This dissertation reports on studies on the role of the mean state in modulating climate variability at interannual and decadal time scales. In the atmosphere, the nonlinear superposition of mean flow and anomalous flow has important implications for many phenomena associated with variables that are nonlinear by definition, such as the vertical wind shear and surface wind speed. In the first part of this dissertation, the influence of mean flow and anomalous flow on vertical wind shear variability is studied in observations and numerical model simulations. At interannual timescales, the ENSO-shear relationship is compared between observations and numerical model simulations. It is shown that there is strong influence of mean flow on the ENSO-shear relationship. For same anomalous flow, different mean flows could give rise to a different ENSO-shear relationship. The nonlinear superposition of mean flow and anomalous flow also helps explains the dipole mode of tropical Atlantic vertical wind shear variability seen in observations and models, which implies opposite variation of vertical wind shear over the two sides of the tropical Atlantic. This has important implications for predicting phenomena such as Atlantic hurricanes, whose variations are modulated by vertical shear variability. The dissertation also addresses the role of the mean surface wind in decadal variability and predictability, as manifested through the Wind-Evaporation-SST (WES) feedback. The nonlinear superposition of anomalous surface wind on the mean trade wind can give rise to a positive WES feedback, which can amplify tropical climate variability. To study this feedback, we carried out ensembles of decadal climate predictions using the CAM3 atmospheric model coupled to a slab ocean model (CAM3- SOM) with prescribed ocean transport and simple extrapolative prescriptions of future external forcings. Mechansitic sensitivity runs using the CAM3-SOM were also carried out, where the WES feedback was switched off by prescribing climatological surface wind. Results suggest that switching off the WES feedback enhances the prediction skill over some regions, especially over the eastern tropical Pacific, by increasing the signal- to-noise ratio. To address the issue of cold bias noted in the decadal prediction experiments, we carried out additional sensitivity experiments where we used an adaptive formulation for the prescribed oceanic heat transport (Q-flux) in the slab ocean. The results from these experiments demonstrate that the mean oceanic heat transport plays a crucial role in influencing decadal predictability, by helping improve predictions of the trend component of decadal variations.

Over the 1951-2009 time period, 47% of all tropical systems in the Atlantic Basin transitioned to post-tropical storms. These storms are capable of producing hurricaneforce winds, torrential, flooding rains and storm surge that floods coastal areas. This study adds to previous climatological work by completing a case-study of Hurricane Ike (2008) and examining how teleconnections such as the El Niño Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) contribute to the strength of a transitioning post-tropical storm. T-tests performed show strong statistical relationships between an increase (decrease) in post-tropical storm frequency and warm PDO – La Niña (cold PDO – La Niña), cold PDO – ENSO neutral (warm PDO – ENSO neutral), and warm (cold) AMO conditions. Moreover, nearly significant results were found for the same increase (decrease) and La Niña seasons since (pre) 1980 and for cold (warm) PDO conditions. Modeling the MJO suggests that increased (decreased) relative humidity associated with the wet (dry) phase could increase (decrease) precipitation output from the storm and decrease (increase) forward speed of the storm, decreasing (increasing) wind speeds observed at the surface.

abstract: The numerical climate models have provided scientists, policy makers and the general public, crucial information for climate projections since mid-20th century. An international effort to compare and validate the simulations of all major climate models is organized by the Coupled Model Intercomparison Project (CMIP), which has gone through several phases since 1995 with CMIP5 being the state of the art. In parallel, an organized effort to consolidate all observational data in the past century culminates in the creation of several "reanalysis" datasets that are considered the closest representation of the true observation. This study compared the climate variability and trend in the climate model simulations and observations on the timescales ranging from interannual to centennial. The analysis focused on the dynamic climate quantity of zonal-mean zonal wind and global atmospheric angular momentum (AAM), and incorporated multiple datasets from reanalysis and the most recent CMIP3 and CMIP5 archives. For the observation, the validation of AAM by the length-of-day (LOD) and the intercomparison of AAM revealed a good agreement among reanalyses on the interannual and the decadal-to-interdecadal timescales, respectively. But the most significant discrepancies among them are in the long-term mean and long-term trend. For the simulations, the CMIP5 models produced a significantly smaller bias and a narrower ensemble spread of the climatology and trend in the 20th century for AAM compared to CMIP3, while CMIP3 and CMIP5 simulations consistently produced a positive trend for the 20th and 21st century. Both CMIP3 and CMIP5 models produced a wide range of the magnitudes of decadal and interdecadal variability of wind component of AAM (MR) compared to observation. The ensemble means of CMIP3 and CMIP5 are not statistically distinguishable for either the 20th- or 21st-century runs. The in-house atmospheric general circulation model (AGCM) simulations forced by the sea surface temperature (SST) taken from the CMIP5 simulations as lower boundary conditions were carried out. The zonal wind and MR in the CMIP5 simulations are well simulated in the AGCM simulations. This confirmed SST as an important mediator in regulating the global atmospheric changes due to GHG effect. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2013

