Submesoscale instabilities in mesoscale eddies
The lateral buoyancy gradients along with lateral and vertical shear of the flow can mean mesoscale eddies are unstable to submesoscale instabilities, particularly in the mixed layer. A wind stress at the surface of a mesoscale eddy leads to the input of potential vorticity on one side of the eddy and the extraction of potential vorticity at the other side of the eddy. This can lead to the type of instabilities that occur varying around the eddy as well as the growth rate of instabilities varying around the eddy.
I have examined the implications of this in a number of papers that are primarily based on idealised simulations of an eddying field. More information can be found here, while two papers have been published on this: the first as part of our examination of the seasonal cycle in a submesoscale model and a second looking at the mixed layer - thermocline exchange due to symmetric instability in an anticyclone. A further paper is in review at JPO that looks at the broader mix of submesoscale instabilities that may be found in mesoscale eddies
Dipole break-up and the formation of sub-surface anticyclones
Sub-surface anticyclones are routinely observed in the Arctic Ocean. Some of these are thought to originate from the instabilities of surface fronts. We carry out idealised simulations of surface fronts subject to a surface stress. We find that sub-surface eddies can form when cyclone-anticyclone dipoles are broken-up by the effect of the Ekman transport on the surface-layer cyclone. A short slideshow setting out the main results can be found here while the paper in JPO can be found here)