Adilson W. Gandu

Impact of tropical heat sources on the South American tropospheric upper circulation and subsidence

The nonlinear adjustment of the wind and mass fields to idealized tropical heat sources is studied with a simple nonlinear primitive equation model with emphasis on the upper level circulation over South America and neighboring oceanic regions during the austral summer. Numerical experiments are performed with (1) an idealized symmetrical heat source in the Amazon region, (2) the asymmetry induced in source (1) by the SACZ, (3) the effect of the Atlantic ITCZ off the Amazon mouth, (4) the African heat source, (5) the West Pacific source, and (6) the central Pacific source during the warm phase of ENSO. The linear response is obtained through the reduction of the heat source by a factor of 10 and subsequent multiplication of the results by the same factor. Two basic questions are discussed: (1) are localized heat sources important for the development of the observed cyclonic flow in the midequatorial Atlantic and (2) where is the compensating subsidence associated with the Amazon heat source located? The nonlinearity helps organizing a weak cyclonic curvature in the midequatorial Atlantic, with the inclusion of source (2). The basic state generated by the west Pacific source, and primarily by the central Pacific source, has a large impact on the cyclonic curvature on the equatorial Atlantic. The compensating subsidence associated with the Amazon source is concentrated on the southwest side of the source. The SACZ extension helps to enhance the subsidence over the northern Argentina, and the Atlantic ITCZ enhances the subsidence over northeast Brazil and central equatorial Atlantic. Nonlinearity weakens the subsidence at the 500 hPa level inducing a more barotropic structure in the dynamical response to the heating.

Interações entre nuvens, chuvas e a biosfera na Amazônia.

A review of results obtained within the Physical Climate component of LBA with respect to the interaction between the biosphere and cloud and rain formation in the Amazon Basin, in different seasons and different regions within the Basin is presented. The deforestation effect and the effect of biomass burning are discussed and the physical processes highlighted based on the data collected in several LBA intensive field campaigns. The complex interactions and the progress in the understanding their evolution based on the new datasets is presented.

Radar-observed spatial and temporal rainfall variability near the Tapajós-Amazon confluence

Na Amazonia as series climatologicas estao baseadas na rede de estacoes meteorologicas de superficie que estao instaladas preferencialmente nas margens de rios. Portanto, o efeito de brisas fluviais que promovem precipitacao no interior do continente nao esta sendo contabilizado nas medidas realizadas nestas estacoes. Alem disto, estudos anteriores encontraram maximo de precipitacao no periodo noturno sobre rios. Assim, este artigo examina a variabilidade espacial e temporal da precipitacao na regiao de confluencia dos rios Tapajos e Amazonas em Santarem, visando descrever a importância da brisa fluvial na distribuicao da precipitacao durante a tarde e definir a extensao da area onde ocorre maxima precipitacao no periodo noturno. A refletividade medida pelo radar meteorologico banda S, instalado em Santarem para um periodo de tres anos foi utilizada, tendo estes dados sido calibrados atraves dos dados do sensor de precipitacao instalado abordo do satelite TRMM. A intensidade de precipitacao foi estimada utilizando a relacao ZR para o caso convectivo tropical. No periodo noturno, a maxima precipitacao foi encontrada ao longo do rio Amazonas, consistente com a hipotese de que esta precipitacao estaria associada a passagem das linhas de instabilidade neste periodo, talvez esta precipitacao tambem esteja sendo reforcada pela canalizacao do rio e pela confluencia do vento de retorno da brisa fluvial durante a noite. Para o periodo diurno, observou-se duas bandas de precipitacoes localizadas no interior do continente, uma ao longo da margem leste e outra ao sul dos rios Tapajos e Amazonas, respectivamente.

Weather forecasting for Eastern Amazon with OLAM model

O modelo OLAM tem como caracteristica a vantagem de representar simultaneamente os fenomenos meteorologicos de escala global e regional atraves de um esquema de refinamento de grades. Durante o projeto REMAM, o modelo foi aplicado para alguns estudos de caso com objetivo de avaliar o desempenho do modelo na previsao numerica de tempo para a regiao leste da Amazonia. Estudos de caso foram feitos para os doze meses do ano de 2009. Os resultados do modelo para estes casos foram comparados com dados observados na regiao de estudo. A analise dos dados de precipitacao mostrou que o modelo consegue representar a distribuicao media da precipitacao acumulada e os aspectos da sazonalidade da ocorrencia dos eventos, mas nao consegue prever individualmente a acumulacao de precipitacao local. No entanto, avaliacao individual de alguns casos mostrou que o modelo OLAM conseguiu representar dinamicamente e prever, com alguns dias de antecedencia, o desenvolvimento de fenomenos meteorologicos costeiros como as linhas de instabilidade, que sao um dos mais importantes sistemas precipitantes da Amazonia.

Impacto da temperatura da superfície do mar na simulação da Zona de Convergência do Atlântico Sul

During austral summer, several regions of Brazil are affected by intense precipitation, generally associated with the South Atlantic Convergence Zone (SACZ). The general aim of this work was to investigate the influence of spatial and temporal resolution of sea surface temperature (SST) data in simulating precipitation associated with SACZ. Simulations with the model BRAMS (Brazilian developments on the Regional Atmospheric Modeling System) were performed for two SACZ events, occurred in 1998 (El Nino) and 1999 (La Nina). The amount of accumulated precipitation in oceanic SACZ was larger in experiments with warmer SST. Statistical indices were used in order to verify the models performance in the simulation of precipitation in the regions that compound SACZ (oceanic, coastal and amazon), with different SST datasets. Different time-space resolution of the SST data set does not have significant influence on the SACZ simulated with the BRAMS model. The model is more efficient in identifying occurrence/non-occurrence of rain than in localizing more intense nuclei, and its performance was better (worse) in amazon (oceanic) region of SACZ.