<p>Accurate modeling of land-atmosphere interaction would help us understand the persistent weather conditions and further contribute to the skill of seasonal climate prediction. In this study, seasonal variations in radiation and precipitation forcing are included in a stochastic soil water balance model to explore the seasonal evolution of soil moisture probabilistic structure. The theoretical results show soil moisture tends to exhibit bimodal behavior only in summer when there are strong positive feedback from soil moisture to subsequent rainfall. Besides the statistical analysis of soil moisture – rainfall feedback, simplified mixed-layer models, coupled with soil-plant-atmosphere continuum, are also used to study heat flux partitioning, cloud initiation, and strength of moist convection. Approximate analytical solutions to the mixed-layer model are derived by applying Penman-Monteith approach, which help explain the roles of equilibrium evaporation and vapor pressure deficit in controlling the diurnal evolution of boundary layer. Results from mixed-layer model also define four regimes for possible convection in terms of cloud/no-cloud formation and low/high convection intensity. Finally, cloud-topped mixed-layer model is developed to simulate the boundary-layer dynamics after the cloud formation, when the evaporative and radiative cooling other than surface heat flux may significantly contribute to the growth of the boundary layer.</p> / Dissertation

No description available.

La dynamique de la couche limite atmosphérique d'une vallée alpine est influencée par le relief environnant et par l’écoulement de grande échelle qui la surmonte. La paramétrisation de cette circulation atmosphérique requiert donc de caractériser finement ces effets. C'est l’objectif de ce travail de thèse : comprendre l’influence du relief environnant une vallée sur les bilans de masse et de chaleur au travers d’une section de cette vallée, par conditions stables et sèches et lorsque le vent synoptique est faible mais non négligeable. Le travail s’appuie sur des simulations numériques.Plusieurs vallées idéalisées ont tout d’abord été considérées: une vallée infiniment longue (bidimensionnelle) et une vallée tridimensionnelle, qualifiée de supérieure, ouvrant soit sur une plaine (cas “vallée-plaine”), soit sur une autre vallée, qualifiée d’inférieure. Cette seconde vallée est soit plus large (cas “drainage”) ou plus étroite (cas “quasi-stagnation”).Dans les vallées tridimensionnelles, deux régimes principaux ont été identifiés, quelle que soit le cas considéré : un régime transitoire, avant que le vent de vallée (descendant) ne se développe, puis un régime quasi-stationnaire, quand le vent de vallée est complètement développé. La présence d’une vallée inférieure réduit la variation de température le long de la vallée, de sorte que le vent de vallée y est plus faible que dans le cas vallée-plaine. En conséquence, la durée du régime transitoire augmente et est maximum pour le cas quasi-stagnation. Lorsque la vallée inférieure est très étroite, la variation de température peut même changer de signe, conduisant à un vent de vallée montant, de la vallée inférieure vers la vallée supérieure. Durant ce régime transitoire, le taux de refroidissement moyenné sur le volume de la vallée est maximum, sa valeur dépendant du cas considéré. En conclusion, les cas drainage et quasi-stagnation conduisent à une couche limite dans la vallée supérieure plus froide et plus profonde que dans le cas vallée-plaine.Dans le régime quasi-stationnaire, le taux de refroidissement moyenné sur le volume de la vallée est plus faible que dans le régime transitoire et varie peu en fonction du cas considéré. En effet, lorsque la vallée inférieure devient plus étroite, le réchauffement lié aux effets advectifs diminue car la vitesse du vent de vallée diminue, de sorte que la contribution (refroidissante) du flux de chaleur sensible diminue également. La conservation de la masse dans la couche limite de la vallée supérieure est assurée par un équilibre entre la convergence des vents de pente au sommet de la couche limite (alimenté par un courant de retour au-dessus (et en sens inverse) du vent de vallée descendant) et la divergence du vent de vallée, les effets de subsidence loin des parois de la vallée jouant un rôle négligeable.Le cas réaliste de la vallée de l’Arve autour de Passy durant une période d’observation intensive de la campagne de mesures PASSY-2015 a permis de caractériser l’impact des vallées environnant Passy sur les bilans de masse et de chaleur dans la vallée. Une couche d’air froid persistante se forme en fond de vallée, suite à l’advection d’air chaud associée au passage d’une crête anticyclonique au-dessus de l’Europe. Les écoulements le long des vallées tributaires présentent une grande variabilité durant la phase persistante de l’épisode, dépendant de la variabilité de l’écoulement à grande échelle, et ont un impact majeur sur l’intensité de la couche d’air froid et la hauteur de l’inversion qui la surmonte. La forte stratification près du sol conduit à leur décollement au-dessus du fond de vallée, les empêchant d'y pénétrer. L’évolution de l’écoulement à grande échelle durant l’épisode a un profond impact sur la dynamique proche du fond de vallée. Durant