Quasi-objective eddy visualization from sparse drifter data.

We employ a recently developed single-trajectory Lagrangian diagnostic tool, the trajectory rotation average ( TRA ¯ ), to visualize oceanic vortices (or eddies) from sparse drifter data. We apply the TRA ¯ to two drifter data sets that cover various oceanographic scales: the Grand Lagrangian Deployment and the Global Drifter Program. Based on the TRA ¯, we develop a general algorithm that extracts approximate eddy boundaries. We find that the 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.