Дисертації з теми "Intraseasonal Oscillation in Atmosphere"
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1
Teng, Haiyan. "Interannual variations of the boreal summer intraseasonal oscillation." Thesis, University of Hawaii at Manoa, 2003. http://proquest.umi.com/pqdweb?index=0&did=765086511&SrchMode=2&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1233255418&clientId=23440.
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2
Burton, Kenneth R. "Influence of Antarctic oscillation on intraseasonal variability of large-scale circulations over the Western North Pacific /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Mar%5FBurton.pdf.
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3
Burton, Kenneth R. Jr. "Influence of Antarctic oscillation on intraseasonal variability of large-scale circulations over the Western North Pacific." Thesis, Monterey California. Naval Postgraduate School, 2005. http://hdl.handle.net/10945/2310.
Повний текст джерелаАнотація:
Approved for public release, distribution is unlimitedThis study examines Southern Hemisphere mid-latitude wave variations connected to the Antarctic Oscillation (AAO) to establish connections with the 15- to 25-day wave activity in the western North Pacific monsoon trough region. The AAO index defined from the leading empirical orthogonal functions of 700 hPa height anomalies led to seven distinct circulation patterns that vary in conjunction with the 15- to 25-day monsoon trough mode. For nearly one half of the significant events the onset of 15- to 25-day monsoon trough convective activity coincided with a peak negative AAO index and the peak in monsoon trough convection coincided with a peak positive index. The remaining events either occur when the AAO is not significantly varying or when the AAO-related Southern Hemisphere mid-latitude circulations do not match 15- to 25-day transitions. When a significant connection occurs between the Southern Hemisphere mid-latitude circulations related to the AAO and the 15- to 25-day wave activity in the western North Pacific monsoon trough, the mechanism is via equatorward Rossby-wave dispersion. When wave energy flux in the Southern Hemisphere is directed zonally, no connection is established between the AAO and the alternating periods of enhanced and reduced convection in the western North Pacific monsoon trough.
Captain, United States Air Force
4
McDaniel, Brent. "Intraseasonal Dynamical Evolution of the Northern Annular Mode." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6965.
Повний текст джерелаАнотація:
Recent observational and modeling studies indicate a robust dynamical coupling between the stratosphere and troposphere during boreal winter. This coupling occurs in association with the Northern Annular Mode (NAM), which itself accounts for a significant fraction of the variability of the extratropical circulation. While monthly NAM dynamics have been studied previously, the mechanisms that give rise to NAM variability on short intraseasonal timescale are still unclear.
We perform regression analyses, case studies, and composites based on periods of dynamical growth/decay to investigate the roles of the different proposed mechanisms in driving the atmospheric variability observed in association with the NAM on short intraseasonal timescales. More specifically, lag-regression analyses are used to identify the mean canonical structures present during the evolution of a typical NAM event. Illustrative case studies of robust stratospheric NAM events but with different tropospheric signals are contrasted in order to identify the underlying dynamical reasons for the observed differences. Finally, composite analyses of NAM tendencies are performed to isolate the structural and dynamical evolution of NAM events. Zonal-mean and three-dimensional eddy-flux diagnoses are used to examine the role of eddy-mean flow interaction in driving the wind tendencies characteristic of the NAM. In particular, Plumb flux analyses are employed to quantify the contribution of regional stationary wave anomalies toward the zonal mean wind tendency field. Potential vorticity inversions are also used to determine the role of stratospheric anomalies in inducing tropospheric circulations.
The case study analyses indicate that preexisting tropospheric PV anomalies can mask the downward penetration of an initial stratospheric NAM signal into the troposphere. PV inversions further suggest that a minimum requirement for a direct downward stratospheric influence is that the stratospheric NAM signal be robust in the lower stratosphere.
The dynamical composites show a remarkable degree of reverse symmetry between the zonal-mean dynamical evolution of positive and negative NAM events. Anomalous Eliassen-Palm fluxes are observed in the troposphere and stratosphere, consistent with index of refraction considerations and an indirect downward influence of the stratosphere on the troposphere. The patterns of anomalous wave driving, primarily due to low-frequency planetary scale waves, provide the main forcing of the zonal mean wind tendency field. Regional wave activity fluxes indicate that the wave driving pattern represents the manifestation of planetary scale anomalies over the North Atlantic.
5
Agudelo, Paula A. "Role of Local Thermodynamic Coupling in the Life Cycle of the Intraseasonal Oscillation in the Indo-Pacific Warm Pool." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19834.
Повний текст джерелаАнотація:
Intraseasonal oscillations (ISOs) are important elements of the tropical climate with time-scales of 20-80 day. The ISO is poorly simulated and predicted by numerical models. This work presents a joint diagnostic and modeling study of the ISO that examines the hypothesis that local coupling between the ocean and the atmosphere is essential to the existence and evolution of the ISO in the Indo-Pacific warm pool region. Low-level moistening during the transition phase preconditions the atmosphere for deep convection. The vertical structure of ISO from the ECMWF coupled model during different phases of the oscillation as well as the skill of the model in simulating the processes that occur during the transition phase were studied. The forecast skill of the vertical structure associated with the ISO is greater for winter than for summer events. Predictability of the convective period is poor when initialized before the transitional phase. When initialized within the transition period including lower tropospheric moistening, predictability increases substantially, although the model parameterizations appears to trigger convection quickly without allowing an adequate buildup of CAPE during the transition. The model tends to simulate a more stable atmosphere compared to data, limiting the production of deep convective events. Two different one-dimensional coupled models are used to analyze the role of local ocean-atmosphere coupling in generating ISO. The ocean component is a one-dimensional mixed layer model. In the first model the atmospheric component corresponds to the SCCM. Results suggest that convection in the model tends to be "overactive," inhibiting development of lower frequency oscillations in the atmosphere. In the second case, the atmospheric component is a semi-empirical model that allows reproducing the coupled ISO over long integration periods including only local mechanisms. In the semi-empirical scheme the rate of change of atmospheric variables is statistically related to changes in SST. The stable state of this model is a quasi-periodic oscillation with a time scale between 25 and 80 days that matches well the observed ISO. Results suggest that the period of the oscillation depends on the characteristics of the ocean mixed layer, with a higher frequency oscillation for a shallow mixed layer.
6
Zuluaga-Arias, Manuel D. "Spatial and temporal distribution of latent heating in the South Asian monsoon region." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31753.
Повний текст джерелаАнотація:
Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2010.Committee Chair: Peter J. Webster; Committee Member: Judith A. Curry; Committee Member: Robert X. Black. Part of the SMARTech Electronic Thesis and Dissertation Collection.
7
Matthews, Adrian John. "The intraseasonal oscillation." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358464.
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8
Hoyos, Carlos D. "Intraseasonal Variability: Processes, Predictability and Prospects for Prediction." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04102006-135125/.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2006.Dr. Peter J. Webster, Committee Chair ; Dr. Judith A. Curry, Committee Member ; Dr. Robert Dickinson, Committee Member ; Dr. Robert X. Black, Committee Member ; Dr. Predrag Cvitanovic, Committee Member.
9
Charlesworth, Oliver. "Intraseasonal European climate variability and interactions with the Madden-Julian Oscillation." Thesis, University of East Anglia, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490613.
Повний текст джерелаАнотація:
The seasonally-varying interaction between the Madden-Julian Oscillation (MJO) and .the northern extratropics, specifically the North Atlantic and Europe region, on intraseasonal timescales is studied. When the MJO is observed using composite and Monte-Carlo significance testing, a direct response to the tropical dynamics is found over the North Atlantic and Europe. When the MJO convection is active over the Indian Ocean, significant anticyclonic anomalies at the 95% confidence level are frequently found over the UK and eastern North Atlantic region. Approximately 10 to 20 days later, when the MJO convection is active over Indonesia, the extratropical anomalies occur in similar locations with opposite sign. Using a systematic two-month sliding season approach to investigate the interaction, the anomalies are present for the majority of the year, favouring the boreal spring. The relationship between the MJO and the North Atlantic Oscillation (NAO) for each of the 12 seasons throughout the year is quantified for the first time using regression analysis. Although correlations between the MJO and NAO are weak, further regressions between the MJO and a North Atlantic 1000 hPa geopotential height index just east of the UK gives very strong boreal springtime correlations of up to r=0.50 and anti-correlations of r=-0.53. An Intermediate Global Circulation Model (IGCM) is used to model the MJO to investigate the mechanisms behind the strong tropical-extratropical interactions. Various stages of representing the MJO in the model are presented using fixed and time dependent heating profiles and many of the observed extratropical features are reproduced as a response to the forcing. Direct comparisons between the observations and the model results are made and the level at which it is able to reproduce the North Atlantic and European anomalies is discussed.
10
Valad?o, Cati Elisa de Avila. "Impacts of the Madden-Julian oscillation on intraseasonal precipitation over northeast Brazil." Universidade Federal do Rio Grande do Norte, 2015. http://repositorio.ufrn.br/handle/123456789/20695.
