Blumenthal, Martin Benno. "Interpretation of equatorial current meter data as internal waves." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/51460.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, and Woods Hole Oceanographic Institution, 1987.Bibliography: v. 2, leaves 376-381.
by Martin Benno Blumenthal.
Ph.D.
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Yu, Xuri. "Dynamics of seasonal and interannual variability in the equatorial Pacific." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11065.
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Drysdale, Euain Fraser. "Modelling of equatorial wave motions in the middle atmosphere." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:9ae75869-a15b-465e-af64-c608cca8b34c.
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A three-dimensional mechanistic model of the middle atmosphere is used to model various classes of equatorial wave motions that are observed in the atmosphere. These waves are thought to be largely responsible for the forcing of the quasi-biennial oscillation (QBO) in the tropical lower stratosphere. By generating a combination of different classes of equatorial waves in the model, an oscillation which has many similarities to the observed QBO is produced in the model. The numerical model used is run in a variety of configurations, including running it at different vertical resolutions and with two different radiation parameterisation schemes. It is found that model used in the project must be modified to allow the accurate modelling of equatorial waves. Several modelling problems are encountered while applying the modifications necessary in the model; the steps necessary to rectify these problems are detailed in this thesis. Equatorial waves are then forced in this modified model under a range of conditions and their interaction with the mean flow is observed. Their dissipation mechanisms and the influence of changes in model conditions on these waves are investigated. The model is found to be generally very successful in modelling these equatorial waves. Modelling of the QBO is one of the principle aims of this project and a QBO is successfully generated in a variety of model configurations. The modelled QBO is found to be sensitive to changes in the temperature structure of the model (brought about by changes in the model's radiation scheme) and several experiments are performed in order to learn what processes affect this sensitivity. A QBO is then generated in series of model runs where the state of the model is varied from very idealised (where temperatures in the model are relaxed towards an isothermal state by the radiation scheme) to a state that is far more realistic (a perpetual January run with realistic boundary information). A fairly realistic QBO is generated throughout many of the experiments. The properties of this QBO are investigated and compared to the observed QBO. The model is then run with planetary waves forced in addition to the QBO. The interaction between the planetary waves and the QBO is investigated. It is found that the planetary waves have little effect on the QBO propagation. The QBO however has a fairly strong modulating effect on the planetary waves in certain regions.
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Soares, Jacyra Ramos. "On the reflection of the equatorial waves at eastern ocean boundaries." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239653.
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Andersen, Joseph. "Investigations of the Convectively Coupled Equatorial Waves and the Madden-Julian Oscillation." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10438.
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The Madden-Julian Oscillation (MJO) and the Convectively Coupled Equatorial Waves (CCEW) are coherent structures of convection and various large-scale fields. These phenomena are not well understood, despite their importance to the tropical climate. A toy model of the CCEW consisting of a pair of shallow water wave modes coupled by a simple convective parameterization is considered. The linear behavior of the system is analyzed, showing a growth spectrum that is similar to the spectrum that is observed. To explore the processes involved in propagation and maintenance of the MJO disturbance, we analyze the MSE budget of the disturbance within a numerical model. In an idealized experiment, the column-integrated long-wave heating is the only significant source of column-integrated MSE acting to maintain the MJO-like anomaly balanced against the combination of column-integrated horizontal and vertical advection of MSE and Latent Heat Flux. Eastward propagation of the MJO-like disturbance is associated with MSE generated by both column-integrated horizontal and vertical advection of MSE, with the column long-wave heating generating MSE that retards the propagation. The contribution to the eastward propagation by the column-integrated horizontal advection term is dominated by meridional advection of MSE by anomalous synoptic eddies caused by the suppression of eddy activity ahead of the MJO convection. This suppression is linked to the barotropic conversion mechanism; with the gradients of the low frequency wind experienced by the synoptic eddies within the MJO envelope acting to modulate the Eddy Kinetic Energy. The meridional eddy advection’s contribution to poleward propagation is dominated by the mean state’s (meridionally varying) eddy activity acting on the anomalous MSE gradients associated with the MJO. In a follow-up experiment, the variations in the propagation speed of MJO with variations in the imposed SST distribution are seen to be driven by the variations in meridional advection of the mean MSE profile by the MJO-related winds, which are in turn dominated by the variations in the mean MSE profile due to the variations of the SST. A brief investigation of the MSE budget for a more realistic case shows an increase in the MSE sink due to meridional advection as the MJO progresses from genesis over the Indian Ocean to decay in the central Pacific. The increase in this sink appears to be the cause of MJO’s demise.Physics
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Aveiro, Henrique Carlotto. "Electric and magnetic field signatures of gravity waves and 2-day planetary waves in the equatorial E-region." Instituto Nacional de Pesquisas Espaciais, 2009. http://urlib.net/sid.inpe.br/mtc-m18@80/2008/12.16.11.31.
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Observações do eletrojato equatorial (EEJ) utilizando radares VHF mostram ecos retro-espalhados em dois tipos de irregularidades de densidade eletrônica, explicadas pelas instabilidades de dois-feixes modificada (ecos Tipo I) e deriva de gradiente (ecos Tipo II). Das velocidades das irregularidades Tipo II obtidas de dados de radar, inferimos os campos elétricos verticais (E_z). A análise harmônica de tais campos mostra a presença de campos elétricos induzidos por ondas de gravidade (GW) no EEJ. Calculamos a razão entre os campos elétricos relacionados a GW e o campo elétrico vertical total. Este fator é um indicador da eficiência na produção de um campo elétrico causado por um vento neutro devido a uma onda de gravidade. Também, analisamos os efeitos da atividade da onda planetária de 2 dias no EEJ utilizando um radar coerente e oito magnetômetros instalados próximos ao equador magnético. A análise de wavelets dos dados de magnetômetros revela uma assinatura de 2 dias na maré semidiurna geomagnética. O campo elétrico ionosférico zonal da região E, derivado de medidas de radar coerente, mostra oscilações de 2 dias, em acordo com tais observações nos dados de magnetômetros. Uma anti-correlação entre as periodicidades de marés (diurna e semi-diurna) e a assinatura de dois dias é também mostrada nos campos elétricos. Os resultados são comparados com observações simultâneas de ondas planetárias de dois dias nos ventos meridionais e ionossondas disponíveis na literatura. Finalmente, nossos resultados são discutidos com base na análise da atividade magnética do período.Equatorial electrojet (EEJ) observations using VHF radars show backscattered echoes from two types of electron density irregularities explained by the modified two-stream (Type I) and the gradient drift (Type 11) instabilities. From the Type II irregularity velocities obtained by radar data we have inferred the vertical electric fields (E_z). The harmonic analysis of such fields shows the presence of gravity waves-induced electric fields in the EEJ. We calculated the ratio between GW-related electric fields and the total E_z. This factor is an indicator of the efficiency in the production of an additional electric field due to a gravity wave neutral wind. Also, we analyze the effects of the 2-day wave activity in the EEJ using one coherent radar and eight magnetometer stations located dose to the dip equator. The wavelet analysis of the magnetometer data reveals a 2-day signature in the semidiurnal geomagnetic tide. The E-region zonal background ionospheric electric field derived from coherent radar measurements shows 2-day oscillations in agreement with such oscillations in the magnetometer data set. An anticorrelation between the tidal periodicites (diurnal, and semidiurnal) and the 2-day signature is also shown in the electric fields. The results are compared with simultaneous observations of 2-day planetary wave in meridional winds and ionosondes available in the literature. Our results are discussed based on the analysis of the magnetic activity.
