Ocean Surface Currents (OSC) can be considered as the cumulative results of local and remote factors, including highly variable winds, surface and internal waves, tides, mixed layer depth and buoyancy fluxes. Interacting with larger scale flows, the influence of these random forces on OSC is not trivial. As often observed, this can lead to well ordered and long lived coherent mesoscale structures, with horizontal scales of 30-300 km, and with time scales of 3-30 days. But, local and non-local interactions also induce transient frontal sub-mesoscale structures, developing complicated patterns with eddies, filaments and shear currents with horizontal scales of 1-10 km, vertical scales of 50-200 m, and ephemeral time scales of 1-3 days.

Although surface currents in the ocean are not the simple addition of different current components, in this first version of GlobCurrent products the combined currents are intended as the sum (referred to as total current) of the geostrophic and the Ekman components at the surface. Another product provides similar combined currents at 15m depth. The geostrophic and ekman components are available independently in two other different GlobCurrent products.

25 years of data are available, spanning the period from the beginning of 1993 to the end of 2017, on a 1/25° resolution grid and with a 3-hourly temporal resolution. More details on the calculation of the single components of this combined current can be found in the GlobCurrent Algorithm Theoretical Baseline Document, in the geostrophic currents handbooks and in the Ekman currents handbook. In particular, it should be noted that despite the high temporal (3-hourly) and spatial (1/25°) resolution of the GlobCurrent products grids, by construction, the effective resolution of the geostrophic and Ekman currents is of the order of 5-10 days / 50-100 km. These resolutions will be improved in the future versions of the GlobCurrent products. In addition, due to the reduced accuracy of altimeter measurements in coastal areas, users should be aware that some geostrophic velocities in very local areas close to the coast may be erroneous. These velocities will be flagged in the future versions of the GlobCurrent products.