Eventos combinados entre o Dipolo do Oceano Índico e as diferentes tipologias de El Niño – Oscilação sul e sua associação com a precipitação do Sudeste da América do Sul

Abstract

This study aims to identify the impact of rainfall over Southeastern South America (SEAS) during the simultaneous occurrence of the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Unlike important previous studies, this work considers the concurrent occurrence of these two modes of climate variability, including combinations with the same sign and with opposite signs across all ENSO typologies (Eastern, Central, and Mixed). To obtain the results, the IOD phases were initially identified using the Dipole Mode Index (DMI), while the ENSO phases were identified through the Oceanic Niño Index (ONI). The impacts on precipitation over SEAS were assessed using rainfall anomaly composites. To understand the mechanisms associated with these anomalies, composite maps of geopotential height anomalies at 200 hPa and omega anomalies at 200 hPa and 500 hPa were also produced. The results first revealed a predominance of combinations between ENSO and IOD events with the same sign, particularly in the Mixed ENSO typology. Another noteworthy finding was the absence of co-occurrence between Eastern and Central El Niño events with negative IOD (IOD-) events. The dissertation hypothesis — that ENSO effects over SEAS would be stronger when combined with IOD phases of the same sign — was partially confirmed. Events such as Eastern El Niño and Eastern La Niña indeed showed intensified effects when associated with IOD phases of the same sign. However, opposite-sign combinations between the modes, such as Mixed El Niño with IOD-, Central La Niña with IOD+, and Mixed La Niña with IOD+, proved to be more effective in terms of the intensity of impacts over SEAS. Another relevant result was observed in the combination of Central La Niña and IOD-, which produced intense positive precipitation anomalies over SEAS, indicating that, in this case, the Indian Ocean interannual mode outweighed the ENSO effects.