la nuit en effet, la canalisation de cet écoulement réduit la variation de température le long de la vallée contrôlant le vent de vallée, favorisant la stagnation de l’air. / Alpine valleys are rarely closed systems, implying that the atmospheric boundary layer of a particular valley is influenced by the surrounding terrain and large-scale flows. A detailed characterisation and quantification of these effects is required in order to design appropriate parameterisation schemes for complex terrains. The focus of this work is to improve the understanding of the effects of surrounding terrain (plains, valleys or tributaries) on the heat and mass budgets of the stable boundary layer of a valley, under dry and weak large-scale wind conditions. Numerical simulations using idealised and real frameworks are performed to meet this goal. Several idealised terrains (configurations) were considered: an infinitely long valley (i.e. two-dimensional), and upstream valleys opening either on a plain (valley-plain), on a wider valley (draining) or on a narrower valley (pooling). In three-dimensional valleys, two main regimes can be identified for all configurations: a transient regime, before the down-valley flow develops, followed by a quasi-steady regime, when the down-valley flow is fully developed. The presence of a downstream valley reduces the along-valley temperature difference, therefore leading to weaker down-valley flows. As a result, the duration of the transient regime increases compared to the respective valley-plain configuration. Its duration is longest for pooling configuration. For strong pooling the along-valley temperature difference can reverse, forcing up-valley flows from the narrower towards the wider valley. In this regime, the volume-averaged cooling rate is found maximum and its magnitude dependent on the configuration considered. Therefore pooling and draining induce colder and deeper boundary layers than the respective valley-plain configurations. In the quasi-steady regime the cooling rate is smaller than in the transient regime, and almost independent of the configuration considered. Indeed, as the pooling character is more pronounced, the warming contribution from advection to the heat budget decreases because of weaker down-valley flows, and so does the cooling contribution from the surface sensible heat flux. The mass budget of the valley boundary layer was found to be controlled by a balance between the convergence of downslope flows at the boundary layer top and the divergence of down-valley flows along the valley axis, with negligible contributions of subsidence far from the slopes. The mass budget highlighted the importance of the return current above the down-valley flow, which may contribute significantly to the inflow of air at the top of the boundary layer. A case-study of a persistent cold-air pool event which occurred in February 2015 in the Arve River Valley during the intensive observation period 1 of the PASSY-2015 field campaign, allowed to quantify the effects of neighbouring valleys on the heat and mass budgets of a real valley atmosphere. The cold-air pool persisted because of warm air advection at the valley top, associated with the passage of an upper-level ridge over Europe. The contributions from each tributary valley to the mass and heat budgets of the valley atmosphere were found to vary from day to day within the persistent stage of the cold-air pool, depending on the large-scale flow. Tributary flows had significant impact on the height of the inversion layer and the strength of the cold-air pool, transporting a significant amount of mass within the valley atmosphere throughout the night. The strong stratification of the near-surface atmosphere prevented the tributary flows from penetrating down to the valley floor. The evolution of the large-scale flow during the episode had a profound impact on the near-surface circulation of the valley. The channelling of the large-scale flow at night, can lead to the decrease of the horizontal temperature difference driving the near-surface down-valley flow, favouring the stagnation of the air close to the ground.

A estrutura do vento varia de acordo com as características do terreno e com a rugosidade da superfície terrestre, desacelerando proporcionalmente sua intensidade de acordo com a proximidade do solo, o que determina a constituição da camada limite atmosférica (C.L.A.). As características do escoamento sobre e no entorno de características topográficas obtusas tais como morros são de grande interesse em muitas aplicações, especialmente aquelas ligadas à engenharia de vento. Esta pesquisa foca a investigação da C.L.A. sobre terrenos complexos, analisando a estrutura do escoamento turbulento, a separação e a recomposição do mesmo. Para tanto, dois métodos são empregados e comparados na presente investigação para identificar a influência da orografia complexa sobre o escoamento do vento: padrões ou códigos de carga de vento e análises experimentais em túnel de vento. Nove modelos experimentais de morros isolados, sendo quatro simétricos bidimensionais, quatro simétricos tridimensionais e um assimétrico, todos com a consideração de dois tipos de terreno, categoria I – plano e categorias III-IV – medianamente rugosas são analisados. A partir