ABSTRACT: This article presents a study of three different passive devices (spires, screens, and a carpet) separately and in various combinations, to simulate the atmospheric boundary layer (ABL) in a wind tunnel with a short test chamber (465×465x1200mm). The influence of distances between these devices on the formation of the ABL is established, and optimization of variation of thicknesses of the screens (thin, medium, and coarse) on pressure loss is explored. The results obtained in this work gave support for the analysis of the atmospheric flow and turbulence at Alcantara Launching Center (ALC) in order to launch Brazilian space vehicles under safe conditions. The results show that the “spires” and the thin screen are the devices that require the least area to form an ABL in a test chamber. The physical proximity of two devices (the spires and the medium screen) also influences the size of the ABL formed, which varies from 180 to 200 mm. The power law exponent ranged from 0.12 up to 0.14 after the insertion of a carpet.

Neste artigo apresenta-se uma avaliação da precipitação estimada através do radar S-POL (banda S) e pelo algoritmo 3B42_V6 do satélite TRMM, durante o experimento do período chuvoso de 1999 do projeto TRMM-LBA na Bacia Amazônica, enfocando-se a variabilidade diária. Para tal, utilizam-se técnicas estatísticas baseadas em tabela de contingência e índices, bem como a análise harmônica. Demonstra-se que precipitação determinada com o radar é coerente com as observações de rede de pluviômetros. O ciclo diário exibe um máximo principal no final da tarde, e um pico secundário à noite, que é associado à propagação de Linhas de Instabilidades no interior da Bacia Amazônica. O algoritmo 3B42_V6 reproduz características importantes do ciclo diário de precipitação: (i) o máximo intenso às 2100 UTC (1700 HL); (ii) precipitação noturna mais intensa durante o regime de Oeste. Uma importante aplicação deste estudo é o uso dos resultados para avaliação de modelos numéricos de simulação do tempo e do clima, principalmente no que concerne à representação da convecção sobre a região.

The rainfall estimated with a S-band radar, and by the 3B42_V6 TRMM satellite algorithm, is evaluated by comparing it with rain gauge measurements during the 1999 rainy season in the Amazon Basin, with focus on the diurnal cycle. Statistic analyses based on contingency tables, skill scores, and harmonic analysis were used. The radar estimation is in agreement with the rain gauges measurements. The diurnal cycle exhibits a main maximum during the afternoon and a secondary one at night, which is associated to Squall Lines propagation over the Amazon Basin. It is also shown that the 3B42_V6 algorithm captured important features of the rainfall diurnal cycle: (i) the maximum at 2100 UTC (1700 LST); (ii) the nocturnal rainfall is strongest during Westerly regimes. These results are important for numerical weather and climate prediction model evaluation, especially when concerning the convection activity over the region.

Abstract: Alcântara Space Center (ASC) is the Brazilian gate to the space where rockets of different sizes are launched. At ASC there is a relative topographical variation, coastal cliff, which modifies the atmospheric boundary layer characteristics and can cause interference for operations of rockets. In the present work, a simplified model (mock-up) was studied in a wind tunnel. A scale factor of 1:1000 was used and the atmospheric flow was measured using the hot wire anemometer (HWA) and particle image velocimetry (PIV) techniques. Using of HWA it was possible to calculate values of average wind speed and fluctuations in a set of points of the section of tests that representing the region of the ASC. Through these measures, other meteorological parameters that represent the atmospheric flow, such as the friction velocity (u*), the roughness length (z0) from the logarithmic profile and the alpha exponent (a) of the power law were calculated. With the use of the PIV´s technique, the streamlines and the vorticity fields were obtained and it was noticed that the vorticity generated downwind of the coastal cliff has a strong turbulence (vorticities around 2000 s-1). A rectangular building (simulating the mobile integration tower) was inserted at the mock-up and the downwind turbulence was similar to the one generated by the coastal cliff.

