Global estimate of eddy dissipation from a diagnostic energy balance

Abstract

Mesoscale eddies play a key role in the transport and mixing of ocean tracers such as heat and carbon. They widely contribute to the stratification of the ocean and form the highest reservoir of kinetic energy. However, although baroclinic instabilities are believed to be a central mechanism of eddy generation, little is known about their dissipation. Notably, how and where the kinetic energy flows out from the mesoscale reservoir remains uncertain. In the ocean, the mechanical energy is dissipated by a variety of processes but only a small part occurs in the top few hundred meters of the water column, adding some difficulty to their measurement. Here, a simplified equation of the mesoscale energy budget is used to get a global estimation of the eddy dissipation rate. We first validate this framework in a global ocean simulation using a parameterized eddy energy budget. With the ocean stratification as the main input, we then apply this framework to an observation-based density climatology and a global reconstruction of the eddy kinetic energy field. We find a global mesoscale dissipation rate of about 0.45 TW, in agreement with recent independent estimates. The results also show an intense dissipation near western boundary currents, where both large levels of energy and large baroclinic conversion rates occur.  The resulting dissipation map brings new insights for closing the ocean kinetic energy budget as well as constraining future mesoscale parameterizations and associated mixing processes.