Correlation between oceanic patterns and precipitation in basins that compose the Brazilian SIN to improve the long-time forecast

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Wednesday, 5 February 2014
Hall C3 (The Georgia World Congress Center )
Maria de Souza Custodio, University of São Paulo, Sao Paulo, Brazil; and P. D. Madeira, C. G. M. Ramos, and A. L. F. de Macedo

The South American climate presents tropical, subtropical and extratropical features because of its territorial extension, being influenced by a variety of dynamical systems with different spatial and temporal scales which result in different climatic regimes in their subregions. Furthermore, the regime of precipitation on South America is influenced by low-frequency phenomena as El Niño-Southern Oscillation (ENSO), the Atlantic dipole and the Madden Julian Oscilation (MJO), in other words, is directly influenced by variations of the Sea Surface Temperature (SST). Due to the importance of the precipitation in many sectors including the planning of productive activities, such as agriculture, livestock and hydropower energy, many studies about climate variations in Brazil have tried to determine and explain the mechanisms that affect the precipitation regime. However, because of complexity of the climate system, and consequently their impacts on the global precipitation regime, its interactions are not totally understood and therefore misrepresented in numerical models used to forecast climate. The precipitation patterns over hydrographic basin which form the Brasilian National Interconnected System (Sistema Interligado Nacional-SIN) are not completely understood, therefore the climate forecast of these regions still presents considerable failure which need to be corrected due to its economic importance. There are several methodologies and meteorological models able to predict the climate for the next twelve months, however these methods still have significant failures. Many studies have shown the relationship between SST (ENSO region and Atlantic ocean) and precipitation patterns, but it is focusing mainly on La Plata Basin (LPB) and focus in ENSO and its relationship with the SST pattern for to Atlantic Ocean. However operational experience suggest a strong relationship between other oceanic regions and the direct effect in precipitation on South America. To understanding and quantifying this relationship is important for the improvement and increasing the accuracy of the long-time forecast for the South America. In this context, the purpose of this work is to determine the precipitation patterns on the Brazilian SIN, based on SST and circulation observed data. Through those patterns elaborate a long-time (twelve months) climate forecast model for those regions. This study is separated in two parts, first identify patterns and second elaborate the forecast model. We analyzed 30 years (1983 to 2012) of SST over Pacific and Atlantic Ocean, wind (850 and 200 hPa) and precipitation month observed data. The regions where precipitation was analyzed refer to mainly basins of the SIN and they are: Paraná, São Francisco, Tocantins, Iguaçu, Paranaíba, Grande, Uruguai e Parapanema. The precipitation data of those regions (SIN basins) and interannual (ENSO) and intraseasonal (MJO) SST anomalies were analyzed through statistical analyses and were correlated in spatial and time scales. Determined the patterns between precipitation, SST and wind, we elaborated a statistical model of long-time climate forecast for each region, with which it is expected an improvement of up to 20% of climate prediction in these basins. In this first stage was evident a high correlation between precipitation in the basins of SIN and SST Pacific anomalies over the region of Niño, as well as on the coast of Chile and Peru. The effect of SST anomalies (Niños regions) on precipitation in the South America is already known, however the quantification was not yet well understood. The coast of Chile determines the positioning and movement of cold fronts directly affecting rainfall in southern and southeastern of Brazil, then the correlation and rain pattern indicated the parameters for the climate prediction model. The anomalies over the Atlantic ocean presents high correlation with the precipitation in North and Northeast of Brazil, as well as its connection with the Pacific anomalies. This quantification generated climatic parameters for predictions for these regions. The relationship between the canonical ENSO events and precipitation regime on the basins were also quantified which represents a high degree of assertiveness in predicting climate of these regions. Long-time prognostic equations for the mainly hydrographic Brazilian basins SIN (Uruguai, Iguaçu, Paranapanema, Grande, Paranaíba, São Francisco e Araguaia/Tocantins) used SST prognostic date from CPC/NCEP and altitude wind prognostics. The equations are applied for twelve months period, with showed satisfactory results for the precipitation parameter.