Made available in DSpace on 2014-08-20T14:25:49Z (GMT). No. of bitstreams: 1 dissertacao_joao_omena.pdf: 2555778 bytes, checksum: 3d55cd24bdb3d73793d94f037d1c79ea (MD5) Previous issue date: 2010-02-18 / The Rio Grande do Sul is a State with characteristics in agriculture, that the basis of its economy. In addition, the State also receives many tourists in the region of tumuc and coast. These factors suffer influence of temperature and that a study is necessary to state that the economy is not affected. It is known that there is an ocean influence in meteorological variables and emphasizes that the Pacific Ocean is the largest of the oceans. The sea surface temperatures (SST) of the Pacific Ocean, have a configuration with long-term variations, similar to El Niño, called the Pacific Decadal Oscillation (PDO) and it was discovered that the PDO influences in precipitation in the State (Rebello, 2006). Objective is to study the possible influences of PDO maximum and minimum temperature. For this data used the maximum and minimum temperature from 1925 to 2008 surface stations INMET homogeneous temperature zones and PDO index. Anomaly calculations were made of average temperature minimum and average maximum for each station and their respective monthly averages. With these results calculated the PDO index percentile and the average maximum temperature anomalies and minimal. The percentile served to separate bands ranges below normal, up to 40%, between 40% and 60% being the transition track or normal and above 60% as above normal range. The contingency table was also used as a tool to better organize your data and separate them in cases of normal temperature, maximum below (T. Max. ( - )), normal, and above the normal (T.Max. ( + )) and the minimum temperature is below normal (T. Min. ( - )), normal, and above the normal (T. Min. ( + )). After the establishment of contingency table was necessary to calculate percentage results. For better orientation was done a climatology for each region homogeneous separated into upper and lower limits, where values that are within this limit are considered in the normal range. The test was done the Chi square and as a result it was noted that the invalidity of the test is true. It was possible to check this work in R1 the PDO warm influenced an increase maximum temperature and decrease minimum temperature; the cold PDO influenced in R2 an increase minimum temperature and warm PDO decrease maximum temperature and minumum temperature. Cold PDO influenced in R3 increase the maximum and minimum tmeperature and warm PDO decrease maximum temperature and increase minimum temperature; in R4 the cold PDO influenced an increase maximum and minimum temperature and the warm PDO decreased the maximum and minimum temperature. All these results are given in number of cases over the course of the year. However doesn t have significant among variables. So, the State Rio Grande do Sul maximum and minimum temperature are influencied by PDO but this was insignificant. / O Rio Grande do Sul é um estado com características na agricultura, que é a base da sua economia. Além disso, o Estado também recebe muitos turistas na região de serra e litorânea. Esses fatores sofrem influência da temperatura e isso se faz necessário um estudo para que a economia do Estado não seja afetada. Sabese que existe uma influência dos oceanos nas mais diversas variáveis meteorológicas e ressalta-se que o Oceano Pacífico é o maior dos oceanos. As temperaturas da superfície do mar (TSM) do Oceano Pacífico, apresentam uma configuração com variações de longo prazo, semelhante ao El Niño, denominada Oscilação Decadal do Pacífico (ODP) e foi descoberto que a ODP influencia na precipitação do Estado (Rebello, 2006). Objetiva-se estudar as possíveis influências da ODP na temperatura máxima e mínima. Para isso utilizou-se os dados de temperatura máxima e mínima no período de 1925 a 2008 das estações de superfície do INMET em regiões homogêneas de temperatura e os índices de ODP. Foram realizados cálculos de anomalias de temperatura média máxima e média mínima para cada estação e suas respectivas médias mensais. Com esses resultados calculou-se o percentil dos índices de ODP e das médias das anomalias de temperatura máxima e mínima. O percentil serviu para separar intervalos de faixas abaixo da normal, até 40%, entre 40% e 60% sendo a faixa de transição ou normal e acima de 60% como sendo a faixa acima da normal. A Tabela de Contingência também foi usada como ferramenta para organizar melhor os dados e separá-los em número de casos de temperatura máxima abaixo da normal, (T. Max.( - )), normal, e acima da normal (T. Max.( + )) e o mesmo com a temperatura mínima sendo abaixo da normal (T. Min.( - )), normal, e acima da normal (T. Min.( + )). Após a elaboração da Tabela de Contingência foi necessário calcular em porcentagem seus resultados. Para uma melhor orientação foi feito uma climatologia para cada região homogênea separadas em limites inferior e superior, onde os valores que estiverem dentro desse limite são considerados na faixa de normalidade. Foi feito o teste do Qui-quadrado e como resultado observou-se que a nulidade do teste é verdadeira. Foi possível verificar no trabalho que R1 a ODP quente influenciou num aumento da temperatura máxima e diminuição da temperatura mínima; em R2 a ODP fria influenciou num aumento da temperatura mínima e a ODP quente numa diminuição da temperatura máxima e diminuição da temperatura mínima; em R3 a ODP fria influenciou num aumento da temperatura máxima e mínima e a ODP quente numa diminuição da temperatura máxima e aumento da temperatura mínima; em R4 a ODP fria influenciou num aumento da temperatura máxima e mínima e a ODP quente numa diminuição da temperatura máxima e mínima. Todos esses resultados se deram em número de casos ao decorrer do ano. E apesar disso não houve significância entre as variáveis estudadas. Sendo assim, as temperaturas máximas e mínimas do estado do Rio Grande do Sul sofrem influência da ODP, mas não se obteve significância estatística.

