Determining flow field singularities from drifter trajectories

We use the method developed by Kirwan et al. and Halide to obtain the differential kinematic properties (DKP) and the position and velocity of a flow field singularity from a single drifter trajectory. This method, hereinafter called the OK method, has been successfully tested using artificial trajectories that were generated from flow fields containing one singularity. The OK method requires fourth‐order time derivatives of data. A new regression method that calculates DKP from a cluster of drifters is presented. This new regression method does not artificially set the flow center to the cluster centroid. It has been successfully tested by application to the trajectories generated from flow fields containing one singularity. Depending upon the spatial distribution of drifters relative to the singularity, the new regression method can be much less sensitive to noise than the OK method. Trajectories generated by flow fields with both saddle and vortex points were analyzed. Both methods worked when trajectories were close to the singularity, but not otherwise. Trajectories measured on the Scotian shelf were not amenable to either method of analysis, presumably because the trajectories did not result from only one singularity.