Composite Analysis of Explosive Cyclones in the Southern Atlantic Ocean

Abstract

Composite analysis of the atmospheric mechanisms in South Atlantic explosive cyclones was performed utilising ERA5 reanalysis for the 2010–2020 period. By a manual tracking method, 271 cases were found (127 weak, 104 moderate and 40 intense). The cyclones follow the preferential displacement from northwest to southeast. There is a trend that, as the explosive cyclone's intensity increases, its trajectory becomes less zonal and has a more significant impact in the coastal areas of Southern Brazil and Uruguay. These intensity frequencies were discretized through a compositing technique for studying explosive cyclones. The results revealed that explosive cyclones begin following the classical model from Bjerknes and Solberg, and, at the end of the explosive phase, they tend to become Shapiro–Keyser type, especially in moderate and intense ones. Vertical movements appeared more significantly at the beginning of the explosive stage. It was observed that intense explosive cyclones transition from the equatorial side of the high-level jet to the polar side. In addition, surface latent heat flux may significantly impact the cyclone's development both in the beginning and during the explosive phase, especially in intense systems. A horizontal dipole pattern is seen for surface sensible heat fluxes, as the ocean loses and gains heat in the cold and warm sectors, respectively, at roughly the same amount.