de uma simulação experimental da camada limite em túnel de vento, é possível parametrizar os efeitos do vento sobre terrenos complexos (MILLER, 1995). A definição de variáveis, tais como: o perfil de velocidade do vento, a intensidade de turbulência, os efeitos topográficos na velocidade do vento constituem-se em elementos fundamentais para cálculos estruturais de edificações situadas no entorno. Foram desenvolvidas simulações experimentais no túnel de vento de camada limite Prof. Joaquim Blessmann, da Universidade Federal do Rio Grande do Sul. Na superfície do modelo assimétrico, na radial principal do mesmo, foram localizados nove perfis de medição, contendo cada um, vinte alturas de investigação. Os demais modelos tiveram como foco de análise o cume dos mesmos, também com perfis definidos nas mesmas alturas. As medições da velocidade do vento e da intensidade da turbulência foram procedidas por um sistema de anemometria de fio quente. Os dados obtidos em túnel de vento foram confrontados com expressões empíricas calculadas para os mesmos pontos segundo cinco códigos ou padrões de carga de vento, pontuando também as correlações entre os mesmos e entre estes com a norma brasileira NBR 6123 (1988). Os modelos, códigos ou padrões analisados foram: Jackson e Hunt (1975) e Davenport, Surry e Lemelin (1988), models e as normas a seguir nominadas:Norma Brasileira: cargas de vento em Edificações - NBR 6123 (1988); European Standard:Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures;National Building Code of Canada, 2005, (NRCC 2005). Além do estudo comparativo acerca da resposta estimada pelos códigos nominados, esta pesquisa constitui-se em um banco de dados de medições em pontos localizados nos morros nominados, em túnel de vento. O comparativo entre os padrões mostra a inexistência de uma harmonização entre os mesmos para a consideração dos parâmetros a serem empregues para o cálculo de cargas de vento. Estas diferenças na definição dos parâmetros básicos para o carregamento de vento em estruturas determinam grandes dificuldades na unificação de formatos recomendados na previsão das cargas de vento. Comparativamente aos dados experimentais, os padrões, em geral, mostram-se conservadores para os dois tipos de morros analisados, simétrico e assimétrico, para os dois tipos de terreno, tanto considerando-se análises em 2D ou 3D. / The structure of the wind varies with the characteristics of the terrain and roughness land surface, slowing its intensity proportionally according to the surrounding terrain, which determines the onset of boundary layer (ABL). The characteristics of the flow over and around topographic features such as hills are of great interest in many applications, especially those related to wind engineering. From an experimental simulation of the boundary layer wind tunnel, it is possible to parameterize the effects of wind over complex terrain (MILLER, 1995). The definition of variables, such as the profile of wind speed, the turbulence intensity, the topographic effects on wind speed are key elements in structural calculations for buildings situated around the area. This research focuses on the investigation of the ABL complex terrain conditions, analyzing the structure of turbulent flow and characterization of separation and reattachment of the flow. Experimental simulations were developed in the wind tunnel of the atmospheric boundary layer Prof. Joaquim Blessmann, Federal University of Rio Grande do Sul in nine models of hills, four symmetrical two-dimensional, four- symmetrical threedimensional and one asymmetrical, all considering two types of terrain, category I - plan and Category III-IV- moderately rough. The surface of the asymmetric model was measured in nine profiles ploted on the main radial of the hill, with twenty heights each, and the other models were examined at top of the hill. The measurements were performed with a system of hot wire anemometry to measure the wind velocity and intensity of turbulence. The identification of the data obtained in the wind tunnel were confronted with empirical expressions for the same points, in order to establish the correlations between patterns and among these with NBR 6123 (1988). Two models and five codes of wind loads are analyzed: Jackson and Hunt (1975) and e Davenport, Surry e Lemelin (1988) Models and Brazilian Association of Technical Standards: Wind Load on Buildings, NBR 6123 (1988); European Standard: Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures; National Building Code of Canada, 2005, (NRCC 2005) codes. This study focuses not only the comparison of the response estimated by international codes nominees, but also a data bank of wind tunnel data to validate this tool based on empirical expressions. The comparison of the patterns shows a lack of consideration for international harmonization of the parameters to be employed for the calculations of wind loads. These differences in defining the basic parameters for the wind loading on structures determines difficulties to unify the formats recommended in the prediction of wind loads. Compared to the experimental data, the patterns will generally show up conservative for both types of mounts analyzed, symmetrical and asymmetrical, for both types of terrain, both considering 2D or 3D.

