O objetivo desta pesquisa foi investigar a relação linear existente entre a Temperatura de Superfície do Mar (TSM) dos oceanos Pacífico e Atlântico e a vazão do rio Madeira, localizado na parte sul da região Norte do Brasil. A investigação foi feita nas escalas mensal, sazonal e anual, para o período de 1968 a 2009. A hipótese de que alterações climáticas na região Norte do Brasil estariam associadas a episódios de aquecimento e resfriamento dos oceanos globais, já que quando ocorrem têm o potencial de modificar o padrão de precipitação em áreas remotas do globo, foi a motivação central da pesquisa. A pesquisa foi desenvolvida com base em análises estatísticas para os dados de TSM, índices climáticos e a vazão do rio Madeira. Observou-se que a vazão mensal do rio Madeira apresenta correlação linear significativa com áreas específicas dos oceanos Atlântico e Pacífico. No Oceano Atlântico Norte, são significativas as correlações obtidas nos setores tropical (área AT3) e norte (área AT1). O setor subtropical do Atlântico Norte (AT2) apresenta correlações lineares não tão expressivas como suas áreas tropical e norte. O Atlântico Sul não apresenta áreas com correlações lineares significativas com a vazão. As áreas com correlação significativa do Atlântico Norte (AT1) apresentam valores negativos máximos entre -0,6 e -0,4. Os valores de correlação linear entre a vazão mensal do rio Madeira e a TSM do Atlântico (AT2) apresentam um pequeno aumento para os cálculos realizados com defasagem temporal de até nove meses, entre 0,3 a 0,4 para 5 meses de defasagem entre a vazão e a TSM. A TSM do setor oeste do Pacífico tropical apresenta fortes valores negativos de correlação linear com a vazão do rio Madeira, com valores máximos que variam entre -0,7 e -0,4. Tal qual acontece para o Atlântico, as águas superficiais do Pacífico tropical oeste apresentam um pequeno aumento dos valores de correlação linear para defasagens maiores entre a TSM e a vazão. As áreas com forte correlação negativa no setor oeste do Pacífico tropical foram denominadas PA1, no norte, e PA3, no sul. Uma pequena área com correlação significativa e positiva a leste da bacia do Pacífico, junto à costa do Chile, foi denominada PA2. Nesta área os valores máximos de correlação linear entre a vazão mensal e a TSM variam entre 0,2 e 0,4. A análise de correlação linear entre a vazão anual do rio Madeira e índices climáticos indicam que os índices ODP, MEI e OAN são os mais bem correlacionados com a vazão, apresentando valores iguais a 0,89, 0,86 e 0,85, respectivamente. Com base na TSM das áreas bem correlacionadas com a vazão do rio Madeira e nos índices climáticos considerados, foi desenvolvido um modelo estocástico de regressão linear múltipla para a previsão da vazão trimestral com antecedência de um trimestre. A TSM das áreas do setor oeste do Pacífico tropical, PA1, e do Atlântico Norte tropical, AT3, constituíram as variáveis selecionadas para a elaboração do modelo estocástico. O modelo estocástico foi desenvolvido para o início da série temporal considerada, de 1968 a 1988, e apresentou um ajuste linear com coeficiente de determinação igual a 78%. A verificação do modelo foi feita para o final da série, de 1989 a 2009. O erro médio normalizado calculado pela diferença entre os valores de vazão previstos pelo modelo e os observados foi igual a 40%. Desta forma, conclui-se que a vazão trimestral do setor sul da região Norte do Brasil é uma variável que pode ser prevista com base na variabilidade da temperatura das águas superficiais dos oceanos Pacífico e Atlântico. A análise do comportamento atmosférico com base em períodos específicos de anomalias de TSM no Atlântico Norte tropical indica que a ocorrência de TSMs mais altas (baixas) que o normal foram acompanhadas por ventos de leste mais fracos (fortes). Foram analisados os campos atmosféricos médios para os meses chuvosos de novembro a março para as variáveis Velocidade Vertical (Omega) em 500 e 850 hPa, divergência e vorticidade do vento. Os resultados obtidos demonstram que em média, a variabilidade atmosférica foi determinante no que se refere às anomalias apresentadas pela vazão. / The objective of this research was to investigate the linear relation