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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.
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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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Sitler, Todd William. "An observational study of long waves in the equatorial Pacific Ocean during the 1991-1993 El Nino." Thesis, Monterey, California. Naval Postgraduate School, 1994. http://hdl.handle.net/10945/28415.
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Approved for public release; distribution is unlimitedLong waves in the equatorial Pacific Ocean during the 1991-1993 El Nino event were examined using temperature, current, and wind time series from the Tropical Oceans-Global Atmosphere Tropical Atmosphere-Ocean (TOGA-TAO) moored buoy array. Numerous episodes of long wave activity were detected. The most prominent episodes were associated with eastward propagating equatorial Kelvin waves and with westward propagating tropical instability waves and mixed Rossby-gravity waves. Equatorial Kelvin waves, which were generated by westerly wind events in the western and central Pacific, were evident in the data between 2 deg N to 5 deg S and from 170 deg W to 110 deg W. These Kelvin waves, which were most pronounced from 75 to 300 m, had periods of 40 to 70 days, eastward phase speeds of 1.9 to 6.5 m/s, and zonal wavelengths on the order of 10,000 km. These waves were most evident in the northern hemisphere fall and winter. The period of greatest Kelvin wave activity was August 1991 -May 1992, during the peak phase of the 1991-1993 El Nino event
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Ponte, Rui Vasques de Melo. "Observations and modelling of deep equatorial currents in the central Pacific." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/58499.
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Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1988.Includes bibliographical references (leaves 178-180).
Analysis of vertical profiles of absolute horizontal velocity collected in January 1981, February 1982 and April 1982 in the central equatorial Pacific as part of the Pacific Equatorial Ocean Dynamics (PEQUOD) program, revealed two significant narrow band spectral peaks in the zonal velocity records, centered at vertical wavelengths of 560 and 350 stretched meters (sm). Both signals were present in all three cruises, but the 350 sm peak showed a more steady character in amplitude and a higher signal-to-noise ratio. In addition, its vertical scales corresponded to the scales of the conspicuous alternating flows generically called the equatorial deep jets in the past (the same terminology will be used here). Meridional velocity and vertical displacement spectra did not show any such energetic features. Energy in the 560 sm band roughly doubled between January 1981 and April 1982. Time lagged coherence results suggested upward phase propagation at time scales of about 4 years. East-west phase lines computed from zonally lagged coherences, tilted downward towards the west, implying westward phase propagation. Estimates of zonal wavelength (on the order of 10000 km) and period based on these coherence calculations, and the observed energy meridional structure at this vertical wavenumber band, seem consistent, within experimental errors, with the presence of a first meridional mode long Rossby wave packet, weakly modulated in the zonal direction. The equatorial deep jets, identified with the peak centered at 350 sm, are best defined as a finite narrow band process in vertical wavenumber (311-400 sm), accounting for only 20% of the total variance present in the broad band energetic background. At the jets wavenumber band, latitudinal energy scaling compared well with Kelvin wave theoretical values and a general tilt of phase lines downward towards the east yielded estimates of 10000-16000 km for the zonal wavelengths.
by Rui Vasques de Melo Ponte.
Ph.D.
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Horinouti, Takeshi. "Excitation of waves by organized cumulus convection and their interaction with the mean flow in the equatorial middle atmosphere." 京都大学 (Kyoto University), 1997. http://hdl.handle.net/2433/202444.
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Jacobi, Christoph. "The quasi 16-day wave in the summer midlatitude mesopause region and its dependence on the equatorial quasi-biennial oscillation." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-213442.
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Aus täglichen Analysen des sommerlichen zonalen Grundwindes im Mesopausenbereich, der am Observatorium Collm der Universität Leipzig gemessen wurde, werden niederfrequente Variationen im Zeitbereich planetarer Wellen (10 - 20 Tage) bestimmt. Obwohl die direkte Ausbreitung derartiger Wellen durch die stratosphärischen und mesosphärischen Ostwinde verhindert wird, werden in manchen Jahren trotzdem Oszillationen gemessen, die mit planetaren Wellen im Zusammenhang stehen können. Dies unterstützt die Theorie, daß sich planetare Wellen von der Winterhalbkugel entlang der Zonen schwachen Windes bis in die Mesopausenregion mittlerer und polarer Breiten ausbreiten. Betrachtet man die interanuelle Variabilität dieser Wellen, fällt eine Abhängigkeit von der äquatorialen quasi 2-jährigen Schwingung (QBO) auf, wobei während der Ostphase der QBO die Wellenaktivität gering ist, während sie in der Westphase der QBO stärker sein kann. Der Einfluß der QBO auf die sommerliche Wellenaktivität wird vom 11-jährigen Sonnenfleckenzyklus moduliert, wobei während des solaren Maximums stärkere Aktivität zu verzeichnen istFrom daily estimates of the summer mesopause region zonal prevailing wind measured at the Collm Observatory of the University of Leipzig long-term variations in the period range of planetary waves (10-20 days) are detected. Although the direct propagation of these waves from lower layers into the mesosphere is not possible because of the wave filtering in the summer stratospheric and mesospheric easterlies, in some years oscillations are found that can be connected with planetary waves, supporting the theory of the propagation of these waves from the equatorial region to the midlatitude and polar upper mesosphere along the zero wind line. The interannual variability of these waves shows a dependence on the equatorial quasi-biennial oscillation (QBO), so that in general during the east phase of the QBO the planetary wave activity is small, while during the QBO west phase it can be larger. The influence of the QBO on the planetary wave activity is modulated by the I I-year solar cycle, so that the strongest signal is found during solar maximum
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Lima, Newton Silva de. "Estudo da propagação de ondas de gravidade na ionosfera equatorial, utilizando observações em Manaus (2,9°s, 60°w)." Universidade Federal do Amazonas, 2009. http://tede.ufam.edu.br/handle/tede/3275.
