Abstract

In contrast with the atmosphere, which is heated from below by solar radiation, the ocean is heated and cooled at the surface. To drive a large-scale overturning circulation in this context, it is generally assumed that either interior mixing by winds and tides, or wind-driven pumping is required; in their absence, the circulation is thought to collapse to a shallow surface cell. We demonstrate, using a primitive equation model with an idealized domain, that surface temperature forcing alone can drive an inter-hemisphere overturning provided that there is a channel unblocked in the zonal direction, such as in the Southern Ocean. With this geometry, rotating horizontal convection, in combination with asymmetric surface cooling between the north and south, drives a deep-reaching two-cell overturning circulation. The resulting vertical stratification closely resembles that in the real ocean, suggesting buoyancy forcing plays a much larger role in the climate system than usually assumed.