Collocations of surface drifter and GlobCurrent (centered five-day) 15-m zonal and meridional velocity estimates

GlobCurrent is an analysis that linearly combines the geostrophic and Ekman components. Drifters respond locally to a combination of geostrophic, Ekman, tidal, inertial, Stokes, and wind drift processes, including processes on scales smaller and faster than the GlobCurrent grid can resolve. Collocations of drifters (whose drogues move roughly with the 15-m current) and GlobCurrent (also at 15 m, with additional samples at daily intervals from two days before to two days after collocation) are included in this dataset. Six-hourly drifter velocity has been estimated following Hansen and Poulain (1996). We restrict attention to drifters whose continuous drogue presence was confirmed by objective or subjective means (Rio et al. 2012, Lumpkin et al. 2013). The resulting geographic distribution for 1993-2015 (Fig. 1) yields more than eleven million drifter and GlobCurrent zonal and meridional velocity estimates. (A comparable number of drifters lost their drogues and, being more responsive to surface wind forcing, are omitted.)