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This work studies the behavior of gravity waves (GW) in the ionosphere over the city of Manaus (2,9oS, 60oW). For that purpose, ionograms which are specters of frequency in function of the altitude and the secular variation of the height for a set of fixed frequencies (3, 4, 5, 6, 7 8 MHz). The observations were analyzed carried through by a system of called radar ionosonde. This system operates in the radio frequency band between 1and 20 MHz. The studied period comprehends a part of solar cycle 23, that is, since August of 2002 until December of 2006. Additionally, it was also observed that the ionosphere presents strong disturbances during geomagnetically quiet periods. These disturbances are attributed to the propagation of gravity waves which are generated in the lower atmosphere and propagate up to the high atmosphere and ionosphere.
Este trabalho investiga o comportamento de ondas de gravidade (OG) na ionosfera sobre a cidade de Manaus (2,9oS, 60oW). Para tal, foram analisados ionogramas que são espectros de freqüência em função da altitude e a variação temporal da altura, para um conjunto de freqüências fixas (3, 4, 5, 6, 7 8 MHz). As observações foram realizadas por um sistema de radar chamado ionossonda; que pera na faixa de rádio freqüência entre 1 e 20 MHz. O período estudado compreende uma parte do ciclo solar 23, ou seja, desde agosto de 2002 até dezembro de 2006. Observou-se que a ionosfera apresenta fortes perturbações durante períodos geomagneticamente calmos. Estas perturbações são atribuídas a propagação de ondas de gravidade que são geradas na baixa atmosfera e se propagam até a alta atmosfera e ionosfera.
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Moss, Andrew. "Wave dynamics of the stratosphere and mesosphere." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707571.
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Gravity waves play a fundamental role in driving the large-scale circulation of the atmosphere. They are influenced both by the variation in their sources and the filtering effects of the winds they encounter as they ascend through the atmosphere. In this thesis we present new evidence that gravity waves play a key role in coupling the troposphere, stratosphere and mesosphere. In particular, we examine the connection of gravity waves to two important large-scale oscillations that occur in the atmosphere, namely the Madden-Julian Oscillation (MJO) in the troposphere and the Mesospheric Semi-Annual Oscillation (MSAO). We present the first ever demonstration that the MJO acts to modulate the global field of gravity waves ascending into the tropical stratosphere. We discover a significant correlation with the MJO zonal-wind anomalies and so suggest that the MJO modulates the stratospheric gravity-wave field through a critical-level wave-filtering mechanism. Strong evidence for this mechanism is provided by consideration of the winds encountered by ascending waves. The Ascension Island meteor radar is used for the first time to measure momentum fluxes over the Island. These measurements are then used to investigate the role of gravity-wave in driving a dramatic and anomalous wind event that was observed to occur during the first westward phase of the MSAO in 2002. Gravity waves are shown to play an important role in driving this event, but the observations presented here also suggest that the current theory of the mechanism describing these anomalous mesospheric wind events is not valid. Both of these studies highlight the critical importance of gravity waves to the dynamics of the atmosphere and highlight the need for further work to truly understand these waves, their processes and their variability.
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Jacobi, Christoph. "The quasi 16-day wave in the summer midlatitude mesopause region and its dependence on the equatorial quasi-biennial oscillation." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 9 = Meteorologische Arbeiten aus Leipzig ; 3 (1998), S. 117-129, 1998. https://ul.qucosa.de/id/qucosa%3A15084.
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Aus täglichen Analysen des sommerlichen zonalen Grundwindes im Mesopausenbereich, der am Observatorium Collm der Universität Leipzig gemessen wurde, werden niederfrequente Variationen im Zeitbereich planetarer Wellen (10 - 20 Tage) bestimmt. Obwohl die direkte Ausbreitung derartiger Wellen durch die stratosphärischen und mesosphärischen Ostwinde verhindert wird, werden in manchen Jahren trotzdem Oszillationen gemessen, die mit planetaren Wellen im Zusammenhang stehen können. Dies unterstützt die Theorie, daß sich planetare Wellen von der Winterhalbkugel entlang der Zonen schwachen Windes bis in die Mesopausenregion mittlerer und polarer Breiten ausbreiten. Betrachtet man die interanuelle Variabilität dieser Wellen, fällt eine Abhängigkeit von der äquatorialen quasi 2-jährigen Schwingung (QBO) auf, wobei während der Ostphase der QBO die Wellenaktivität gering ist, während sie in der Westphase der QBO stärker sein kann. Der Einfluß der QBO auf die sommerliche Wellenaktivität wird vom 11-jährigen Sonnenfleckenzyklus moduliert, wobei während des solaren Maximums stärkere Aktivität zu verzeichnen ist.From daily estimates of the summer mesopause region zonal prevailing wind measured at the Collm Observatory of the University of Leipzig long-term variations in the period range of planetary waves (10-20 days) are detected. Although the direct propagation of these waves from lower layers into the mesosphere is not possible because of the wave filtering in the summer stratospheric and mesospheric easterlies, in some years oscillations are found that can be connected with planetary waves, supporting the theory of the propagation of these waves from the equatorial region to the midlatitude and polar upper mesosphere along the zero wind line. The interannual variability of these waves shows a dependence on the equatorial quasi-biennial oscillation (QBO), so that in general during the east phase of the QBO the planetary wave activity is small, while during the QBO west phase it can be larger. The influence of the QBO on the planetary wave activity is modulated by the I I-year solar cycle, so that the strongest signal is found during solar maximum.
