An evaluation of different objective detection methods of atmospheric blockings over Southeastern Pacific and South Atlantic oceans: impact on the blocking climatology

Abstract

Episodes of atmospheric blocking over Southeastern Pacific and South Atlantic oceans significantly affect the weather over South America. In Brazil, blocking events have been associated with heat waves and droughts or abnormally dry periods. Since there is no unique definition of atmospheric blocking, different objective methods for identifying and quantifying atmospheric blocking have been developed in recent decades, primarily targeting Northern Hemisphere blocks. For this reason, the observed frequency and characteristics of blocking depend on the method adopted, leading to changes in the resultant blocking climatology. In the Southern Hemisphere, studies addressing atmospheric blocking are still scarce. More specifically, there is no study assessing the reliability of the different identification methods in the Southern Hemisphere. To address this gap, this work examines blocking properties produced by five different objective detection methods over the Southeast Pacific and Southern Atlantic oceans, using ERA5 data. The five indexes used in this study rely on the 500 hPa geopotential field and were developed by modifying the approaches employed in earlier studies by Lejeñas (1984), D’Andrea et al. (1998), Schwierz et al. (2004), Davini et al. (2012), and Mendes et al. (2022). The study also examines the variations in the blocking climatologies that arise from using different objective detection methods. Additionally, in order to evaluate the accuracy of each objective method applied, the results are compared with observed blocking episodes. Moreover, atmospheric fields are analyzed to verify if a synoptic blocking pattern was present during the objectively identified blocking events.