Modelling surface currents in the Eastern Levantine Mediterranean using surface drifters and satellite altimetry

•We present an efficient algorithm that blends drifter data and altimetry data.•It is used to continuously improve surface velocity estimation in the East-Med.•Assimilating a drifter datum gives correction in a radius of 20 km and a 24 h window.•Improvement of velocity estimation is shown near the Lebanese coast.•Accurate eddy estimation (dimension and intensity) in S.E. of Cyprus is shown.

We present a new and fast method that blends altimetric and drifter positions data in order to predict the surface velocity in the Eastern Levantine Mediterranean. The method relies on a variational assimilation approach where a velocity correction is continuously obtained by matching observed drifter positions with those predicted by a simple advection model. The background velocity used in the advection of the drifters is the aggregate of a geostrophic and a wind-driven component and the velocity correction is constrained to be divergence free. The algorithm employs a sliding time window that assimilates at once and inside each frame, an entire trajectory of drifters. We show that with few drifters, our method improves the estimation of velocity in two typical situations: an eddy between the Lebanese coast and Cyprus, and velocities along the Lebanese coast.