OCEANIC INDICES AND THEIR RELATIONS WITH THE MONTHLY PRECIPITATION IN RIO GRANDE DO SUL STATE, BRAZIL

ABSTRACT. Climatic indices were obtained from the Sea Surface Temperature (SST) in the Atlantic and Pacific oceans, available on the website of the EarthSystem Research Laboratory (ESRL), which belongs to the Physical Science Division (PSD) of the National Oceanic and Atmospheric Administration (NOAA). Theseindices were created to represent the variations of SST in the Southwest Atlantic, Equatorial Pacific and South Pacific, with the aim of studying their influence on precipitationvariability in the state of Rio Grande do Sul (RS), Brazil. The precipitation dataset was obtained from the National Institute of Meteorology – Instituto Nacional de Meteorologia (INMET – 8◦ Distrito de Meteorologia – Porto Alegre) and State Foundation for Agricultural Research – Fundacao Estadual de Pesquisas Agropecuarias(FEPAGRO). Afterwards, there were made cross-correlations between the indices, and correlations between the indices and the precipitations of the RS for the period 1948-2009. The precipitation correlations were simultaneous and lagged, with the indices preceding the precipitation up to 2 months, to determine the predictive powerof the indices, and estimate the evolution of this variable in the spatiotemporal domain. The index of the Southwest Atlantic SST was not significant for the precipitationof RS in the months from November to February. The highest degree of association between the indices of the Equatorial Pacific and South Pacific with precipitationwere found in November. In general, it was observed that the significant coefficients in the simultaneous correlations remained until lag 2, i.e., the SST in the Equatorial Pacific and South Pacific can be good predictors of the rain quality for the state of the RS, up to 2 months in advance. Keywords: Equatorial Pacific, South Pacific, Southwest Atlantic, correlation analysis. RESUMO. Foram determinados indices climaticos obtidos da Temperatura da Superficie do Mar (TSM) nos oceanos Atlântico e Pacifico, disponiveis na pagina dainternet do Earth System Research Laboratory (ESRL), pertencente a Physical Science Division (PSD) da National Oceanic and Atmospheric Administration (NOAA). Esses indices foram criados para representar as variacoes de TSM no Atlântico Sudoeste e Pacifico Equatorial e Sul, com o objetivo de estudar suas influencias navariabilidade da precipitacao do Estado do Rio Grande do Sul (RS). Os dados de precipitacao foram obtidos do Instituto Nacional de Meteorologia (INMET, 8◦ Distritode Meteorologia – Porto Alegre) e Fundacao Estadual de Pesquisas Agropecuarias (FEPAGRO). Posteriormente, foram realizadas correlacoes cruzadas entre os indices, e correlacoes entre os indices e as precipitacoes do RS para o periodo de 1948-2009. As correlacoes com as precipitacoes foram simultˆaneas e com defasagem, comos indices precedendo a precipitacao em ate 2 meses, para determinar o carater preditivo do indice em questao, e estimar a evolucao dessa variavel no dominio espaco temporal.O indice das TSMdo Atlântico Sudoeste nao foi significativo para as precipitacoes do RS nos meses de novembro a fevereiro. Omaior grau de associacao entreos indices do Pacifico Equatorial e Sul com as precipitacoes foi encontrado em novembro. No geral, foi observado que os coeficientes significativos nas correlacoes simultâneas, permaneceram ate o lag 2, ou seja, as TSM do Pacifico Equatorial e Sul podem ser bons previsores da qualidade da chuva para o Estado do RS, com ate 2 meses de antecedencia. Palavras-chave: Pacifico Equatorial, Pacifico Sul, Atlântico Sudoeste, analise de correlacao.