Influências das condições termodinâmicas nos eventos extremos de precipitação na cidade de Belém e região metropolitana

Abstract

The goal of this dissertation is to verify the importance of thermodynamic factors on occurrence of extreme precipitation events in the city of Belém (PA) and the metropolitan area, during the period of August 2008 to December 2009. To this end, precipitation and radiosonde data were used. For dynamic and thermodynamic analysis, satellite images, surface charts and SKEW T-LOG P diagram were used. The study of thermodynamics of the atmosphere was made based on the theories of Convective Available Potential Energy (CAPE) and Convective Inhibition Energy (CINE). The decis method was used to classify the extreme precipitation events, in order to associate them to the values of CAPE and CINE and then verify the accuracy of these values when the extreme event occur. At this occasion, it was verified that the studied region has strong connective activity during all the year, hence the monthly mean values are between 900 J/kg and 1900 J/kg. It was also verified that not always high CAPE and low CINE determine precipitation. That situation in fact determine profound convection, but to ensure precipitation there is the need of dynamic enforcement. The results clearly show that when the precipitation process depended on CAPE exclusively, it was necessary to have a high value in order to generate profound convection and, consequently, precipitation. Otherwise, at the dynamic contribution precipitation process it was not necessary a significant value of CAPE, in that case not over 1000 J/kg. The CINE was always lower at the rainy season showing monthly mean values lower than 300 J/kg. That doesn’t means that as lower the CINE, higher is the precipitation. When inhibition is present, the instability keep growing during the day, and with that, clouds with accentuated vertical development, then the points where were the inhibitors weaken first, will be the preferential point to start the storm. From this, when the instability is high and the inhibitor mechanism exists (CINE) , in a large area, the most propitious place to trigger a storm are the points where CINE and NCE start to diminish and the thermic inversion, that sometimes happens, start to be broken. During this research it was clear that for the occurrence of extreme precipitation events during the rainy season there is the need of ITCZ influence and during the dry season the dynamic factor that contributes is the Instability Line (LI).