CSIRO Marine and Atmospheric Research
Past Seminars

AN OVERVIEW OF THE SOUTHERN INDIAN OCEAN CIRCULATION USING A FINITE DIFFERENCE INVERSE MODEL

A finite-difference inverse model is used to quantify the large-scale ocean circulation in the Southern Indian Ocean. It is applied to a historical hydrographic data set, complemented with the CIVA and JADE data acquired as part of the French contribution to WOCE. The inverse model resolution is 1° in latitude and 2° in longitude. The dynamics are steady-state. The estimated circulation is in geostrophic balance and satisfies mass, heat and potential vorticity conservations. The wind and air-sea heat for! cings are annual means from ERS1 and ECMWF respectively. It is shown that the heat flux conservation controls the zonal-averaged meridional mass flux and that the potential vorticity balance is needed for realistic bottom circulation patterns.

The main features of the various current systems of the Southern Indian Ocean are quantified and reveal a topographic control of the deep and bottom circulation. The cyclonic Weddell Gyre is mainly baratropic, it transports 45 Sv, and has an eastern extension limited by the southern part of the Antarctic Circumpolar Current.

The bottom circulation north of 50°S is complex. However, the Deep Western Boundary Currents are identified as well as cyclonic recirculations.

Between 26°S and 32°S, the meridional overturning circulation amounts to 14.4 Sv, the maximum transport being observed at 1400m. The main contribution to the overturning circulation comes from east of the Mozambique Ridge due to a weak Agulhas Current of 55 Sv. At 32°S, east of the Mozambique Ridge, 11 Sv are transported by the Agulhas Undercurrent. The heat gain south of 32°S is 0.33 PW.