Long‐Term Monitoring of the Brazil Current Transport at 22°S From XBT and Altimetry Data: Seasonal, Interannual, and Extreme Variability

Abstract

The seasonal and interannual variability of the Brazil Current (BC) at 22°S is examined using expendable bathythermograph (XBT) transect and satellite altimetry data from 1993 to 2017. The XBT‐based mean absolute geostrophic transport of the BC is estimated as 4.7 ± 1.9 Sv, with additional 0.9 ± 0.9 Sv along the shelf. The strong agreement between the absolute dynamic height and altimetric sea surface height is used in two methods to reconstruct a daily time series of the BC transport since 1993. The altimetry‐based methods can represent well the BC transport seasonal cycle, whereas the XBT‐based estimates are slightly aliased by the strong regional mesoscale variability. At interannual timescales, the BC transport is significantly correlated (r = 0.43) with the wind stress curl in the western half of the basin with a lag of 19 months, which is consistent with baroclinic adjustment timescales. Other sources of variability can be observed in a case study of the summer 2009/2010 event, which was characterized by strong sea surface temperature anomalies of approximately 3 °C. During the event, the BC reached 11 Sv for nearly 3 months, partly driven by an increased coastal upwelling from a cyclonic wind stress anomaly, a standing eddy along the section, and thermosteric anomalies that reached the offshore side of section in February. Heat anomalies were transported southward along the subtropical gyre following the BC path in a period of 2 months, which is consistent with advective timescales. Potential implications for extreme sea level and summer precipitation events in South America are discussed.

Synergy of In Situ and Satellite Ocean Observations in Determining Meridional Heat Transport in the Atlantic Ocean

“…The negative gyre component is attributed to the southward flowing Brazil Current at the western boundary, which transports warm water poleward. The Q gyre is roughly the same from 25°S to 34.5°S, around −0.17 ± 0.03 PW, but much smaller at 20°S, about −0.06 ± 0.02 PW, due to weak, eddy-dominated Brazil Current at this location (e.g., Goes et al, 2019;Soutelino et al, 2011). The weak northward return flow linked to the weak gyre circulation at 20°S also contributes to the smaller Q gyre at this location.…”

Propagating Modes of Variability and Their Impact on the Western Boundary Current in the South Atlantic

“…Our objective is to link the CEOF modes of variability (of SSH) with the variability in volume transport of the western boundary current. For this, the absolute geostrophic volume transport of the BC is estimated using SSH and XBT transects at 22.5°S and 34.5°S following the method described in Goes et al (). In short, statistical relationships are built between the dynamic height calculated from the XBT data and altimetric SSH, which are then used to infer the dynamic height and geostrophic velocity fields in time from 1993 to 2016.…”

“…The reconstructed geostrophic volume transport of the BC is then estimated at 22.5°S and 34°S for the period of 1993 to 2016. Details on the XBT data handling and processing can be found in Goes et al ().…”

“…They found significant correlations of the volume transport with the Southern Annular Mode, SASD, and the ENSO at interannual time scales. A recent study by Goes et al () uses observation‐based estimates of the BC and investigates how the propagation of anomalous sea surface height (SSH) in the South Atlantic can influence its variability. The present study is an extension of Goes et al () and Schmid and Majumder () where we investigate the influence of SSH propagating modes to the western boundary and explore how the regional and interbasin teleconnection patterns influence the variability of the BC at interannual time scales.…”

More Than 50 Years of Successful Continuous Temperature Section Measurements by the Global Expendable Bathythermograph Network, Its Integrability, Societal Benefits, and Future

“…During the warm SST event, the XBT-derived geostrophic BC transport (12 Sv) was three times larger than average. This anomalous transport was physically linked to increased coastal upwelling and baroclinicity in the region (Goes et al, 2019). These processes enhance the SST gradient across the BC off Cabo Frio, Brazil, which generates wind convergence/curl and thickens the atmospheric boundary layer, impacting local weather and precipitation (e.g., Pezzi et al, 2016).…”