CoAuthors

Marie-Hélène Rio (CLS, France); Isabelle Pujol (CLS, France); Gilles Reverdin (LOCEAN, France); Nicolas Kolodziejczyk (LOCEAN, France)

We investigate the surface current variability in the North Atlantic subtropical gyre during the Sub-tropical Atlantic surface salinity experiment Strasse/SPURS in August 2012-September 2013, based on altimetric current products and surface drifters drogued at 15-meters. More than 100 drifters were deployed for this experiment which provide some estimate of current circulation, as well as temperature and salinity data. First, we investigate the wind-component in the surface drifter velocities, following Rio et al (2012)'s approach, as a linear response to wind stress. We find a large seasonal cycle in the low-pass (filtering at 30-hours) drifter velocities response to wind stress, with highest proportional response during summer, and a fast transition through spring. Based on contemporary Argo float data, this seems inversely proportional to mixed layer depth. The drifter current response to wind stress differs only slightly from what is found using earlier drifters in the same region, and shows a spring intensity increase, which is very pronounced. These data sets suggest some remaining biases in the mean AVISO product altimetric currents, with small differences between the two drifter data sets which will be discussed. We then investigate the use of regional altimetric mapped sea level and geostrophic currents using a corrected average current field. The characteristics of the along-track filtering of the altimetric data and the parameters of the objective mapping have been optimized for this region in order to retain as much of the signal as possible, but to avoid increasing too much the 'noise' and errors in the estimated currents. This implies in particular less along track filtering than is currently done. Based on comparison to the drifter currents and the oceanographic surveys of Strasse/SPURS, we will discuss the performance of this new product, during periods when data from three satellite missions could be combined.