Eddy activity in the South Indian Ocean from ERS-1 altimetry

Sea level anomalies from ERS-1 altimetry data have been used to calculate eddy kinetic energy (EKE) in the South Indian Ocean (10-40° S, 30-120° E). A significant proportion of the sea level variability is caused by the passage of westward propagating Rossby waves, which will be briefly mentioned. The EKE fields are used to investigate the seasonal changes in the eddy distributions. The clearest annual signal is in the Leeuwin Current, which displays markedly higher eddy energy in austral winter than in austral summer. The South Equatorial Current shows high energy at 10-20° S, strongest in winter. To the east of Madagascar, low EKE is seen to the west of the point at which the South Equatorial Current branches: the northern branch passing around the northern tip of Madagascar, while the southern branch becomes the eddy rich East Madagascar Current, which is markedly more variable in winter. Wind fields from the ERS-1 scatterometer enable us to study seasonal changes in the wind stress curl field, which influence the patterns of the EKE.