Eddy forcing of the mean flow in the Southern Ocean

Abstract

We examine the force (or acceleration) exerted by eddies on the mean flow of the Southern Ocean using mapped sea surface height anomalies derived from satellite altimeter measurements. We compare this with the position of jets in the mean flow indicated by regions of increased gradient in the mean sea surface temperature. The eddy force itself is not of primary importance; rather, the curl of that force affects the mean flow, so the irrotational force due to the gradient of eddy kinetic energy can be ignored, leaving a remainder that can be interpreted in terms of the eddy vorticity flux. Unlike previous modeling and altimetric studies, we find that the eddies act to decelerate some of the strongest jets and act as vorticity sources for others. The strongest jets are clearly not accelerated by eddies. A problem of interpretation does remain, however, since it is not clear how sea surface temperatures are related to the mean flow. This ambiguity can only be completely resolved by measurement of the mean flow, requiring a geoid that is accurate at length scales of order 100 km.