Submitted by Pedro Barros (pedro.silvabarros@ufpe.br) on 2018-07-05T20:54:17Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) TESE Christine Carine Tchamabi.pdf: 11335817 bytes, checksum: eb21c463e69dfd534cdc017cb583c6ea (MD5) / Made available in DSpace on 2018-07-05T20:54:17Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) TESE Christine Carine Tchamabi.pdf: 11335817 bytes, checksum: eb21c463e69dfd534cdc017cb583c6ea (MD5) Previous issue date: 2017-03-16 / FACEPE / A influência da presença do arquipélago de Fernando de Noronha (FN, 3°51'S-32°25'W) e do Atol das Rocas (AR, 3°52'S-33º49'W) sobre a estrutura físico-biogeoquímicano Atlântico tropical foi investigada utilizando-se dados in situ, observações de satélites e técnicas de modelagem matemática e simulação numérica. Inicialmente, para examinar os efeitos das presenças das ilhas sobre a circulação e estrutura termohalina, o modelo Regional Ocean Modeling System (ROMS) foi empregado com alta resolução horizontal (1/70º) para simular dois cenários climatológicos distintos: com a presença de FN e AR (cenário I); e com a remoção artificial das ilhas (cenário NI). Os resultados das simulações do cenário I, validados a partir da comparação com dados de observação, indicam que as instabilidades geradas pelos obstáculos (ilhas) dão origem ao desenvolvimento de turbilhões a jusante de FN e AR (von Karman Street), na esteira do ramo central da Corrente Sul Equatorial (cSEC). Essas estruturas de mesoescala têm influência sobre as propriedades termodinâmicas das águas em torno dessas ilhas, incrementando a mistura vertical na base da camada de mistura e induzindo um resfriamento subsuperficial, particularmente no período em que a cSEC é fortalecida. Os resultados das simulações biogeoquímicas (ROMS-PISCES, Pelagic Interactions Scheme for Carbon and Ecosystem Studies) confirmam a importância desses processos, indicando um aumento da concentração de clorofila-a e de nutrientes a jusante de FN e AR. Os resultados indicam que as anomalias físico-biogeoquímicas induzidas pela presença das ilhas contribuem para a redução do fluxo de CO2liberado do oceano para a atmosfera, decorrente principalmente da redução da pCO2 no mar pelo incremento da ação fotossintética na região. Por fim, os resultados das simulações físicas foram acoplados ao modelo lagrangeano IBM-ICHTHYOP (Individual-Based Model – ICHTHYOP). Estas últimas simulações, realizadas considerando-se como exemplo o ictioplancton do Dentão (Lutjanus jocu), indicaram que a retenção de larvas ocorre nos dois sistemas insulares ao longo de todo o ano, sendo mais numa vez fortemente correlacionada com a variabilidade da cSEC. Os resultados confirmam a existência de conectividade superficial entre o arquipélago de Fernando de Noronha e do Atol das Rocas. / The influence of the presence of Fernando de Noronha archipelago (FN, 3°51'S-32°25'W) and Rocas Atoll (AR, 3°52'S-33º49'W) in physical biogeochemical parameters in the tropical Atlantic has been investigated using in situ data, satellite observations, mathematical modeling techniques and numerical simulation. Initially, to examine the effects of the presence of islands on the circulation and thermohaline structure, the model Regional Ocean Modeling System (ROMS) was employed with high horizontal resolution (1/70º) to simulate two distinct climatological scenarios: I); and with the artificial removal of islands (scenario NI). The results of the simulations of scenario I, validated through the comparison with observation data, indicate that the instabilities generated by obstacles (islands) give rise to the development of eddies downstream of FN and AR (von Karman Street) in the wake of the central branch of the South Equatorial Current (cSEC). These mesoscale structures have a strong influence on the thermodynamic properties of water surrounding of these islands, increasing vertical mixingat the base of the mixed layer and inducing a subsurface cooling, particularly in the period in which the cSEC is strengthened. The results of the biogeochemical simulations (ROMS-PISCES, Pelagic Interactions Scheme for Carbon and Ecosystem Studies) confirm the importance of these processes, indicating an increase in the concentration of chlorophyll-a and nutrients downstream of FN e AR. The analysis of results indicates that the physico-beogeochemical anomalies induced by the presence of islands contribute to the reduction of CO2flux released from ocean into the atmosphere, resulting mainly on the reduction of the partial pressure of gas at sea by the increase of photosynthetic action in the region. Finally, the results of the physical simulations were coupled withthe Lagrangian model IBM-ICHTHYOP (Individual-Based Model – ICHTHYOP). These last simulations, performed considering the ichthyoplankton Dog Snapper (Lutjanus jocu), showed that the retention of larvae occurs on both insular systems throughout the year, being once again strongly correlated with the variability of the cSEC. The results confirm the existence of superficial connectivity between the Fernando de Noronha archipelago and Rocas Atoll.

