Variability of the Southern Hemisphere stratospheric polar vortex and its association with surface climate over Southern and Southeastern Brazil

This study analyzes the variability of the Southern Hemisphere (SH) stratospheric polar vortex during the cold season (April–October) from 1979 to 2023 using ERA5 reanalysis data. Climatological analyses of zonal wind and potential vorticity reveal a seasonal strengthening of the vortex through mid-winter, followed by a breakdown toward late spring. Correlations between stratospheric winds (a proxy to polar vortex intensity) and surface temperature and precipitation in Southern and Southeastern Brazil show that a stronger vortex leads to colder months in both regions and to a decrease in precipitation in the South, but the correlations are generally weak. A stronger link is observed with the Southern Annular Mode (SAM), and the influence of SAM on cyclogenesis in the coast of South America is proposed as the mechanism leading to temperature and precipitation anomalies in the studied regions. Self-Organizing Map (SOM) analysis identifies dominant circulation patterns at 10, 50, and 100 hPa, showing that the most frequent modes of variability correspond to a displacement of the vortex toward lower latitudes, and the most anomalous state occurs mainly in early to mid-spring, coinciding with SH sudden stratospheric warming events in 2002 and 2019. These results provide a concise characterization of the SH polar vortex’s seasonal evolution and variability, highlighting the conditions under which extreme stratospheric events can influence regional climate.