Meridional overturning and large-scale circulation of the Indian Ocean

Abstract

The large scale Indian Ocean circulation is estimated from a global hydrographic inverse geostrophic box model with a focus on the meridional overturning circulation (MOC). The global model is based on selected recent World Ocean Circulation Experiment (WOCE) sections which in the Indian Basin consist of zonal sections at 32° S, 20° S and 8° S, and a section between Bali and Australia from the Java-Australia Dynamic Experiment (JADE). The circulation is required to conserve mass, salinity, heat, silica and "PO" (170PO4+O2). Near-conservation is imposed within layers bounded by neutral surfaces, while permitting advective and diffusive exchanges between the layers. Conceptually, the derived circulation is an estimate of the average circulation for the period 1987-1995. A deep inflow into the Indian Basin of 11 ± 4 Sv is found, which is in the lower range of previous estimates, but consistent with conservation requirements and the global data set. The Indonesian Throughflow (ITF) is estimated at 15 ± 5 Sv. The flow in the Mozambique Channel is of the same magnitude, implying a weak net flow between Madagascar and Australia. A net evaporation of -0.6 ± 0.4 Sv is found between 32° S and 8° S, consistent with independent estimates. No net heat gain is found over the Indian Basin (0.1 ± 0.2 PW north of 32° S) as a consequence of the large warm water influx from the ITF. Through the use of anomaly equations, the average dianeutral upwelling and diffusion between the sections are required and resolved, with values in the range 1-3×10-5 cm s-1 for the upwelling and 2-10 cm2 s-1 for the diffusivity. Copyright 2000 by the American Geophysical Union.