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Costa, Carine de Godoi Rezende. "Dinâmica e interação oceano-atmosfera de ondas de instabilidade tropical e ondas de Rossby curtas." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-10042014-165427/.
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A hipótese principal deste trabalho é que as anomalias de precipitação na ZCIT com períodos de 20 a 50 dias e dimensão zonal de 1000 a 1500 km, causadas remotamente por Ondas de Instabilidade Tropical (OITs) e/ou Ondas de Rossby Curtas (ORCs) podem causar anomalias de salinidade da superfície do mar. Para responder à hipótese, o presente trabalho quantifica a influência dos padrões propagantes da temperatura da superfície do mar sobre variáveis atmosféricas na escala das ORCs e OITs. Os coeficientes de regressão do vapor dágua integrado verticalmente e da precipitação revelam que a influência da temperatura superficial na atmosfera se dá remotamente à região de domínio das ondas, alcançando a ZCIT. A distribuição das anomalias do divergente do vento corrobora a ideia de aceleração dos ventos sobre águas quentes e desaceleração sobre águas frias. A carência de correlações estatisticamente significativas entre a precipitação e a salinidade superficial, devido à baixa qualidade dos dados, não permitiu que a hipótese principal fosse avaliada. Entretanto, fica evidente a influência destas ondas em variáveis atmosféricas que alteram o balanço de evaporação e precipitação que tem influência direta na salinidade superficial. Denominamos ORCs as oscilações com período de _49 dias e comprimento de onda de _1500 km e OITs os padrões com _21 dias e _1000 km. A identificação dinâmica destas ondas foi feita através da teoria linear de ondas equatoriais no modelo de águas rasas quase-geostrófico para um oceano invíscido de 1,5 camadas. Os dados de anomalia da altura da superfície do mar revelaram apenas a existência de ORCs, enquanto que a temperatura da superfície do mar apresentou o sinal de ambas as ondas, sendo as OITs dominantes até 6_ do Equador. A principal contribuição deste trabalho é a confirmação da hipótese de que OITs e ORCs coexistem, são distinguíveis e geram alterações no vento por mecanismos similares. Até o presente momento, desconhecemos outro estudo que alie a separação teórica dos padrões oceânicos propagantes obtidos por satélites à quantificação da variabilidade atmosférica associada às anomalias de TSM em bandas do espectro zonal-temporal características de ondas dinamicamente distintasWe hypothesize that rainfall anomalies with 2050 days and 10001500 km on the Intertropical Convergence Zone (ITCZ) can induce sea surface salinity anomalies. We argue that these precipitation anomalies are remotely caused by Tropical Instability Waves (TIWs) and Short RossbyWaves (SRWs). We have quantified the sea surface temperature influence on atmospheric fields at the TIWs and SRWs spectral bands through regression analysis. In that, wind anomalies are larger over temperature anomalies. Winds tend to accelerate over positive temperature anomalies and slow down over negative anomalies. Changes on water vapor and rainfall occur predominantly on the ITCZ, far from the strongest temperature anomalies near the equator. However, we couldnt address the main hypothesis due to the lack of significant correlation between rainfall and sea surface salinity anomalies. We speculate that this is a consequence of the low quality of the salinity data used in this study. We have identified TIWs as the waves with _21 days and _1000 km and SRWs as the oscillations with _49 days and _1500 km. The identification of the dynamics was made according to equatorial long waves theory based on a linear, quasi-geostrophic, 1.5 layers, inviscid ocean model. Sea surface height anomalies could only reveal SRWs. Sea surface temperature anomalies show both type of waves, with TIWs dominating within 6_ from the equator. Our main contribution was to show that TIWs and SRWs coexist, can be isolated and change wind field through similar mechanisms. We do not know any other study that linked theoretical identification of dynamically different oceanic waves to the atmospheric variability in a quantitative fashion
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Phlips, P. J. "Models of the heat-induced circulation in the tropical atmosphere." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371572.
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Wohlwend, Christian Stephen. "Modeling the Electrodynamics of the Low-Latitude Ionosphere." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/11.
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The electrodynamics of the Earth's low-latitude ionosphere is dependent on the ionospheric conductivity and the thermospheric neutral density, temperature, and winds present. This two-part study focused on the gravity wave seeding mechanism of equatorial plasma depletions in the ionosphere and the associated equatorial spread F, as well as the differences between a two-dimensional flux tube integrated electrodynamics model and a three-dimensional model for the same time period. The gravity wave seeding study was based on a parameterization of a gravity wave perturbation using a background empirical thermosphere and a physics-based ionosphere for the case of 12 UT on 26 September 2002. The electrodynamics study utilized a two-dimensional flux tube integrated model in center dipole coordinates, which is derived in this work. This case study examined the relative influence of the zonal wind, meridional wind, vertical wind, temperature, and density perturbations of the gravity wave. It further looked at the angle of the wave front to the field line flux tube, the most influential height of the perturbation, and the difference between planar and thunderstorm source gravity waves with cylindrical symmetry. The results indicate that, of the five perturbation components studied, the zonal wind is the most important mechanism to seed the Rayleigh-Taylor instability needed to develop plasma plumes. It also shows that the bottomside of the F-region is the most important region to perturb, but a substantial E-region influence is also seen. Furthermore, a wave front with a small angle from the field line is necessary, but the shape of the wave front is not critical in the gravity wave is well developed before nightfall. Preliminary results from the three-dimensional model indicate that the equipotential field line assumption of the two-dimensional model is not valid below 100 km and possibly higher. Future work with this model should attempt to examine more of the differences with the two-dimensional model in the electric fields and currents produced as well as with the plasma drifts that lead to plume development.
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Brady, Esther C. "Observations of wave-mean flow interaction in the Pacific equatorial undercurrent." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/51482.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and, Woods Hole Oceanographic Institution, 1991.GRSN 539404
Includes bibliographical references (p. 207-216).
by Esther Collison Brady.
Ph.D.