O formato do perfil de velocidades do vento varia de acordo com as características locais da superfície terrestre e de rugosidade do terreno, parâmetros que definem o perfil da Camada-Limite Atmosférica (CLA). As características do escoamento do ar atmosférico sobre e ao redor de acidentes geográficos, tais como morros e colinas, são de grande interesse para aplicações relacionadas à Engenharia de Turbinas e Parques Eólicos. No topo de morros, ocorre a aceleração do vento, fenômeno que pode representar um fator decisivo para a instalação de aerogeradores. Este trabalho dedica-se ao estudo do comportamento da CLA como função da inclinação e rugosidade superficial da elevação, fazendo uso da Dinâmica de Fluidos Computacional (CFD) para construir perfis de velocidade do vento e de intensidade de turbulência. O problema de fechamento das Equações Médias de Reynolds (RANS) é contornado com o uso do modelo de turbulência k-ω SST; os resultados numéricos obtidos são comparados com dados experimentais medidos em túnel de vento sobre modelos em escala dos morros. São testados oito modelos de morros com declives que variam de 25° a 64° para dois tipos de categorias de terreno, em 2D e 3D, e são aplicados dois códigos analíticos para representar o perfil de velocidades de entrada. Resultados numéricos para os perfis de velocidade apresentam diferença inferior a 4% em relação aos respectivos dados obtidos experimentalmente. Os perfis de intensidade de turbulência apresentam diferença máxima na casa dos 7% em comparação aos dados experimentais, o que é explicado pelo fato de que não é possível inserir o perfil de entrada de intensidade de turbulência nas simulações numéricas. Em alternativa, foi usado um valor constante resultado da média dos valores dos perfis usados no túnel de vento. Os modelos de morro em 3D apresentam maior concordância nos resultados de velocidade que os modelos em 2D e que ademais quanto maior é a inclinação do morro maior é a concordância com as medições experimentais. / The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 64° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data, this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used. The 3D models present greater concordance in the speed results than the 2D models and that in addition the greater the slope of the hill, the greater the agreement with the experimental measurements.

abstract: This thesis focuses on an improved understanding of the dynamics at different length scales of wind farms in an atmospheric boundary layer (ABL) using a series of visualization studies and Fourier, wavelet based spectral analysis using high fidelity large eddy simulation (LES). For this purpose, a robust LES based neutral ABL model at very high Reynolds number has been developed using a high order spectral element method which has been validated against the previous literature. This ABL methodology has been used as a building block to drive large wind turbine arrays or wind farms residing inside the boundary layer as documented in the subsequent work. Studies conducted in the thesis involving massive periodic wind farms with neutral ABL have indicated towards the presence of large scale coherent structures that contribute to the power generated by the wind turbines via downdraft mechanisms which are also responsible for the modulation of near wall dynamics. This key idea about the modulation of large scales have seen a lot of promise in the application of flow past vertically staggered wind farms with turbines at different scales. Eventually, studies involving wind farms have been progressively evolved in a framework of inflow-outflow where the turbulent inflow is being fed from the precursor ABL using a spectral interpolation technique. This methodology has been used to enhance the understanding related to the multiscale physics of wind farm ABL interaction, where phenomenon like the growth of the inner layer, and wake impingement effects in the subsequent rows of wind turbines are important owing to the streamwise heterogeneity of the flow. Finally, the presence of realistic geophysical effects in the turbulent inflow have been investigated that influence the flow past the wind turbine arrays. Some of the geophysical effects that have been considered include the presence of the Coriolis forces as well as the temporal variation of mean wind magnitude and direction that might occur due to mesoscale dynamics. This study has been compared against field experimental results which provides an important step towards understanding the capability of the mean data driven LES methodology in predicting realistic flow structures. / Dissertation/Thesis / Turbulent flow past a large periodic wind farm / Doctoral Dissertation Mechanical Engineering 2018

