Análise de uma linha de instabilidade costeira na região leste do estado do Pará

Abstract

At the State of Pará it is observed, mainly in the months May to August, Instability Lines that formed along the coastal line, called Coastal Instability Lines (CIL) because of that. This work has the objective to study the CIL that occurred during the “Experimento de Campo de Período Chuvoso” of the DESMATA-MilênioLBA Project, in April 2002. For this study it was utilized surface and altitude data, enhanced geostationary satellite images and meteorological fields from MM5 model. In relation to surface observed data results showed that, in general, CIL did not provoke significant changes in meteorological conditions, with the exception of a pronounced fall in air temperature, observed near the maximum intensity time of the CIL. The selection of the CIL that occurred on 17-18 April allowed to evaluate in details, the structure of the upper air meteorological fields and simulated ones during its 8 hours life time, approximately. The results showed that this CIL occurred in an environment with low values of humidity, high temperatures and little instability. Before and during the occurrence of the LIC, the horizontal wind velocities were small, in general lower than 5 m/s. A jet from East was observed at 850 hPa (with values of 11 m/s) after the occurrence of the CIL, therefore with no association to the CIL. The returned fields with MM5 model showed very well the temperature horizontal gradient at the coastal region, important to the generation of the maritime breeze circulation, main factor of CIL formation. The horizontal wind fields showed a clear distinction in the air flow, on the one hand between the surface and 850 hPa level, and on the other hand between the ocean and the continent. An interesting result was found at 850 hPa level, where the wind was parallel to the coast even 3 hours before the formation of the CIL, remaining this way till the beginning of the its weakening when it suffers a rotation becoming from East.