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Mosquera, Vasquez Kobi A. "L'onde de Kelvin équatoriale océanique intrasaisonnière et les événements El Nino du Pacifique central." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30324/document.
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Le phénomène El Niño est le mode dominant de la variabilité du climat aux échelles de temps interannuelles dans le Pacifique tropical. Il modifie considérablement le climat régional dans les pays voisins, dont le Pérou pour lequel les impacts socio-économiques peuvent être dramatiques. Comprendre et prévoir El Niño reste un enjeu prioritaire pour la communauté climatique. Des progrès significatifs dans notre compréhension du phénomène El Niño et dans notre capacité à le prédire ont été réalisés dans les années 80, en particulier grâce à la mise en place du système d'observation dans le Pacifique tropical (programme de TOGA, en particulier, ainsi que l'émergence de l'ère des satellites). À la fin du XXe siècle, alors que de nouvelles théories scientifiques ont été proposées et testées, les progrès réalisés dans le domaine de la modélisation numérique et de l'assimilation de données ont conduit à l'idée que le phénomène El Niño pourrait être prévu avec au moins deux ou trois saisons à l'avance. Or, depuis le début du 21ième siècle, les manifestations du phénomène El Niño ont réduit cette expectative: un nouveau type d'El Niño est a été découvert - identifié par des anomalies de température moins intenses et localisées dans le centre du Pacifique équatorial. Ce phénomène, connu sous le nom CP El Niño pour El Niño Pacifique Central ou El Niño Modoki a placé la communauté scientifique devant un nouveau défi. Cette thèse est une contribution à l'effort international actuel pour comprendre la dynamique de ce nouveau type d'El Niño, dans le but de proposer des mécanismes expliquant sa présence accrue au cours des dernières décennies. Plus précisément, l'objectif de cette thèse est d'étudier le rôle des ondes longues équatoriales dans le Pacifique tropical sur la dynamique océanique et la thermodynamique associées au phénomène El Niño de type Pacifique Central. Cette thèse s'intéresse tout d'abord au premier CP El Niño du 21ième siècle, le phénomène El Niño 2002/03, à partir des sorties d'un modèle de circulation océanique général. Ensuite, nous documentons les caractéristiques des ondes équatoriales de Kelvin aux fréquences Intra Saisonnières (ISKw) sur la période 1990-2011, fournissant une statistique de l'activité des ondes ISKw durant l'évolution des événements El Niño de type Central Pacifique. Nos résultats montrent que l'onde ISKw subit une forte dissipation dans le Pacifique Est, qui est interprétée comme provenant de la dispersion des ondes lorsqu'elles rencontrent le front zonal de la stratification dans l'Est du Pacifique (i.e. la pente de la thermocline d'Ouest en Est). Une réflexion partielle de l'onde ISKw en onde de Rossby équatoriale de près de 120°W est également identifiée, ce qui peut expliquer le confinement dans le Pacifique central des anomalies de température de surface associées aux événements El Niño de type Central Pacifique. Nous suggérons que la fréquence accrue au cours des dernières années des événements CP El Niño peut être associée à l'état froid - de type La Niña - observé dans le Pacifique Equatorial depuis les années 90 et les changements dans la variabilité saisonnière de la profondeur de la thermocline depuis les années 2000The El Niño phenomenon is the dominant mode of climate variability at interannual timescales in the tropical Pacific. It modifies drastically the regional climate in surrounding countries, including Peru for which the socio-economical impacts can be dramatic. Understanding and predicting El Niño remains a top-priority issue for the climatic community. Large progress in our understanding of El Niño and in our ability to predict it has been made since the 80s thanks to the improvement of the observing system of the tropical Pacific (TOGA program and emergence of the satellite era). At the end of the Twentieth century, whereas new theories were proposed and tested, progress in numerical modeling and data assimilation led to the idea that El Niño could be predicted with at least 2 or 3 seasons in advance. The observations since the beginning of the 21st century have wiped out such expectation: A new type of El Niño, known as the Central Pacific El Niño (CP El Niño) or Modoki El Niño has put the community in front of a new challenge. This thesis is a contribution to the current international effort to understand the dynamics of this new type of El Niño in order to propose mechanisms explaining its increased occurrence in recent decades. More specifically, the objective of the thesis is to study the role of the oceanic equatorial waves in the dynamic and thermodynamic along the equatorial Pacific Ocean, focusing on the CP El Niño. This thesis first takes a close look at the first CP El Niño of the 21st century of this type, i.e. the 2002/03 El Niño, based on an Oceanic General Circulation Model. Then it documents the characteristics of the IntraSeasonal Kelvin waves (ISKws) over the period 1990-2011, providing a statistics on the ISKws activity during the evolution of CP El Niño events. We find that the ISKw experiences a sharp dissipation in the eastern Pacific that is interpreted as resulting from the scattering of energy associated to the zonal contrast in stratification (i.e. sloping thermocline from west to east). Partial reflection of the ISKw as Rossby waves near 120°W is also identified, which may explain the confinement of CP El Niño warming in the central Pacific. We suggest that the increased occurrence of CP El Niño in recent years may be associated to the La Niña-like state since the 90s and changes in the seasonality of the thermocline since the 2000s
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Awo, Founi Mesmin. "Modes interannnuels de la variabilité climatique de l'Atlantique tropical, dynamiques oscillatoires et signatures en salinité de surface de la mer." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30171/document.
