Seasonal variability in the Agulhas Retroflection Region

The objective of this article is to present evidence for the existence of seasonal variability in sea surface height (SSH) anomaly in the Agulhas Retroflection region. TOPEX/POSEIDON altimeter data are used to estimate seasonal changes in the mesoscale SSH variability. There is a seasonal oscillation of SSH variability characterized by a maximum during the austral summer and a minimum during the austral winter. The amplitude of this seasonal change is approximately 30% of its mean value. During the winter season the spatial distribution of SSH variability resembles that of the annual mean variability, with relative maxima centered at approximately 18°E, 27°E and 38°E. During the summer there is an additional maximum which extends from approximately 20°E to 25°E and from 40° to 42°S. Analysis of longitude-time diagrams reveals that at low latitudes planetary waves propagate freely throughout the basin. Along the latitude of the Agulhas Retroflection region, the East Madagascar Ridge hampers the westward propagation of planetary waves. It is speculated that the difference between summer and winter patterns is caused by an inertially driven bifurcation of the Agulhas Current.