In this study, we propose an easy and robust algorithm to identify and track extratropical cyclone events using 850 hPa relative vorticity data, gaussian filter and connected-component labeling technique, which recognize the cyclone as areas under a threshold. Before selecting the events, the algorithm can include essential characteristics that are good metrics of intensity, like minimum mean sea level pressure and maximum 10-m winds. We implemented the algorithm in the Southern Hemisphere, using a 41-year high resolution dataset. Sensitivity tests were performed to determine the best parameters for detection and tracking, such as degree of smoothing, thresholds of relative vorticity at 850 hPa and the minimum area within the threshold. Two case studies were used to assess the positive and negative points of the methodology. The results showed that it is efficient in obtaining the position of extratropical cyclones in their most intense stage, but it does not always perform well during cyclolysis. We compare the methodology using 1-h temporal resolution to that using a 6-hours temporal resolution, and their reproducibility regarding the literature. The extratropical cyclone climatology in the Southern Hemisphere is provided and discussed. The algorithm developed here can be applied to datasets with good spacial and temporal resolution, providing a better inventory of extratropical cyclones.

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.