Easterly wave disturbances on tropical south Atlantic and their impact over northeast Brazil

This study presents a 21-year climatology (1998–2018) of Easterly Wave Disturbances (EWDs) over the Tropical South Atlantic (TSA). The identification of these systems was performed subjectively using infrared satellite images and fields of relative vorticity and streamlines at 1000, 850, 700, 500, and 200 hPa levels from the ERA-Interim (ERAI) reanalysis. Additionally, the TracKH automatic tracking algorithm was applied, successfully capturing approximately 66% of the subjectively identified events. A total of 518 EWDs were recorded during the study period, with 97% reaching the Northeast Brazil (NEB) region, and 64% exhibiting convective characteristics. The highest frequency of events was observed between April and August, with an average of approximately 25 EWDs per year. The primary genesis areas were located between 20°S–5°N and 35°W–15°W. The trajectories and dissipation predominantly occurred along the NEB's eastern coastline, particularly between Alagoas and Rio Grande do Norte. Dissipation generally occurred rapidly after the systems moved inland. Several atmospheric systems were identified as key contributors to EWD genesis, including the Intertropical Convergence Zone (ITCZ), Upper-Tropospheric Cyclonic Vortices (UTCV), cold fronts, and convective clusters originating from the west coast of Africa. These factors played a significant role in the intensification and organization of the disturbances.  During the wet season, the synoptic patterns associated with EWDs revealed anomalous cyclonic and confluent circulations, along with convergence and negative vorticity from low levels up to 200 hPa, where only a trough feature was observed. Negative anomalies of vertical motion and temperature, coupled with increased relative humidity, were also identified, fostering favorable conditions for enhanced convection and precipitation associated with the disturbances.