between the sea surface temperature (SST) over Pacific and Atlantic oceans and the outflow of the Madeira river, located at the southern part of the Northern region of Brazil. The investigation considered monthly, seasonal and annual scales, to the period between 1968 to 2009. The consideration about the influence of heating and cooling of oceanic areas over climate around the world constitutes the main hypothesis taken in account in the study. The research was developed based on statistical analysis considering SST, climatic indexes and river outflow data. The monthly outflow for Madeira River shows significant linear correlation to SST at specific areas over Atlantic and Pacific. Over North Atlantic, the linear correlation values are significant at the tropical and north sectors, namely AT3 and AT1, respectively. The subtropical sector of North Atlantic presents positive correlation but not too expressive as the tropical and north areas of Atlantic. South Atlantic does not present significant values of linear correlation with the river outflow. The area with significant correlation over North Atlantic (AT1) presents maximum negative values ranging between -0,6 and -0,4. In general, the greater the interval between river outflow and SST data, greater is the linear correlation values. SST data from the western sector of tropical Pacific presents strong negative correlation with Madeira River outflow data, and shows maximum values ranging between -0,7 and -0,4. The areas to the West of Pacific showing high negative correlation were named PA1 and PA3, to northern and southern sectors, respectively. A small area that shows significant positive linear correlation to the river outflow data, PA2, is located over the eastern side of Pacific basin, very closed to the coast of Chile. In this area, the linear maximum correlation values range between 0,2 and 0,4. Linear correlation analysis between annual river outflow data and climatic indices indicates that PDO, MEI and NAO are those more correlated with the river outflow data, presenting values equal to 0,89, 0,86 e 0,85, respectively. Based on averaged SST and climatic indices well correlated to the Madeira River outflow data, a stochastic model was developed in order to forecast the river outflow in seasonal scale. SST from west of tropical Pacific, PA1, and from tropical North Atlantic, AT3, were selected to build up the stochastic model. The stochastic model was developed considering the first half of the total series, between 1968 and 1988, while the last period was used to validate the model, between 1989 and 2009. The linear adjusting over the first period reach a determining coefficient equal to 78% and the normalized mean error obtained for the second period was equal to 40%. Thus, we conclude that the seasonal outflow for Madeira River is a climatic variable that can be forecast based on the SST variability over specific areas on Pacific and Atlantic oceans. The analysis of atmospheric behavior based on specific periods of SST anomalies in the tropical North Atlantic indicates that the occurrence of SSTs higher (lower) than normal was accompanied by easterly winds weak (strong). We analyzed the average atmospheric fields for the rainy months from November to March for variables Vertical Speed (Omega) at 500 and 850 hPa, divergence and vorticity of the wind. The results show that approximately the atmospheric variability was decisive with regard to the deficiencies presented by the ouflow.

Um aspecto importante a ser apontado no presente trabalho é o fato de se ter acompanhado de um modo ininterrupto, durante 10 dias, as anomalias nas distribuições das propriedades físicas da água do mar. Os resultados experimentais obtidos na região costeira a oeste de Cabo Frio durante este período mostraram a preponderância dos processos advectivos e difuzivos que alteram a distribuição da temperatura e da salinidade na superfície do mar. Essa anomalia pode ser indicada por nuvens do tipo cúmulos formada por convecção penetrante, fato verificável pela comparação dos dados térmicos de superfície com fotografias obtidas pelo satélite ERTS. / Temperature and salinity variations between Guanabara Bay and Cabo Frio (17/8 a 26/8/1971).

