Tracer Stirring Around a Meddy : The Formation of Layering

Abstract:

The dynamics of the formation of layering surrounding meddy-like vortex lenses is investigated from a tracer stirring point of view using a tracer advection model as well as Primitive Equation (PE) and Quasi Geostrophic (QG) models. Recent in situ data inside a meddy as well as high resolution PE simulations reveal the formation of highly density-compensated layers in temperature and salinity at the periphery of the vortex core. Passive tracer experiments suggest that the vertical variance cascade is triggered by the vertical shear of the azimuthal velocity field resulting in the generation of thin layers. The time evolution of this process down to scales of O(10m) is quantified and a simple scaling is proposed and shown to describe precisely the thinning down of the layers as a function of the initial azimuthal tracer gradients and the vertical shear of the azimuthal velocity. Non-linear QG simulations were performed and analysed and a step-by-step interpretation of these results on the evolution of layering is proposed in the context of tracer stirring.