A new climatology of South American extratropical cyclogenesis with an intercomparison among ERA5, JRA55 and the Brazilian Navy

In South America, the most destructive extratropical cyclones occur over the southeastern quadrant of the continent, a region that includes some of the world's largest population centres. However, there are few studies of cyclogenesis in this region, and little is known about how the varying origins of these storms impact subsequent behaviour. By supplementing an observational record with current reanalysis data, this study reveals the general characteristics of cyclones that develop in the lee regions of the Andes and those that develop nearer the Atlantic coast. The comparative climatologies demonstrate that cyclone development in these separate contexts is driven by topography, local atmospheric circulations and basin‐scale climate oscillations. The analysis further reveals a low‐frequency seesaw of lee and coastal cyclogenesis, with cross‐basin ocean temperature differences playing a teleconnectional role. Graphical presenting: (1) Cyclone tracking for Brazilian Navy (MB), ERA5, and JRA55 in lee and coastal areas; (2) A time series spanning 1980‐2020 for lee and coastal regions using all datasets; (3) Sea Surface Temperature (SST) and local atmospheric circulation anomalies for high (a) and low (b) frequencies of lee, and coastal cyclogenesis (c, d); and (4) Sections depicting vorticity advection (a, c) and vortex stretching (b, d) for lee (a, b) and coastal (c, d) areas. All figures are focused on lee and coastal cyclogenesis.