Les coups de vent d’ouest (WWEs) issu de la variabilité synoptique atmosphérique jouent un rôle crucial dans les irrégularités d’ENSO en contribuant au déclenchement et au développement de sa phase chaude, El Niño. Les WWEs sont des événements haute fréquence peu prévisibles et dont les origines atmosphériques restent encore débattues. Dans le but d’affiner la prévisibilité d’ENSO, cette thèse caractérise la part stochastique de la part prévisible des WWEs ainsi que de leur réponse océanique et couplée. Dans une première partie, j’ai relié l’occurrence et les caractéristiques des coups de vent à des phénomènes de grande échelle comme l'oscillation de Madden-Julian, les ondes de Rossby atmosphériques et ENSO, à partir d’analyse d’observations. Ensuite, la forte sensibilité de la réponse océanique des WWEs à l’état de l’océan a été mise en évidence grâce à une série de simulations océaniques forcées. Finalement, une simulation d’ensemble réalisée avec un modèle couplé océan-atmosphère a permis d'explorer le rôle des WWEs dans l’évolution contrastée des années 1997,2014 et 2015 qui présentaient des conditions similaires et favorables au déclenchement d'El Niño. Les résultats de ce travail montrent que la stochasticité des WWEs aboutit à une limitation intrinsèque de la prévisibilité des caractéristiques d’El Niño. / Equatorial Pacific Westerly Wind Events (WWEs) impact ENSO evolution through their oceanic response and strongly contribute to its irregularities. WWEs are characterized by episodes of anomalous, short-lived, strong westerlies developing over the western Pacific warm pool. This thesis characterize the atmospheric origins and the oceanic and coupled impacts of these events in order to improve ENSO prediction. First, we show that, at intraseasonnal timescale, the Madden-Julian oscillation and the convectively coupled Rossby waves provide favourable conditions for the occurence of WWEs and confirm their modulation by ENSO at interannual timescale. Oceanic simulation with idealized forcing further allow characterizing and understanding the modulation of the SST response to WWE by the oceanic background state. Finally, The role of WWEs in the contrasted evolution of El Niño in 1997,2014 and 2015, which exhibited favourable conditions for El Niño to develop, is explored in ensemble simulations using a coupled ocean-atmosphere model. It is shown that the stochasticity of the WWEs acts as a strong limitation for ENSO predictability.

This master's thesis deals with design of equatorial fork mount for astronomical telescope. The issue of space object watching equipment is deeply analysed. The enclosures of analysis are used in design project. Important aspects are accuracy of motion and high resolution of mount. These parameters are compared with series manufactured equatorial mounts.

Purpose of this master´s thesis is a construction proposal of German Equatorial Mount capable to load capacity to 20kg inclusive both shaft-actuators. The solution contains design options of actuators of mount, design proposal of partial systems and parts and calcualtions. More is contain drafts of overal assembly, motor pinion and shaft.

