CoAuthors

Claire Dufau (CLS, France); Hélène Etienne (CLS , France); Sandrine Mulet (CLS, France)

Accurate estimate of ocean surface currents is both a challenging issue and a growing end-users requirement. Advancing the quantitative estimation of ocean surface currents from satellite sensor synergy and demonstrating the impact in user-led scientific, operational and commercial applications is the main objective of the GlobCurrent project, a Data User Element (DUE) from the European Space Agency (ESA). In the framework of this study, a global reanalysis of 12 years (2002-2014) of global ocean currents at two depths (surface and 15m) has been calculated as the sum of the geostrophic and Ekman components. The geostrophic component is based on the SSALTO-DUACS multimission altimeter maps of velocity and the CNES-CLS13 Mean Dyanmic Topography. Ekman currents at two levels (surface and 15m) are calculated from an empirical model. The model parameters (amplitude and angle) have been derived as to minimize the misfit between wind stress data and the ageostrophic component extracted from in-situ drifter velocities (SVP drifters at 15m depth, Argo floats at the surface). Parameters have been fitted by month, longitude and latitude and a number of tests have been performed to investigate the impact of taking into account other information as the Mixed Layer Depth (from an Argo floats based climatology), effective wind stress, and Stokes drift from the WaveWatchIII model. The best model accounts for up to 50% of the observations variability. Currents have been calculated over a 12 years period (2002-2014) and validated through comparison to independent in-situ observations and other existing observed products.