Повний текст джерелаАнотація:
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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
The impacts of the Madden?Julian Oscillation (MJO) on precipitation over Northeast Brazil (NEB, also known as Nordeste) are evaluated based on daily raingauge data from 492 stations over 30-year period (1981-2010). Composites of precipitation, outgoing longwave radiation and moisture-flux anomalies are performed for each phase of the MJO based on the Jones?Carvalho MJO index. To distinguish the MJO signal from other patterns of climate variability, daily data are filtered using a 20 - 90 day band-pass filter; only days classified as MJO events are considered in the composites. A preliminary analysis based on precipitation data was conducted for a small scale area located in NEB?s semiarid interior, in an area known as Serid?. The Serid? is one of the driest regions in NEB, and is recognized by the United Nations Convention to Combat Desertification as particularly vulnerable to desertification. Composites of rainfall anomalies were computed for each of the eight phases of the MJO during February-May, which is Serid??s main rainy season. Results showed that the rainfall patterns in Serid? undergo substantial changes (from enhancement to suppression) as the convective center of the MJO propagates eastward. When combining the MJO signals for wet and dry phases, the difference represents about 50 - 150% modulation of the mean rainfall over Serid?. Then a comprehensive analysis of the role of the MJO in modulating the spatiotemporal variation of NEB?s precipitation was performed, considering all four seasons. The results showed strong seasonality of the MJO impact on precipitation. The most spatially coherent signals of precipitation anomalies occurred in the austral summer, when about 80% of the raingauge stations showed increased precipitation during phases 1 - 2 and suppressed precipitation in phases 5 - 6 of the oscillation. Although the MJO impacts precipitation on intraseasonal timescales in all seasons in most locations, these impacts vary in magnitude and depend on the phase of the oscillation. Precipitation anomalies over NEB are explained by the interaction of convectively coupled Kelvin-Rossby waves with the dominant climatic features in each season. During the austral summer and spring, westerly regimes increased precipitation over most NEB. In the austral winter and fall, precipitation anomalies exhibited more complex spatial variability. In these seasons precipitation anomalies in eastern coastal areas depended on the strength of the South Atlantic anticyclone, which is largely modulated by Rossby waves. The strengthening of the anticyclone intensified the convergence of the trade winds in coastal areas and precipitation windward of the coastal range. Conversely, the intensification of the subsidence was responsible for precipitation deficits in the lee side of the range. These conditions were typically observed when easterly regimes dominate over tropical South America and NEB, decreasing moisture flow from the Amazon.
Este estudo tem como objetivo investigar os impactos da oscila??o de Madden-Julian (OMJ) na precipita??o da regi?o Nordeste do Brasil (NEB). Para tanto foram utilizados dados di?rios de precipita??o baseados em 492 pluvi?metros distribu?dos na regi?o e cobrindo um per?odo de 30 anos (1981 ? 2010). As an?lises atrav?s de composi??es de anomalias de precipita??o, radia??o de onda longa e fluxo de umidade, foram obtidas com base no ?ndice da OMJ desenvolvido por Jones-Carvalho. Para distinguir o sinal da OMJ de outros padr?es de variabilidade clim?tica, todos os dados di?rios foram filtrados na escala de 20 ? 90 dias; portanto somente dias classificados como eventos da OMJ foram considerados nas composi??es. Uma an?lise preliminar baseada apenas nos dados de precipita??o foi feita para uma pequena ?rea localizada no interior semi?rido do NEB, conhecida como Serid?. Essa microrregi?o ? uma das ?reas mais secas do NEB e foi reconhecida pela Conven??o das Na??es Unidas para o Combate ? Desertifica??o e Mitiga??o dos Efeitos das Secas como particularmente vulner?vel ? desertifica??o. Composi??es de anomalias de precipita??o foram feitas para cada uma das oito fases da OMJ durante Fevereiro-Maio (principal per?odo chuvoso da microrregi?o). Os resultados mostraram a exist?ncia de varia??es significativas nos padr?es de precipita??o (de precipita??o excessiva ? deficiente) associados ? propaga??o da OMJ. A combina??o dos sinais de precipita??o obtidos durantes as fases ?midas e secas da OMJ mostrou que a diferen?a corresponde cerca de 50 ? 150% de modula??o das chuvas na microrregi?o. Em seguida, uma investiga??o abrangente sobre o papel da OMJ sobre toda a regi?o Nordeste foi feita considerando-se as quatro esta??es do ano. Os resultados mostraram que os impactos da OMJ na precipita??o intrassazonal do NEB apresentam forte sazonalidade. A maior coer?ncia espacial dos sinais de precipita??o ocorreram durante o ver?o austral, quando cerca de 80% das esta??es pluviom?tricas apresentaram anomalias positivas de precipita??o durante as fases 1 ? 2 da OMJ e anomalias negativas de precipita??o nas fases 5 ? 6 da oscila??o. Embora impactos da OMJ na precipita??o intrassazonal tenham sido encontrados na maioria das localidades e em todas as esta??es do ano, eles apresentaram varia??es na magnitude dos sinais e dependem da fase da oscila??o. As anomalias de precipita??o do NEB observadas s?o explicadas atrav?s da intera??o existente entre as ondas de Kelvin-Rossby acopladas convectivamente e as caracter?sticas clim?ticas predominantes sobre a regi?o em cada esta??o do ano. O aumento de precipita??o observado sobre a maior parte do NEB durante o ver?o e primavera austrais encontra-se associado com o fluxo de umidade de oeste (regime de oeste), o qual favorece a atividade convectiva em amplas ?reas da Am?rica do Sul tropical. Por outro lado, as anomalias de precipita??o durante o inverno e outono austrais apresentaram uma variabilidade espacial mais complexa. Durante estas esta??es, as anomalias de precipita??o observadas nas esta??es localizadas na costa leste do NEB dependem da intensidade do anticiclone do Atl?ntico Sul, o qual ? modulado em grande parte por ondas de Rossby. As caracter?sticas topogr?ficas do NEB parecem desempenhar um papel importante na variabilidade observada na precipita??o, principalmente nestas ?reas costeiras. A intensifica??o do anticiclone aumenta a converg?ncia dos ventos al?sios na costa contribuindo para a ocorr?ncia de precipita??o observada ? barlavento do planalto da Borborema. Por outro lado, o aumento da subsid?ncia parece ser respons?vel pelos d?ficits de precipita??o observados ? sotavento. Tais condi??es mostraram-se t?picas durante o predom?nio do regime de leste sobre a regi?o tropical da Am?rica do Sul e o NEB, durante o qual ocorre uma diminui??o no fluxo de umidade proveniente da Amaz?nia.
11
Drbohlav, Hae-Kyung Lee. "Mechanism of the intraseasonal oscillation in the South Asian summer monsoon region." Thesis, University of Hawaii at Manoa, 2002. http://proquest.umi.com/pqdweb?index=0&did=765064431&SrchMode=1&sid=1&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1209149181&clientId=23440.
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12
Ruth, Sarah L. "The quasi-biennial oscillation in the middle atmosphere." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303598.
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13
Batstone, Crispian Peter. "Ocean-atmosphere interactions within the Madden-Julian Oscillation." Thesis, University of East Anglia, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398818.
Повний текст джерела
14
Fraza, Erik. "The Global 3-Dimensional Structure of the Pacific Decadal Oscillation." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1281395658.
Повний текст джерела
15
Klingaman, Nicholas Pappas. "The intraseasonal oscillation of the Indian summer monsoon : air-sea interactions and the potential for predictability." Thesis, University of Reading, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501512.
Повний текст джерелаАнотація:
Summer monsoon rainfall accounts for at least 80% of the annual-total precipitation in many Indian states. Intraseasonal variations (ISV) in rainfall produce floods and droughts that can devastate agriculture. ISVs are dominated by a 30-50 day northward-propagating oscillation (NPISO) between the eastern equatorial Indian Ocean (EEqIO) and India. This thesis evaluates the hypothesis that atmosphere-ocean interactions are critical to the NPISO's period, intensity, and propagation. Two simple NPISO indices are created from lag correlations in outgoing longwave radiation between the oscillation's two poles. The index in which India leads the EEqIO better captures the NPISO, implying that convection in the EEqIO cannot predict Indian rainfall. An idealized NPISO lifecycle suggests that air-sea interactions occur via atmospheric thermodynamic forcing and a feedback from SSTs on low-level atmospheric stability.
16
Hood, Lon L. "QBO/solar modulation of the boreal winter Madden-Julian oscillation: A prediction for the coming solar minimum." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/624342.
Повний текст джерелаАнотація:
The Madden-Julian oscillation (MJO), also known as the 30-60day oscillation, is the strongest of the intraseasonal climate oscillations in the tropics and has significant derivative effects on extratropical circulation and intraseasonal climate. It has recently been shown that the stratospheric quasi-biennial oscillation (QBO) modulates the amplitude of the boreal winter MJO such that MJO amplitudes are larger on average during the easterly phase (QBOE) than during the westerly phase (QBOW). A major possible mechanism is the decrease in static stability in the lowermost stratosphere under QBOE conditions resulting from relative upwelling associated with the QBO-induced meridional circulation. Here evidence is presented that tropical upwelling changes related to the 11year solar cycle also modulate the boreal winter MJO. Based on 37.3years of MJO amplitude data, the largest amplitudes and occurrence rates, and the weakest static stabilities in the tropical lower stratosphere, occur during the QBOE phase under solar minimum (SMIN) conditions while the smallest amplitudes and strongest static stabilities occur during the QBOW phase under solar maximum (SMAX) conditions. Conversely, when the QBO and solar forcings are opposed (QBOW/SMIN and QBOE/SMAX), the difference in occurrence rates becomes statistically insignificant. During the coming solar minimum, at least one additional winter in the QBOE/SMIN category should occur (possibly as early as 2017/2018) during which especially large MJO amplitudes are expected and an initial test of these results will be possible. Plain Language Summary An ongoing issue in climate science is the extent to which upper atmospheric processes, including solar forcing, can influence tropospheric climate. It has recently been shown that an internal oscillation of the stratosphere, the quasi-biennial oscillation, can modulate the amplitude and occurrence rate of intraseasonal climate oscillations in the tropical Pacific during northern winter. These intraseasonal oscillations, the most important of which is the 30-60day Madden-Julian oscillation, have significant derivative effects on climate outside of the tropics, including impacts on rainfall events over the continental United States. Here evidence is presented that the amplitude of the Madden-Julian oscillation during northern winter is also modulated by the 11year solar cycle. The modulation is such that amplitudes and occurrence rates are largest under solar minimum conditions when the quasi-biennial oscillation is in its easterly phase and smallest under solar maximum conditions when the quasi-biennial oscillation is in its westerly phase. However, the available time record (37.3years of satellite measurements) is limited. During the coming solar minimum, at least one additional winter in the solar minimum/easterly category should occur (possibly as early as 2017/2018) during which larger-than-average amplitudes are expected and an initial test of the proposed relationship will be possible.
17
Youderian, Bria Danielle. "Influence of the Atlantic Multidecadal and the Pacific Decadal Oscillations on Hemispheric Air Temperature and Cloud Cover." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1250099376.