The Southwest Atlantic Ocean is characterized, in winter, by the presence of an oceanographic front between the Brazil Current (BC) and the Brazilian Coastal Current (BCC). The BC/BCC oceanographic front generates intense thermal horizontal gradients between cold waters of the southern Brazilian continental shelf, dominated by the BCC, and the offshore warm waters, dominated by the BC. This study analyses, for the first time in the known literature, the coupling mechanisms between the ocean and the atmosphere from observational data taken simultaneously during an oceanographic research cruise in the southern Brazilian coast during 11-21 June 2014. In this field experiment, atmospheric radiosondes were launched and hydrographic stations were taken to measure the ocean s temperature and salinity. The study area was chosen based on the local thermal gradients presented by the BC/BCC front. Five oceanographic transects were performed perpendicular to the coast starting at the locality of Paranaguá (Paraná State) and ending in Chuí (Rio Grande do Sul State).The winter meteorological and oceanographic features were considered in the determination of ship s route. The installation of a micrometeorological tower at the bow of the ship allowed the realization of direct measurements of heat, momentum and CO2 fluxes. This study analyses the large scale meteorological conditions and explores the behavior of the marine atmospheric boundary layer using radiosondes data taken in situ. In the period when the data were collect, typical winter conditions were observed in the study area, like the cold front passage associated to an incursion of a post-frontal cold air mass and an extratropical cyclone formation. Meteorological and oceanographic measurements performed by the instruments installed on the ship were utilized to estimate the heat fluxes through bulk formulas method. This estimates were lately compared to the heat fluxes measured directly by the sensors installed in the of the ship s bow. Measurements were obtained using the Eddy Covariance method, broadly used in micrometeorological research. To obtain the turbulent fluxes at the ocean-atmosphere interface adjustments in the observational data are necessary due to the ship s motion. During most of the study period, the sea surface temperature was higher than the air temperature, thus generating a heat transfer from the ocean to the atmosphere. The heat fluxes were commonly positive on both sides of the BC (warm)/BCC (cold) oceanographic front. However, there was some difference on the heat fluxes magnitude between the two sides of the front with more intense heat exchange on the BC side. The present results show that the intense thermal horizontal gradients between the BC and the BCC waters that occur during winter in the southern coast of Brazil, the transient atmospheric systems and the air thermal advection have an important role on the marine atmospheric boundary layer modulation and on the heat and CO2 fluxes between the ocean and the atmosphere. Meteorological and oceanographic observations are fundamental to widen our understanding of the processes occurring at the ocean-atmosphere interface which are known to have primary importance on weather and climate forecast. / O Oceano Atlântico Sudoeste é caracterizado, no inverno, pela presença de uma frente oceanográfica entre a Corrente do Brasil (CB) e a Corrente Costeira do Brasil (CCB). A frente oceanográfica CB/CCB gera intensos gradientes horizontais termais entre as águas frias da plataforma continental do Sul do Brasil, dominadas pela CCB, e águas quentes do oceano profundo, dominadas pela CB. Esse trabalho analisa, pela primeira vez na literatura conhecida, os mecanismos de acoplamento entre o oceano e a atmosfera a partir de dados observacionais da atmosfera e do oceano que foram tomados simultaneamente durante um cruzeiro de pesquisa oceanográfica na costa sul do Brasil entre 11 a 21 de junho de 2012. Nesse experimento, foram lançadas radiossondas atmosféricas e realizadas estações hidrográficas para medidas de temperatura e salinidade do oceano. A área de estudo foi escolhida com base no gradiente termal local apresentado pela frente CB/CCB. Foram realizados cinco transectos perperndiculares à costa sul do Brasil, iniciando-se na localidade de Paranaguá (PR) até o Chuí (Rio Grande do Sul). As características oceanográficas e meteorológicas de inverno foram consideradas na determinação da derrota do navio. A instalação de uma torre micrometeorológica na proa do navio permitiu a realização de medições diretas dos fluxos de calor, momentum e CO2. Este estudo analisa as condições meteorológicas de grande escala e investiga o comportamento da camada limite atmosférica marinha a partir dos dados in situ das radiossondagens. No período em que os dados foram coletados foram observadas condições atmosféricas típicas de inverno, como a passagem de frente fria associada à incursão de uma massa de ar frio pós-frontal e a formação de ciclone extratropical. Observações meteorológicas e oceanográficas realizadas pelos instrumentos instalados no navio foram utilizadas para estimar os fluxos de calor pelo método bulk formulas. Essas estimativas foram comparadas aos fluxos medidos diretamente pelos sensores instalados na proa do navio. As medidas são obtidas utilizando o método de Covariância de Vórtices, usado amplamente em pesquisas micrometeorológicas. Para obter os fluxos turbulentos na interação oceano-atmosfera são necessárias correções nos dados observados devido ao movimento do navio. Durante a maior parte do período estudo, a temperatura da superfície do mar esteve maior do que a temperatura do ar, gerando uma transferência de calor do oceano para atmosfera. Os fluxos de calor foram, geralmente, positivos em ambos os lados da frente oceanográfica CB (quente)/CCB (frio). Contudo, há diferença na magnitude dos fluxos de calor entre os dois lados da frente com a troca foi mais intensa no lado da CB. Os resultados apresentados mostram que os intensos gradientes horizontais termais entre as águas da CB e da CCB que ocorrem durante o inverno ao largo da costa do RS, os sistemas transientes e as advecções térmicas têm um papel importante na modulação da camada limite atmosférica marinha e nos fluxos de calor e CO2. Observações meteorológicas e oceanográficas são fundamentais para ampliar o entendimento dos processos que ocorrem na interface oceano-atmosfera e tem importância primária para a previsão do tempo e clima.