A variabilidade climática é um objeto característico da Geografia já que anomalias positivas ou negativas de seus elementos, principalmente precipitação e temperatura, podem afetar de forma significativa a vida da população atingida. Na presente pesquisa, a variabilidade da vazão na bacia amazônica brasileira para o período de 1976 a 2010 é estudada por meio de técnicas estatísticas, tais como correlação linear, regressão linear simples e múltipla, análise de agrupamento e análise de ondeletas. Campos de componentes atmosféricos são apresentados para a compreensão da circulação atmosférica anômala que leva a anomalias de vazão. O objetivo é compreender com mais profundidade possíveis associações entre a variabilidade da vazão fluvial e da temperatura da superfície do mar, TSM, em regiões oceânicas específicas, reconhecendo-se para isso o acoplamento oceano-atmosfera que modula a variabilidade climática global. Este estudo compreendeu o uso de dados de vazão e precipitação do sistema Hidroweb/ANA, dados de TSM, radiação de onda longa e vento do conjunto de dados da Reanálise I, do NCEP/NCAR, e dados de precipitação do Global Precipitation Climatology Project, GPCP. A maior parte das análises considerou o tratamento de dados na escala mensal. O estudo verificou que há variabilidade espacial para a resposta da correlação linear entre a TSM e a vazão na bacia amazônica brasileira, verificada em cada uma das sub-regiões homogêneas definidas para esta pesquisa. Diferenças espaciais também foram verificadas nos resultados dos testes para tendência linear, identificando-se um padrão de tendência positiva da vazão na parte norte da bacia amazônica brasileira, e, negativa na porção sul. Sugere-se que a tendência negativa na porção sul esteja, em parte, associada à expansão das áreas agrícolas e, portanto, à intensificação do desmatamento. Cada uma das sub-regiões apresentou padrões espaciais de correlação linear diferenciados com os oceanos, mas, de forma geral, verifica-se que os eventos ENOS são importantes na definição da variabilidade da bacia amazônica, sendo mais efetivos nas anomalias de vazão das sub-regiões Norte, Amazonas-Foz e Sul, enquanto que a variabilidade da temperatura da superfície do mar no Atlântico Tropical Norte está bem associada à variabilidade da vazão nas sub-regiões Central e Oeste. A análise dos campos atmosféricos médios para anos caracterizados por ENOS neutros permitiu identificar que a sub-região Oeste apresentou resultados de influência de processos climáticos regionais que influenciaram anomalias positivas e negativas de vazão. Desta forma, a hipótese da tese de que, observando-se as particularidades de associação entre a temperatura da superfície do mar e a vazão fluvial para cada sub-região amazônica seria possível elaborar um modelo estocástico de previsão mais adequado a cada sub-região, sendo cada um mais apropriado a cada subregião, exprimindo maior acurácia e significância estatística, foi confirmada. Cada uma das sub-regiões consideradas apresenta intervalos de tempo preferenciais em que a correlação com a superfície dos oceanos é máxima. Assim, conclui-se que a bacia amazônica não pode ser considerada como um todo quanto à análise climática, já que foram confirmadas variabilidades espaciais de tendência linear dos dados de vazão, correlação entre vazão e precipitação e correlação com anomalias da temperatura da superfície do mar. / Climate variability is a characteristic object of geography, as positive or negative anomalies of its elements, especially precipitation and temperature may significantly affect the lives of the population. In this research, the variability of flow in the Brazilian Amazon basin for the period 1976-2010 is studied through statistical techniques such as linear correlation, simple and multiple linear regression, cluster analysis and wavelet analysis. Fields of atmospheric components are presented for comprehending the anomalous atmospheric circulation which leads to flow abnormalities. The objective is to understand more deeply possible associations between the variability of river flow and sea surface temperature, SST, in specific ocean regions, in order to recognize ocean-atmosphere coupling that modulates the global climate variability. This study has encompassed the use of flow and precipitation data of Hidroweb system/ANA, SST data, longwave radiation and wind of NCEP/NCAR Reanalysis I dataset, and precipitation data of Global Precipitation Climatology Project, GPCP. Most of the analyzes considered the treatment of data in the monthly scale. The study found that there is spatial variability to the response of the linear correlation between SST and the flow in the Brazilian Amazon basin seen in each one of the homogeneous subregions defined for this research. Spatial differences were also verified in the results of tests for linear trend, identifying