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Maloney, Eric Daniel. "Frictional convergence and the Madden-Julian oscillation /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/10049.
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Agard, John Vincent. "A global and tropical quasi-decadal oscillation of the atmosphere and Ocean." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/114373.
Повний текст джерелаАнотація:
Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 72-75).
An oscillatory, quasi-periodic signal with a period of around 10 years was found in radiosonde- and satellite-measured datasets of lower stratospheric temperature. Power spectrum analysis and Fourier decomposition were used to characterize the temporal and vertical manifestations of the signal, while EOF analyses were used to analyze its spatial characteristics. The oscillation was found to be unrelated to the solar activity cycle, while it displayed coherence with similar oscillatory signals in ENSO, PDO and AMO indices, as well as with a quasi-decadal signal in SST data. Finally, the quasi-decadal signal in lower stratospheric temperature was found to have a small but measurable contribution to the signal of tropical cyclone potential intensity in the Atlantic MDR.
by John Vincent Agard.
S.B.
20
Donald, Alexis. "The application of the real-time multivariate Madden-Julian Oscillation Index to intraseasonal rainfall forecasting in the mid-latitudes." University of Southern Queensland, Faculty of Sciences, 2004. http://eprints.usq.edu.au/archive/00001423/.
Повний текст джерелаАнотація:
The Madden-Julian Oscillation is a tropical atmospheric phenomenon detected as anomalies in zonal winds, convection and cloudiness. This perturbation has a definitive timescale of about thirty to sixty days, allowing its signal to be extracted from background data. The Madden-Julian Oscillation originates over the western Indian Ocean and generates a convective region which moves east along the equatorial region. This perturbation is thought to contribute to the timing and intensity of the eastern hemisphere monsoons, the El Niño/ Southern Oscillation and tropical storms and cyclones. The current understanding of the Madden-Julian Oscillation is that it restricts the bulk of its' influence to the tropics, however some evidence suggested that the impact is more extensive. Analysis of about 30 years of data showed significant modulation of rainfall by the equatorial passage of the MJO. The real-time multivariate Madden-Julian Oscillation Index was used to estimate the location and amplitude of the Madden-Julian Oscillation, and forms the basis of the basic rainfall prediction tool developed. The method developed here clearly linked the low latitude passage of the Madden-Julian Oscillation with suppressed and enhanced rainfall events in the Australasian region and beyond. A rudimentary forecasting capability at the intraseasonal time scale has been developed suitable for assisting Australian agricultural sector. A subsequent and independent analysis of global mean sea level pressure anomalies provided evidence of teleconnections between the Madden-Julian Oscillation and higher latitude atmospheric entities. These anomalies confirm the existence of teleconnections capable of producing the rainfall pattern outputs. The MJO is strongly influenced by the season. However the seasonally dependant analysis of rainfall with respect to the Madden Julian Oscillation conducted was inconclusive, suggesting aspects of the MJO influence still require clarification. Considering the importance of rainfall variability to the Australian agricultural sector the forecasting tool developed, although basic, is significant.
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Lavender, Sally L. "Modelling the intraseasonal variability of the West African monsoon : influence of the Madden-Julian oscillation and regional soil moisture anomalies." Thesis, University of East Anglia, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504848.
Повний текст джерелаАнотація:
The mechanisms controlling the intraseasonal variability of the West African monsoon (WAM) are investigated. Knowledge of these mechanisms will help to improve forecasting capabilities over the West African region. There are two dominant modes of variability, one within the 25-60-day band and one with an average period of 15 days. Observations show that the 25-60-day variability in rainfall over West Africa is influenced by the Madden-Julian oscillation (MJO). A number of mechanisms have been suggested. However, previous observational studies are not able to easily distinguish between cause and effect. Intraseasonal convective anomalies over West Africa are simulated in an atmospheric general circulation model (AGCM) as a response to imposed sea surface temperature (SST) anomalies associated with the MJO over the equatorial warm pool region. Negative midtropospheric temperature anomalies, associated with negative SSTs and reduced convection, over the warm pool propagate eastwards as a Kelvin wave and westwards as a Rossby wave, reaching Africa approximately 10 days later. The negative midtropospheric temperature anomalies act to destabilise the troposphere resulting in .enhanced convection over West Africa. Variability in soil moisture has the potential to feedback on the atmosphere and hence rainfall, on a regional scale. The I5-day westward-propagating mode found previously in rainfall is detected in soil moisture observations. A set of AGCM experiments is performed to analyse the influence of soil moisture on the WAM. The I5-day westwardpropagating signal in precipitation is found to exist in the model independent of soil moisture. However, soil moisture is found to feedback into the atmosphere via changes in evaporation which ultimately result in anomalies in the low level circulation. The anomalies in low-level circulation can then change the supply of moist, unstable air to the region, influencing the convective anomalies.
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Quilfen, Yves. "Variations interannuelles de l'atmosphere atlantique tropicale et interactions avec l'ocean." Paris 6, 1987. http://www.theses.fr/1987PA066592.
Повний текст джерелаАнотація:
La variabilite interannuelle du systeme couple ocean-atmosphere dans l'ocean atlantique tropical est etudiee a l'aide de donnees historiques. Les fichiers de donnees couvrent l'atlantique entre 30 non=n et 20 non=s, de 1964 a 1979. Les differentes echelles de temps et d'espace sont determinees par l'intermediaire de l'analyse en composantes principales des fichiers de pression atmospherique au niveau de la mer, de temperature de surface de la mer et de tension du vent. Un signal basse frequence est associe a la variabilite atmospherique dans la zone equatoriale. Il fait partie des variations de la circulation atmospherique zonale a l'echelle planetaire et enregistre ainsi la signature dans l'atlantique des evenements chauds du pacifique (bien connus sous le nom de "el nino - oscillation sud"). Un tel index se revele tres utile dans la perspective d'une prevision des evenements chauds de l'atlantique. Il est cependant necessaire de prendre en compte les traits particuliers de l'atlantique tropical parce que: 1) le cycle saisonnier dans l'ocean atlantique peut etre important dans le developpement des anomalies a long terme du systeme couple; 2) les variations intrinseques du systeme couple dans l'atlantique induisent des anomalies a grande echelle independamment du systeme global planetaire (par exemple en 1968); 3) la position meridienne des structures (par exemple de l'itoz) souligne l'importance des anticyclones subtropicaux, specialement celui des acores
23
施錦杯 and Kam-pui Sze. "Effects of the interaction of atmosphere and ocean on humanactivities." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31254378.
Повний текст джерела
24
Semedo, Alvaro A. M. "The North Atlantic oscillation influence on the wave regime in Portugal : an extreme wave event analysis /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Mar%5FSemedo.pdf.
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Sze, Kam-pui. "Effects of the interaction of atmosphere and ocean on human activities /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21301414.
Повний текст джерела
26
Li, Wei 1982. "The variability of North American winter surface temperature and its relation to the sea surface temperature /." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101604.
Повний текст джерелаАнотація:
The first two empirical orthogonal functions of the winter (DJF) surface air temperature (SAT) over North America are associated with the North Atlantic Oscillation (NAO) and the Pacific/North American (PNA) pattern in the NCEP reanalysis. Lagged correlations between the North American SAT structures and the sea surface temperature (SST) were computed. There is a small lag between the tri-pole SST anomaly pattern of the North Atlantic Ocean and the first SAT mode. The second SAT mode lags the eastern Tropical Pacific SST anomaly by two months, associated with ENSO through the winter. A similar analysis is conducted on the seasonal forecasts to see if the forecast models capture the above links. GCM3 captures the ENSO forcing and has the PNA response. GEM captures the link between the SAT and the tripole SST anomaly pattern in North Atlantic. Although GEM captures the ENSO signal, it cannot form the PNA to further this tropical forcing into North America.
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Marshall, Samuel David. "Sloping convection : an experimental investigation in a baroclinic annulus with topography." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ca9cfaf5-49e8-4e30-b93a-65c27d1c8a15.
Повний текст джерелаАнотація:
This thesis documents a collection of experimental investigations in which a differentially-heated annulus was used to investigate the effects of topography on the atmospheric and oceanic circulation. To this end a number of experiments were devised, each using a different topographic base to study a different aspect of the impact of topography, motivated by the most notable outstanding questions found in a review of the literature, namely exploring the effects of topographic resonance, blocking via partial barriers, and azimuthally differential-heating via thermal topography. First of all, whilst employing sinusoidal wavenumber-3 topography to extend the experimental parameter space of a similar study, namely Read and Risch (2011), a new regime within a region of structural vacillation was encountered. Denoted as the ‘stationary-transition’ regime, it featured periodic oscillations between a dominant stationary wavenumber-3 flow and axisymmetric or chaotic flow. An investigation into topographic resonance followed, keeping the wavenumber-3 base, but with a sloped lid to add a beta effect to the annulus. This acted to increase the occurrence of stationary waves, along with the ‘stationary-transition’ regime, which was discovered to be a near-resonant region where nonlinear topographic resonant instability led to a 23 to 42 ‘day’ oscillatory structure. The base was then replaced with an isolated ridge, forming a partial barrier to study the difference between blocked and unblocked flow. The topography was found to impact the circulation at a level much higher than its own peak, causing a unique flow structure when the drifting flow and the topography interacted in the form of an ‘interference’ regime at low Taylor Numbers, as well as forming an erratic ‘irregular’ regime at higher Taylor Numbers. Lastly, this isolated ridge was replaced by flat heating elements covering the same azimuthal extent, in order to observe whether thermal topography could be comparable to mechanical topography. These azimuthally-varying heating experiments produced much the same results as the partial barriers study, despite the lack of a physical peak or bottom-trapped waves, suggesting that blocking is independent of these activities. Evidence of resonant wave-triads was noted in all experiments, though the component wavenumbers of the wave-triads and their impact on the flow was found to depend on the topography in question.
28
Boschat, Ghyslaine. "Variabilité interannuelle et prévisibilité du système Mousson Indienne d'Eté - Oscillation Australe El Niño." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00789861.