Abstract: The Alcântara Space Center (ASC) region has a peculiar topography due to the existence of a Coastal cliff, which modifies the atmospheric boundary layer characteristic in a way that can affect rocket launching operations. Wind tunnel measurements can be an important tool for the understanding of turbulence and wind flow pattern characteristics in the ASC neighborhood, along with computational fluid dynamics and observational data. The purpose of this paper is to describe wind tunnel experiments that have been carried out by researchers from the Brazilian Institutions IAE, ITA and INPE. The technologies of Hot-Wire Anemometer and Particle Image Velocimetry (PIV) have been used in these measurements, in order to obtain information about wind flow patterns as velocity fields and vorticity. The wind tunnel measurements are described and the results obtained arepresented.

The influence of the height of the ocean boundary layer in the region where the Alcântara Space Center is located, was studied. The topography of the region is very complex and it includes a 50 m coastal cliff. A 2D numerical code was used, where the equations were written using the vorticity-velocity formulation. High order compact finite differences schemes were used for the spatial derivatives and the time integration was performed with a fourth-order Runge-Kutta scheme. The coastal cliff was specified through the immersed boundary method. The numerical results showed that the height of the ocean boundary layer influences the formation of the height of the internal boundary layer of the cliff, increasing the turbulence in the region.

Se estudió la influencia de la altura de la capa límite oceánica (CLO) en la región del centro de lanzamiento de cohetes de Alcántara, en Brasil. La región es geográficamente compleja y está constituida de un acantilado con un desnivel de 50 m. Un programa de simulación de flujo 2D fue utilizado en el estudio, con una formulación de vorticidad-velocidad. Se utilizó técnicas compactas de diferencias finitas de alto orden para la discretización del espacio, y la integración en el tiempo fue realizada por el método de Runge-Kutta de cuarto orden. El acantilado fue especificado con el método de fronteras sumergidas. Los resultados numéricos demostraron que la altura de la capa límite oceánica tiene influencia en la formación de la altura de capa limite interna del acantilado, aumentando así la turbulencia en la región.

Os parâmetros do "Simplified Simple Biosphere Model"-SSiB foram validados e posteriormente calibrados para os sítios de pastagem da Fazenda Nossa Senhora Aparecida (62º22'W; 10º45'S) e de floresta da Reserva Biológica do Jaru (62º22'W; 10º45'S), ambos situados no estado de Rondônia. Foram utilizadas medidas micrometeorológicas e hidrológicas obtidas durante o período seco de 2001, como parte do Experimento de Grande Escala da Biosfera-Atmosfera na Amazônia - LBA. Os resultados indicam que o modelo simulou bem o saldo de radiação, tanto na pastagem quanto na floresta. O fluxo de calor latente foi superestimado nos dois sítios nos períodos de simulação, o que deve estar relacionado aos parâmetros utilizados no cálculo dessa variável. O modelo subestimou o fluxo de calor sensível na pastagem e na floresta, principalmente no período noturno; porém, para a floresta, os valores foram mais próximos daqueles observados. Com os parâmetros ajustados, melhores estimativas dos fluxos de calor latente e de calor sensível foram geradas e, conseqüentemente, representou melhor as partições de energia na floresta e na pastagem.

The parameters of the Simplified Simple Biosphere Model - SSiB were validated and subsequently calibrated for the Fazenda Nossa Senhora Aparecida (62º22'W; 10º45'S) pasture site and the Reserva Biológica do Jaru (62º22'W; 10º45'S) forest site, both located in the state of Rondônia. Micrometeorological and hydrological data collected during the dry period of 2001, as part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia - LBA, were used. The results showed that the model simulated well the net radiation, both at the pasture and at the forest. The latent heat flux was super-estimated in both sites. The model sub-estimated the sensible heat flux at the pasture and at the forest, mainly during the night period; notwithstanding, the values for the forest were nearer to the observed ones. With the calibrated parameters, the model generated better estimations of the latent and the sensible heat fluxes, thus better representing the energy partition both at the forest and at the pasture.