Global warming and climate change deeply influence weather and climate extremes, causing substantial property damage and loss every year around the world. Given the importance of heating differences between low-latitude and Arctic regions, which produce heat sources and cold sources that each influence global circulations, we investigate three extreme weather events in different regions in order to better understand the possible connections between extreme events and global circulation changes. This study begins with climate variations in the low-latitude western North Pacific. In early summer, the timing of the wet season has shifted from late May to early June since 1979. This change influences the water supply in Southeast Asia. Our analysis results indicate that the increase in global temperatures is suggested to have induced this change. During the hurricane season, deep convection in the western North Pacific has a 20-year frequency of timing variations, oscillating between July and August and influencing hurricane activity. These variations have not been previously identified and do not have any driven forcings, but a precursor deep-convection signal is found in the spring. Mid-latitude weather and climate can be influenced by tropical deep convection through the Pacific North American teleconnection. Our analysis results suggest that the wintertime Californian drought is mainly modulated by a teleconnection pattern from the tropics and natural variations in North Pacific circulation. Another key factor that influences mid-latitude circulation is Arctic temperature variations. We find an increase in the subseasonal Arctic warming event, suggesting more weather extremes in the mid-latitudes. Evidence suggests that sea-ice loss and the increase in tropical deep convection results in the increased likelihood of a subseasonal Arctic warming event.

No description available.

The recent, rapid decline in Arctic summer sea ice extent has prompted questions as to the rates and magnitude of previous sea ice decline and the affect of this physical change on icerelated ecosystems. However, satellite data of sea ice only extends back to 1978, and mapped observations of sea ice prior to the 1970s are sparse at best. Inventories of boreal ecosystems are likewise hampered by a paucity of investigations spanning more than the past few decades. Paleoclimate records of sea ice and related primary productivity are thus integral to understanding how sea ice responds to a changing climate. Here I examine modern sedimentation, decadal-scale climate change in the recent past, and centennial- to millennial-scale changes of the past 400 ka using both qualitative and quantitative diatom data in concert with sedimentology and organic geochemistry. Diatom taxonomy and corresponding ecological affinities are compiled in this study and updated for the Bering Sea region and then used as recorders of past climate changes. In recent decades, the Pacific Decadal Oscillation and the strength of the Aleutian Low are reflected by subtle changes in sediment diatom assemblages at the Bering Sea shelf-slope break. Farther back in time, the super-interglacial, marine isotope stage (MIS) 11 (428-390ka), began in Beringia with extreme productivity due to flooding of the Bering Land Bridge. A moisture-driven advance of Beringian glaciers occurred while eustatic sea level was high, and insolation and seasonality both decreased at the global peak of MIS 11. Atlantic/Pacific teleconnections during MIS 11 include a reversal in Bering Strait throughflow at 410 ka and a relationship between North Atlantic Deep Water Formation and Bering Sea productivity. Finally, concentrations of the biomarker-based sea ice proxy, IP25, are compared to sea ice concentration across the Bering and Chukchi seas. Changes in the concentration of IP25 in the sediments may be driven by the length of time that the epontic diatom bloom lasts. When combined with a sediment-based proxy for sea surface temperatures, IP25 can be used to reconstruct spring ice concentration.

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.