Повний текст джерелаАнотація:
La Mousson Indienne d'été (ISM) et l'Oscillation Australe El Niño (ENSO) sont parmi les phénomènes climatiques les plus énergétiques et importants de la planète. Bien qu'ils soient localisés dans la région tropicale Indo-Pacifique, ces deux phénomènes peuvent avoir des répercussions climatiques à l'échelle globale via les téléconnections atmosphériques. Cette thèse vise à améliorer notre compréhension et la prévisibilité interannuelle d'ENSO et de l'ISM, en analysant leurs téléconnections grandes échelles, et en déterminant le rôle, dans cette prévisibilité, des modes majeurs de variabilité interannuelle observés dans les régions tropicales et extratropicales de l'Indo-Pacifique. A partir de diagnostiques statistiques d'observations sur les périodes 1950-1976 et 1979 2007, et d'expériences de sensibilité réalisées à l'aide du modèle couplé SINTEX F, nous montrons l'importance des latitudes tempérées dans la prévisibilité du système ENSO-mousson. Des précurseurs robustes des évènements ENSO et ISM sont identifiés dans les régions du Pacific Nord et de l'Océan Indien Sud pendant l'hiver boréal précédent, apportant ainsi de la prévisibilité plus tôt que leurs traditionnels précurseurs tropicaux. De plus, cette prévisibilité de la mousson d'été est accrue pour les pluies en fin de saison (Août- Septembre). Cette deuxième partie de la saison de mousson se caractérise également par l'émergence de processus couplés océan-atmosphère dans l'Océan Indien, pouvant contrecarrer l'effet d'ENSO sur la mousson. Une amplification de ces rétroactions locales pourrait expliquer l'affaiblissement de la relation ENSO-mousson observé lors des dernières décennies.
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Jacobi, Christoph. "Possible signal of tropospheric circulation patterns in middle atmosphere dynamics, Collm (51.3°N, 13°E) mesosphere lower thermosphere winds: 1979 - 2008." Universität Leipzig, 2009. https://ul.qucosa.de/id/qucosa%3A16368.
Повний текст джерелаАнотація:
Time series of monthly mean Collm mesosphere/lower thermosphere winds 1979 - 2008 are analyses with respect to a possible correlation with North Atlantic Oscillation (NAO) and Southern Oscillation (SO) indices. There is a positive correlation with both indices until the middle 1990s, but later the correlation decreases or even reverses. Owing to the coupling of the SO with the NAO the change of correlation occurs broadly at the same time. The change of correlation is probably connected with changes of the middle atmosphere mean dynamics.Zeitreihen von Monatsmittelwerten des Windes in der Mesosphäre/unteren Thermosphäre über Collm werden auf mögliche Korrelationen mit der Nordatlantischen Oszillation (NAO) und der Südlichen Oszillation (SO) hin untersucht. Während eine positive Korrelation bis in die 1990er Jahre existiert, schwächt sich diese in der Folge ab und kehrt sich teilweise um. Da NAO und SO gekoppelt sind, erfolgen diese Änderungen etwa zur selben Zeit. Die Änderung der Kopplung steht wahrscheinlich in Verbindung mit einer generellen Änderung der Dynamik der mittleren Atmosphäre.
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Chen, Ying-quei. "Pedictability of ENSO : optimal error growth and forecast skill /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10023.
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31
Melaragno, Scott Andrew. "The Global Three-Dimensional Structure for the Developmental Phase of ENSO." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1281658857.
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SOUSA, Edicarlos Pereira de. "Padrões climáticos de eventos extremos de chuva utilizando análise multivariada e de ondeletas no Estado de Minas Gerais." Universidade Federal de Campina Grande, 2016. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1485.
Повний текст джерелаАнотація:
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Capes
O estado de Minas Gerais, localizado na região Sudeste do Brasil, possui um território planáltico, com áreas mais elevadas situadas na porção sul. O clima é predominantemente tropical e tropical de altitude, com temperaturas oscilando, normalmente, entre 17 e 20°C. Tais características o tornam, muitas vezes, susceptível a fortes chuvas, provocando transtornos diversos à população. Desse modo, buscou-se analisar a variabilidade da chuva mineira através de técnicas que fossem capazes de definir padrões espaciais e temporais de eventos secos e chuvosos, assim como modulá-los nas escalas tempo-frequência. Para isso, calculou-se o Índice de Precipitação Normalizada (IPN) mensal e trimestral no período 1977-2012. A fim de encontrar padrões espaço-temporais e regiões homogêneas (RH) do IPN mensal e trimestral, utilizaram-se as técnicas da Análise em Componentes Principais (ACP) e Agrupamentos (AA). A técnica da Transformada de Ondeletas (TO) foi aplicada para algumas localidades das diferentes RH em diversas escalas. A TO possibilitou encontrar oscilações importantes no sinal da precipitação, mostrando as componentes dominantes da variabilidade da chuva na área pesquisada. Nos espectros de fase e global de energia da TO, para a chuva mensal, predominou o ciclo anual em todas as localidades. Além da escala anual, observaram-se interações com escalas inferiores a doze meses, possivelmente decorrentes da sazonalidade da precipitação. A TO da precipitação e da Radiação de Onda Longa (ROL) diárias evidenciou frequências maiores que as da chuva mensal. A análise dos espectros de fase e de energia global, nas regiões centro-sul e oeste, apresentou maior energia no início das séries da precipitação e de ROL. Contribuições mais elevadas ocorreram nas escalas sinóticas e intrassazonais, principalmente nas localidades de Viçosa, Bom Despacho, Ituiutaba e Lavras. Esses padrões temporais estão associados com a Oscilação de Madden-Julian (OMJ), intensificando a atuação de sistemas moduladores do clima de Minas Gerais. Oscilações em escalas menores que dez dias foram detectadas nos anos de 2011 e 2012 e podem estar associadas aos sistemas de curto prazo que contribuíram para a chuva mineira. No caso de 2011, os eventos de chuva observados em meados de janeiro foram modulados pelos episódios da Zona de Convergência do Atlântico Sul (ZCAS) e reforçados pela atuação da OMJ.
The state of Minas Gerais, located in southeastern Brazil, has a plateaux area, with higher areas in the southern part. The climate is predominantly tropical and tropical altitude, with temperatures ranging normally between 17 and 20°C. These characteristics make it often susceptible to heavy rains, causing many disorders the population. Thus, it sought to analyze the variability of the rain of Minas Gerais through techniques that were able to define spatial and temporal patterns of dry and wet events, and modulate them in the time-frequency ranges. For this, we calculated the Standardized Precipitation Index (SPI) monthly and quarterly in the period 1977-2012. In order to find spatiotemporal patterns and homogeneous regions (HR) of the monthly and quarterly SPI, we used the techniques of Principal Components Analysis (PCA) and Cluster Analysis (CA). The technique of Wavelets Transform (WT) has been applied to some locations of the different HR at various scales. The WT possible find important variations in rainfall signal, showing the dominant components of rainfall variability in the studied area. In phase spectra and global energy of WT, for the monthly rainfall, dominated the annual cycle in all locations. In addition to the annual scale, there were interactions with scales less than twelve months, possibly due to the seasonality of precipitation. The WT of precipitation and Outgoing Longwave Radiation (OLR) daily reported higher frequencies than the monthly rainfall. Analysis of phase spectra and global power, in south-central and western regions, showed higher energy at the beginning of the series of precipitation and OLR. Higher contributions occurred in the synoptic and intraseasonal scales, especially in the localities of Viçosa, Bom Despacho, Ituiutaba and Lavras. These temporal patterns are associated with the Madden-Julian Oscillation (MJO), intensifying the activity of modulators systems climate of Minas Gerais. Oscillations at smaller scales than ten days were detected in 2011 and 2012 and may be associated with short-term systems that contributed to the Minas Gerais rainfall. In the case of 2011 rain events observed in mid-January they were modulated by episodes of South Atlantic Convergence Zone (SACZ) and reinforced by the performance of MJO.
33
Illig, Serena. "Variabilité basse fréquence de l'Atlantique Tropical:Rôle de la dynamique océanique équatoriale et Influence d'El Niño Southern Oscillation." Phd thesis, Université Paul Sabatier - Toulouse III, 2005. http://tel.archives-ouvertes.fr/tel-00260664.
Повний текст джерелаАнотація:
L'objectif de cette thèse est l'étude de la variabilité interannuelle en Atlantique Tropical: nous étudions les rôles des processus couplés liés à la dynamique linéaire et ceux liés à l'influence de la variabilité du Pacifique Tropical de type El Niño. Les résultats obtenus suggèrent que la variabilité associée aux propagations d'ondes de Kelvin et de Rossby joue un rôle essentiel dans l'ajustement océanique au forçage par le vent et plus généralement dans les processus couplés océan-atmosphère en Atlantique Équatorial. Les résultats de simulations couplées montrent que l'énergie dans la bande de fréquences 1-3 ans est en partie liée aux interactions locales air-mer, tandis que la variabilité associée au Pacifique Tropical domine les basses fréquences (3-7 ans). Nos résultats soulignent la complexité du système océan-atmosphère en Atlantique Équatorial, dont la prédictibilité dépend fortement de la variabilité du Pacifique Tropical et de la variabilité atmosphérique intra-saisonnière.
34
Gutierrez, Enver Manuel Amador Ramirez. "Interação multi-escala entre o oceano e a atmosfera e a variabilidade de baixa frequência." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/14/14133/tde-27062013-112941/.
