On the relationship between the South Atlantic Convergence Zone and sea surface temperature during Central-East Brazil extreme precipitation events

Abstract

The precipitation in Central-East Brazil (CEB) from December to February is heavily influenced by the South Atlantic Convergence Zone (SACZ). The SACZ not only causes considerable rainfall but also has an impact on the underlying ocean. This study examines the extreme precipitation events in CEB and their relationship with the SACZ and sea surface temperature (SST). Empirical Orthogonal Function (EOF) analyses of daily precipitation and vertical velocity at 500 hPa data diagnose the extremes. The grouped events of similar positioning and intensity resulted in 170 extremely wet and 172 dry events. Results indicate that the variability of the SACZ is responsible for extremely wet precipitation events in CEB. Composites of precipitation, SST, and wind anomalies at 850-hPa and 200-hPa characterize their occurrence and resemble SACZ high-intensity variability. Conversely, extremely dry CEB conditions are associated with SACZ southern events (51 events) and SACZ inactivity (121 events). The latter refers to major drought events when upper-level cyclonic circulation favors dry air descending and inhibiting convection over CEB. SACZ southern events have similar atmospheric dynamical patterns as SACZ events but are displaced to the south. The meridional displacement of the South Atlantic Low-Level Jet (SALLJ) and its confluence with the northeasterly flow of the South Atlantic Subtropical High (SASH) are identified as the causes of the cooling or heating of the underlying ocean. The intensity of the extreme event is related to the strength of lower-level wind circulation, while upper-level wind circulation anomalies favor the lower-level effects. The persistence of the systems is related to the development of SST anomalies.