a pattern of positive trend of the flow in the northern part of the Brazilian Amazon basin, and negative in the southern portion. It suggests that the negative trend in the southern portion is partly associated with the expansion of agricultural areas and therefore, the intensification of deforestation of forested areas. Each one of the subregions showed different spatial patterns of linear correlation with the oceans, but in general, ENSO events are important in defining the variability of the Amazon basin, being more effective in flow anomalies of North, Amazonas-Foz and South subregions, whereas the variability of sea surface temperature in the Tropical North Atlantic is well associated with the variability of flow in the Central and West subregions. The analysis of average atmospheric fields for years characterized by neutral ENSO was able to identify that the West subregion presented results of influence of regional climate processes which influenced anomalies of positive and negative flow. Thus, the hypothesis of the thesis that, by observing the association of the particularities between sea surface temperature and river flow for each Amazon subregion would be possible to develop a more appropriate stochastic model to each subregion, being each one more adequate to every subregion, expressing greater accuracy and statistical significance, was confirmed. Each one of the subregions considered presents preferential time intervals at which the correlation to the ocean surface is maximal. Therefore, it is concluded that the Amazon basin cannot be considered as a whole regarding its climate analysis, seeing that spatial variabilities of linear trend of flow data were confirmed, correlation between flow and precipitation and correlation with sea surface temperature anomalies.

Resultados da reanálise SODA v2.2.6 (Carton, Giese, 2008) e da Renálise do Século 20 v2 (Compo, et al., 2011) foram analisados para verificar alterações dos modos de variabilidade da TSM (o modo do Gradiente Meridional de Temperatura (GMT) e o Modo Zonal) no Atlântico Tropical (de 1929 a 2008) através de funções empíricas ortogonais (EOF) e funções empíricas ortogonais associadas (jEOF). A evolução do padrão espacial do modo do GMT se inicia com a configuração de dipolo de temperatura, com eixo central em ≈ 5ºN evoluindo para o GMT com variabilidade concentrada no Atlântico Tropical Norte. O Modo Zonal apresenta inicialmente variabilidade associada à região equatorial (entre 5ºS e 5ºN) e à costa sudoeste africana, que evolui para um gradiente meridional de TSM, centrado em ≈ 5ºN. Sua variabilidade concentra-se exclusivamente no Atlântico Tropical Sul. A variabilidade equatorial se degenera ao longo do período, devido ao aumento, gerado pelo vento, da profundidade das isopicnais na termoclina. No equador o acoplamento entre o oceano e a atmosfera ocorre nos períodos de T = 30 meses e T ≈ 34 meses, com o vento antecedendo a temperatura em 1 e 2 meses, respectivamente. O Modo Zonal apresenta acoplamento com o vento durante a segunda metade das análises. O período associado é de T ≈ 34 meses, com o vento antecedendo a temperatura em cerca de 1 mês. O modo do GMT está associado aos ventos no Atlântico Tropical Norte e Atlântico Tropical Sul. Os períodos de acoplamento são de T = 96 e T = 60 meses, com o vento antecedendo a TSM em 3 e ≈ 2 meses respectivamente. / The results of SODA v2.2.6 reanalysis (Carton, Giese, 2008) and 20th Century Reanalysis v2 Project (Compo, et al., 2011) were analyzed in order to verify changes of the SST modes (the Meridional Temperature Gradient mode (GMT) and the Zonal Mode) in the Tropical Atlantic (1929 to 2008) using Empirical Orthogonal Functions (EOF) and joint Empirical Orthogonal Functions (jEOF). The spatial distribution of GMT starts initially as a temperature dipole centred at ≈ 5ºN. It evolves into a meridional gradient with variability concentrated at the Tropical North Atlantic. The zonal mode variability is initially associated with the equatorial region (between 5ºS and 5ºN) and with the northwestern african coast. It evolves into a merdional gradient with central axis located at 5ºN. Its variability is concentrated exclusively in the Tropical South Atlantic. The equatorial variability degenerates throughout the period, due to the inhibition of the isopicnal uplift by the wind. At the equator, the coupling occurs in periods of T = 30 months and T ≈ 34 months, with the wind preceding the TSM by 1 and 2 months, respectively. The zonal mode presents coupling with the wind only during the second half of the analysis. The periods are of T = 34 months, with wind preciding TSM by about 1 month. GMT mode is associated to the winds of both Tropical North Atlantic and Tropical South Atlantic. Coupling periods are of T = 96 and T = 60 months, with the wind preceding TSM in 3 and ≈ 2 months respectively.

