Associação entre as correntes de jato e zonas frontais no nordeste brasileiro

Abstract

The Northeast Brazilian Jet Streams (NEBJS) and the Frontal Zones are among the main systems that influence the pluviometric regime and the adverse phenomena formation in the Brazilian Northeast (NEB). The main goal of this study was to identify and evaluate the connection between the CJNEB and the Frontal Zones that reached the NEB during 2017. Reanalysis data from the National Centers for Environmental Prediction and National Oceanic and Atmospheric Adminstration (NCEP/NOAA/NCAR) with a resolution of 2.5º latitude by 2.5º longitude were used. The Grid Analysis and Display System (GrADS) software was used to visualize the meteorological fields. Through it, maps of streamlines (1000hPa, 500hPa and 200hPa), vorticity, mean sea level pressure, equivalent potential temperature advection and layer thickness were created. Images from the Geostationary Operational Environmental Satellite (GOES) and METEOSAT satellites in the infrared channel helped to identify the cloudiness associated with the frontal zones. Data from automatic stations of the National Institute of Meteorology (INMET) and the National Center for Monitoring and Alerts for Natural Disasters (CEMADEN) were used for the analysis of precipitation associated with CJNEB and Frontal Zones. Six baroclinic cyclones with frontal zones that formed and moved to the NEB were identified during year, with 02 cases occurring in the spring, 02 cases in the autumn and the other 02 cases during the winter. Detailed analysis showed that all frontal zones, that reached the NEB, were associated with jet streams at the upper levels of both hemispheres (Southern Hemisphere (SH) Subtropical Jet Stream and Northern Hemisphere (NH) Subtropical Jet Stream). Strict troughs from the Southern Hemisphere were located near the NEB in the Atlantic Ocean in all cases. Upper Tropospheric Cyclonic Vortex (UTCV) was formed in SH in 4 cases and in NH in 2 cases. Two patterns of connection between the CJNEB and the frontal zones were identified: in the frequent pattern (5 cases, pattern 1) the HN currents acted on the east side of the frontal zone and the HS currents acted on the west side; in one different case (pattern 2) the currents coming from the NH acted on both sides of the frontal zone. Associated precipitation was identified for all occurrences. The least amount of precipitations were registered in the northern cities (São Luís/MA and Teresina/PI), but were records close to 30 mm/24h in 02 cases. Precipitation greater than 30 mm/24h were more frequent in Bahia (5 cases in Salvador and 3 cases in Joao Pessoa).