Comparing explosive cyclogenesis cases of different intensities occurred in Southern Atlantic

Abstract

Six events of explosive cyclogenesis occurred in the south Atlantic were compared using reanalysis data and satellite water vapor imagery. Cases of different intensities (weak, moderate and strong) occurred during 2014 summer season and 2012 winter season were studied. Despite the similarities the tropopause anomaly was more prominent and vertical movements were stronger in the strong cyclogenesis cases.The tropopause anomalies behind the cold front and ahead of the warm front appear only in the mature stage of the weak and moderate cases while in the strong case it is already evident and more intense behind the cold front since the beginning of the cycle. In all the cases confl uence of the jet streams took place at higher levels forming a jet streak with difl uence occurring downstream and the cyclone beginning in the exit region. The trajectories of the cyclones were in the southeast direction but longer and more meridional in the strong cases. The results indicated the baroclinicity of the region as the main mechanism for the development of these cyclones as well as the amplitude of the upper level jet stream perturbation. Furthermore, all the explosive cyclones developed following the Shapiro & Keyser cyclone conceptual model.

Analysis of the Most Intense Explosive Cyclone that Occurred Between 2010 and 2020 in the South Atlantic

“…Ocean heat fluxes were insignificant for the development, and dynamic tropopause anomalies were consistent with the literature (Hoskins, 1985;Santurette and Georgiev, 2005). These characteristics were also found by Avila et al (2021), with more emphasis on the intense ones.…”

“…This trapping indicates the seclusion of warm air as the cold front advances over the warm front due to its density. The configuration presented seems to demonstrate a Shapiro-Keyser system (Reboita et al, 2017;Avila et al, 2021), where the cold front becomes more meridional and disconnects from the cyclone. Heat fluxes reach their maximums in the cold part of the cyclone, as well as wind reach approximately 33 m/s (120 km/h) in the same region, while the system is in phase with the cut-off low at higher levels.…”

“…In explosive cyclones, the troughs deepen the tropopause over the cold side due to their interaction with air masses. In this case, it is considered that there is a fold in the dynamic tropopause (Uccellini et al, 1985;Avila et al, 2016Avila et al, , 2021Nunes and Avila, 2017;Heo et al, 2019), which entails a maximum of potential vorticity (PV). For the Southern Hemisphere, cyclonic PV is negative, and according to Santurette and Georgiev (2005), 1,5 units of potential vorticity represents dynamic tropopause.…”

From a Shapiro–Keyser extratropical cyclone to the subtropical cyclone Raoni: An unusual winter synoptic situation over the South Atlantic Ocean

“…Recently, Avila et al . (2021) documented six explosive cyclones from 2012 to 2014 over the SAO that developed following the Shapiro–Keyser model, reinforcing that this is a common development path for explosive cyclones.…”

“…Using the Sanders and Gyakum (1980) formulation of the Normalised Central Pressure Deepening Rate (NDR), the cyclone reached 1.33 NDR, which is enough to classify it as a moderate (1.3 ≤ NDR < 1.8; see Sanders (1986)) explosive extratropical cyclone. Recently, Avila et al (2021) documented six explosive cyclones from 2012 to 2014 over the SAO that developed following the Shapiro-Keyser model, reinforcing that this is a common development path for explosive cyclones.…”