Volcanism is the cause of great non-anthropogenic perturbations on the Earth climate through energy imbalance changes. There is still much to be uncovered relative to its impacts on the Southern Hemisphere, even more with respect to the Southern Ocean. The South Atlantic and its Southern Ocean sector response to volcanism are examined using simulation results from the Last Millennium Ensemble Experiment of the Community Earth System Model (CESM-LME), for the period 850-2005. Composite results point to significant changes in sea surface temperature and salinity in the first austral summer following the eruption. North of 60S, there is ocean cooling, as expected because of the higher albedo related to the volcanic forcing. In contrast, near the Antarctic Peninsula in the Weddell Sea, a local warming of ∼ 0.8ºC is observed (significant at the 90% level). Salinity shows positive anomaly (∼0.1) at the northern region off Antarctic Peninsula from the first year after the eruption to the fourth subsequent year. Oceanic surface anomalies weaken after the fifth subsequent year, however it is still present in deeper layers (∼500m). At the same time, wind stress changes are evident, results show a poleward shift (∼2º), strengthening (∼10%) of the prevailing westerlies and the reversal in direction of the meridional wind stress component in the northern Antarctic Peninsula. As consequence, there is intensification of the Antarctic Circumpolar Current southern extension. Together with the stronger westerlies, the mixing in the northern Antarctic Peninsula is enhanced, bringing up warmer subsurface waters, therefore explaining the anomalous surface warming after the eruption. The 1991 Mt. Pinatubo eruption response is also investigated. CESM-LME, observations and reanalysis have shown similar behavior, however for the second subsequent year, thus suggesting the occurrence of the same mechanism identified after Last Millennium eruptions. / Vulcanismo é uma das maiores causas naturais de mudanças no clima. Poucos estudos tiveram foco no seu impacto no hemisfério sul, principalmente no Oceano Austral. Desta forma, o impacto de erupções vulcânicas é investigado no Oceano Atlântico Sul incluindo o seu setor austral, em resultados do modelo CESM-LME (Community Earth System Model Last Millennium Ensemble) entre 850 e 2005. Os resultados utilizando composições mostram mudanças significativas na temperatura e salinidade da superfície do oceano no primeiro verão austral depois da erupção. Ao norte de 60S, há uma anomalia negativa de ∼ -0.8ºC na temperatura em superfície, devido ao maior albedo após a erupção. No entanto, próximo à Península Antártica no Mar de Weddell, é visto uma anomalia positiva de ∼0.8ºC (significativa a 90%). A salinidade apresenta mudanças importantes entre o primeiro e o quarto ano após a erupção, com anomalia positiva (∼0.1) ao norte da Península Antártica. A resposta ao vulcanismo em superfície desaparece no quinto ano sequente, mas permanecem anomalias em profundidade (∼500m). O campo de vento também se altera no mesmo ano, os ventos de oeste migram para sul (∼2º) e se intensificam (∼10%), além da componente meridional inverter seu sentido ao norte da Península Antártica. Como consequência, é observada intensificação da borda sul da Corrente Circumpolar Antártica. Junto com isto, há aumento da mistura próximo à Península Antártica, desta forma, águas subsuperficiais mais quentes afloram, explicando a anomalia quente após a erupção. Finalmente, é verificada a ocorrência de resposta similar após a erupção do Monte Pinatubo (1991). Resultados do CESM-LME tiveram comportamento aproximado quando comparados com dados observacionais e reanálise. O aquecimento próximo à Península Antártica é evidenciado no segundo ano após a erupção, sugerindo a ocorrência do mesmo mecanismo do último milênio.

