Lagrangian Measurement

A Lagrangian measurement follows a moving water parcel and records properties along its path, the complement to the Eulerian frame fixed in space. Surface drifters tracking the 15 m current, subsurface Argo floats drifting at park depth, and acoustically tracked RAFOS floats all return Lagrangian trajectories from which velocity is the time derivative of position. The frame maps where water goes, so it resolves dispersion, stirring, and connectivity between regions that fixed moorings cannot show. Lagrangian statistics, the integral time scale and the diffusivity tensor, parameterize eddy transport in models. The Global Drifter Program and Argo together supply the global Lagrangian record.