In the Tropical Atlantic Ocean, the main mode of SST variability is the Atlantic Equatorial Mode or Atlantic Niño, which is strongly associated with rainfall patterns in northeastern Brazil and the West Africa Monsoon. The region of largest interannual variability, where the Atlantic Cold Tongue forms, is also a region of consistent biases in climate models. In this study, we investigate the interannual variability of the Tropical Atlantic and its changes in the recent decades in terms of the Bjerknes Feedback Index in a set of seven ocean reanalyses for the periods 1980-1999 and 2000-2010 and for an XX century ocean reanalysis for 1950-2010. Warming trends are observed in SSTs in the cold tongue region, as well as a decrease interannual variability. These in turn are associated with a weakening in the Bjerknes Feedback in the early XXI century, resulting from a stronger thermal damping and weaker thermocline feedback, associated with a weaker response of equatorial zonal thermocline slope to equatorial zonal wind stress. However, the spread among the reanalysis products is large, which makes necessary the use of multiple products and an ensemble analysis to minimize errors and obtain more robust results. This is further reinforced as no significant shifts in the Bjerknes Feedback Index were found for the period previous to 1980, since only one reanalysis product covers this period and its individual errors are large. / No Atlântico Tropical, o principal modo de variabilidade da temperatura da superfície do mar é o modo equatorial, ou El Niño do Atlântico, que está fortemente associado aos padrões de precipitação no Nordeste do Brasil e à Monção Oeste-Africana. A região de maior variabilidade interanual, onde se forma a Língua Fria do Atlântico, é também uma região de consistente discordância entre modelos climáticos. Neste estudo, são investigadas a variabilidade interanual do Atlântico Tropical e suas mudanças nas últimas décadas por meio do Índice do Feedback de Bjerknes considerando um grupo de sete reanálises oceânicas para os períodos de 1980-1999 e 2000-2010 e uma reanálise do século XX para 1950-2010. Um aquecimento é observado na região da língua fria, assim como uma diminuição na variabilidade interanual. Essas mudanças estão ligadas a um enfraquecimento do Feedback de Bjerknes no início do século XXI, como resultado de um amortecimento térmico mais intenso e um enfraquecimento do feedback da termoclina, associado a uma resposta mais fraca do gradiente zonal da termoclina equatorial à tensão de cisalhamento do vento. Contudo, a dispersão entre as reanálises é alta, o que torna necessária a análise comparativa de múltiplos produtos, visando obter resultados mais robustos. Da mesma forma, não foi possível tirar conclusões sobre mudanças no Feedback de Bjerknes no período anterior a 1980, uma vez que somente uma reanálise cobria este período e os erros individuais são grandes.

