Oceanic SACZ produces an abnormally wet 2021/2022 rainy season in South America

Abstract

The oceanic South Atlantic Convergence Zone (SACZ) has played a major role during South America’s 2021/2022 summer extreme rainy season, being responsible for more than 90% of the precipitation in some regions of Southeast Brazil and in some regions of the Southwestern Atlantic Ocean (SWA). The summer of 2021/2022 was unique and rare and considered an abnormally humid season as verified by official Brazilian Institutes. First, the unusual number of cases of SACZ episodes (seven), was the highest recorded in the last decade. Second, all the cases that occurred were oceanic SACZ that assumed characteristics of an Atmospheric River and produced an excessively anomalous amount of precipitation during this period. Excess precipitation along with the regions located in mountainous and very uneven relief, which by orographic effects favors high precipitation volumes, were responsible for amplifying the observed impacts, such as landslides and floods that caused several losses to society. We also showed the main effects of coupling and interaction between the waters of the surface layer of the SWA and the atmosphere. Our learning from this study ends with the unprecedented results of how the marine atmospheric boundary layer (MABL) is locally modulated by the sea surface temperature (SST) that lies just below it. Until the present moment, we emphasize that this important mechanism has not been widely highlighted in the literature, showing that even though the ocean is colder than before oceanic SACZ is established, it is still warmer than the overlying air, thus, the ocean continues to be an active source of heat and moisture for the atmosphere and enhances the MABL instability process.