Sea surface temperature (SST) anomalies caused by a warm core eddy (WCE) in the Southwestern Atlantic Ocean (SWA) rendered a crucial influence on modifying the marine atmospheric boundary layer (MABL). During the first cruise to support the Antarctic Modeling and Observation System (ATMOS) project, a WCE that was shed from the Brazil Current was sampled. Apart from traditional meteorological measurements, we used the Eddy Covariance method to directly measure the ocean–atmosphere sensible heat, latent heat, momentum, and carbon dioxide (CO₂) fluxes. The mechanisms of pressure adjustment and vertical mixing that can make the MABL unstable were both identified. The WCE also acted to increase the surface winds and heat fluxes from the ocean to the atmosphere. Oceanic regions at middle and high latitudes are expected to absorb atmospheric CO₂, and are thereby considered as sinks, due to their cold waters. Instead, the presence of this WCE in midlatitudes, surrounded by predominantly cold waters, caused the ocean to locally act as a CO₂ source. The contribution to the atmosphere was estimated as 0.3 ± 0.04 mmol m⁻² day⁻¹, averaged over the sampling period. The CO₂ transfer velocity coefficient (K) was determined using a quadratic fit and showed an adequate representation of ocean–atmosphere fluxes. The ocean–atmosphere CO₂, momentum, and heat fluxes were each closely correlated with the SST. The increase of SST inside the WCE clearly resulted in larger magnitudes of all of the ocean–atmosphere fluxes studied here. This study adds to our understanding of how oceanic mesoscale structures, such as this WCE, affect the overlying atmosphere.

The oceanic South Atlantic Convergence Zone (SACZ) has played a major role during South America’s 2021/2022 summer extreme rainy season, being responsible for more than 90% of the precipitation in some regions of Southeast Brazil and in some regions of the Southwestern Atlantic Ocean (SWA). The summer of 2021/2022 was unique and rare and considered an abnormally humid season as verified by official Brazilian Institutes. First, the unusual number of cases of SACZ episodes (seven), was the highest recorded in the last decade. Second, all the cases that occurred were oceanic SACZ that assumed characteristics of an Atmospheric River and produced an excessively anomalous amount of precipitation during this period. Excess precipitation along with the regions located in mountainous and very uneven relief, which by orographic effects favors high precipitation volumes, were responsible for amplifying the observed impacts, such as landslides and floods that caused several losses to society. We also showed the main effects of coupling and interaction between the waters of the surface layer of the SWA and the atmosphere. Our learning from this study ends with the unprecedented results of how the marine atmospheric boundary layer (MABL) is locally modulated by the sea surface temperature (SST) that lies just below it. Until the present moment, we emphasize that this important mechanism has not been widely highlighted in the literature, showing that even though the ocean is colder than before oceanic SACZ is established, it is still warmer than the overlying air, thus, the ocean continues to be an active source of heat and moisture for the atmosphere and enhances the MABL instability process.

Quality control measures for ocean waves observations are necessary to give confidence of their accuracy. It is common practice to detect anomalies or outliers in surface displacement observations by applying a standard deviation threshold. Besides being a purely statistical method, this quality control procedure is likely to flag extreme wave events erroneously, thereby impacting higher order descriptions of the wave field. In this paper we extend the use of the statistical phase-space threshold, an established outlier detection method in the field of turbulence, to detect anomalies in a wave record. We show that a wave record in phase-space (here defined as a diagram of displacement against acceleration) can be enclosed by a predictable ellipse where the major and minor axis are defined by the spectral properties of the wave field. By using the parameterized ellipse in phase-space as a threshold to identify wave anomalies, this is a semi-physical filtering method. Wave buoy data obtained from a mooring deployed near King George Island, Antarctica (as part of the Antarctic Modeling Observation System, ATMOS) and laser altimeter data obtained at the Northwest Shelf of Australia were used to demonstrate the functioning of the filtering methodology in identifying wave anomalies. Synthetic data obtained using a high-order spectral model is used to identify how extreme waves are positioned in phase-space. Quality control measures for ocean waves observations are necessary to give confidence of their accuracy. It is common practice to detect anomalies or outliers in surface displacement observations by applying a standard deviation threshold. Besides being a purely statistical method, this quality control procedure is likely to flag extreme wave events erroneously, thereby impacting higher order descriptions of the wave field. In this paper we extend the use of the statistical phase-space threshold, an established outlier detection method in the field of turbulence, to detect anomalies in a wave record. We show that a wave record in phase-space (here defined as a diagram of displacement against acceleration) can be enclosed by a predictable ellipse where the major and minor axis are defined by the spectral properties of the wave field. By using the parameterized ellipse in phase-space as a threshold to identify wave anomalies, this is a semi-physical filtering method. Wave buoy data obtained from a mooring deployed near King George Island, Antarctica (as part of the Antarctic Modeling Observation System, ATMOS) and laser altimeter data obtained at the Northwest Shelf of Australia were used to demonstrate the functioning of the filtering methodology in identifying wave anomalies. Synthetic data obtained using a high-order spectral model is used to identify how extreme waves are positioned in phase-space.