Neste trabalho foi investigado o impacto da evolução dos eventos El Niño (EN) de acordo com as fases distintas da Oscilação Decadal do Pacífico (positiva, ODP(+) e negativa, ODP(-)) nas mudanças no transporte de umidade sobre o Sudeste da América do Sul (SEAS) durante o verão austral de 1950-1999. A resposta da variabilidade do Jato de Baixos Níveis a leste do Andes (JBN) e de algumas propriedades dos ciclones extratropicais sobre o cone sul do continente as modificações na circulação associadas aos eventos mencionados acima foi analisada. Foi mostrado que existem poucas mudanças significativas no regime de precipitação sobre a América do Sul ao se considerar a influência dos anos neutros do Pacífico Equatorial durante a ODP(+) quando comparado com os anos da ODP(- ). Entretanto, os eventos EN da ODP(+) indicam diferenças no padrão de anômalo de ondas em altos níveis em resposta as diferentes anomalias de Temperatura de Superfície do Mar (TSM) dos oceanos Pacífico e Atlântico Equatorial quando comparado com os eventos da ODP(-). Como conseqüência foram observadas anomalias positivas de precipitação no SEAS associadas à intensificação do fluxo convergente de umidade em baixos níveis oriundo do Atlântico Equatorial e região Amazônica para esta região durante os eventos EN da ODP(+). Todavia, os eventos da ODP(-) apresentaram anomalias positivas de precipitação apenas ao sul do SEAS e negativas ao norte desta como resposta ao movimento descendente e divergência anômala sobre o centro-leste do Brasil seguido de enfraquecimento do fluxo de umidade transportado pelos ventos alísios em direção aos subtrópicos. Os experimentos numéricos com Community Atmosphere Model versão 3.0 serviram para ajudar na interpretação das análises observacionais onde foi sugerido que o fenômeno EN é mais importante para forçar as anomalias climáticas de verão do continente do que o modo de ODP. A maior freqüência de casos de JBN detectados com o critério 1 de Bonner durante anos de EN da ODP(+) em relação a ODP(-) foi proporcional à quantidade de eventos selecionados em cada categoria. Em geral, os casos de JBN anômalo se deslocaram desde a Amazônia até o Sul do Brasil e Nordeste da Argentina, mas foi na ODP(-) que o sistema foi mais intenso apesar de apresentar menor potencial para o transporte de umidade para o SEAS quando comparado com os casos da ODP(+). Através do esquema numérico de Murray e Simmonds foi observado que, coerentemente com a intensificação do fluxo convergente de ar quente e úmido dos trópicos para o SEAS, os eventos EN da ODP(+) apresentaram ciclones extratropicais mais freqüentes e com pressões centrais mais baixas sobre o extremo Sul do Brasil, Uruguai, Nordeste da Argentina e vizinhanças do Atlântico Sudoeste em comparação com os eventos da ODP(-). / This work investigates the impact of the El Niño (EN) events and their evolution according to the PDO phases (warm, PDO(+) and cold, PDO(-)) focusing on the moisture transport exchanges from the north to the Southeast of the South America (SESA) during the austral summer period of 1950-1999. The variability of the Low Level Jet east of the Andes (LLJ) and some properties of extratropical cyclones over the southern cone of the continent in response to the modifications in the atmosphere circulation due to above mentioned events is analyzed. It is shown that on the South America continent there are not any significant changes in precipitation distribution during the neutral years in the Equatorial Pacific for PDO(+) when compared to the years of PDO(-). However, the EN events during PDO(+) indicate some differences in the anomalous wave pattern at high levels due to the variability of the Sea Surface Temperature (SST) anomalies on the Equatorial Pacific and Atlantic oceans when compared with the events for PDO(-). This implies in positive precipitation anomalies over the SESA which is associated to the enhancement of convergent moisture flux in this region. However, the events for PDO(-) showed positive precipitation anomalies only over the southern part of the SEAS and negative to the north which is associated to the downward motion and anomalous divergence over the centraleastern Brazil. This pattern may have contributed for weakening the moisture flux transported by the trade winds towards the subtropics. Numerical experiments with the Community Atmosphere Model version 3.0 also helped on the interpretation of the observational analysis where was suggested that EN events are more important to force the climate anomalies in the summer season over the continent than the PDO mode. The frequency of LLJ cases detected with the Bonner criterion 1 during the years of EN for PDO(+) is bigger than for PDO(-). The spatial position pattern for both categories of the anomalous LLJ is from the Amazon to Southern Brazil and Northeastern Argentina. During the PDO(-) the jet is more intense, however it seems to transport less moisture towards the SEAS region when compared to the PDO(+) cases. The extratropical cyclones tracked through a numerical scheme showed higher frequency and lower central pressures on the extreme of Southern Brazil, Uruguay, Northeastern Argentina and around the Southwest Atlantic during the EN events of PDO(+) when compared to the events of PDO(-). This is in agreement with the largest flux convergence of warm and humid air from the tropics to these areas.

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.