Invited Paper: Eddy-mixed layer interactions: theory and parameterizations

Eddy transport of large-scale momentum and material tracers exert a profound influence on the oceanic general circulation, and on the exchange of heat, freshwater, and anthropogenic tracers between the ocean and the atmosphere. In the stratified interior, the eddy transport is dominated by geostrophic eddies and it is directed along density surfaces. At the ocean surface the presence of boundaries and air-sea fluxes upsets the geostrophic balance and breaks the adiabatic constraint. A climate process team composed of scientists from 10 different institutions has been funded by NSF and NOAA to study the physics of eddy transport in the upper ocean, its representation in ocean models, and its climate impact. In the first part of the talk I will discuss the physics of eddy transport at the ocean surface focusing on: modification of air-sea fluxes by the mesoscale eddy field, restratification and destratification of the upper ocean by mesoscale frontogenesis and subsequent frontal instabilities, coupling between geostrophic eddies and small-scale turbulence through loss of balance. I will show that these processes strongly modulate air-sea fluxes, sea surface temperatures, mixed layer depth, and the properties of waters subducted in the ocean interior. In the second part of the talk I will present parameterization schemes that reproduce the physics of upper ocean eddies and discuss their climate sensitivity in general circulation models.