Повний текст джерелаАнотація:
No presente trabalho utiliza-se um m´etodo multi-escala para estudar de forma te´orica as intera¸coes nao lineares entre o oceano e a atmosfera atrav´es de ressonancia onda-onda. Desenvolve-se uma hierarquia de modelos acoplados oceano-atmosfera nao lineares que foram escalonados convenientemente para representar as principais escalas de variabilidade clim´atica (i.e., intrasazonal, interanual, e decenal). A enfase dos modelos desenvolvidos foi dado para a regiao tropical. As fontes de nao linearidade inclu´das no modelo sao de dois tipos: I) nao linearidade intr´nsica (advectiva) e II) nao linearidade relacionada com os termos da f´sica e ambas sao abordadas neste trabalho. Para obter as equa¸coes que regem a dinamica de intera¸coes ressonantes a partir da hierarquia de modelos acoplados, aplicou-se um m´etodo perturbativo multi-escala. As solu¸coes sao escritas em termos de solu¸coes de ordem dominante e solu¸coes seculares. Para as solu¸coes de ordem dominante e seculares utilizam-se as fun¸coes base do problema linear, em uma aproxima¸cao do tipo Galerkin. As propriedades das fun¸coes base permitem calcular de forma anal´tica os coeficientes de intera¸cao associados com os termos nao lineares, assim como tamb´em permitem projetar estes termos nos modos de oscila¸cao natural do sistema (ressonancia). Com este m´etodo obt´em-se modelos reduzidos que permitem determinar as contribui¸coes de diversos processos para a evolu¸cao em escala lenta de um determinado modo de variabilidade natural. Para aplicar estes conceitos ao problema de acoplamento oceano-atmosfera utiliza-se como Ansatz (hip´otese inicial para a solu¸cao do problema) um tripleto composto por duas ondas atmosf´ericas e uma onda oceanica, sendo uma onda de Kelvin e de Rossby na atmosfera e uma onda Kelvin no oceano. O tripleto escolhido representa uma aproxima¸cao de v´arios fenomenos encontrados na regiao tropical, e.g. o desenvolvimento do El Nino, a intera¸cao da oscila¸cao de Madden-Julian com o oceano, a intera¸cao entre el Nino e variabilidade intrasazonal. No presente trabalho ´e mostrado que existe a ressonancia envolvendo ondas atmosf´ericas e oceanicas e que a modula¸cao em baixa frequencia produto desta ressonancia pode afetar desde escalas r´apidas sin´oticas equatoriais, intrasazonais, interanuais e at´e variabilidade da ordem de dezenas de anos. Palavras chave: Dinamica Equatorial nao linear, Intera¸coes Ressonantes, Modelos Acoplados Oceano-Atmosfera, El Nino, Oscila¸cao de Madden Julian, Oscila¸coes Decenais (Decadal)In the present work a multiscale method is used to study resonant nonlinear wave-wave interactions between the ocean and the atmosphere. A hierarchy of coupled atmosphere-ocean models is developed using typical scalings found in the tropical region with the aim to represent some of the dominant modes of climate variability (intraseasonal, interannual and decadal). The sources of nonlinearity included into model are of two types: I) intrinsic nonlinearity (advective form) and II) nonlinearity related to physical terms. A multi-scale perturbation method is applied to obtain equations governing dynamics of ressonant interactions. The solutions are described in terms of dominant and secular solutions. For the dominant modes basis functions of the linear problem are used in a approximation of the Galerkin type. The properties of the basis functions allows the analytical computation of the interaction coefficients associated with non-linear terms and the projection into the natural oscillation modes of the system (resonance). Using this method it is possible to obtain reduced models to determine the contributions of several processes to the slow time evolution of a specific mode of natural variability. To apply these concepts to the problem of atmosphere-ocean coupling an Ansatz composed of a three waves (two atmospheric Rossby and Kelvin waves and an ocean Kelvin wave) is used. The triad chosen represents a aproximation of several phenomena found in the tropical region, e.g. desenvolving of El Nino, interaction of the Madden-Julian oscillation with the ocean, interaction between El Nino and intra-seasonal variability, etc. It is shown that system allows a resonance involving atmospheric and oceanic waves and that the low-frequency modulation resulting from these ressonance can affect the system from fast equatorial synoptic scales to decadal timescales, including the intermediate scales i.e., intraseasonal and interannual.
35
Vautard, Robert. "Les echelles de temps de la circulation atmospherique : couplage interne et approches de la parametrisation des modes rapides." Paris 6, 1987. http://www.theses.fr/1987PA066657.
Повний текст джерелаАнотація:
Les interactions entre les modes lents et les modes rapides de la circulation atmospherique sont examinees a travers deux problemes. Le premier concerne le couplage entre les ondes de gravite et les ondes de rossby. En raison des erreurs d'observation, les modeles de prevision numerique engendrent des ondes de gravite rapides irrealistes. Ces modes doivent donc etre initialement filtres. Le probleme est aborde de maniere theorique par l'etude de l'existence et des proprietes d'une variete invariante de l'espace des phases, appelee "variete lente", qui est sensee contenir l'attracteur du systeme atmospherique. Nous montrons au moyen d'exemples et de theoremes mathematiques qu'une telle variete peut exister, mais que les algorithmes actuels ne convergent pas vers elle. Le deuxieme probleme concerne la generation de la variabilite basse-frequence de l'atmosphere. Nous montrons que la dynamique lente de grande echelle est largement gouvernee par le forcage qu'induisent les transitoires rapides de petite echelle. L'existence de plusieurs structures de grande echelle associees a des regimes de temps, maintenues par les ondes baroclines rapides venant se superposer, est demontree dans le cadre d'un modele quasi-geostrophique. L'alternance entre ces regimes contribue a l'essentiel de la variabilite basse-frequence aux latitudes temperees. Cette notion de "regime de temps", jusqu'ici definie de maniere vague, est abordee de facon quantitative et objective au moyen d'une methode variationnelle statistico-dynamique. Celle-ci permet la reconnaissance de plusieurs types de circulation persistante dont l'une constitue le phenomene de "blocage". Dans ce phenomene, nous montrons que les transitoires ont un effet positif et important pour le maintien de la structure de l'anomalie
36
Chen, Chia-Jeng. "Hydro-climatic forecasting using sea surface temperatures." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48974.
Повний текст джерелаАнотація:
A key determinant of atmospheric circulation patterns and regional climatic conditions is sea surface temperature (SST). This has been the motivation for the development of various teleconnection methods aiming to forecast hydro-climatic variables. Among such methods are linear projections based on teleconnection gross indices (such as the ENSO, IOD, and NAO) or leading empirical orthogonal functions (EOFs). However, these methods deteriorate drastically if the predefined indices or EOFs cannot account for climatic variability in the region of interest. This study introduces a new hydro-climatic forecasting method that identifies SST predictors in the form of dipole structures. An SST dipole that mimics major teleconnection patterns is defined as a function of average SST anomalies over two oceanic areas of appropriate sizes and geographic locations. The screening process of SST-dipole predictors is based on an optimization algorithm that sifts through all possible dipole configurations (with progressively refined data resolutions) and identifies dipoles with the strongest teleconnection to the external hydro-climatic series. The strength of the teleconnection is measured by the Gerrity Skill Score. The significant dipoles are cross-validated and used to generate ensemble hydro-climatic forecasts. The dipole teleconnection method is applied to the forecasting of seasonal precipitation over the southeastern US and East Africa, and the forecasting of streamflow-related variables in the Yangtze and Congo Rivers. These studies show that the new method is indeed able to identify dipoles related to well-known patterns (e.g., ENSO and IOD) as well as to quantify more prominent predictor-predictand relationships at different lead times. Furthermore, the dipole method compares favorably with existing statistical forecasting schemes. An operational forecasting framework to support better water resources management through coupling with detailed hydrologic and water resources models is also demonstrated.
37
Vialard, Jérôme. "Variabilité océan-atmosphère du secteur Indo-Pacifique." Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00755963.
Повний текст джерелаАнотація:
Les océans Pacifique et Indien tropicaux se partagent la plus grande étendue d'eau chaude et de convection profonde de la planète. Cette région est le siège de la branche ascendante de la circulation de Walker, circulation atmosphérique d'échelle planétaire parfois décrite comme la " machine thermique " de la Terre. Cette région, dont les répercussions sur le climat sont importantes, est aussi source de variabilité océanique et atmosphérique aux échelles intrasaisonnières et interannuelles . En effet, la variabilité interannuelle associée à El Niño, dans l'océan Pacifique, et - dans une moindre mesure - au dipôle de l'Océan Indien (DOI) ont des conséquences climatiques marquées sur les pourtours de ces bassins et à l'échelle du globe. La variabilité intrasaisonnière liée à l'oscillation de Madden-Julian (OMJ) a également des conséquences climatiques marquées : modulations des moussons indiennes et australiennes et un rôle potentiellement important dans le déclenchement d'ENSO. Dans ce mémoire, je vais décrire mes travaux de recherche sur la variabilité océanique et atmosphérique aux échelles intrasaisonnière et interannuelle dans les Océans Indien et Pacifique. El Niño ou le DOI sont des modes couplés : c'est la rétroaction positive découlant des interactions océan-atmosphère qui est source de variabilité (le " Bjerknes feedback "). À l'échelle intrasaisonnière, le rôle du couplage océan-atmosphère semble moins primordial, et modifie seulement des modes de variabilité essentiellement atmosphériques ou océaniques. Par exemple, les ondes d'instabilité dans le Pacifique Est sont le résultat d'une instabilité interne océanique. Cependant, elles affectent la stabilité atmosphérique, les vents de surface, et cela tend à réduire légèrement leur activité. À l'inverse, l'OMJ est un phénomène dont la source est atmosphérique, naissant du couplage entre dynamique et convection dans les tropiques. Toutefois, nous verrons que ce phénomène a une réponse océanique forte dans l'Océan Indien, à la fois en termes de dynamique et de thermodynamique. Le degré d'influence du couplage dans les propriétés de l'OMJ reste toutefois une question largement ouverte. Nous nous intéresserons aussi à la question des interactions entre ces différents modes de variabilité. Nous verrons par exemple comment la variabilité intrasaisonnière atmosphérique peut déclencher un El Niño, comment El Niño peut supprimer l'activité des ondes tropicales d'instabilité et l'effet retour, comment le DOI module l'activité de l'OMJ et enfin, quelles sont les interactions entre DOI et El Niño. Je présenterai alors une région de l'Océan Indien assez emblématique de ces interactions d'échelle, et dans laquelle j'ai développé une activité d'observations (campagnes océanographiques Cirene de 2005 à 2008 et projet de campagne TRIO). La bande 5°S-10°S dans l'Océan Indien est une région très particulière. En raison de la structure des vents, la thermocline y est proche de la surface et la couche de mélange est peu profonde, ce qui induit une forte réactivité de la température de surface aux sollicitations de l'atmosphère. De plus, la température de surface en hiver boréal est proche du seuil de convection, impliquant une sensibilité accrue de l'atmosphère à de petites variations de température. Ces deux facteurs augmentent le couplage océan atmosphère dans cette région qui a une variabilité très marquée aux échelles synoptiques (cyclones), intrasaisonnières (OMJ) et interannuelle (réponse à El Niño, mais aussi au DOI). Cette région a enfin des conséquences climatiques marquées (sur l'intensité des pluies de la mousson suivante, sur le nombre de cyclones dans le secteur La Réunion-Madagascar, sur la convection au-dessus du continent maritime, et même sur l'Amérique du Nord). Pour conclure, je présenterai ma réflexion sur mes axes de recherches futurs, ainsi que mes projets en termes de campagnes et réseaux d'observations.
