A robust framework for comparing Lagrangian and gridded Eulerian velocity fields: an example application to surface drifters and altimetry-derived surface currents

Abstract. A novel framework for comparing Lagrangian and gridded Eulerian velocity fields is proposed. The method involves three steps that individually leverage the strengths of each reference frame to provide robust intercomparisons, while also allowing the user to adapt the individual steps to the process of interest. The utility of the methodology is then demonstrated by applying it to a comparison between a set of 34 Lagrangian surface drifters deployed on the continental shelf around the southern tip of Greenland and Eulerian altimetry-derived surface currents with and without Ekman velocities. We conclude that the methodology sufficiently addresses differences between the reference frames and accurately identifies errors when they exist. This result enables us to conclude that the altimetry-derived surface currents accurately resolve the important components of the shelf circulation around the southern tip of Greenland and can be used to track pathways of fresh water around Greenland.