Sack Lunch Seminar (SLS)

Competition between Chaotic Advection and Diffusion: Stirring and Mixing in a 3D Eddy Model

In submesoscale ocean features, both vertical motions and diffusion can be non-negligible factors. Vertical motions allow for chaotic advection to be present even in steady flows, as has been shown for an Ekman-driven rotating cylinder analogue of a submesoscale eddy. The current work considers the importance of diffusion as compared to chaotic advection for tracers in this rotating cylinder. Three methods are used to quantify the relative importance: scaling arguments; the spread of ensembles of trajectories; and numerical simulations of dye release. Through these complementary methods, I show that chaotic advection will dominate turbulent diffusion in the widest chaotic regions. In thin chaotic regions, diffusion is at least as important as chaotic advection. This scale separation indicates a lower limit to when Lagrangian coherent structures are useful.