Meridional overturning and large-scale circulation of the Indian Ocean

The large scale Indian Ocean circulation is estimated from a global hydrogr aphic inverse geostrophic box model with a focus on the meridional overturn ing circulation (MOC), The global model is based an selected recent World O cean Circulation Experiment (WOCE) sections which in the Indian Basin consi st of zonal sections at 32 degreesS, 20 degreesS and 8 degreesS, and a sect ion between Bah and Australia from the Java-Australia Dynamic Experiment (J ADE). The circulation is required to conserve mass, salinity, heat, silica and "PO" (170PO(4)+O-2). Near-conservation is imposed within layers bounded by neutral surfaces, while permitting advective and diffusive exchanges be tween the layers. Conceptually, the derived circulation is an estimate of t he average circulation for the period 1987-1995. A deep inflow into the Ind ian Basin of 11 +/- 4 Sv is found, which is in the lower range of previous estimates, but consistent with conservation requirements and the global. da ta set. The Indonesian Throughflow (ITF) is estimated at 15 +/- 5 Sv. The f low 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 S v is found between 32 degreesS and 8 degreesS, consistent with independent estimates. No net heat gain is found over the Indian Basin (0.1 +/- 0.2 PW north of 32 degreesS) as a consequence of the large warm water influx from the ITF. Through the use of anomaly equations, the average dianeutral upwel ling and diffusion between the sections are required and resolved, with val ues in the range 1-3 x 10(-5) cms(-1) for the upwelling and 2-10 cm(2) s(-1 ) for the diffusivity.