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Between 3-12 December 2012, the Oceanographic Vessel Alpha Crucis held oceanographic stations in the Southwestern Atlantic Ocean in support to both SAMOC (South Atlantic Meridional Overturning Circulation) and ACEx (Atlantic Ocean Carbon Experiment) projects. During the research cruise, the vessel performed 19 measurements with the release of weather balloons with radiosondes. From the data collected by the radiosondes, it was possible to verify the variability of the marine atmospheric boundary layer (MABL) over different synoptic conditions occurring in the area and period of study. From meteorological and oceanographic data collected throughout the trajectory of the ship by an automatic weather station and the onboard termosalinograph, it was possible to estimate the latent and sensible heat fluxes between the ocean and the atmosphere from bulk parameterization. In order to better understand the importance of the local forcing mechanisms imposed by the sea surface temperature (SST) and the large-scale forcing by the current synoptic conditions in the study period, 19 measurements were divided into four transects along the complete ship's trajectory, where the data were grouped with respect to the active synoptic weather conditions in the study area. Our results demonstrate that in the absence of large-scale transient systems acting in the study area, the MABL was modulated by the SST field. This was observed in the first transect, were we found a thick and turbulent MABL with its top at around 600 m and more intense heat fluxes (up to 209 W/m² of latent heat and 47 W/m² of sensible heat) mainly over the warm waters associated with the Brazil Current (BC). Over cooler waters of the transect, outside the domain of the BC, the MABL was shallower, around 200 m, with less intense heat fluxes (up to 1.4 W/m² of latent heat and -16.8 W/m² of sensible heat). In the second transect with the formation of an extratropical cyclone in the La Plata river mouth region, we noted the impact of the synoptic atmospheric conditions influencing the evolution of the MABL during the prefrontal condition when a MABL stratification was verified. During the pos frontal situation, the MABL was a well developed one, with a 1200 m height. In the pos frontal environment, latent heat fluxes (average 290 W/m² with a peak of 468 W/m²) and sensible heat fluxes (average of 18 W/m² with a peak of 45 W/m²) indicate a heat flux directed from the ocean to the atmosphere much more intense in his latent component. On the other hand, in the prefrontal region, lower values of the latent heat fluxes (average of 18 W/m² with a minimum of 15.8 W/m²) and sensible heat fluxes (-63.4 W/m²) were found. During the third transect with the incursion of the warm air mass, the MABL became shallower over the cooler waters of the Brazilian Coastal Current. Along of the entire third transect the SST was lower than the air temperature and this transect presented a stable boundary layer. Throughout the fourth and final transect, there was a secondary cyclogenesis off the coast of the Rio Grande do Sul state in southern Brazil, just north of the cyclone that has been formed in the vicinity of the La Plata river mouth. This cyclone has developed rapidly and has moved toward the Southwestern Atlantic Ocean, leaving the study area in the cold sector of the cyclone. With the incursion of the cold air mass, the MABL become thicker and more turbulent with its top around 600 m. The values of latent heat fluxes ranged between 461.2 W/m² over the warm waters associated with the BC and 30.2 W/m² on the cooler waters outside the domain of the BC. This work offers an analysis of movel meteorological and oceanographic observations taken simultaneously in the Southwestern Atlantic Ocean. These observations are fundamental to widen our understanding on the physical processes occurring at the ocean-atmosphere interface and have primary importance for the weather and climate forecast of the south-southwestern region of Brazil. / Entre os dias 3 a 12 de dezembro de 2012, o Navio Oceanográfico Alpha-Crucis realizou estações oceanográficas no Oceano Atlântico Sudoeste em apoio aos projetos SAMOC (South Atlantic Meridional Overturning Circulation) e ACEx (Atlantic Ocean Carbon Experiment). Durante o cruzeiro de pesquisa, o navio realizou 19 medições, com o lançamento de balões meteorológicos com radiossondas. A partir dos dados coletados pelas radiossondas, foi possível verificar a variabilidade da camada limite atmosférica marinha (CLAM) durante distintas condições sinóticas atuantes na área e período de estudo. A partir de dados meteorológicos e oceanográficos coletados ao longo de toda a derrota do navio através da estação meteorológica automática e do termosalinógrafo de bordo, foi possível estimar os fluxos de calor latente e sensível entre o oceano e a atmosfera a