Relação entre o MEI (Multivariate Enso Index) e a precipitação pluvial no estado do Rio Grande do Sul

Abstract

On Rio Grande do Sul the seasons of the year are well defined being felt, in its peculiar characteristics, the winter, the spring, the summer and the autumn. The pluviometric regime is quite regular and the precipitations are well distributed during all the year on the State. The Multivariate Enso Index (MEI) lacks of a study about its relations with the precipitation. It is a numeric index that integrates the action of different factors that characterize the phenomenon and that oscilate between positive values for the hot phase, the El Niño, and negative values for the cold phase, the La Niña. It considers, in its composition, the following variables: sea level pressure, zonal and meridional wind components at the surface, the Sea Surface Temperature (SST), the air temperature at the surface and a cloudiness indicator. This work had the objective to study the relations between the MEI and the SST of the Niño regions with the pluvial precipitations on Rio Grande do Sul State. For this, it were utilized total monthly data of pluvial precipitation from 40 meteorological stations of Rio Grande do Sul, bimonthly data of MEI and SST of the Niño regions for the period 1950 to 2002. The correlation coefficients between pluvial precipitation of Rio Grande do Sul with MEI and the Niños regions showed low values due to the fact of using only the months of the beginning and end of the event. The MEI, although being an index more complex in relation to the metodologic point of view, it does not improve the correlation coefficients with the pluvial precipitation of the State of Rio Grande do Sul and always presents lesser or equal values to that obtained when using the TSM of Niños regions in the bimonths of oct/nov and nov/dec.The Niños 3 and 4 regions are the most influents in the pluvial precipitation positive anomalies of Rio Grande do Sul for the bimonth oct/nov. On the other hand, the Niño 4 region is the most influent in the case of pluvial precipitation negative anomalies for the same bimonth. In relation to the bimonth nov/dec only the Niño 3 has more influence in the pluvial precipitation positive anomalies in Rio Grande do Sul.