Ce travail de thèse est consacré à l’étude de la structure électrique de la croûte terrestre dans deux régions du Vietnam, au Nord dans le delta du Fleuve Rouge et au Sud dans la région de la faille de la Rivière Saigon, et en Afrique de l’Ouest, où les données utilisées sont celles acquises durant l’Année Internationale de l’Electrojet Equatorial (AIEE). La technique utilisée est celle du sondage magnétotellurique. Deux des régions étudiées (le sud du Vietnam et l’Afrique de l’Ouest) sont situées au voisinage de l’équateur magnétique. Du fait de la présence de l’électrojet équatorial, l’hypothèse de l’onde plane, sur laquelle est basée la magnétotellurique, n’y est vérifiée que pour une gamme de périodes limitée. La modélisation de l’induction par un électrojet gaussien nous a permis de caractériser l’effet de source associé à l’électrojet équatorial, et de déterminer pour chacune des zones étudiées les gammes de périodes pour lesquelles cet effet de source est négligeable. Nous avons par ailleurs montré que l’effet de source associé à l’électrojet équatorial dépend des principales caractéristiques de la structure électrique du sous-sol, et de la distance entre le centre de l’électrojet équatorial et la position examinée. Dans le delta du fleuve Rouge, le profil magnétotellurique est orienté SO-NE. Long d’environ 32 km, il recoupe les failles majeures du système de failles du Fleuve Rouge. Les données magnétotelluriques ont été inversées pour obtenir une coupe transversale de résistivité électrique pour les trois premiers kilomètres. Cette coupe de résistivité électrique et une coupe de densité obtenue par modélisation des données gravimétriques acquises le long du même profil, ainsi que des informations déduites de forages effectués au voisinage du profil ont été utilisées pour proposer une coupe géologique de la région étudiée. Dans la région de la faille de la Rivière Saigon, le profil magnétotellurique, long d’environ 15 km, recoupe le trajet supposé de la faille. La structure électrique des premiers kilomètres de la croûte a été déterminée par inversion 2-D des données pour les gammes de périodes qui ne sont pas affectées par l’électrojet équatorial (< 0,7 s). La coupe transversale de résistivité électrique ainsi obtenue nous a permis de proposer une nouvelle localisation de la faille de la Rivière Saigon, à la limite entre un domaine résistant, le bloc de Da Lat au nord-est, et un domaine moins résistant, le bloc de Can Tho au sud-ouest. Cette nouvelle localisation est à environ 2,2 km au sud-ouest de la localisation généralement supposée pour cette faille. En Afrique de l’Ouest, nous avons montré que les données de jour sont affectées par l’électrojet équatorial pour toute la gamme de période étudiée (>120 s); ces données n’ont donc pas été utilisées pour déterminer la structure électrique de la croûte et du manteau supérieur. L’inversion 2-D des données de nuit, montre la présence d’une structure subverticale, relativement conductrice, qui sépare le Craton Ouest-africain très résistant des terrains situés sous le bassin du fleuve Sénégal. / This thesis is devoted to the study of the electrical structure of the Earth’s crust in two regions of Vietnam (the Red River Delta in the north and the region of the Saigon River fault in the south) and in West Africa. The data were those acquired during the International Year of the Equatorial Electrojet (IYEE). The technique used is the magnetotelluric (MT) sounding method. Two of the regions studied (southern Vietnam and West Africa) are located near the magnetic equator. Due to the presence of the equatorial electrojet in these regions, the assumption of plane wave, on which MT relies, is valid for a limited range of periods. Modeling of the induction by a Gaussian electrojet allowed us to characterize the source effect associated with the equatorial electrojet, and to determine for each studied region the period ranges for which the source effect is negligible. We have also shown that the source effect associated with the equatorial electrojet depends on the main features of the electrical structure of the basement, and the distance between the center of the equatorial electrojet and the location of the considered station. In the Red River Delta at the north, the MT profile is oriented SW-NE. It is about 32 km long, and goes across the major faults of the Red River fault system. MT data were applied 2-D inversion to obtain a electrical cross-section for the first three kilometers of the crust. This electrical cross-section, a density cross-section obtained by modeling of gravity data collected along the same profile, and information derived from holes drilled in the vicinity of the profile, both were used to construct a geological section of the study area. In the region of the Saigon River fault, the magnetotelluric profile is about 15 km long. It goes across the supposed location of the fault. The electrical structure of the first three kilometers of the crust was determined by 2-D inversion of data for periods which are not affected by the equatorial electrojet (< 0.7 s). The electrical cross-section obtained allowed us to propose a new location for the Saigon River fault; it corresponds to the boundary between a resistant domain, the block of Da Lat in the north-east, and a less resistant domain, the block of Can Tho in the south-west. This new location is about 2.2 km southwest of the location currently assumed for this fault. In West Africa, we have shown that electromagnetic impedances derived using day time data are affected by the equatorial electrojet for the whole range of period studied (> 120 s), so these data have not been used to determine the electrical structure of the crust and the upper mantle. The 2-D inversion of nighttime data shows the presence of a subvertical structure, relatively conductive, which separates the West African Craton which is very resistant from the geological structures beneath the Senegal River basin.

This study aims to unravel the ecological and evolutionary dynamics within the calcareous nannofossil communities at the Eocene/Oligocene (E/O) transition and during the Oligocene time when Cenozoic 'icehouse' conditions were established. The main question this study aims to answer is whether the changes in the nannofossil assemblages were controlled by intrinsic evolutionary trends or if the changes were controlled by environmental factors such as changes in temperature and nutrient availability in the surface water. These questions are addressed with detailed analyses of the taxonomy, biostratigraphy and fluctuations in abundance and diversity of calcareous nannofossil assemblages from a continuous latest Eocene through Oligocene sediment section from the ODP Site 1218 (8°53.38´N, 135°22.00´W), paleo-equatorial Pacific Ocean. An improved nannofossil taxonomy and biostratigraphy has been established. At the E/O transition, changes in the nannofossil preservation mimics changes in calcium carbonate content. A detailed investigation of late Eocene and Oligocene sediments yields age estimates for ten nannofossil bioevents. Morphometric studies of the Reticulofenestra umbilicus-R. hillae show that these cannot be subdivided into two different morphospecies. Based on different morphometry and stratigraphic ranges, the Oligocene Sphenolithus lineage appears to be the result of a combined anagenetic and cladogenetic evolution. A new nannolith species is described: Triquetrorhabdulus longus. High-resolution nannofossil data indicate changes in the composition, abundance and diversity of the mid-Oligocene assemblages. Intervals of high diversity index coincide with Oi-glaciation events. However, visual examination of the variations in abundance of nannofossil taxa do not appear to correlate with changes in either oxygen or carbon isotopes. This presumably indicates that a dynamic equilibrium did not exist between these Oligocene nannoplankton assemblages and changes in surface water temperature or productivity conditions. / Doctoral Thesis in Marine Geoscience at Stockholm University, Sweden 2009

