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Brazil has the largest amount of fresh water in the world. Two-thirds of what flows in the Amazon River alone could supply the world's demand. Yet much of the nation now faces drought. It's the worst in many decades in a nation that grows more than one-third of the world's sugar crops and produces almost 15% of the world's beef.This year, between March and May, dry weather in Brazil's south-central region led to a 267 km 3 shortage of water held in rivers, lakes,

RESUMONeste estudo é realizada uma investigação, via modelagem computacional, das influências remotas que as anomalias positivas da temperatura da superfície do mar (TSM) na região da Confluência das correntes do Brasil e das Malvinas (CBM), exercem no regime hidrometeológico das regiões Sul e Sudeste do Brasil. Essa região é marcada por uma intensa frente oceânica formada pelo encontro das águas transportadas pela Corrente do Brasil (CB) e das águas transportadas pela Corrente das Malvinas (CM). Essa investigação foi realizada com a utilização do modelo climático Community Atmosphere Model 2.01 (CAM 2.01), sendo utilizadas anomalias numéricas da TSM, geradas dentro do código do modelo, visando a reprodução do episódio ocorrido no verão de 2005, tanto em relação a sua distribuição espacial, quanto temporal. Foram observadas alterações significativas no padrão ondulatório da circulação vertical da atmosfera em parte da América do Sul, o que acarretou em uma diminuição da precipitação na região Sul do Brasil e condições mais favoráveis para a configuração da Zona ABSTRACT: INFLUENCE OF EXTRATROPICAL SOUTH ATLANTIC SST ANOMALIES AT BRAZIL-MALVINAS CONFLUENCE REGION OVER THE HYDROMETEOROLOGICAL SUMMER REGIME OF SOUTHERN AND SOUTHEASTERN BRAZILThis study analyses the influence of the extratropical South Atlantic sea surface temperature (SST) anomalies in the Southern and Southeastern Brazilian hydrometeorological pattern. The BrazilMalvinas Confluence (BMC) is one of the most important South Atlantic Ocean features. This region is characterized by a strong thermal front formed by the confluence between the warm waters transported by the Brazil Current (BC) and the cold waters carried by the Malvinas Current (MC). The knowledgement of its dynamics could represent an important advance to understand its connection with locally and remotely generated ocean and atmospheric processes. This investigation is made with computational modeling using a Community Atmosphere Model (CAM 2.01). The spatial and time SST anomalies were numerically generated inside the model code in such a way to reproduce the summer 2005 event. Significant changes were observed in this experiment in the vertical atmospheric circulation pattern. The precipitation over South Brazil region decreased and more favorable conditions to the South Atlantic Convergence Zone (SACZ) formation appeared over the northern part of the Southeastern Brazil region. These model generated patterns were similar to those observed during the summer 2005, especially the precipitation anomalies results.

The South Atlantic Convergence Zone (SACZ) plays a key role in the South American monsoon system (SAMS) precipitation regime, and accounts for around 25% of the rainfall volume over Southeast Brazil between October and April, on average, with peaks of 56% in March and 41% in January. Due to its often varying position and multi-variable structure, diagnosing or quantifying SACZ episodes may lie on subjective criteria. The present study provides a climatological characterization of different SACZ types, based on their position, and differences in dynamics analysed from 19 SAMS wet periods. A cycle in SACZ configurations is identified during the rainy season: northernmost (southernmost) episodes are more likely to occur during the onset/demise (peak) months of the SAMS. Objective SACZ indices are developed taking the principal components of the dynamics of the SACZ as explanatory variables, not including precipitation. The most sensitive threshold proposed for the identification of mean SACZ type yields simultaneous true positive rate of 86%, false alarm rate of 28%, true negative rate of 72% and false negative rate of 15%, for example. The indices have potential to bring gains in predictability to SACZ-related precipitation in Southeast Brazil, apart from allowing the objective diagnosis of SACZ episodes. The indices are also correlated with the South American precipitation dipole and may be used to identify anomalous SAMS precipitation at longer time scales as well.

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The present work shows how thick boundary layers can be produced in a short wind tunnel with a view to simulate atmospheric flows. Several types of thickening devices are analysed. The experimental assessment of the devices was conducted by considering integral properties of the flow and the spectra: skin-friction, mean velocity profiles in inner and outer co-ordinates and longitudinal turbulence. Designs based on screens, elliptic wedge generators, and cylindrical rod generators are analysed. The paper describes in detail the experimental arrangement, including the features of the wind tunnel and of the instrumentation. The results are compared with experimental data published by other authors and with naturally developed flows