partir de parametrizações bulk. Para entender a importância dos mecanismos de forçamento local impostos pela temperatura da superfície do mar (TSM) e de grande escala imposto pelas condições sinóticas vigentes no período de estudo, as 19 medições foram divididas em 4 transectos realizados ao longo da trajetória, onde os dados foram agrupados com respeito às condições atmosféricas sinóticas atuantes. Os resultados do trabalho demonstram que, na ausência de sistemas transientes de grande escala atuantes na região de estudo, a CLAM foi modulada pelo campo de TSM. Isso foi observado no primeiro transecto, onde a CLAM apresentou-se espessa e turbulenta com seu topo em torno de 600 m e com fluxos de calor mais intensos (chegando até 209 W/m² de calor latente e 47 W/m² de calor sensível) principalmente sobre as águas quentes associadas à Corrente do Brasil (CB). Sobre águas mais frias, a CLAM foi mais rasa, em torno de 200 m e com fluxos de calor menos intensos (chegando até 1,4 W/m² de calor latente e -16,8 W/m² de calor sensível). No segundo transecto, com a formação de um ciclone extratropical, nota-se o impacto das condições sinóticas influenciando a evolução da CLAM durante a condição pré-frontal, onde se verificou uma estratificação da CLAM. Na condição pós-frontal, a CLAM apresentou-se bem desenvolvida, com uma altura de 1200 m e os fluxos de calor latente (média de 290 W/m² e com pico de 468 W/m²) e calor sensível (média de 18 W/m² e com pico de 45 W/m²) indicam um fluxo de calor do oceano para a atmosfera muito mais intenso em sua componente latente. Por outro lado, na região pré-frontal, valores mais baixos de fluxos de calor latente (média de 18 W/m² e com um mínimo de -15,8 W/m²) e calor sensível (-63,4 W/m²) foram encontrados. Durante o terceiro transecto com a incursão da massa de ar quente, a CLAM ficou mais rasa sobre as águas mais frias da Corrente Costeira do Brasil. Ao longo de todo o terceiro transecto a TSM esteve menor que a temperatura do ar e esse apresentou uma camada limite estável. Ao longo do último transecto, verificou-se uma ciclogênese secundária na costa do Rio Grande do Sul, imediatamente ao norte do ciclone que havia se formado nas proximidades da desembocadura do Rio da Prata. Esse se desenvolveu rapidamente e se deslocou para o Oceano Atlântico Sudoeste, deixando a região de estudo sob o setor frio do ciclone. Com a incursão da massa de ar frio, a CLAM ficou mais espessa e turbulenta com seu topo em torno de 600 m. Os valores dos fluxos de calor latente variaram entre 461,2 W/m² sobre as águas quentes associadas à da CB e 30,2 W/m² sobre as águas mais frias fora do domínio dessa. Esse trabalho oferece uma análise de observações meteorológicas e oceanográficas inéditas tomadas simultaneamente no Oceano Atlântico Sudoeste. Essas observações são fundamentais para ampliar o entendimento dos processos físicos que ocorrem na interface oceano-atmosfera e tem importância primária para a previsão do tempo e clima na região sul-sudeste do Brasil.

O formato do perfil de velocidades do vento varia de acordo com as características locais da superfície terrestre e de rugosidade do terreno, parâmetros que definem o perfil da Camada-Limite Atmosférica (CLA). As características do escoamento do ar atmosférico sobre e ao redor de acidentes geográficos, tais como morros e colinas, são de grande interesse para aplicações relacionadas à Engenharia de Turbinas e Parques Eólicos. No topo de morros, ocorre a aceleração do vento, fenômeno que pode representar um fator decisivo para a instalação de aerogeradores. Este trabalho dedica-se ao estudo do comportamento da CLA como função da inclinação e rugosidade superficial da elevação, fazendo uso da Dinâmica de Fluidos Computacional (CFD) para construir perfis de velocidade do vento e de intensidade de turbulência. O problema de fechamento das Equações Médias de Reynolds (RANS) é contornado com o uso do modelo de turbulência k-ω SST; os resultados numéricos obtidos são comparados com dados experimentais medidos em túnel de vento sobre modelos em escala dos morros. São testados oito modelos de morros com declives que variam de 25° a 64° para dois tipos de categorias de terreno, em 2D e 3D, e são aplicados dois códigos analíticos para representar o perfil de velocidades de entrada. Resultados numéricos para os perfis de velocidade apresentam diferença inferior a 4% em relação aos respectivos dados obtidos experimentalmente. Os perfis de intensidade de turbulência apresentam diferença máxima na casa dos 7% em comparação aos dados experimentais, o que é explicado pelo fato de que não é possível inserir o perfil de entrada de intensidade de turbulência nas simulações numéricas. Em alternativa, foi usado um valor constante resultado da média dos valores dos perfis usados no túnel de vento. Os modelos de morro em 3D apresentam maior concordância nos resultados de velocidade que os modelos em 2D e que ademais quanto maior é a inclinação do morro maior é a concordância com as medições experimentais. / The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 64° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data, this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used. The 3D models present greater concordance in the speed results than the 2D models and that in addition the greater the slope of the hill, the greater the agreement with the experimental measurements.