A key element of hydrologic routing models is the storage-discharge relationship assumed to follow a certain mathematical form, usually a linear or a power function, the parameters of which are calibrated based on existing inflow-outflow data. While this assumption simplifies the model calibration process, it also constrains the models to operate by this function throughout their flow range. In view of the complex and nonlinear river flow behavior, this approximation undoubtedly introduces errors. This research presents a new hydrologic river routing approach that is not limited by the above assumption. River reaches are modeled as cascades of interacting conceptual reservoirs, with storage-discharge functions identified by the data. A novel parameter estimation approach has been developed to identify these functions and all other model parameters based on control theory concepts. After calibration, these functions indeed exhibit different mathematical forms at different regions of their active variation range. The new approach is applied and successfully demonstrated in real world reservoir and river routing applications from the Nile River Basin. A Bayesian forecasting scheme was also developed that uses the new approach to generate flow forecasts with explicit uncertainty characterization.

A comprehensive hydrological study of large watersheds in Africa e.g. the Congo basin and the Nile basin has not been vigorously pursued for various reasons. One of the major reasons is the lack of adequate modeling tools that would not be very demanding in terms of input data needs and yet inclusive enough to cover such wide extents (over 3 million square kilometers for the Congo basin). Using a coupled run of the Community Atmospheric model (CAM3) and Community Land Model (CLM3) components of the Community Climate System of Models (CCSM), this study looks into the spatial and temporal variation of precipitation and river runoff in the Congo basin in the light of increasing trends in deforestation of the tropical forests. The effect of deforestation on precipitation and runoff is investigated by changing the land cover-type from the current configuration of broadleaf evergreen/deciduous, non-Artic grass and corn to a mostly grass type of vegetation. Discharge simulation for the river Congo is centered at the point of entrance to the Atlantic Ocean. Although the CLM3 does not presently simulate the observed river runoff to within at least one standard deviation it gives an opportunity to iteratively improve on the land surface parameterization with a possibility of future accurate prediction of mean monthly river runoffs under varying climate scenarios and land use practices. When forced with the National Center for Environment and Prediction (NCEP) re-analysis data the CLM3 runoff simulation results are relatively more stable and much closer to the observed. An improved CLM3 when coupled to CAM3 or other Global Climate Models is definitely a better tool for investigative studies on the regional hydrological cycle in comparison to the traditional methods. There was a slight reduction in rainfall in the first experiment which mimicked a severe form of deforestation and a slight increase in rainfall following low level of deforestation. These changes in rainfall were however statistically insignificant when compared to the control simulation. There was notable heterogeneity in the spatial distribution of the changes in rainfall following deforestation.

WINDMI is a low dimensional plasma physics-based model of the coupled magnetosphere-ionosphere system. The nonlinear system of ordinary differential equations describes the energy balance between the basic nightside components of the system using the solar wind driving voltage as input. Of the eight dynamical variables determined by the model, the region 1 field aligned current and ring current energy is compared to the westward auroral electrojet AL index and equatorial geomagnetic disturbance storm time Dst index. The WINDMI model is used to analyze the magnetosphere-ionosphere system during major geomagnetic storms and substorms which are community campaign events. Numerical experiments using the WINDMI model are also used to assess the question of how much interplanetary shock events contribute to the geoeffectiveness of solar wind drivers. For two major geomagnetic storm intervals, it is found that the magnetic field compressional jump is important to producing the changes in the AL index. Further, the WINDMI model is implemented to compute model AL and Dst predictions every ten minutes using real-time solar wind data from the ACE satellite as input. Real-Time WINDMI has been capturing substorm and storm activity, as characterized by the AL and Dst indices, reliably since February 2006 and is validated by comparison with ground-based measurements of the indices. Model results are compared for three different candidate input solar wind driving voltage formulas. Modeling of the Dst index is further developed to include the additional physical processes of tail current increases and sudden commencement. A new model, based on WINDMI, is developed using the dayside magnetopause and magnetosphere current systems to model the magnetopause boundary motion and the dayside region 1 field aligned current which is comparable to the auroral upper AU index. / text