Fabrício Sanguinetti Cruz de Oliveira

We present a comprehensive characterization of 1386 cyclonic eddies generated in the Brazil–Malvinas Confluence (BMC) between 1993 and 2022, using satellite altimetry and the META3.2_DT eddy trajectory atlas. By isolating locally generated cyclones over a record spanning three decades, this study distinguishes between retained and exported eddies and links their fate to geometric, kinematic, energetic, and regional circulation constraints. Eddies were analysed in terms of effective radius, amplitude, swirling speed, mean eddy kinetic energy (EKE), lifespan, propagation direction, seasonal genesis, and final detection location. Most cyclones were last detected within the BMC domain, while only 14% escaped the study area. Escaped eddies had longer mean lifespans and larger net displacements than retained eddies, but export was not determined by lifespan alone. Net displacements were more frequent toward the eastern quadrants, whereas westward displaced eddies were generally more confined near the continental margin. Spatial patterns revealed a persistent corridor of eddy formation along the continental slope, modulated by bathymetric gradients and the seasonal displacement of the BMC front. The strongest mean swirling speeds and EKE values were concentrated within the main Brazil Current and Malvinas Current confluence zone, while larger effective radii were not necessarily collocated with the most energetic cells. Annual mean EKE associated with cyclonic eddies showed a weak but statistically significant positive trend during complete calendar years from 1993 to 2021, without a significant increase in interannual variance. Case studies illustrated contrasting pathways, including prolonged retention within the confluence, temporary offshore displacement followed by return, and export toward the open ocean. Taken together, the results show that locally generated cyclonic eddies in the BMC do not follow a single evolutionary pathway. Their persistence, displacement, and energetic expression emerge from the combined influence of eddy coherence, regional circulation, availability of open ocean pathways, and bathymetric constraints.

The Antarctic Circumpolar Current (ACC) is strongly influenced by the Southern Hemisphere Westerly winds (SHW), which is projected to intensify and shift poleward under increasing anthropogenic radiative forcing. However, the extent of ACC frontal jet responses to these changes remains uncertain. Using simulations from two CMIP6 (Coupled Model Intercomparison Project Phase 6) models (GFDL‐CM4 and HadGEM3‐GC31‐MM) under the SSP5‐8.5 (Shared Socioeconomic Pathway) scenario, we analyze ACC jet displacements. Our results reveal spatially heterogeneous shifts, with the most pronounced changes in the southeastern Indian Ocean, particularly along the 110°E–120°E sector, where weaker topographic constraints allow for greater jet mobility. In contrast, minimal displacements occur in the South Pacific and South Atlantic, despite substantial SHW shifts. These findings suggest that topographic anchoring is the dominant regulator of ACC frontal jet positioning in a warming climate while localized exceptions highlight the complexity of jet–topography interactions.

Extratropical cyclones are meteorological systems that significantly influence South America's climate through complex interactions between contrasting air masses and ocean–atmosphere dynamics. This study investigates the role of ocean heat fluxes in the formation and intensification of extratropical cyclones over the South Atlantic. We analysed latent and sensible heat and humidity exchanges between the atmosphere and ocean throughout the life cycle of six case studies, including three intense and three explosive cyclones offshore the coast of South America. Data from the CFSR/CFSv2 reanalysis provided parameters such as latent and sensible heat fluxes, specific humidity, zonal and meridional wind components and sea surface temperature (SST) at 6‐h intervals. The results indicate that latent heat flux associated with SST plays a fundamental role in baroclinic development, while sensible heat fluxes have a secondary role affecting the cyclones' deepening rates. Specific humidity in the warm sector was a crucial factor in the intensification of all the cases studied. As the cyclones dissipate, a weakening of the system is observed, accompanied by a decrease in heat fluxes. This study enhances our understanding of the oceanic influences on extratropical cyclones, improving the ability to monitor and forecast these impactful weather systems.

