Abstract
The South Atlantic convergence zone (SACZ) is the main summer-typical atmospheric phenomenon occurring in South America, and it is of great interest because it regulates the rainy season in the most populated regions of Brazil. Frequency variability, persistence, and geographical position of the SACZ and its relationship with intraseasonal variability is well described in the literature. However, the influence of extratropical forcing on the SACZ is not well understood. Consequently, the aim of this study is to evaluate the role of the Antarctic Oscillation (AAO) in SACZ events. The persistence and frequencies of SACZ events, mean, standard deviation of total precipitation per event, lag composite of daily precipitation and geopotential height anomalies were obtained for each phase of the AAO. Therefore, frequency, persistence and total precipitation of SACZ events were higher in positive AAO (AAO+) than negative AAO (AAO−). A teleconnection mechanism between the extratropics and the SACZ region is evident in AAO+, through intensification of the polar and subtropical jets, in the days preceding SACZ. The same was not observed in the AAO−, where the anomalies were confined in the subtropical region and displaced to the South Atlantic Ocean.
Highlights
The South Atlantic convergence zone (SACZ) is a north-southeast oriented convective cloud cover that persists for at least four consecutive days [1] and extends from southern Amazonia to the southwest Atlantic Ocean
Due to the importance of the SACZ and Antarctic Oscillation (AAO) in the precipitation regime of the subtropical region of South America, the goal of this study was to analyze the role of AAO phases in precipitation and atmospheric circulation at high and low levels during the events of the SACZ, with the following questions being considered: (1) Is the frequency and persistence of SACZ events different between the phases of the AAO?; (2) How is the variability of the SACZ precipitation in each phase of the AAO?; (3) Are there any changes in the atmospheric circulation pattern associated with the SACZ in each phase of the AAO?
SACZ region, region, especially especially in in the the southeast southeast region, region, where where the the daily precipitation of the is greater than the daily precipitation of the summer
Summary
The South Atlantic convergence zone (SACZ) is a north-southeast oriented convective cloud cover that persists for at least four consecutive days [1] and extends from southern Amazonia to the southwest Atlantic Ocean. Already in AAO+, the authors observed that during the autumn, there are negative anomalies of precipitation in southern Brazil and weak positive anomalies in the southeast. Due to the importance of the SACZ and AAO in the precipitation regime of the subtropical region of South America, the goal of this study was to analyze the role of AAO phases in precipitation and atmospheric circulation at high and low levels during the events of the SACZ, with the following questions being considered: (1) Is the frequency and persistence of SACZ events different between the phases of the AAO?; (2) How is the variability of the SACZ precipitation in each phase of the AAO?;. (3) Are there any changes in the atmospheric circulation pattern associated with the SACZ in each phase of the AAO?
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