Um aspecto importante a ser apontado no presente trabalho é o fato de se ter acompanhado de um modo ininterrupto, durante 10 dias, as anomalias nas distribuições das propriedades físicas da água do mar. Os resultados experimentais obtidos na região costeira a oeste de Cabo Frio durante este período mostraram a preponderância dos processos advectivos e difuzivos que alteram a distribuição da temperatura e da salinidade na superfície do mar. Essa anomalia pode ser indicada por nuvens do tipo cúmulos formada por convecção penetrante, fato verificável pela comparação dos dados térmicos de superfície com fotografias obtidas pelo satélite ERTS. / Temperature and salinity variations between Guanabara Bay and Cabo Frio (17/8 a 26/8/1971).

Resultados da reanálise SODA v2.2.6 (Carton, Giese, 2008) e da Renálise do Século 20 v2 (Compo, et al., 2011) foram analisados para verificar alterações dos modos de variabilidade da TSM (o modo do Gradiente Meridional de Temperatura (GMT) e o Modo Zonal) no Atlântico Tropical (de 1929 a 2008) através de funções empíricas ortogonais (EOF) e funções empíricas ortogonais associadas (jEOF). A evolução do padrão espacial do modo do GMT se inicia com a configuração de dipolo de temperatura, com eixo central em ≈ 5ºN evoluindo para o GMT com variabilidade concentrada no Atlântico Tropical Norte. O Modo Zonal apresenta inicialmente variabilidade associada à região equatorial (entre 5ºS e 5ºN) e à costa sudoeste africana, que evolui para um gradiente meridional de TSM, centrado em ≈ 5ºN. Sua variabilidade concentra-se exclusivamente no Atlântico Tropical Sul. A variabilidade equatorial se degenera ao longo do período, devido ao aumento, gerado pelo vento, da profundidade das isopicnais na termoclina. No equador o acoplamento entre o oceano e a atmosfera ocorre nos períodos de T = 30 meses e T ≈ 34 meses, com o vento antecedendo a temperatura em 1 e 2 meses, respectivamente. O Modo Zonal apresenta acoplamento com o vento durante a segunda metade das análises. O período associado é de T ≈ 34 meses, com o vento antecedendo a temperatura em cerca de 1 mês. O modo do GMT está associado aos ventos no Atlântico Tropical Norte e Atlântico Tropical Sul. Os períodos de acoplamento são de T = 96 e T = 60 meses, com o vento antecedendo a TSM em 3 e ≈ 2 meses respectivamente. / The results of SODA v2.2.6 reanalysis (Carton, Giese, 2008) and 20th Century Reanalysis v2 Project (Compo, et al., 2011) were analyzed in order to verify changes of the SST modes (the Meridional Temperature Gradient mode (GMT) and the Zonal Mode) in the Tropical Atlantic (1929 to 2008) using Empirical Orthogonal Functions (EOF) and joint Empirical Orthogonal Functions (jEOF). The spatial distribution of GMT starts initially as a temperature dipole centred at ≈ 5ºN. It evolves into a meridional gradient with variability concentrated at the Tropical North Atlantic. The zonal mode variability is initially associated with the equatorial region (between 5ºS and 5ºN) and with the northwestern african coast. It evolves into a merdional gradient with central axis located at 5ºN. Its variability is concentrated exclusively in the Tropical South Atlantic. The equatorial variability degenerates throughout the period, due to the inhibition of the isopicnal uplift by the wind. At the equator, the coupling occurs in periods of T = 30 months and T ≈ 34 months, with the wind preceding the TSM by 1 and 2 months, respectively. The zonal mode presents coupling with the wind only during the second half of the analysis. The periods are of T = 34 months, with wind preciding TSM by about 1 month. GMT mode is associated to the winds of both Tropical North Atlantic and Tropical South Atlantic. Coupling periods are of T = 96 and T = 60 months, with the wind preceding TSM in 3 and ≈ 2 months respectively.

