A study of the south-east Indian Ocean from altimetric, wind and XBT data

Abstract

The dynamics of the seasonal and interannual sea level variability in the south-east Indian Ocean are investigated using Topex/Poseidon altimetric data and a combination of ERS-1 and ERS-2 winds and a simple dynamic model. This region is important for climate studies, in relation to the interannual variations of the tropical oceans and atmosphere. The eastern Indian region is directly affected by the strong seasonal monsoons as well as a remote ocean forcing from the tropical Indian Ocean and the western Pacific via the Indonesian Throughflow. As a result, the dynamics of the south-east Indian Ocean are unique, with a very large mesoscale variability off western Australia. This eastern boundary is the likely generating region for the westward propagating Rossby waves observed in the subtropical band. The signature of these waves is evident in both the ocean dynamic height and sea surface temperature. To investigate the origin of the observed sea surface variability, we use the vorticity equation with the low-frequency quasi-geostrophic assumption to calculate the sea level response to local wind forcing or remote forcing from the eastern boundary. We use ERS-1 scatterometry for the wind forcing; eastern boundary conditions are given by XBT data. First results indicate that a significant correlation exists between the wind forced model's results and the sea level variability observed by T/P around 15 °S, emphasising the importance of the local wind on the eastern Indian Ocean tropical dynamics. In contrast, the subtropical variability seem to be associated with remote forcing.