Results from a numerical model of the northern Indian Ocean: circulation in the south Arabian Sea

A three-dimensional primitive equation numerical circulation model has been applied to the northern Indian Ocean. The model domain extends from 20°S to the Asian continent in the north and from Africa in the west to 120°E. The high vertical resolution of the model enables a better depiction of the vertical structure and processes in the upper layers than has been hitherto possible. The model also accounts for the large fresh water inputs from rivers on the Indian subcontinent. We describe here the results from a climatological simulation forced by monthly climatological winds, focusing principally on the southern Arabian Sea. The model results are supplemented with observational data from the NASA TOPEX altimeter to study the circulation in the northern Indian Ocean. Overall, the model successfully captures many of the important circulation features observed. This includes the reversing Somali Current in the Arabian Sea and the equatorial current system. Along the southwest coast of India, an anticyclonic feature known as the c has been observed to form during northeast monsoon and propagate to the west. A cyclonic feature also forms in the same location during the southwest monsoon. The formation and propagation of these features are central to the circulation and variability of the southern Arabian Sea and are clearly seen in TOPEX altimetric records for 1993 and 1994. They are also reasonably well depicted in the climatological simulations presented here.