Estudos de periodicidades: séries temporais de chuvas no Nordeste do Brasil.

Abstract

Monthly and annual totais of precipitation from 96 stations in Northeast Brazil, period 1912-1981, were analyzed. Five rain regimes were identified and used for establishing corresponding climatic regimes. Such climatic regimes are named RM1 and RM2; RL1 and RL2; RD; and located at the North, East and South Brazilian Northeast subregions. Harmonic analysis was employed for identifying ciclic components of each station precipitation time series.The analysis showed that different periodicities are distributed throughout Brazilian Northeast region, suggesting that more than one physical system contributes for rains in that region. Particu 1 ar1y, a thirteen-year periodicity appears more frequentiy. It is suggested that this periodicity is correlated with occ-urrence (at each 13.2 years) of a strong "El Nino" and, a 1 s o , related to the eleven-year cycle of sunspot number. Statistical correiat ions between annual prec i p i tat ion time series of the climatic regimes were determined. They suggest that, possibly, more than one physical system in a global scale acts on the different sub-regions of Northeast Brazil, (North, East and South) also that a global physical system acts, year after year, over the whole region. A weak correlation was found between precipitation of the climatic regimes and sunspot number. A linear regression model was employed for the extreme values (máxima, minima) of precipitation and sunspot number. Such model was used for predicting mean regional precipitation for each climatic regime. Because of the weak correlation between precipitations of climatic regimes and sunspot number, this regression model is considered to have a high degree of uncertainty.