Seasonal and spatial SST variability in the Agulhas retroflection and Agulhas return current

Abstract

Multichannel sea surface temperature data from the NOAA advanced very high-resolution radiometer for the three-year period October 1991–September 1994 were analysed to characterise spatial and temporal sea surface temperature (SST) variability in the Agulhas retroflection and Agulhas return current regions south and east of Africa. Empirical orthogonal function (EOF) analysis revealed an unusual, coherent, large-scale pattern of SST variability associated with a dominant annual cycle, with interannual variability. The first EOF mode accounted for approximately 75% of the variability in the three-year record. The structure of the fronts and their role in determining the SST variability were explored. The major characteristics of the seasonal expression were found to be (1) annually varying SST anomalies with a maximum range of 10.6°C, (2) stronger horizontal sea surface temperature gradients across the subtropical front in winter than in summer, and (3) an unexpectedly patchy spatial SST variability of the Agulhas return current. The SST results have been discussed in comparison with recent sea level variability measured from TOPEX/POSEIDON in 1993.