Multiscale interaction between the ocean and the atmosphere and the low frequency variability

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

Multiscale interaction between the ocean and the atmosphere and the low frequency variability

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

Asymptotic approach for the nonlinear equatorial long wave interactions

In the present work we use an asymptotic approach to obtain the long wave equations. The shallow water equation is put as a function of an external parameter that is a measure of both the spatial scales anisotropy and the fast to slow time ratio. The values given to the external parameters are consistent with those computed using typical values of the perturbations in tropical dynamics. Asymptotically, the model converge toward the long wave model. Thus, it is possible to go toward the long wave approximation through intermediate realizable states. With this approach, the resonant nonlinear wave interactions are studied. To simplify, the reduced dynamics of a single resonant triad is used for some selected equatorial trios. It was verified by both theoretical and numerical results that the nonlinear energy exchange period increases smoothly as we move toward the long wave approach. The magnitude of the energy exchanges is also modified, but in this case depends on the particular triad used and also on the initial energy partition among the triad components. Some implications of the results for the tropical dynamics are disccussed. In particular, we discuss the implications of the results for El Nĩo and the Madden-Julian in connection with other scales of time and spatial variability. © Published under licence by IOP Publishing Ltd

A modeling study: On the influence of high frequency ocean-atmosphere interactions over intra-seasonal oscillations (during the El Nino 1997-98)

The ability of numerical models in reproducing the MJO has been analysed in several studies. In the present work, the intraseasonal oscillations, emphasizing the MJO, were studied, by coupling an intermediate complexity model named QTCM (QuasiEquilibrium Tropical Circulation Model) with a slab mixed layer ocean model. The slab mixed layer ocean model was used to rectify the time evolution of the specified sea surface temperature (SST). This rectification was done at the atmospheric model integration time step at every twenty minutes. In this way, the high frequency correction allows us to have a systematic ocean-atmosphere interaction at time scales shorter than one day. The coupled model was integrated for a period that runs from january 1990 to december 1999, so the El Niño 1997-98 was included in the simulations. The component waves at intraseasonal time scales, were studied also with the use of the space-time spectral analysis projected in a dispersion diagram, useful to separate the modes which shows distinctive dispersive properties. The general results showed that the inclusion of the coupling leads to an improvement in the representation of the intraseasonal modes with eastward propagation, increasing its variability and its propagation mainly over the Maritime Continent. These improvements ocurred in special during El Niño 1997-98.Pages: 1337-134

Multivariate analysis of the energy cycle of the South American rainy season

The South American (SA) rainy season is studied in this paper through the application of a multivariate Empirical Orthogonal Function (EOF) analysis to a SA gridded precipitation analysis and to the components of Lorenz Energy Cycle (LEC) derived from the National Centers for Environmental Prediction (NCEP) reanalysis. The EOF analysis leads to the identification of patterns of the rainy season and the associated mechanisms in terms of their energetics. The first combined EOF represents the northwest-southeast dipole of the precipitation between South and Central America, the South American Monsoon System (SAMS). The second combined EOF represents a synoptic pattern associated with the SACZ (South Atlantic convergence zone) and the third EOF is in spatial quadrature to the second EOF. The phase relationship of the EOFs, as computed from the principal components (PCs), suggests a nonlinear transition from the SACZ to the fully developed SAMS mode by November and between both components describing the SACZ by September-October (the rainy season onset). According to the LEC, the first mode is dominated by the eddy generation term at its maximum, the second by both baroclinic and eddy generation terms and the third by barotropic instability previous to the connection to the second mode by September-October. The predominance of the different LEC components at each phase of the SAMS can be used as an indicator of the onset of the rainy season in terms of physical processes, while the existence of the outstanding spectral peaks in the time dependence of the EOFs at the intraseasonal time scale could be used for monitoring purposes. Copyright (C) 2009 Royal Meteorological Societ

The annual cycle of the Atmosphere heat budget fousing on the southern hemisphere

Based on NCEP/NCAR reanalysis and World Ocean Atlas 2005, the long-term variation of the Atmosphere heat budget has been investigated. The aim of this work was to evaluate the role of each component of the climate system on the planet energy balance, focusing on the atmospheric variability over the Southern Ocean and the Antarctic Continent. The calculation was performed according to the formulation used by Oort and Vonder Haar (1976). As expected, the ocean has shown a huge dominance on heat storage around the globe. A large seasonal variation on both oceanic and atmospheric systems was evident. Results show unusual atmospheric variability over the southern polar region. After removing the seasonal cycle, the atmospheric heat storage anomaly displays significant intraseasonal variability at high latitudes. EOF and Wavelets analysis show that the atmospheric heat storage changed from the beginning of the record with a distinct 2 months cycle, which is well defined between 60◦S and 90◦S. According to the EOF analysis it grew more intense from mid 20th to early 21st centuries, reflecting the warming trend.Utilizando dados da re-análise NCEP/NCAR e do World Ocean Atlas 2005, foi investigada a variação de longo termo do balaço de calor da atmosfera. O objetivo deste trabalho foi avaliar o papel de cada componente do sistema climático no balanço de energia do planeta, especialmente a variabilidade atmosférica sobre o Hemisfério Sul e o continente antártico. Foi adotada a formulação proposta por Oort and Vonder Haar (1976). Como esperado, o oceano apresentou grande dominância em termos do armazenamento do calor no âmbito global. A variabilidade sazonal ficou evidente tanto para o oceano quanto para atmosfera. Foi observada uma variabilidade incomum no termo atmosférico sobre a região polar sul. Removendo o ciclo sazonal, a anomalia do armazenamento de calor pela atmosfera mostra uma variabilidade em escala intrasazonal em altas latitudes. Análises de EOF e Wavelets mostram que o armazenamento de calor pela atmosfera alterou-se entre o início e o fim do período analisado, evidenciando uma oscilação com período de 2 meses muito bem marcada entre as latitudes de 60◦S e 90◦S. De acordo com a EOF, esse modo de variabilidade intensificou-se entre meados do século XX e início do século XXI, refletindo a tendência de aquecimento

New developments in seasonal prediction at CPTEC/INPE Brazil

The new implementations at CPTEC referring to Long-Range Forecasts are presented and discussed. A cluster analysis has been applied to the ensemble members to identify different groups that show different behaviour with respect to anomaly precipitation. In this technique we do clustering of members with similar behaviour, resulting in several different clusters. Thus, in regions with large dispersion, the cluster analysis can be an useful tool to replace the ensemble average. Another technique that is being applied to the daily results from the model prediction is the prediction of Madden-Julian Oscillation. It is already known that intraseasonal oscillations have influence on South America convection, and it is important to analyse this kind of variability in the model results to increase the predictability in some regions that are strongly affected. The seasonal prediction has also been performed, in an experimental way, using the AGCM with the Grell ensemble convection scheme, replacing the Kuo scheme. A new AGCM that has been developed at CPTEC, based on CPTEC/COLA AGCM, but with a different structure of integration, has been tested for climate simulations using resolution of T126L42. The efficiency of this model is much higher than the operational one, and allow the higher resolution runs. The introduction of an updated vegetation set and an estimated soil humidity field from an hydrological model is also discussed.Pages: 539-54