The Antarctic Circumpolar Current (ACC) is strongly influenced by the Southern Hemisphere Westerly (SHW), which is projected to intensify and shift poleward under increasing anthropogenic radiative forcing. However, the extent of ACC frontal jet responses to these changes remains uncertain. Using simulations from two CMIP6 (Coupled Model Intercomparison Project Phase 6) models (GFDL-CM4 and HadGEM3-GC31-MM) under the SSP5-8.5 (Shared Socioeconomic Pathway) scenario, we analyze ACC jet displacements. Our results reveal spatially heterogeneous shifts, with the most pronounced changes in the southeastern Indian Ocean, where weaker topographic constraints allow for greater jet mobility. In contrast, minimal displacements occur in the South Pacific and South Atlantic, despite substantial SHW shifts. These findings suggest topographic anchoring as a key regulator of ACC frontal jet positioning in a warming climate.

Composite analysis of the atmospheric mechanisms in South Atlantic explosive cyclones was performed utilising ERA5 reanalysis for the 2010–2020 period. By a manual tracking method, 271 cases were found (127 weak, 104 moderate and 40 intense). The cyclones follow the preferential displacement from northwest to southeast. There is a trend that, as the explosive cyclone's intensity increases, its trajectory becomes less zonal and has a more significant impact in the coastal areas of Southern Brazil and Uruguay. These intensity frequencies were discretized through a compositing technique for studying explosive cyclones. The results revealed that explosive cyclones begin following the classical model from Bjerknes and Solberg, and, at the end of the explosive phase, they tend to become Shapiro–Keyser type, especially in moderate and intense ones. Vertical movements appeared more significantly at the beginning of the explosive stage. It was observed that intense explosive cyclones transition from the equatorial side of the high‐level jet to the polar side. In addition, surface latent heat flux may significantly impact the cyclone's development both in the beginning and during the explosive phase, especially in intense systems. A horizontal dipole pattern is seen for surface sensible heat fluxes, as the ocean loses and gains heat in the cold and warm sectors, respectively, at roughly the same amount.

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.

The Brazil–Malvinas Confluence (BMC) is one of the most dynamical regions of the global ocean. Its variability is dominated by the mesoscale, mainly expressed by the presence of meanders and eddies, which are understood to be local regulators of air-sea interaction processes. The objective of this work is to study the local modulation of air-sea interaction variables by the presence of either a warm (ED1) and a cold core (ED2) eddy, present in the BMC, during September to November 2013. The translation and lifespans of both eddies were determined using satellite-derived sea level anomaly (SLA) data. Time series of satellite-derived surface wind data, as well as these and other meteorological variables, retrieved from ERA5 reanalysis at the eddies’ successive positions in time, allowed us to investigate the temporal modulation of the lower atmosphere by the eddies’ presence along their translation and lifespan. The reanalysis data indicate a mean increase of 78% in sensible and 55% in latent heat fluxes along the warm eddy trajectory in comparison to the surrounding ocean of the study region. Over the cold core eddy, on the other hand, we noticed a mean reduction of 49% and 25% in sensible and latent heat fluxes, respectively, compared to the adjacent ocean. Additionally, a field campaign observed both eddies and the lower atmosphere from ship-borne observations before, during and after crossing both eddies in the study region during October 2013. The presence of the eddies was imprinted on several surface meteorological variables depending on the sea surface temperature (SST) in the eddy cores. In situ oceanographic and meteorological data, together with high frequency micrometeorological data, were also used here to demonstrate that the local, rather than the large scale forcing of the eddies on the atmosphere above, is, as expected, the principal driver of air-sea interaction when transient atmospheric systems are stable (not actively varying) in the study region. We also make use of the in situ data to show the differences (biases) between bulk heat flux estimates (used on atmospheric reanalysis products) and eddy covariance measurements (taken as “sea truth”) of both sensible and latent heat fluxes. The findings demonstrate the importance of short-term changes (minutes to hours) in both the atmosphere and the ocean in contributing to these biases. We conclude by emphasizing the importance of the mesoscale oceanographic structures in the BMC on impacting local air-sea heat fluxes and the marine atmospheric boundary layer stability, especially under large scale, high-pressure atmospheric conditions.

IMPACTS OF SOUTHERN HEMISPHERE WESTERLIES ON THE BRAZIL CURRENT AT 30ºS