Efeitos da zona de convergência do atlântico sul (zcas) sobre as chuvas na região sul da Amazônia brasileira

Abstract

This study investigated the dominant atmospheric flow patterns in the months of November through March (NDJFM) associated with the occurrence of the South Atlantic Convergence Zone (SACZ) in Southern Amazônia, designated Target Area (TA), in the period 1999-2010. For this purpose the techniques of the Power Spectrum Spectral Analysis (PSA), Empirical Orthogonal Function Analysis (EOF), The ETA NWP Model, and the Fuzzy Analysis were employed. The datasets used were: NCEP/NCAR Reanalyses for the variables ROL, wind, temperature and Humidity, and TRMM and INMET station data for rainfall. The area-averaged precipitation over the TA was subjected to PSA and found two peaks in the power spectrum approximately near 11 and 38 days that correspond to the two well-known phenomena, SACZ and the Madden-Julian Oscillation (OMJ), respectively. The precipitation and other variable data-sets are filtered using two windows: 10-20 days and 20-100 days. The filtered data sets are submitted to EOF analysis and the first two components of each of the two windows are analyzed. The Fuzzy technique was used to classify the events into Strong, Moderate and Weak as well as Oceanic SACZ, Coastal SACZ and Continental or Amazon SACZ. An objective method was proposed and utilized to identify the SACZ events active over TA. The results are: (1) In all 28 cases of SACZ with activity over the TA are objectively identified in the 10- year period, and the objective method supplied a more consistent set of events than the set given in the monthly bulletin, Climanálise, of the CPTEC. (2) The Fuzzy method permitted to classify satisfactorily the different types of SACZ. (3) During the SACZ events the possibility of the occurrence of intense rainfall during a day (> 20 mm) is more than twice as the climatological value. (4) Amazon SACZ and Coastal SACZ events account for about 71% of the rainfall of the season over the TA. (5) The patterns of atmospheric flow Fields are distinct in different types SACZ, especially in terms of moisture convergence and can be used for operational medium range forecasts in Amazônia. (6) When there was superposition of favorable conditions of the phases of the two principal components, the precipitation intensified. (7) In general, this work provided additional details about the SACZ events active over the Amazon Basin that complements the previous knowledge about the phenomenon.