Shallow overturning circulation of the Western Indian Ocean

The Indian Ocean differs from the other two oceans in not possessing an eastern equatorial upwelling regime. Instead, the upwelling occurs dominantly in the northwestern Arabian Sea and, to a lesser degree, around the Indian subcontinent. Subduction, on the other hand, occurs dominantly in the Southern Hemisphere. The result is a shallow Cross-Equatorial Cell connecting both regimes. The northward flow at thermocline levels occurs as part of the Somali Current and the southward upper-layer return flow is carried by the Ekman transports that are directed southward in both hemispheres. The main forcing is by the Southwest Monsoon that overwhelms the effects of the Northeast Monsoon and is the cause for the annual mean Northern Hemisphere upwelling and southward Ekman transports. In the Southern Hemisphere, the annual mean upwelling at the northern rim of the Southeast Trades causes a zonally extended open-ocean upwelling regime that is apparent in isopycnal doming in the 3-12 degrees S band; it drives a shallow Subtropical Cell.