Explosive cyclones occurred between 2010 and 2020 in the South Atlantic under the perspective of two detection schemes.

Under two detection schemes, this study analyzes one of the most destructive weather systems - the explosive cyclones - in the South Atlantic, from 2010 to 2020. Then, two methods are presented to study these systems: the Observational Method (OBSM) and the Automated Method (AUTM). The first uses visual analysis of the mean sea level pressure (mslp) fields and functions to identify the local minimums using the Grid Analysis and Display (GrADS) software. The second utilizes a function from OpenGrADS called mfhilo. It shows the local minimum in the grid using laplacian, magnitude, and percentile. Two shell algorithms for data manipulation are used for the AUTM: one to trace the cyclones' trajectories according to a previously defined fixed area and the other to separate them into explosives. The OBSM methodology showed 271 cases averaging 25 yearly and revealed important characteristics regarding the intensities. According to AUTM's methodology, from the 2705 ordinary cyclone cases identified, 299 are explosives. There is a clear seasonality pattern in the systems' distribution along South America, similar to OBSM, but more highlighted. In summer, they concentrate at high latitudes, while in winter and spring, they are assembled near southern Brazilian and Uruguayan coasts.

South Atlantic explosive cyclones in 2014-2015: study employing NCEP2 and MERRA-2 reanalyses.

An analysis of explosive cyclone cases was produced by comparing the reanalysis of MERRA-2 (high spatial resolution) and NCEP2 (low spatial resolution) to South Atlantic in the 2014-2015 period. A total of 51 cases were found, of which 49 were detected by the first reanalysis and 33 by the second (2 cases identified by NCEP2 were not identified by MERRA-2). Spring was the dominant season in the formation of the cases in both reanalyses. It was observed that most systems are formed preferentially eastward of a preexisting trough at higher levels, while others are formed under an almost zonal upper airstream. This difference is more evident in the NCEP2. It was also diagnosed that the MERRA-2 shows more clearly the diffluence in the 250 hPa flow. The analysis of the composite fields revealed a negative horizontal tilt of the trough in 500 hPa, influenced by intense convection as the system develops. Besides, it pointed to a more pronounced jet stream in intense explosive cyclones and more prominent diffluence in non-intense cases. Since the NCEP2 reanalysis detected fewer cases (and only 2 intense) than MERRA-2, it was considered that the former is less suited to the analysis of this type of event.