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Dans cette thèse, nous avons abordé plusieurs thématiques liées aux modes de variabilité climatique dans l'Atlantique tropical à l'échelle interannuelle. Les analyses statistiques nous ont permis dans un premier temps de mettre en évidence les deux principaux modes dominants de cette variabilité interannuelle: un mode équatorial et un mode méridien. Le mode équatorial est responsable d'anomalies de température de surface de la mer (SST) principalement dans le Golfe de Guinée et est identifié par des variations de la pente du niveau de la mer dans la bande équatoriale. Il est dû à des rétroactions dynamiques entre le vent, le niveau de la mer et la SST. Quant au mode méridien, il se manifeste par des fluctuations inter-hémisphériques de SST et est contrôlé par des rétroactions dynamiques et thermodynamiques entre le vent, l'évaporation et la SST. L'évaluation du couplage de ces variables clés du mode méridien nous a permis de proposer un modèle conceptuel pour expliquer les principaux mécanismes responsables des oscillations du mode méridien. Le modèle a montré que le mode méridien résulte de la superposition d'un mécanisme auto-entretenu basé sur les rétroactions positives et négatives générant des oscillations régulières de haute fréquence (2-3 ans) et d'un autre mécanisme d'oscillation basse fréquence (4-9 ans) lié à l'influence d'ENSO du Pacifique Est. Comme l'évolution de ces deux modes est fortement liée au déplacement méridien de la zone de convergence intertropicale (ITCZ) qui transporte les pluies, nous avons ensuite identifié la signature de ces modes sur la salinité de la surface de la mer à l'aide observations in situ et d'une simulation numérique régionale. Les processus océaniques et/ou atmosphériques responsables de la signature de chaque mode ont été également identifiés grâce à un bilan de sel dans la couche de mélange du modèle validé. Le bilan de sel a révélé que le forçage atmosphérique, lié à la migration de l'ITCZ, contrôle la région équatoriale tandis que l'advection, due à la modulation des courants, du gradient vertical et le mélange à la base de la couche de mélange, explique les variations de SSS dans les régions sous l'influence des panaches. [...]In this thesis, we investigate several topics related to the interannual climatic modes in the tropical Atlantic. Statistical analyses allows us to extract the two main dominant modes of interannual variability: an equatorial mode and a meridional mode. The equatorial mode is responsible for Sea Surface Temperature (SST) anomalies mainly found in the Gulf of Guinea and is linked to variations of the sea-level slope in the equatorial band. It is due to dynamic feedbacks between zonal wind, sea level and SST. The meridional mode is characterised by inter-hemispheric SST fluctuations and is controlled by dynamic and thermodynamic feedbacks between the wind, evaporation and SST. After quantifying the coupling between key variables involved in the meridional mode, we develop a conceptual model to explain the main mechanisms responsible for meridional mode oscillations. The model shows that the meridional mode results from the superposition of a self-sustaining mechanism based on positive and negative feedbacks generating regular oscillations of high frequency (2-3 years) and another low frequency oscillation mechanism (4-9 years) related to the influence of ENSO. As the evolution of these two modes is strongly linked to the meridional shift of the Intertropical Convergence Zone (ITCZ) and associated rainfall maximum, we identify the signature of these modes on Sea Surface Salinity (SSS) using in situ observations and a regional numerical simulation. Oceanic and/or atmospheric processes responsible for the signature of each mode are also identified through a mixed-layer salt budget in the validated model. The salt balance reveals that the atmospheric forcing, related to the ITCZ migration, controls the equatorial region while the advection, due to the modulation of current dynamics, the vertical gradient and mixing at the base of the mixed layer, explains SSS variations in regions under the influence of plumes. Finally, we study the Equatorial Kelvin wave characteristics and influences on the density that are involved in the meridional and equatorial mode connection processes, using a very simplified model of gravity wave propagation along the equator. After a brief description of this model, which was initially constructed to study dynamics in the equatorial Pacific, we apply it to the specific case of the equatorial Atlantic by validating its analytical and numerical solutions under adiabatic conditions. [...]
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Donohue, Kathleen A. "Wave propagation in the central equatorial Pacific Ocean." 1995. http://catalog.hathitrust.org/api/volumes/oclc/35904424.html.
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Mack, Andrew P. "High-frequency internal waves in the upper eastern equatorial Pacific." 1997. http://catalog.hathitrust.org/api/volumes/oclc/41182637.html.
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Tsai, Yu-Ying, and 蔡玉嫈. "Equatorial waves observed using FORMOSAT-3 GPS Occultation." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/8d2n48.
Full textAbstract:
碩士國立中央大學
太空科學研究所
96
Structure and propagation of equatorial atmospheric Kelvin waves and the latitudinal migration of intertropical convergence zone （ITCZ） during August 2006 and February 2008 are observed using FORMOSAT-3/COSMIC data. Zonal Kelvin wave derived from temperature fluctuations at 19 km characterize eastward phase propagation with the phase speed 2680 km/day, the wave periods are 12-17 days for zonal wave number 1 and 8-12 days for wave number 2. The vertical structure of Kelvin wave tilts eastward with height between 18-30 km, the phase propagates downward with the phase speed 0.5-1 km/day, and vertical wavelengths are 4-6 km in 2006 and 6-10 km in 2007. Integrated water vapor derived from COSMIC data shows one year variation in time-latitude section, high value region moved to the most southern part and northern part on February and August. It shows the characteristics of the latitudinal migration of ITCZ.
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Sun, Chaojiao. "Dynamic instability of stratified shear flow in the upper equatorial Pacific." Thesis, 1997. http://catalog.hathitrust.org/api/volumes/oclc/39803516.html.
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Gall, Jeffrey S. Frank William M. "The role of equatorial Rossby waves in tropical cyclogenesis /." 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-3735/index.html.
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Seidel, Howard Franklin. "Impact of realistic mean flow on equatorial waves in the Pacific Ocean." 1999. http://catalog.hathitrust.org/api/volumes/oclc/43964645.html.
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Fern, C. L., and 馮志龍. "Simulations of Pure Two-Stream Waves in the Equatorial E-region Ionosphere." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/74234128445303163268.
