An Observations and Model-based Analysis of the Temporal Variability of the Brazil Current
An Observations and Model-based Analysis of the Temporal Variability of the Brazil Current
Abstract:
Transport estimates of the Brazil Current from observations and models are analyzed to improve our understanding of the structure and variability of this current, which is an important component of the Meridional Overturning Circulation in the South Atlantic. The observed transports are derived from a
three-dimensional field of the horizontal velocity in the subtropical South Atlantic covering the years 2000 to 2014. Earlier studies already showed the latitude-dependence of this transport. The observations used herein show an increase of the mean meridional transport of the Brazil Current from 4 Sv at 24S to 11 Sv at 35oS and 15 Sv at 38oS. These new estimates agree well with earlier estimates from quasi-synoptic sections, most of which are near 24oS and 35oS. A comparison of the observed mean transports with those from three data assimilating models (Hybrid Coordinate Model, NCEP Global Ocean Data Assimilation System, Simple Ocean Data Assimilation) shows quite good agreement north of 33oS. Farther south two of the models have significantly higher transports than the observations while the third model remains close to the observed transports. Therefore, the uncertainty of estimates of the western boundary transport are more challenging here which increases the challenge of deriving the Meridional Overturning Circulation south of 33oS. With respect to the temporal variability of the Brazil Current, the observed transport at 24oS varies between 1 Sv and 7 Sv without a significant mean seasonal cycle due to large interannual variability that results in different phasing (i.e. in some years the maximum occurs in austral summer and the minimum in austral winter while the opposite is the case in other years). Such phase changes are also found in two of the three models. In addition, similar characteristics with larger amplitudes are also visible at 35oS and 38oS. Reasons for these interannual variations will be analyzed.
three-dimensional field of the horizontal velocity in the subtropical South Atlantic covering the years 2000 to 2014. Earlier studies already showed the latitude-dependence of this transport. The observations used herein show an increase of the mean meridional transport of the Brazil Current from 4 Sv at 24S to 11 Sv at 35oS and 15 Sv at 38oS. These new estimates agree well with earlier estimates from quasi-synoptic sections, most of which are near 24oS and 35oS. A comparison of the observed mean transports with those from three data assimilating models (Hybrid Coordinate Model, NCEP Global Ocean Data Assimilation System, Simple Ocean Data Assimilation) shows quite good agreement north of 33oS. Farther south two of the models have significantly higher transports than the observations while the third model remains close to the observed transports. Therefore, the uncertainty of estimates of the western boundary transport are more challenging here which increases the challenge of deriving the Meridional Overturning Circulation south of 33oS. With respect to the temporal variability of the Brazil Current, the observed transport at 24oS varies between 1 Sv and 7 Sv without a significant mean seasonal cycle due to large interannual variability that results in different phasing (i.e. in some years the maximum occurs in austral summer and the minimum in austral winter while the opposite is the case in other years). Such phase changes are also found in two of the three models. In addition, similar characteristics with larger amplitudes are also visible at 35oS and 38oS. Reasons for these interannual variations will be analyzed.