A estrutura do vento varia de acordo com as características do terreno e com a rugosidade da superfície terrestre, desacelerando proporcionalmente sua intensidade de acordo com a proximidade do solo, o que determina a constituição da camada limite atmosférica (C.L.A.). As características do escoamento sobre e no entorno de características topográficas obtusas tais como morros são de grande interesse em muitas aplicações, especialmente aquelas ligadas à engenharia de vento. Esta pesquisa foca a investigação da C.L.A. sobre terrenos complexos, analisando a estrutura do escoamento turbulento, a separação e a recomposição do mesmo. Para tanto, dois métodos são empregados e comparados na presente investigação para identificar a influência da orografia complexa sobre o escoamento do vento: padrões ou códigos de carga de vento e análises experimentais em túnel de vento. Nove modelos experimentais de morros isolados, sendo quatro simétricos bidimensionais, quatro simétricos tridimensionais e um assimétrico, todos com a consideração de dois tipos de terreno, categoria I – plano e categorias III-IV – medianamente rugosas são analisados. A partir de uma simulação experimental da camada limite em túnel de vento, é possível parametrizar os efeitos do vento sobre terrenos complexos (MILLER, 1995). A definição de variáveis, tais como: o perfil de velocidade do vento, a intensidade de turbulência, os efeitos topográficos na velocidade do vento constituem-se em elementos fundamentais para cálculos estruturais de edificações situadas no entorno. Foram desenvolvidas simulações experimentais no túnel de vento de camada limite Prof. Joaquim Blessmann, da Universidade Federal do Rio Grande do Sul. Na superfície do modelo assimétrico, na radial principal do mesmo, foram localizados nove perfis de medição, contendo cada um, vinte alturas de investigação. Os demais modelos tiveram como foco de análise o cume dos mesmos, também com perfis definidos nas mesmas alturas. As medições da velocidade do vento e da intensidade da turbulência foram procedidas por um sistema de anemometria de fio quente. Os dados obtidos em túnel de vento foram confrontados com expressões empíricas calculadas para os mesmos pontos segundo cinco códigos ou padrões de carga de vento, pontuando também as correlações entre os mesmos e entre estes com a norma brasileira NBR 6123 (1988). Os modelos, códigos ou padrões analisados foram: Jackson e Hunt (1975) e Davenport, Surry e Lemelin (1988), models e as normas a seguir nominadas:Norma Brasileira: cargas de vento em Edificações - NBR 6123 (1988); European Standard:Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures;National Building Code of Canada, 2005, (NRCC 2005). Além do estudo comparativo acerca da resposta estimada pelos códigos nominados, esta pesquisa constitui-se em um banco de dados de medições em pontos localizados nos morros nominados, em túnel de vento. O comparativo entre os padrões mostra a inexistência de uma harmonização entre os mesmos para a consideração dos parâmetros a serem empregues para o cálculo de cargas de vento. Estas diferenças na definição dos parâmetros básicos para o carregamento de vento em estruturas determinam grandes dificuldades na unificação de formatos recomendados na previsão das cargas de vento. Comparativamente aos dados experimentais, os padrões, em geral, mostram-se conservadores para os dois tipos de morros analisados, simétrico e assimétrico, para os dois tipos de terreno, tanto considerando-se análises em 2D ou 3D. / The structure of the wind varies with the characteristics of the terrain and roughness land surface, slowing its intensity proportionally according to the surrounding terrain, which determines the onset of boundary layer (ABL). The characteristics of the flow over and around topographic features such as hills are of great interest in many applications, especially those related to wind engineering. From an experimental simulation of the boundary layer wind tunnel, it is possible to parameterize the effects of wind over complex terrain (MILLER, 1995). The definition of variables, such as the profile of wind speed, the turbulence intensity, the topographic effects on wind speed are key elements in structural calculations for buildings situated around the area. This research focuses on the investigation of the ABL complex terrain conditions, analyzing the structure of turbulent flow and characterization of separation and reattachment of the flow. Experimental simulations were developed in the wind tunnel of the atmospheric boundary layer Prof. Joaquim Blessmann, Federal University of Rio Grande do Sul in nine models of hills, four symmetrical two-dimensional, four- symmetrical threedimensional and one asymmetrical, all considering two types of terrain, category I - plan and Category III-IV- moderately rough. The surface of the asymmetric model was measured in nine profiles ploted on the main radial of the hill, with twenty heights each, and the other models were examined at top of the hill. The measurements were performed with a system of hot wire anemometry to measure the wind velocity and intensity of turbulence. The identification of the data obtained in the wind tunnel were confronted with empirical expressions for the same points, in order to establish the correlations between patterns and among these with NBR 6123 (1988). Two models and five codes of wind loads are analyzed: Jackson and Hunt (1975) and e Davenport, Surry e Lemelin (1988) Models and Brazilian Association of Technical Standards: Wind Load on Buildings, NBR 6123 (1988); European Standard: Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures; National Building Code of Canada, 2005, (NRCC 2005) codes. This study focuses not only the comparison of the response estimated by international codes nominees, but also a data bank of wind tunnel data to validate this tool based on empirical expressions. The comparison of the patterns shows a lack of consideration for international harmonization of the parameters to be employed for the calculations of wind loads. These differences in defining the basic parameters for the wind loading on structures determines difficulties to unify the formats recommended in the prediction of wind loads. Compared to the experimental data, the patterns will generally show up conservative for both types of mounts analyzed, symmetrical and asymmetrical, for both types of terrain, both considering 2D or 3D.