38
Lutringer-Paquet, Audrey. "Reconstruction de la variabilité des eaux intermédiaires par l'étude géochimique des coraux profonds." Phd thesis, Université Paris Sud - Paris XI, 2005. http://tel.archives-ouvertes.fr/tel-00159102.
Повний текст джерелаАнотація:
Les variations des eaux intermédiaires constituent un point important dans la compréhension desréponses de l'océan aux changements rapides du climat. Cependant, la variabilité de ces masses d'eau
est encore peu documentée en raison du manque d'enregistrements fiables et pouvant être datés de
manière précise. C'est pour répondre à cette attente que cette étude à été proposée : il s'agissait de
développer l'utilisation des coraux profonds et en particulier de leur signal isotopique pour les
reconstitutions paléo-océanographiques.
Dans un premier temps, une méthode de calcul des températures à partir des données isotopiques (CO)
des coraux a été mise au point. Cette méthode a été testée sur 6 coraux prélevés vivants dans
différents sites où les conditions environnementales étaient connues (T-S). Une fois la méthode
établie, elle a été appliquée, dans un deuxième temps, à une carotte sédimentaire du chenal de Rockall
contenant des coraux. Le signal ainsi obtenu a permis de dégager la forte variabilité isotopique des
coraux sur l'Holocène. Ce signal a été interprété en terme de fluctuations de la contribution des eaux à
composante méditerranéennes par rapport aux eaux du Labrador selon des oscillations climatiques
propres à l'Atlantique Nord. En parallèle de ces études, un grand nombre de datations ont été
effectuées sur des coraux des différentes carottes de la marge irlandaise afin de définir le cadre
stratigraphique représenté par ces coraux. Aucun corail d'âge glaciaire n'a été identifié sur ce site,
dégageant ainsi la sensibilité de ce matériel aux variations paléo- environnementales. Un scénario de
développement et de mise en place des coraux selon les conditions hydrographiques a été proposé
pour expliquer la dynamique de croissance des monts carbonatés sur lesquels se développent les
coraux de l'Atlantique Nord-Est. Par ailleurs, les datations au 14C des foraminifères des carottes
montrent la complexité de l'enregistrement sédimentaire pour ces sites de haute énergie et soulignent
l'intérêt des coraux profonds pour reconstruire la variabilité rapide des eaux intermédiaires.
39
Kline, Wayne T. "Climatic Factors Associated with the Rapid Wintertime Increase in Cloud Cover across the Great Lakes Region." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1240256371.
Повний текст джерела
40
Marini, Camille. "Etude des causes et effets de la circulation méridienne de retournement Atlantique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2011. http://tel.archives-ouvertes.fr/tel-00994862.
Повний текст джерелаАнотація:
Nous étudions d'abord l'influence du mode annulaire Sud (SAM) sur la circulation méridienne de retournement Atlantique (AMOC) dans une simulation de contrôle avec IPSLCM4. Une phase positive du SAM, correspondant à une intensification des vents d'Ouest soufflant au Sud de 45° S, entraîne après 8 ans une accélération de l'AMOC, via une téléconnection atmosphérique peu réaliste. Une accélération de l'AMOC suit de 70 ans une phase positive du SAM, due à la propagation d'anomalies de sel du Sud vers le Nord de l'Atlantique. Ensuite, nous étudions dans quelle mesure l'Oscillation Multidécennale Atlantique (AMO) reflète les fluctuations de l'AMOC. Nous utilisons un filtre basé sur un modèle linéaire inverse (LIM) pour décomposer la température de surface de l'océan (SST) Atlantique Nord en une partie liée à la dérive globale, une à El Nino (ENSO), une à la variabilité de basse fréquence du Pacifique, et un résidu. Dans la simulation historique de IPSLCM5, enlever la dérive globale de l'AMO avec LIM induit de meilleures corrélations avec l'AMOC que lorsque ce signal est soustrait par une dérive linéaire. Enlever l'influence de ENSO de l'AMO améliore très légérement ses corrélations avec l'AMOC, tandis qu'enlever la variabilité de basse fréquence du Pacifique les dégrade. La robustesse de ces résultats est vérifiée dans des simulations de contrôle avec 5 modèles. Cette déconstruction de l'AMO est aussi effectuée dans les observations. Enfin, l'impact du forçage volcanique sur les liens AMO-AMOC est étudié dans une simulation du dernier millénaire avec IPSLCM4.
41
Roehrig, Romain. "Variabilité intrasaisonnière de la mousson africaine : caractérisation et modélisation." Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00560954.
Повний текст джерелаАнотація:
La variabilité intrasaisonnière de la mousson d'Afrique de l'Ouest se caractérise par une alternance de phases sèches et humides, dont les impacts pe uvent être dramatiques sur les populations locales. Cette variabilité met en jeu un grand nombre d'échelles spatiales et temporelles, rendant difficile sa compréhension, sa modélisation et sa prévision. Cette thèse propose quelques éclairages sur ces différentes thématiques. La dépression thermique saharienne est un acteur majeur de la mousson africaine. La caractérisation de sa variabilité intrasaisonnière a permis de mettre en évidence, à l'échelle de 15 jours, l'existence d'interactions entre les latitudes moyennes et l'Afrique de l'Ouest. Lors de son passage au-dessus de l'Atlantique et la Méditerranée, un train d'ondes de Rossby module les ventilations de la dépression thermique, et donc sa structure. Les anomalies de circulation, de température et d'humidité, ainsi induites sur le Sahel, pourraient alors expliquer une partie des fluctuations intrasaisonnières de la convection, notamment celles qui naissent sur l'est du Sahel, et qui se propagent ensuite vers l'ouest. L'état moyen et la variabilité intrasaisonnière de la mousson africaine restent un défi pour les modèles de climat, même pour la dernière génération, qui a participé à l'exercice d'intercomparaison CMIP3. La variabilité à haute fréquence de la convection est un élément particulièrement difficile à modéliser. Toutefois, la meilleure prise en compte de facteurs inhibant le développement de la convection pourrait être une étape importante pour améliorer la modélisation de la mousson et la prévision de ses fluctuations intrasaisonnières
42
Flaounas, Emmanouil. "Analyse de la mise en place de la mousson Africaine : dynamique régionale ou forçage de grande échelle ?" Phd thesis, Paris 6, 2010. http://www.theses.fr/2010PA066625.
Повний текст джерелаАнотація:
La saison des pluies en Afrique de l'Ouest est primordiale pour les populations locales. La mise en place de la mousson (MAO) se produit fin juin et correspond à un affaiblissement global de la convection sur la région puis une transition brutale des précipitations de la côte de Guinée vers le Sahel. C'est le mécanisme responsable de ce « saut » qui est étudié ici à partir d'expériences numériques. La capacité du modèle à aire limitée WRF à reproduire la circulation de la MAO en 2006 a d'abord été évaluée. Différentes paramétrisations de la convection et de la couche limite ont été testées et leur impact sur les simulations analysé. Des tests de sensibilité ont ensuite été effectués pour évaluer le rôle de la dépression thermique saharienne et de la SST (mécanismes proposés dans d'autres études) sur la mise en place de la MAO. Les résultats montrent que la phase de transition dépend plus fortement de la dynamique de grande échelle que des éléments régionaux. Plus précisément, la mise en place de la mousson Indienne libère une onde de Rossby qui se propage vers l'ouest, arrive au dessus de l'Afrique du Nord en favorisant les intrusions de masses d'air sec au dessus de l'Afrique de l'Ouest qui inhibent la convection. En parallèle, le gradient méridien de pression de surface est renforcé et la MAO s'intensifie en advectant de l’humidité au dessus du Sahel. Une fois l'onde évacuée, la convection se réorganise au dessus du Sahel où les conditions thermodynamiques sont favorables. L'utilisation de simulations globales avec LMDz a confirmé le rôle de la mousson indienne sur toute la période 1989-2008 avec cependant des années plus ou moins marquées.
43
IZUMO, Takeshi. "Le sous-courant équatorial et les échanges de masse et de chaleur associés dans le Pacifique tropical : variabilité, liens avec les événements El Niño-La Niña." Phd thesis, Université Paul Sabatier - Toulouse III, 2003. http://tel.archives-ouvertes.fr/tel-00006355.
