Long‐Term Monitoring of the Brazil Current Transport at 22°S From XBT and Altimetry Data: Seasonal, Interannual, and Extreme Variability. Issue 6 (7th June 2019)

• Record Type: Journal Article
• Authors: Goes, M.; Cirano, M.; Mata, M. M.; Majumder, S.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 6(2019)
• Page Start: 3645
• Page End: 3663
• Publication Date: 2019-06-07
• Subjects: boundary current -- Sverdrup balance -- coastal upwelling -- coastal sea level -- ocean advection -- marine heat wave; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2018JC014809
• Languages: English
• ISSNs: 2169-9275

Abstract

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. Plain Language Summary: Two methods were developed to create a 25‐yearlong time series of the Brazil Current (BC) volume transport across 22°S using expendable bathythermograph data and altimetry. The seasonal variability of the BC is out‐of‐phase with the wind stress curl across the basin, suggesting that wave adjustment and local winds control the seasonality. At interannual timescales, the wind stress curl in the western side of the basin and the regional upwelling control the BC variability. In the summer of 2009/2010, the BC transport was 3 times stronger than its mean. The event was characterized by a strong warm sea surface temperature anomaly propagating westward into the region and an associated anticyclonic wind stress anomaly. Results suggest that the BC strengthening was linked to a decreased near‐shore sea level of ~20 cm due to increased coastal upwelling, and an increased offshore sea level of 15 cm influenced by the warm anomaly. Key Points: Seasonal variability of the BC is out‐of‐phase with the Sverdrup transport due to baroclinic adjustment The BC transport variability is associated to the wind stress curl in the western part of the basin and coastal upwelling In the 2009/2010 event, anticyclonic winds lower the coastal sea level, and warm anomalies increase sea level offshore, strengthening the BC