Estudo observacional de jatos de baixos níveis no litoral norte e nordeste do Pará durante o período chuvoso e seco

Abstract

This work one describes the characteristics of the vertical structure of the Low- Level Jets (LLJ), proper phenomenon of the Boundary layer using itself for such data of the rawinsondings of Ajuruteua City of Bragança collected during the Experiments DESMATA and CiMeLA carried through in the periods of 08 the 22 of April of 2002 and 27 of October the 15 of November of 2003, respectively. The numerical model of mesoescala BRAMS was also used to simulate the space and temporal structures of the JBN in reply to the physical force associates the superficial conditions. The observationais results had indicated that the JBN occur with more frequently during the night, with intensities varying between 8 and 10m/s located around 600m above of the surface, during the rainy period. Of occurred cases 70% they had beed situated above of 500m and were directed of NE-E in the point of maximum speed. For the dry period the speed of the JBN varied of 12 and 15m/s and exactly was located around 800m, being that 55% of the cases had occurred during the night and 91.7% of the cases had occurred above of 500m. The numerical results had indicated that the JBN located in the Paraense coast are resulted of the agreed action of two factors: (1) inertial oscillation and (2) superficial baroclinidad. These two agreed factors had supported the JBN with intensities between 10 and 13m/s during the day and between 14 and 16m/s during the night, located to an altitude in average of 800m above of the surface. The JBN simulated numerically for the models Global, ETA and BRAMS located in 850hPa, being its height overestimated in 7,7% in relation the height observed in the sounding that was in 920hPa. This was also observed that model BRAMS overestimated the speed of the JBN selected for study of case in 3%, possibly was caused by superficial instability and problems of rugosed in the model.