Parâmetros de radar e distribuição do tamanho de gotas de chuvas em sistema de precipitação continental ou marinha no leste do Nordeste do Brasil: sua influência na estimativa de vazão na bacia do rio Mundaú.

Abstract

The methodological approach used in this research work was crucial to reach the main objectives concerning raindrop size distribution spectra originating from continental and maritime precipitation in the eastern part of Alagoas State. The Z-R relations associated with different origins of precipitation were calculated with potential use in improving the rain estimates made at the Radar Meteorológico de Alagoas – SIRMAL. RD-69 Joss-Waldvogel Disdrometer measurements in the northern coast of Alagoas and PPI (Plan Position Indicator) images generated at SIRMAL during the 2003 to 2006 period together with an historical discharge series for the Mundaú River were used in this work. The disdrometer dataset is divided into two subsets. One is composed of rainfall systems coming from the continent and moving eastwards, that is offshore, representing the continental subset. The other is composed of rainfall systems developed over the sea and moving westwards, which is inshore, representing the maritime subset. Statistical distributions (probability density function, exponential and lognormal distribution) were used in order to analyze the enormous amount of data and determine the characteristics of the continental and maritime precipitation. Finally, some Z–R relations (for continental and maritime precipitation) were classified into: convective rain (R > 10 mmh-1) and stratiform rain (R ≤ 10 mmh-1). The raindrop size distribution of continental and maritime precipitation were quite different with regard to the drop amounts, showing an higher number of small droplets and a radar reflectivity (Z) lower for maritime precipitation when compared against those values of continental precipitation, for the same rain rate (R). The ratio of the average convective rain rate ( ̅) and the averaged stratiform rain rate is much higher for sea originated rain than that of continental rain events. The Z-R for continental precipitation was Z=284.74R1.27 and Z=188.3R1.25 for maritime precipitation. These new Z-R relations were used in xii estimating the height H (in mm) of the accumulated water lamina. A Z-R based software, specially developed for this work was used and showed better resulted when specifics Z-Rs is used, even when there is only one data point of river discharge.