High Frequency radars for surface current measurements enable us to reconstruct quasi-synoptic maps of ocean surface velocity field, over large areas and at high spatial (100s of meter) and temporal (30 min) resolutions. These surface current observations allow the computation of Lagrangian trajectories of many virtual particles. Based on these trajectories, one can compute various measures for mixing and identified Lagrangian Coherent Structures.
I will demonstrate, using surface current measurements by High Frequency radar, the existence of temporary submesoscale barriers to mixing, which has important implications for a wide range of predictions. We were also able to verify the existence of these barriers using aerial-photographs. Using a non-stationary Lagrangian stochastic model, I will present a method for estimating the upper bound of the horizontal eddy diffusivity based on the existence of such barriers. Last, by introducing weak vertical motion associated with diurnal convection into the horizontal, time-periodic double-gyre toy model, I will show that the weak vertical motion simplifies the chaotic surface mixing pattern for a wide range of parameters.