Повний текст джерелаАнотація:
Le sous-courant équatorial (EUC), en alimentant l'upwelling équatorial, peut avoir une forte influence sur la température de surface (SST) du Pacifique équatorial Est et donc sur la variabilité associée à El Niño. L'EUC et les cellules de circulation méridienne (shallow subtropical/tropical overturning cells, STCs/TCs) l'alimentant sont étudiés en combinant données in situ et modélisation. Les trajectoires de masses d'eau sont calculées dans des simulations réalistes (le modèle OPA forcé par les vents des réanalyses NCEP sur 1948-1999 ou des satellites ERS sur 1992-1999). Leur analyse met en évidence des cheminements des masses d'eaux propres aux évènements El Niño-La Niña de 1997-1998, avec des recharges et décharges de la bande équatoriale complexes et asymétriques. Cette analyse montre aussi l'apport d'eaux froides par les STCs et l'EUC lors de la brusque transition vers La Niña en mai 1998. Les données de courant et de température des mouillages TAO/TRITON le long de l'équateur à 170°W, 140°W et 110°W sont méthodiquement bouchées sur 1980-2002. On montre que des séries continues du débit, de la température, de la profondeur et de l'énergie cinétique de l'EUC sur toute son extension méridienne peuvent alors être construites. Leur analyse révèle que la forte variabilité interannuelle du débit de l'EUC est une réponse linéaire et quasi-stationnaire à la tension de vent zonale équatoriale intégrée zonalement dans le Pacifique Ouest et central. La température de l'EUC, indispensable pour l'estimation du transport de chaleur, varie elle linéairement avec la différence des profondeurs de la thermocline et de l'EUC dans le Pacifique central. Le modèle numérique, validé entre autre à l'aide des séries de l'EUC, est utilisé pour étudier sur 1951-1999 la circulation équatoriale associée à l'EUC: la convergence dans la pycnocline, l'upwelling équatorial et la divergence en surface à 5°N et 5°S. Leurs variabilités en débit sont quasi-égales à celle de l'EUC, qui est donc un bon indicateur de la force des STCs. Ces variabilités sont principalement causées par la tension de vent zonale intégrée zonalement sur tout le bassin, en accord avec des théories linéaires. Des déphasages avec la SST équatoriale, notamment l'avance de 5 mois de l'upwelling et de la divergence sur la SST, révèlent des relations de cause à effet très intéressantes, confirmées par les bilans de chaleur. La différence de température entre la divergence et la convergence a des variations interannuelles et à plus long-terme égales à celles de la SST équatoriale. Les conséquences sur les bilans et échanges de masse et de chaleur dans la bande équatoriale sont ensuite quantifiées. La variabilité du transport de chaleur méridien associé à la convergence/divergence est due aussi bien aux variations de débit que de température de la convergence et de la divergence. Ainsi, pendant un événement El Niño, la baisse des débits aura tendance à réchauffer la bande équatoriale (recharge), alors que l'augmentation de la différence entre les températures de la divergence et de la convergence aura l'effet contraire (décharge). Pour le Pacifique Est, les variations interannuelles du débit dominent celles de la température de l'EUC pour le transport de chaleur de l'EUC. Les liens avec les théories d'El Niño et sa variabilité décennale sont discutés.
44
Thual, Sulian. "Modèles réduits pour l'etude des mécanismes et de la modulation de l'oscillation australe El Niño." Phd thesis, Université Paul Sabatier - Toulouse III, 2012. http://tel.archives-ouvertes.fr/tel-00772756.
Повний текст джерелаАнотація:
L'Oscillation Australe El Niño (ENSO pour El Niño Southern Oscillation) est la fluctuation climatique la plus intense sur Terre après le cycle saisonnier. L'observation, la compréhension et la prévision de cette fluctuation aux retombées mondiales sont des enjeux scientifiques majeurs. Cette thèse documente divers aspects d'ENSO tels que ses mécanismes, sa modulation et sa prévision. Ces divers aspects sont abordés en développant une hiérarchie de modèles du Pacifique équatorial, de complexité croissante, qui s'étend de modèles conceptuels à une méthode d'assimilation de données dans un modèle de complexité intermédiaire. Nous étudions dans un premier temps les mécanismes de formation d'ENSO. Nous développons une dérivation alternative du modèle conceptuel de recharge/décharge où ENSO résulte d'un ajustement de la thermocline équatoriale à échelle de bassin. Nous implémentons par ailleurs un diagnostic original dans un modèle d'instabilités couplées équatoriales, ce qui met en avant un nouveau mécanisme de formation d'ENSO où les réflexions aux frontières océaniques jouent un rôle secondaire. La stratification moyenne de l'océan contribue à la modulation décenalle des caractéristiques d'ENSO. Cette relation est abordée dans un nouveau modèle réduit qui prend en compte les premiers modes baroclines d'un océan continûment stratifié. L'espace des solutions du modèle est exploré, indiquant un contrôle de la stabilité d'ENSO par les caractéristiques de la thermocline équatoriale. La sensibilité à la stratification au cours des dernières décennies est mise en perspective avec la sensibilité aux rétroactions thermodynamiques et atmosphériques. Nous soulignons en particulier certaines limitations des méthodes usuelles d'estimation de la rétroaction de thermocline dans le Pacifique central. Finalement, nous implémentons une méthode de Filtre de Kalman d'Ensemble dans un modèle intermédiaire du Pacifique équatorial déjà existant, afin d'assimiler des observations de niveau de la mer et d'initialiser des prévisions rétrospectives d'ENSO. Nous montrons que la contrainte majeure du modèle porte sur les modes de bassin qui sont associés au processus de recharge/décharge du Pacifique équatorial. Notre travail fournit un formalisme pour diagnostiquer la modulation des caractéristiques d'ENSO dans les observations, les prévisions et projections climatiques. Les résultats soutiennent la nécessité d'étendre la compréhension des mécanismes d'ENSO, afin de rendre compte de la diversité des régimes observés et d'améliorer les prévisions.
45
Das, Surajit. "Intraseasonal Variability in Aquaplanet Configuration of Community Atmosphere Model." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4625.
Повний текст джерелаАнотація:
The Intraseasonal Oscillation (ISO) plays an important role to modulate deep convective activity
in the tropical region. In this thesis, I aim to understand the role of land and warm oceans
in ISO, using a general circulation model. For this, I conduct a series of experiments in the
Community Atmosphere Model (CAM) with various idealized and realistic surface boundary
conditions to study tropical ISO. To investigate the influence of tropical sea surface temperature
(SST) on ISO and convectively coupled equatorial waves in the global atmosphere, I conduct
experiments with idealized, zonally symmetric SST profiles having different widths of warm
ocean centered at the equator. I use the model in its basic “Aquaplanet” configuration, with
the sun at the equator, i.e. perpetual spring equinox forcing; with idealized zonally symmetric
SST, the aquaplanet model produces a double Intertropical Convergence Zone (ITCZ) on
either side of the equator, and an eastward propagating Madden Julian oscillation (MJO)like
mode with variance at intraseasonal (30 to 96 day) periods and zonal wavenumber one. In the
experiment with the narrowest meridional width of warm SST, the variance of moist convective
activity lies predominantly in equatorially trapped Kelvin wave band. As the width of the
warm equatorial SST is increased, the eastward propagating speed of the MJO-like signal decreases;
for the broadest SST profile (warm SST covering 20 degrees of latitude), the speed of
the model MJO is about 5.5 m s−1, close to the observed speed. This is because the latitudinal
extent of warm SST is comparable to the equatorial Rossby radius, and the model produces off equatorial
Rossby waves of sufficient strength to interact with the Kelvin wave and slow down
the MJO-like mode. The model also generates westward propagating waves with intraseasonal periods and zonal wavenumber 1–3; the structure of these signals, which extend well into the
mid-latitudes, projects onto equatorially trapped Rossby waves with meridional mode numbers
1, 3 and 5, associated with convection that is symmetric about the equator. In addition, the
model generates 30–80 day westward moving signals with zonal wavenumber 4–7, particularly
in the experiment with a narrow region of warm SST. Although these waves are seen in
the wavenumber-frequency spectra in the equatorial region, they have the largest amplitude in
the middle and high latitudes. Thus, our study shows that wider, meridionally symmetric SST
profiles support a strong MJO-like eastward propagation, and even in an aquaplanet setting,
westward propagating Rossby waves comprise a large portion of tropical intraseasonal variability.
In the observations (ERA-Interim daily reanalysis), the MJO signal lies in the range of
zonal wavenumbers 1 to 5. The variance of MJO at higher wavenumbers (2–5) is absent in
the aquaplanet model. For this, I design model experiments in order to study how model MJO
responds to the introduction of continents in the presence of zonally symmetric SST, and a realistic
SST distribution with the Indo-Pacific warm pool and cool SST in the eastern Pacific.
As before, the model is in the aquaplanet-like configuration, to eliminate the effects of seasonality.
Model results are compared with 21 years (1995–2015) ERA-Interim reanalysis data
and analyzed in terms of the moist static energy (MSE) budget to study the growth and propagation
of MJO. When I introduce continents with realistic orography and interactive surface
temperature, soil moisture, and albedo, the variance of model MJO is reduced due to weaker
boundary layer moisture convergence. However,MJO variance extends to higher wavenumbers.
With prescribed climatological January SST boundary condition in the presence of continents,
the variance of model MJO is enhanced by a factor of 2–3, and it is distributed across zonal
wavenumbers 1 to 5, in closer agreement with observations. Thus, I find that the presence of
land by itself is not enough to produce realistic MJO in CAM, but realistic SST distribution is
also necessary to simulate MJO with improved spacetime characteristics. Both in simulations
and ERA-Interim data, column-integrated longwave radiation plays a key role in the growth of
MSE anomaly associated with MJO; in general, meridional and vertical advection of MSE both
acts to promote eastward movement of MJO. In the model experiments, meridional advection of low-level MSE anomaly is most significant in the vicinity of the ITCZ. This indicates that
the physical processes which determine the location of (single or double) ITCZ are linked to
MJO dynamics.
The westward propagating “quasi-biweekly” oscillation (QBWO) with 10–25 day period is
an important intraseasonal mode of the Asian summer monsoon, yet very few model studies focus
on this mode. I study QBWO in the northern and southern tropics in the model and compare
it with ERA-Interim reanalysis data. The pure aquaplanet model produces a double Intertropical
Convergence Zone (ITCZ), winds that are predominantly zonal, and weak quasi-biweekly variance.
