Characterization and Variability of Extratropical Cyclones in the Southwest Atlantic Ocean

Extratropical cyclones are key features that contribute to changes in precipitation, wind, and temperature at midlatitudes, sometimes causing extreme conditions. Despite the southwest Atlantic Ocean being recognized for cyclone formation and intensification, several aspects of spatial and temporal variability remain unclear. Hence, in this study, the overall characteristics of cyclones that form within the southwest Atlantic Ocean are investigated. We also analyze the interannual variability in the frequency of cyclone occurrences across each season. To accomplish this, we use a dataset from the hourly fifth generation of global climate reanalysis from the European Centre for Medium Range Weather Forecasts (ERA5/ECMWF) spanning 41 years. The results revealed increased interannual variability, which fit with a cubic regression for the entire study area, as well as for the northern and southern parts of the area, divided by the 35°S latitude. Seasonally, we found a positive trend of 1.7 per decade in cyclone occurrence for the southern part of the area during summer, with a statistical significance of 95%. The Fourier analysis revealed an energy peak at 2–3 years in the northern part during winter, as well as in the entire area during spring, summer, and autumn. Additionally, important peaks at the 5‐year, 6‐year, and 8–10‐year periods were observed. Moreover, we investigated extreme events and found that those selected by the minimum sea level pressure are more concentrated south of intense events by 10‐m winds. The composites of meteorological fields during intense cyclones that formed near the coastal area suggest that the equatorial entrance of the upper‐level jet stream is a preferential condition for the development of intense events. In addition, our analysis revealed the importance of a wide‐ranging meridional moving trough in the upper and middle level troposphere and the relevance of moisture transport via the northwest low‐level jet from the tropics to the coastal area, which induces intense cyclones in the southwestern Atlantic region.