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博士國立中央大學
太空科學研究所
89
At the altitude range of 95∼110 km in the equatorial E-region ionosphere, a large current in the magnetic equator called the equatorial electrojet is created by a dynamic process involving atmospheric tides. The equatorial electrojet causes the medium to be unstable to generate plasma waves. Radar observations have shown the existence of two classes of plasma waves, called typeⅠand typeⅡ. The typeⅠwave resulting from the two-stream instability is also called two-stream wave. In this paper, the behavior of two-stream wave in the plane perpendicular to the Earth's magnetic field is simulated by a two-dimensional fluid model simulation code in which the electron inertia is neglected while the ion inertia is retained. We consider the suitable two-dimensional simulation space (27×54m ) and successfully excite the dominant 3-meter wave compatible with VHF radar echoes. The analysis methods of two-dimensional Fourier series are derived to express the time variation of mode powers and ω spectra. From the series of simulation results for two-stream waves in the equatorial E-region ionosphere, we have studied the dispersion relations, the resonant coupling, and the echo power variation with the zenith angle rate of approximately 0.3(dB/degree). We have also studied the vertical small-scale waves developed from the distortions of the dominant waves. The vertical waves will cause dominant waves to turn away from the electrojet drift direction (E×B ). The important point about the development of vertical modes is asymmetry. We find that the spectral asymmetry depends on the scale size of plasma waves, that is, the large-scale waves (above 3 meters) propagate in the k‧E＜0 region, and the small-scale (smaller than 3 meters) propagate in the k‧E＞0 region. The simulation result of up-down asymmetry for 3-meter wave is consistent with the radar observations. We believe that the background polarization electric field E driving the electrojet is responsible for the spectral asymmetries. In the same time, owning to the strong and fixed background polarization electric field E , the wave frequency depends only on horizontal wave number Kx . Therefore, the phase velocities of many obliquely propagating two-stream waves (Kz≠0 ) are below the value predicted by linear theory, and this characteristic is prominent especially for large-scale waves.
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Ascani, Francois. "Wave-induced deep equatorial ocean circulation." Thesis, 2008. http://hdl.handle.net/10125/20786.
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Thesis (Ph.D.)--University of Hawaii at Manoa, 2008.For weak Yanai wave amplitude, currents resembling the TEJs are obtained, but only within the beam. They are the mean Eulerian flow, which cancels the Stokes drift of the Yanai waves, yielding a zero-mean Lagrangian flow: the water parcels conserve their potential vorticity (PV) and are stationary over a wave cycle. With stronger amplitude, the Yanai waves become unstable, and lose their energy to small vertical scales where it is dissipated. The resulting vertical decay of the Yanai waves provides a source of PV, allowing water parcels to move meridionally within the beam. This process results in TEJs with a mean Lagrangian zonal flow extending to the west of the beam.
In the Pacific and Atlantic oceans, a complex equatorial current structure is found below the thermocline. The currents are zonal with typical speeds from 5 to 20 cm s-1 and extend as deep as 2500 m. The structure can be divided into two overlapping parts: the Tall Equatorial Jets (TEJs), with large vertical scale and alternating with latitude, and the Equatorial Deep Jets (EDJs), centered on the equator and alternating in the vertical with a wavelength of several hundred meters.
In the present study, using idealized numerical simulations and analytical solutions, we demonstrate that the TEJs could result from a rectification of a beam of monthly-periodic Yanai waves that is generated in the eastern part of the basin by instabilities of the swift equatorial surface currents.
This circulation poses a computational and a theoretical challenge. First, state-of-the-art high-resolution regional models and Ocean General Circulation Models (OGCMs) typically produce a rather weak, inaccurate and incomplete picture of the circulation. Second, the most promising existing theory, based on the rectification of intraseasonal Yanai waves, cannot account for the basin-wide presence of the TEJs.
Includes bibliographical references (leaves 148-157).
Also available by subscription via World Wide Web
158 leaves, bound 29 cm
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Das, Surajit. "Role Of Sea Surface Temperature Gradient In Intraseasonal Oscillation Of Convection In An Aquaplanet Model." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2583.
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In this thesis we examine intra-seasonal oscillations (ISO) in the aqua-planet setup of the Community Atmospheric Model (CAM) version 5.1, mainly based on July and January climatological sea surface temperature (SST). We investigate mainly two questions -what should be the SST distribution for the existence of (a) northward moving ISO in summer, and (b) eastward moving MJO-like modes in winter. In the first part of the thesis we discuss the northward propagation. A series of experiments were performed with zonally symmetric and asymmetric SST distributions. The basic lower boundary condition is specified from zonally averaged observed July and January SST.
The zonally symmetric July SST experiment produced an inter tropical convergence zone (ITCZ) on both sides of the equator. Poleward movement is not clear, and it is confined to the region between the double ITCZ. In July, the Bay of Bengal (BOB) and West Pacific SST is high compared to the rest of the northern tropics. When we impose a zonally asymmetric SST structure with warm SST spanning about 80 of longitude, the model shows a monsoon-like circulation, and some northward propagating convective events. Analysis of these events shows that two adjacent cells with cyclonic and anticyclonic vorticity are created over the warm SST anomaly and to the west. The propagation occurs due to the convective region drawn north in the convergence zone between these vortices.
Zonally propagating Madden-Julian oscillations (MJO) are discussed in the second part of the thesis. All the experiments in this part are based on the zonally symmetric SST. The zonally symmetric January SST configuration gives an MJO-like mode, with zonal wave number 1 and a period of 40-90 days. The SST structure has a nearly meridionally symmetric structure, with local SST maxima on either side of the equator, and a small dip in the equatorial region. If we replace this dip with an SST maximum, the time-scale of MJO becomes significantly smaller (20-40 days). The implication is that an SST maximum in the equatorial region reduces the strength of MJO, and a flat SST profile in the equatorial region is required for more energetic of MJO. This result was tested and found to be valid in a series of further experiments.
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Hyungeun, Shin. "Effect of equatorially trapped waves on the tropical cyclone drift." Thesis, 2019. http://hdl.handle.net/1828/11211.
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The movement of tropical cyclones (TC) is studied numerically based on a two-dimensional barotropic model, using a previously developed non-oscillatory balanced scheme. The model of TC used here takes an exponential form, and its size and strength are selected to be of a middle scale. Without a background flow, TCs move in the northwest direction due to the beta effect. The amplitudes of high wavenumber modes of the asymmetric flow, that are believed to be responsible for the TC drift, are computed using Fourier analysis. The amplitude of wavenumber one and two modes are dominant, so they are indicators of beta conversion of energy. Also, the effect of the monsoon trough on the TC movement is investigated. The results show a sudden change of the TC propagation path, consistent with earlier work. These two studies correspond to previous works. Here, the effect of equatorially trapped waves such as Kelvin, Rossby, and Mixed Rossby Gravity, on the TC path is newly studied by varying the wavenumber and wave speed of the underlying waves. The effect of the waves is considered because they are believed to contribute to cyclogenesis. For studying the effect, the barotropic flow induced by these waves via momentum transport and its variation were simulated for 50 days, and some patterns are found in the change of maximum wind speed. At a given time during the simulation, a TC is injected and the effect of the background wave is analyzed. Using the wavefield of 11 cases from 10 days to 30 days, the trajectories are calculated, and their patterns appear to be stochastic. So, the patterns are identified by calculating the mean path and its spread. The trajectories of TCs are different for different time of the waves. Kelvin waves make small variations on the length and direction of the trajectory of TCs. On the contrary, Rossby waves cause a dramatic change in the TC path and yield longer trajectories. Meanwhile, TCs in MRG waves keep fairly the same direction and usually have longer traveling distance. These changes vary by wave conditions. Therefore, the three kinds of waves have different effects on the trajectories of the TC. For some peculiar cases, the movements are explained based on wavefields.Graduate
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Namazi, Maryam. "Interaction of equatorially trapped waves and a background shear: numerical and theoretical issues." Thesis, 2010. http://hdl.handle.net/1828/3198.
