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This paper analyzed the anomalous rainy austral summer of 2020 over the southeastern region of Brazil (SEB), investigating its possible mechanisms. The SEB experienced dry summers in the years before 2020; however, the austral summer of 2020 in this region was the wettest since 1991. A wave train starting from the Indian Ocean to the Pacific Ocean, plus a wave train from the tropical north (U-shape), and another from the western equatorial Pacific (PSA-like) contributed to an anomalous anticyclonic circulation at high levels southward South America. This merged wave train continued its path with an anomalous cyclonic circulation over the southern region of Brazil and the state of Sao Paulo, and anticyclonic northward, enhancing (inhibiting) convection over SEB (southern Brazil). Besides, the Southern Annular Mode (SAM) pattern was in a positive phase, and there were negative sea surface temperature (SST) anomalies near SEB and Argentina, contributing for the configuration over the continent. Comparisons of the main differences between the austral summer of 2019 (dry) and the summer of 2020 show there was no anomalous divergence at high levels over the Indian Ocean in 2019, triggering a wave train from this region to the Pacific. The two wave trains from the Pacific merged in an anomalous anticyclonic circulation over the southeastern Pacific, near the South American coast. The SAM pattern was neutral in 2019; however, there were positive SST anomalies near SEB, southern Brazil and Argentina coastal. The South Atlantic SST and the wave trains generated an anticyclonic anomalous circulation over the southern Region of Brazil and cyclonic northward, in opposition to the 2020 configuration.
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