Seasonal variability in the Agulhas Retroflection region

The objective of this article is to present evidence for the existence of s easonal variability in sea surface height (SSH) anomaly in the Agulhas Retr oflection region. TOPEX/POSEIDON altimeter data. are used to estimate seaso nal changes in the mesoscale SSH variability. There is a seasonal oscillati on of SSH variability characterized by a maximum during the austral summer and a minimum during the austral winter. The amplitude of this seasonal cha nge is approximately 30% of its mean value. During the winter season the sp atial distribution of SSH variability resembles that of the annual mean var iability, with relative maxima centered at approximately 18 degrees E, 27 d egrees E and 38 degrees E. During the summer there is an additional maximum which extends from approximately 20 degrees E to 25 degrees E and from 40 degrees to 42 degrees S. Analysis of longitude-time diagrams reveals that a t low latitudes planetary waves propagate freely throughout the basin. Alon g the latitude of the Agulhas Retroflection region, the East Madagascar Rid ge hampers the westward propagation of planetary waves. It is speculated th at the difference between summer and winter patterns is caused by an inerti ally driven bifurcation of the Agulhas Current.