Previous studies showed that sea surface salinity (SSS) in the Florida Straits as well as Florida Current transport covaried with changes in North Atlantic climate over the past two millennia. However, little is known about earlier Holocene variability in the Florida Straits. Here, we combine Mg/Ca-paleothermometry and stable oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber (white variety) from Florida Straits sediment core KNR166-2 JPC 51 (24 degrees 24.70? N, 83 degrees 13.14?W, 198m deep) to reconstruct a high-resolution (~30 yr/sample) early to mid Holocene record of sea surface temperature and delta18OSW (a proxy for SSS) variability. We also measured Ba/Ca ratios in the same shell material as a proxy for riverine input into the Gulf of Mexico over the same time interval. After removing the influence of global delta18OSW change due to continental ice volume variability, we propose that early Holocene SSS enrichments were caused by increased evaporation/precipitation ratios in the Florida Straits associated with periods of reduced solar output, increased ice rafted debris in the North Atlantic and the development of more permanent El Nino-like conditions in the eastern equatorial Pacific. When considered with previous high-resolution reconstructions of early Holocene tropical atmospheric circulation changes, our results provide evidence that solar output variability over the Holocene had a significant impact on the global tropical hydrologic cycle over the last 10,000 years.

Climatological winds over the equatorial Indian Ocean (EqlO) are westerly most of the year. Twice a year, in April-May ("spring") and October-December ("fall"), strong, sustained westerly winds generate eastward equatorial jets in the ocean. There are several unresolved issues related to the equatorial jets. They accelerate rapidly to speeds over lms"1 when westerly wind stress increases to about 0.7 dyne cm"2 in spring and fall, but decelerate while the wind stress continues to be westerly; each jet is followed by westward flow in the upper ocean lasting a month or longer. In addition to the semi-annual cycle, the equatorial winds and currents have strong in-traseasonal fluctuations. Observations show strong 30-60 day variability of zonal flow, and suggest that there might be variability with periods shorter than 20 days in the central EqlO. Observations from moored current meter arrays along 80.5°E south of Sri Lanka showed a distinct 15 day oscillation of equatorial meridional velocity (v) and off-equatorial zonal velocity (u). Recent observations from current meter moorings at the equator in the eastern EqlO show continuous 10-20 day, or biweekly, oscillations of v. The main motivation for the present study is to understand the dynamics of intraseasonal variability in the Indian Ocean that has been documented in the observational literature. What physical processes are responsible for the peculiar behavior of the equatorial jets? What are the relative roles of wind stress and large scale ocean dynamics? Does intraseasonal variability of wind stress force intraseasonal jets? What is the structure and origin of the biweekly variability? The intraseasonal and longer timescale variability of the equatorial Indian Ocean circulation is studied using an ocean general circulation model (OGCM) and recent in Abstract ii situ observations. The OGCM simulations are validated against other available observations. In this thesis, we document the space-time structure of the variability of equatorial Indian Ocean circulation, and attempt to find answers to some of the questions raised above. The main results are based on OGCM simulations forced by high frequency reanalysis and satellite scatterometer (QuikSCAT) winds. Several model experiments with idealized winds are used to interpret the results of the simulations. In addition to the OGCM simulations, the origin of observed intraseasonal anomalies of sea surface temperature (SST) in the eastern EqlO and Bay of Bengal, and related air-sea interaction, are investigated using validated satellite data. The main findings of the thesis can be summarized as: • High frequency accurate winds are required for accurate simulation of equatorial Indian Ocean currents, which have strong variability on intraseasonal to interannual time scales. • The variability in the equatorial waveguide is mainly driven by variability of the winds; there is some intraseasonal variability near the western boundary and in the equatorial waveguide due to dynamic instability of seasonal "mean" flows. • The fall equatorial jet is generally stronger and longer lived than the spring jet; the fall jet is modulated on intraseasonal time scales. Westerly wind bursts can drive strong intraseasonal equatorial jets in the eastern EqlO during the summer monsoon. • Eastward equatorial jets create a westward zonal pressure gradient force by raising sea level, and deepening the thermocline, in the east relative to the west. The zonal pressure force relaxes via Rossby wave radiation from the eastern boundary. • The zonal pressure force exerts strong control on the evolution of zonal flow; the decel eration of the eastward jets, and the subsequent westward flow in the upper ocean in the presence of westerly wind stress, is due to the zonal pressure force. • Neither westward currents in the upper ocean nor subsurface eastward flow (the ob served spring and summer "undercurrent") requires easterly winds; they can be gener ated by equatorial adjustment due to Kelvin (Rossby) waves generated at the western (eastern) boundary. • The biweekly variability in the EqlO is associated with forced mixed Rossby-gravity (MRG) waves generated by intraseasonal variability of winds. The biweekly MRG wave in has westward and upward phase propagation, zonal wavelength of 3000-4500 km and phase speed of 4 m s"1; it is associated with deep off equatorial upwelling/downwelling. Intraseasonal SST anomalies are forced mainly by net heat flux anomalies in the central and eastern EqlO; the large northward propagating SST anomalies in summer in the Bay of Bengal are due to net heat flux anomalies associated with the monsoon active-break cycle. Coherent variability in the atmosphere and ocean suggests air-sea interaction.

I examined the hypothesis that high variability in Sea Surface Temperature (SST) and ocean color are associated with higher coral cover and slower rates of decline of coral cover within the Florida Keys National Marine Sanctuary (FKNMS). Synoptic SST time series maps, covering the period 1994-2005, were constructed for the FKNMS with data collected using the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) satellite sensors. The SST data were compared with coral cover time series assessments at 36 sites conducted by the Coral Reef and Evaluation Monitoring Program (CREMP; 1996-2005), sponsored by the Environmental Protection Agency and the State of Florida. Out of the 36 stations, Smith Shoals routinely experienced very different and extreme environmental conditions relative to the rest of the stations, including extreme salinity, suspended sediments, and "black water" events that led to the death of coral reef organisms such as in 2002. Among the other 35 stations, sites that experienced moderately higher SST variability (mean variance > 6) relative to other sites showed a trend toward higher percentage coral cover (r=0.62, p=6.33x10-5, N=35) and relatively slower rates of decline (r=0.41, p=0.02, N=35) over the 12-year study period. The results suggest that coral reefs sites that are continuously exposed to high but not extreme variability in temperature may develop resilience against episodes of extreme cold or elevated SST. Variability of suspended sediments and water clarity were estimated using satellite-derived, normalized water-leaving radiance products. Ocean color data were obtained from the Sea-viewing Wide-Field-of View Sensor (Sea WiFS) from 1998 to 2005. Normalized water-leaving radiance at 443 (Lwn443) was used as a proxy to examine variability in water clarity, and normalized water-leaving radiance at 670 (Lwn670) was used as a proxy to study variability in suspended sediments. A weak relationship was identified between variability of Lwn443 and Lwn670 and coral cover as estimated by CREMP assessments in 2005 (r=0.43, p = 0.01, N=35 and r = 0.47, p = 0.005, N=35, respectively). There was a weak relationship between coral cover change and Lwn670 from 1988 to 2005 (r = 0.46, p = 0.05, N=35), but there no relationship was observed between variability of Lwn443 and change in coral cover (r =0.27, p =0.11, N=35). Further research is required to understand the origin, concentration and composition of dissolved or suspended materials that change the turbidity of waters around reefs of the FKNMS, and whether these changes can be adequately interpreted by examining concurrent satellite imagery. Ultimately, such remote sensing and field research is required to understand how water quality affects the health of coral reefs, and how coral ecosystems adapt to environmental variability.