Quasi-Objective Eddy Visualization from Sparse Drifter Data

We employ a recently developed single-trajectory Lagrangian diagnostic tool, the trajectory rotation average $(\mathrm{\overline{TRA}})$, to visualize oceanic vortices (or eddies) from sparse drifter data. We apply the $\mathrm{\overline{TRA}}$ to two drifter data sets that cover various oceanographic scales: the Grand Lagrangian Deployment (GLAD) and the Global Drifter Program (GDP). Based on the $\mathrm{\overline{TRA}}$, we develop a general algorithm that extracts approximate eddy boundaries. We find that the $\mathrm{\overline{TRA}}$ outperforms other available single-trajectory-based eddy detection methodologies on sparse drifter data and identifies eddies on scales that are unresolved by satellite-altimetry.