An assessment of the Brazil Current baroclinic structure and variability near 22° S in Distinct Ocean Forecasting and Analysis Systems

Abstract

The Brazil Current (BC) is the Western Boundary Current of the South Atlantic subtropical gyre, the dominant dynamic feature in the South Atlantic Ocean. The importance of this current lies in that it is the main conduit of subtropical waters to higher latitudes in the South Atlantic Ocean. This study assesses the structure and variability of the BC across the nominal latitude of 22°S using data from the high-density eXpendable BathyThermograph (XBT) AX97 transect and from three numerical ocean models with data assimilation. This XBT transect was implemented in 2004 and represents one of the longer-term monitoring systems of the BC in existence. The goal of this work is to enhance the understanding of the temporal and spatial variability of the ocean dynamics in the southwestern South Atlantic Ocean by using a suite of hydrographic observations and numerical model outputs. In the present work, 37 XBT transect realizations using data collected between 2004 and 2012 are used. Daily outputs covering the same time period are evaluated from Hybrid Coordinate Ocean Model with the Navy Coupled Ocean Data Assimilation (HYCOM-NCODA) with a 1/12°horizontal resolution, and GLORYS2V3 and FOAM, both with a 1/4°horizontal resolution. These Ocean Forecasting and Analysis Systems (OFAS) are able to capture the mean observed features in the 22°S region, showing a BC core confined to the west of 39°W and an Intermediate Western Boundary Current between the depths of 200 and 800 m. However, the OFAS tend to overestimate the mean BC baroclinic volume transport across the AX97 reference transect and underestimate its variability. The OFAS show that the coastal region between the coastline and the western edge of the AX97 transect plays an important role in the mean BC total transport, contributing to up to 23 % of its value, and further that this transport is not sampled by the XBT observations with its current sampling strategy. In order to understand the variability of the BC, a statistical classification of the BC is proposed, with the identification of three different events: weak, intermediate, and strong.

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

“…The mean (±1σ) transport of the BC east of 40.9°W is 4.7 ± 1.9 Sv southward, similar to the earlier estimates ranging from 4.4 to 5.3 Sv (Evans et al, ). The transport standard deviation (±1.9 Sv) is approximately half of the mean, showing the strong contribution from eddy variability to the BC (e.g., Lima et al, ; Soutelino et al, ). The shelf contribution, defined here as the region west of 40.9°W and shallower than 300 m, is of 0.9 ± 0.9 Sv, giving a total southward transport of 5.5 ± 1.7 Sv.…”

“…From the SSHA maps in Figures c and d, it is observed a stationary eddy near 40°W along the XBT transect, generating a trough in sea level of more than 10 cm throughout the 3‐month period. This is the so‐called Sao Tome eddy, a semipermanent cyclonic feature that develops in the region and can be originated from a detachment of a BC meandering (Calado et al, ; Campos et al, ; Lima et al, ). Therefore, our results suggest that in the summer 2009/2010, a mix of positive SSH anomalies propagated westward, anticyclonic wind anomalies facilitating the coastal upwelling and decreasing the coastal sea level, and a stationary eddy near 40°W along the XBT transect contributed for the strong BC anomaly in that period.…”

Energetics of eddy‐mean flow interactions in the Brazil current between 20°S and 36°S

“…Lima et al . [] compared the HYCOM NCODA product with XBT data collected at 22°S between 2004 and 2012. The authors observed that HYCOM NCODA confirmed the transport and variability of the BC in the region.…”

“…The NCODA system assimilates available satellite and in situ vertical temperature and salinity profiles of expendable bathythermographs (XBTs), Argo floats, and moored buoys [Cummings, 2005;Cummings and Smedstad, 2013]. Lima et al [2016] compared the HYCOM NCODA product with XBT data collected at 228S between 2004 and 2012. The authors observed that HYCOM NCODA confirmed the transport and variability of the BC in the region.…”

A hybrid data assimilation method and its comparison with an Ensemble Optimal Interpolation scheme in conjunction with the numerical ocean model using altimetry data

“…Studies to tackle the representation of physical systems behavior have been carried out and published in the scientific regionally configured numerical models. In particular, one can indicate the Brazilian REMO project (Lima et. al., 2016), Australian Blue Link project (Schiller et.…”