The total energy dissipation rate on the ocean surface, ${ϵ}_t$ (W m${}^{-2}$), provides a first-order estimation of the kinetic energy input rate at the ocean–atmosphere interface. Studies on the spatial and temporal distribution of the energy dissipation rate are important for the improvement of climate and wave models. Traditional oceanographic research normally uses remote measurements (airborne and platforms sensors) and in situ data acquisition to estimate ${ϵ}_t$; however, those methods cover small areas over time and are difficult to reproduce especially in the open oceans. Satellite remote sensing has proven the potential to estimate some parameters related to breaking waves on a synoptic scale, including the energy dissipation rate. In this paper, we use polarimetric Synthetic Aperture Radar (SAR) data to estimate ${ϵ}_t$ under different wind and sea conditions. The used methodology consisted of decomposing the backscatter SAR return in terms of two contributions: a polarized contribution, associated with the fast response of the local wind (Bragg backscattering), and a non-polarized (NP) contribution, associated with wave breaking (Non-Bragg backscattering). Wind and wave parameters were estimated from the NP contribution and used to calculate ${ϵ}_t$ from a parametric model dependent of these parameters. The results were analyzed using wave model outputs (WAVEWATCH III) and previous measurements documented in the literature. For the prevailing wind seas conditions, the ${ϵ}_t$ estimated from pol-SAR data showed good agreement with dissipation associated with breaking waves when compared to numerical simulations. Under prevailing swell conditions, the total energy dissipation rate was higher than expected. The methodology adopted proved to be satisfactory to estimate the total energy dissipation rate for light to moderate wind conditions (winds below 10 m s${}^{-1}$), an environmental condition for which the current SAR polarimetric methods do not estimate ${ϵ}_t$ properly.

The wave pattern on the Brazilian coastline is composed of both wind waves and swell. The wave systems (WSs), extracted from the spectra near the coast produced by numerical wave models, reveal the occasional presence of intense swells, with small significant wave height (HS) and large average period (Ta). This kind of event has nearly no effect over deep water, but its landfall can be accompanied by inundation, mainly when coupled with favorable tides and storm surge. Since these events are not clearly evident in the bulk parameters, this study proposes a methodology (i) to identify intense swells simulated by a coarse grid resolution wave modeling system (CWS) and (ii) to evaluate their importance. In this methodology, monitoring sites are defined along a 100-m isobath contouring the Brazilian coast, where the CWS hindcasts the spectra for a 31-yr period, from 1979 to 2009, obtained by the WAVEWATCH wave model. The spectra are partitioned into WSs, which are used to build cumulative distribution tables (CDTs) for each site. The variable used in the CDT is the flux of energy per unit length perpendicular to the wave propagation (PW), which contains in its definition both HS and Ta. The direction of propagation of a WS is used to compute the components of PW parallel and perpendicular to the coast. From the CDT of the perpendicular component of PW, the percentile of an incoming WS can be found and its intensity ranked. To illustrate the feasibility of this proposal, the method is used to find the 50 most powerful distantly generated swells for two sites: one on the northern and another on the southern Brazilian coast. In addition, the method is applied in two case studies, both accompanied by coastal flooding and erosion: one represents a very powerful WS arriving at the northern coast and the other a less energetic event occurring on the southeastern coast. The analysis of bulk parameters fails to identify the second case as potentially destructive, while the proposed methodology clearly gives some indication.