When continents are introduced in the model with zonally symmetric SST, the northern
ITCZ, as well as quasi-biweekly variance between 10◦N to 24◦N are strengthened in the Pacific
Ocean, bringing model results closer to observations. In the model with continents, the QBWO
signal dwells inside the mean envelope of high atmospheric moisture, or total precipitable water
(TPW), in agreement with observations. However, in the presence of zonally symmetric SST,
the model fails to simulate sufficiently high precipitable water in the region extending from the
north Indian Ocean to East Asia, resulting in very weak QBWO variance. When the model includes
continents and realistic (January) SST boundary conditions, the spatial structure of both
TPW and QBWO variance becomes more realistic. I study the mechanisms of propagation and
maintenance of the quasi-biweekly mode using vorticity budget and moist static energy (MSE)
budget analysis. Advection due to the effect is responsible for the northwestward propagation
of QBWO vorticity, while the propagation of column MSE anomaly is mainly due to horizontal
advection. Surface turbulent heat fluxes and vertical MSE advection are the dominant contributors
to the growth and maintenance of column MSE anomaly in observations and model
respectively. Surface heat flux makes a significant contribution to the growth of quasi-biweekly
MSE anomaly in the presence of land, in association with the enhanced meridional wind, and
vortical structures that resemble moist Rossby waves with a wavelength of about 4000 kilometers.
46
Jiang, Xianan. "The boreal summer intraseasonal oscillation over the south Asian monsoon region." Thesis, 2004. http://proquest.umi.com/pqdweb?index=0&did=766011941&SrchMode=1&sid=5&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1233101729&clientId=23440.
Повний текст джерела
47
Lin, Xin. "Multiscale variability associated with the intraseasonal oscillation over the western Pacific warm pool." 1997. http://catalog.hathitrust.org/api/volumes/oclc/38743663.html.
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48
Schrage, Jon M. "Modulation of intraseasonal (25-70 day) processes by the superimposed ENSO cycle across the Pacific Basin." 1998. http://catalog.hathitrust.org/api/volumes/oclc/41553848.html.
Повний текст джерела
49
Venugopal, Thushara. "Sensitivity of Sea Surface Temperature Intraseasonal Oscillation to Diurnal Atmospheric Forcings in an OGCM." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3347.
Повний текст джерелаАнотація:
Abstract
The diurnal cycle is a dominant mode of sea surface temperature (SST) variability in trop-ical oceans, that influences air-sea interaction and climate processes. Diurnal variability of SST generally ranges from ~0.1 to 2.0◦C and is controlled by atmospheric fluxes of heat and momentum. In the present study, the response of intraseasonal variability (ISV) of SST in the Bay of Bengal (BoB) to diurnal atmospheric forcings, during the summer monsoon of 2007, has been examined using an Ocean General Circulation Model (OGCM). The model is based on the Modular Ocean Model Version 4 (MOM4p0), having a horizontal resolution of 0.25◦ and 40 vertical levels, with a fine resolution of 5 m in the upper 60 m. Numerical experiments were conducted by forcing the model with daily and hourly atmospheric forcings to examine the SST-ISV modulation with the diurnal cycle. Additional experiments were performed to determine the relative role of diurnal cycle in solar radiation and winds on SST and mixed layer depth (MLD). Since salinity, which is decisive in SST variability, varies meridionally in the BoB, two locations were selected for analyses: one in the northern bay at 89◦E, 19◦N where salinity is lower and the other in the southern bay at 90◦E, 8◦N where salinity is higher, as well as observations are available from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoy for comparision with model simulation.
Diurnal atmospheric forcings modify SST-ISV in both southern and northern bay. SST-ISV in the southern bay, is dominantly controlled by the diurnal cycle of insolation, while in the northern bay, diurnal cycle of insolation and winds have comparable contribution. Diurnal cycle enhanced the amplitude of 3 selected intraseasonal events in the southern bay and 3 out of the 6 events in the northern bay, during the study period. In the southern bay, simulated SST variability with hourly forcing was closer to the observations from RAMA, implying that incorporating the diurnal cycle in model forcing rectifies SST-ISV. Moreover, SST obtained with diurnal forcing consists of additional fluctuations at higher frequencies within and in between intraseasonal events; such fluctuations are absent with daily forcing. The diurnal variability of SST is significant during the warming phase of intraseasonal events and reduces during the cooling phase. Diurnal amplitude of SST decreases with depth; depth dependence also being larger during the warming phase.
SST-ISV modulation with diurnal forcing results from the diurnal cycle of upper ocean heat fluxes and vertical mixing. Diurnal warming and cooling result in a net gain or loss of heat in the mixed layer after a day’s cycle. When the retention (loss) of heat in the mixed layer increases with diurnal forcing during the warming (cooling) phase of intraseasonal events, the daily mean SST rise (fall) becomes higher, amplifying the intraseasonal warming (cooling). In the southern bay, SST-ISV amplification is mainly controlled by the diurnal variability of MLD, which modifies the heat fluxes. Increased intraseasonal warming with diurnal forcing results from the increase in radiative heating, due to the shoaling of the daytime mixed layer. Amplified intraseasonal cooling is dominantly con-trolled by the strengthening of sub-surface processes, due to the nocturnal deepening of mixed layer and increased temperature gradients below the mixed layer.
In the northern bay, SST-ISV modulation with diurnal forcing is not as large as that in the southern bay. The mean increase in SST-ISV amplitudes with diurnal forcing is ~0.16◦C in the southern bay, while it is only ~0.03◦C in the northern bay. Reduced response of SST-ISV to diurnal forcings in the northern bay is related to the weaker diurnal variability of MLD. Salinity stratification limits diurnal variability of mixed layer in the northern bay, unlike in the southern bay. The seasonal (June - September) mean diurnal amplitude of MLD is ~15 m in the southern bay, while it is reduced to ~1.5 m in the northern bay. Diurnal variability of MLD, spanning only a few meters is not sufficient to create large modifications in mixed layer heat fluxes and SST-ISV in the northern bay. The vertical resolution of the model limits the shallowing of mixed layer to 7.5 m, thus restricting the diurnal variability of simulated MLD.
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Venugopal, Thushara. "Sensitivity of Sea Surface Temperature Intraseasonal Oscillation to Diurnal Atmospheric Forcings in an OGCM." Thesis, 2013. http://etd.iisc.ernet.in/2005/3347.
Повний текст джерелаАнотація:
Abstract
The diurnal cycle is a dominant mode of sea surface temperature (SST) variability in trop-ical oceans, that influences air-sea interaction and climate processes. Diurnal variability of SST generally ranges from ~0.1 to 2.0◦C and is controlled by atmospheric fluxes of heat and momentum. In the present study, the response of intraseasonal variability (ISV) of SST in the Bay of Bengal (BoB) to diurnal atmospheric forcings, during the summer monsoon of 2007, has been examined using an Ocean General Circulation Model (OGCM). The model is based on the Modular Ocean Model Version 4 (MOM4p0), having a horizontal resolution of 0.25◦ and 40 vertical levels, with a fine resolution of 5 m in the upper 60 m. Numerical experiments were conducted by forcing the model with daily and hourly atmospheric forcings to examine the SST-ISV modulation with the diurnal cycle. Additional experiments were performed to determine the relative role of diurnal cycle in solar radiation and winds on SST and mixed layer depth (MLD). Since salinity, which is decisive in SST variability, varies meridionally in the BoB, two locations were selected for analyses: one in the northern bay at 89◦E, 19◦N where salinity is lower and the other in the southern bay at 90◦E, 8◦N where salinity is higher, as well as observations are available from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoy for comparision with model simulation.
Diurnal atmospheric forcings modify SST-ISV in both southern and northern bay. SST-ISV in the southern bay, is dominantly controlled by the diurnal cycle of insolation, while in the northern bay, diurnal cycle of insolation and winds have comparable contribution. Diurnal cycle enhanced the amplitude of 3 selected intraseasonal events in the southern bay and 3 out of the 6 events in the northern bay, during the study period. In the southern bay, simulated SST variability with hourly forcing was closer to the observations from RAMA, implying that incorporating the diurnal cycle in model forcing rectifies SST-ISV. Moreover, SST obtained with diurnal forcing consists of additional fluctuations at higher frequencies within and in between intraseasonal events; such fluctuations are absent with daily forcing. The diurnal variability of SST is significant during the warming phase of intraseasonal events and reduces during the cooling phase. Diurnal amplitude of SST decreases with depth; depth dependence also being larger during the warming phase.
SST-ISV modulation with diurnal forcing results from the diurnal cycle of upper ocean heat fluxes and vertical mixing. Diurnal warming and cooling result in a net gain or loss of heat in the mixed layer after a day’s cycle. When the retention (loss) of heat in the mixed layer increases with diurnal forcing during the warming (cooling) phase of intraseasonal events, the daily mean SST rise (fall) becomes higher, amplifying the intraseasonal warming (cooling). In the southern bay, SST-ISV amplification is mainly controlled by the diurnal variability of MLD, which modifies the heat fluxes. Increased intraseasonal warming with diurnal forcing results from the increase in radiative heating, due to the shoaling of the daytime mixed layer. Amplified intraseasonal cooling is dominantly con-trolled by the strengthening of sub-surface processes, due to the nocturnal deepening of mixed layer and increased temperature gradients below the mixed layer.
In the northern bay, SST-ISV modulation with diurnal forcing is not as large as that in the southern bay. The mean increase in SST-ISV amplitudes with diurnal forcing is ~0.16◦C in the southern bay, while it is only ~0.03◦C in the northern bay. Reduced response of SST-ISV to diurnal forcings in the northern bay is related to the weaker diurnal variability of MLD. Salinity stratification limits diurnal variability of mixed layer in the northern bay, unlike in the southern bay. The seasonal (June - September) mean diurnal amplitude of MLD is ~15 m in the southern bay, while it is reduced to ~1.5 m in the northern bay. Diurnal variability of MLD, spanning only a few meters is not sufficient to create large modifications in mixed layer heat fluxes and SST-ISV in the northern bay. The vertical resolution of the model limits the shallowing of mixed layer to 7.5 m, thus restricting the diurnal variability of simulated MLD.