The anomalous wet 2020 southeast Brazil austral summer: characterization and possible mechanisms

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Fernanda Cerqueira Vasconcellos
https://orcid.org/0000-0002-5931-1503
Juan Neres de Souza

Abstract

This paper analyzed the anomalous rainy austral summer 2020 over the Southeastern Region of Brazil (SEB), investigating the possible mechanisms. The SEB has been experiencing dry summers in the years before 2020. However, the austral summer 2020 in this region was the wettest summer since 1991. A wavetrain started from the Indian Ocean to the Pacific Ocean, plus a wavetrain from tropical north (U-shape), and another from western equatorial Pacific (PSA-like) contributed for an anomalous anticyclonic circulation at high levels southward South America. This merged wavetrain continued its path with an anomalous cyclonic circulation over the Southern region of Brazil and Sao Paulo State 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 for the main differences between austral summer 2019 (dry) from summer 2020 have shown there is no anomalous divergence at high levels over the Indian Ocean in 2019, triggering a wavetrain from this region to Pacific. The two wavetrains from Pacific merged in an anomalous anticyclonic circulation, over the southeastern Pacific, near South America 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 wavetrains generated an anticyclonic anomalous circulation over the Southern Region of Brazil and cyclonic northward, in opposition configuration of 2020.

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Author Biographies

Fernanda Cerqueira Vasconcellos, Federal University of Rio de Janeiro

Adjunct Professor Meteorology Department - Geoscience Institute

Juan Neres de Souza, Federal University of Rio de Janeiro

Undergraduate student - Meteorology Department - Geoscience Institute

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