Interannual variability of the South American low-level jet frequency and its impact on southeastern South America precipitation

This study provides a comprehensive analysis of the interannual variability of the South American Low-Level Jet (SALLJ) and its impact on precipitation over Southeastern South America (SESA). The research focuses on two core locations of the SALLJ and spans the four conventional seasons (spring, summer, autumn, and winter) from 1979 to 2020. Trend analysis revealed significant increases in the annual, winter, and summer Frequency of occurrence of SALLJ Days (FSD), indicating an upward trend in SALLJ activity. This trend may be a dynamical factor responsible for the increase in SESA precipitation observed in previous studies. Significant relationships were found between the FSD and precipitation anomalies over SESA in all seasons. In the summer, autumn, and winter seasons, a direct relationship between FSD and precipitation anomalies in SESA was found through teleconnections via quasi-stationary Rossby waves of tropical origin associated with El Nino-Southern Oscillation (ENSO). This means that El Nino-like conditions are associated with high FSD and positive precipitation anomalies, and La Nina-like conditions with low FSD and negative precipitation anomalies in SESA. While in spring, the relationship between FSD and ENSO is non-linear, with both high and low FSD seasons during El Nino-like conditions, no direct relationships between FSD and precipitation anomalies were found.