Sea surface temperature fronts in the midlatitude South Atlantic revealed by using microwave satellite data

Abstract

The Subtropical Convergence or Frontal Zone has been little studied in the central South Atlantic Ocean. Despite limited data, some work has suggested that this feature exists continuously across the South Atlantic. Here, satellite microwave sensed sea surface temperature (SST) data, available from June 2002, are analysed for the existence of frontal gradients in the subtropical to subpolar South Atlantic with focus on the central to eastern region. The frontal locations and SST gradients in the southwest South Atlantic and in the Agulhas Current retroflection region obtained from this satellite data are consistent with those estimated previously from hydrographic observations. Evident in the satellite data is pronounced mesoscale variability in subtropical frontal features, particularly south of Africa, and extending west from the Agulhas Current retroflection to at least the Greenwich meridian, and in the southwest South Atlantic. Over the central to eastern part of the basin, the analysis suggests that there is substantial interannual variability in the strength and latitudinal location of the Northern and Southern Subtropical Front, as defined by Belkin and Gordon (1996). Some of this variability may be related to shifts in the winds, including that in the latitude of the strongest wind stress curl. On seasonal scales, this central to eastern region is also characterised by variations in the frontal intensity but shifts in the position of regions of strong gradients are less obvious. Thus the data indicate that there is no continuous subtropical frontal feature across the basin in terms of surface temperature.