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The equatorial atmosphere harbours a large spectrum of waves that are trapped
near and travel along the equator. These equatorially trapped waves interact nonlinearly
with each other, with the extra-tropics and with the planetary-barotropic
waves. Here, we consider advected shallow water equations that represent interactions
of these equatorial waves, associated with the first baroclinic mode, with prescribed
meridional-barotropic shears. We present three well-known numerical schemes for
handling this system and discuss the risk of applying them crudely to equatorial
waves. We study the properties of these waves, such as their phase speed and their
trapping around the equator, using two approaches: linear analysis and the time evolutions
of the system derived by meridional projection of the barotropic-first baroclinic
system. We show that in the sheared environment the symmetric (anti-symmetric)
equatorial waves excite other symmetric (anti-symmetric) equatorial waves of the
same wavenumber and of different strengths.
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Hsu, Shih-Pei, and 徐世裴. "Characteristics of Equatorial Rossby Wave in western North Pacific during Warm Season." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/25562130257435013084.
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碩士國立臺灣大學
大氣科學研究所
103
Equatorial Rossby wave (ER) is most active in western North Pacific (WNP) than in other tropical regions. Its active season starts from mid-May to mid-November when warm SST, cyclonic vorticity, zonal wind convergence and easterly vertical wind shear provide a preferable environment for ER to amplify in WNP. We perform an analysis of space-time filtered ER based on 10 years of data to extract ER signals. Two dominant types of ER are identified through an EOF analysis on 850mb ER vorticity and a subjective inspection of strong ER cases related to tropical disturbances. The 850mb horizontal structure of type-I ER features a wave structure along 7.5°N and 17.5°N. The ER vorticity and divergence are out of phase between the two latitudes within the wave train. The amplitude of the northern center is larger than that of the southern center. Stronger convection appears in the northern side exhibiting a first baroclinic structure. The southern side is associated with weaker convection and an equivalent barotropic vertical structure. The 850mb horizontal structure of type-II ER shows a dominant southwest-northeast tilted wave pattern indicating an unstable ER. For both types of ER, the positive (negative) phase of vorticity is accompanied with convergence (divergence) and convection (suppressed convection). The variance of vorticity for the two types of ER shows that they are most active within 90°E to 160°E and 5°N to 25°N. Type-II ER has a larger amplitude than that of type-I ER. Type-II ER is associated with stronger LF westerly wind anomaly (relative to summer climatology) than type-I ER; therefore LF zonal wind convergence is stronger and located more eastward for type-II ER. ER kinetic energy (KE) budget of multi-scale interaction is used to discuss the relationship between the two types of ER and their low frequency background state (LF). To derive ER KE budget equation, all variables are decomposed into three bands: LF, ER and high frequency field (HF). The contribution to the tendency of ER in the ER band (KT) is separated into generation from LF-ER interaction (KTEL) and HF-related interaction (KTH). KT gains via KTEL and loses through KTH. Two predominant processes contributing to KTEL are barotropic energy conversion (BC) and eddy geopotential flux convergence (GF). BC is mainly contributed by an accumulation of ER kinetic energy through low-frequency zonal wind convergence. Thus ER-II amplifies in a broader zonal extent east of that of ER-I. In addition, the ER momentum flux uv in northeast-southwest tilted type-II ER waves converts low-frequency kinetic energy with zonal wind shear into ER kinetic energy.. GF has positive contribution to KTEL in lower troposphere
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Liu, Yurun. "Nontraditional approximation in geophysical fluid dynamics." Thesis, 2009. http://hdl.handle.net/2152/ETD-UT-2009-05-156.
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In the conventional approach to geophysical fluid dynamics, only the horizontal components of the Coriolis force due to horizontal motions of the fluid are taken into account. All the other components of the Coriolis force, which are called the non-traditional (NT) terms, are considered to be small second order quantities and are usually dropped. This effectively simplifies the system and the nice and clean quasi-geostrophic (QG) equation can be obtained, which is widely used in analytical studies of climate systems. Interest has been drawn to the dropped terms in recent studies. It is shown that in some special cases these second order terms actually have a noticeable influence on the dynamics of the system. However, a full picture of these terms in the dynamics of the real ocean is still lacking. Here, we will start from the fundamental equations of fluid dynamics, and through careful scaling analysis conduct a detailed study of the governing equations of geophysical fluid dynamics while keeping the NT terms. We will specifically investigate the influence of these NT terms on equatorial waves, since near the equator the NT components of the Coriolis force are the most significant.text
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Ferguson, James. "A numerical solution for the barotropic vorticity equation forced by an equatorially trapped wave." Thesis, 2008. http://hdl.handle.net/1828/1218.
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To understand the mechanisms of energy exchange between the tropics and the
midlatitudes, it is necessary to develop simplified climate models. Motivated by
linear wave theory, one such model is derived below. It captures the nonlinear
interaction between barotropic and first baroclinic modes. In particular, it allows
for the study of the barotropic response to a baroclinic forcing. Numerical methods
for handling this nonlinear system are carefully developed and validated. The
response generated by a physically realistic Kelvin wave forcing is studied and is
found to consist mainly of one eastward propagating wave (phase-locked to the
forcing) and two westward propagating (Rossby) waves. The Rossby waves are
shown to be highly constrained by the initial parameters of the forcing and an
explanation of this result is proposed.