Um estudo das condições atmosféricas em janeiros secos e chuvosos no semiárido do Nordeste do Brasil e sua relação com a chuva em meses posteriores na região.

Abstract

The identification of the main atmospheric circulation differences between rainy and dry January months in the semi-arid Northeast region, as well as the analyses of previous months (OND) and following months (FMAM) was one of the objectives of this study. NCEP/NCAR reanalysis data and precipitation from SUDENE were used in the analyses. Dry years, considered as those with normalized precipitation deviation below 25% of the average were 1984, 1987 and 1990. Wet years, with normalized precipitation deviation above 25% of the average were 1979, 1980 and 1985. Dry and wet composites were performed for each month from October throughout May, and the atmospheric features of each composite associated with precipitation were analyzed. The wind field at 200 hPa showed a cyclonic vortex (VCAN) over Northeast region coast in the rainy composites of January and February, while in the dry composites there was an amplified trough over the Atlantic Ocean. The cyclonic vorticity associated with the Northeast trough/VCAN was located over Northeast and moved to the Atlantic Ocean, from October to January, in the rainy composite. In the dry composite, the cyclonic vorticity moved from the Atlantic Ocean to the continent. At low levels, the larger differences were found in the North and South Atlantic subtropical high regions. Another objective of this study was the diagnosis of the atmospheric circulation in the period of 15 to 25 January 1985, and the analysis of precipitation fields obtained from meteorological radar of Petrolina, PE. The 200 hPa wind field analyses showed the contribution of the mid-latitudes troughs of North and South Hemisphere in the intensification of the Northeast trough/VCAN over South Atlantic. The displacement of the Bolivian High to the east of the climatological position was also observed. An anticyclonic center to the northwest of South America and a trough over North Atlantic were in phase with the Bolivian High and the Northeast trough/VCAN, in some days of the analyzed period. Satellite images showed cloudiness associated with the Northeast trough/VCAN and mesoscale convective complexes.