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

Abstract

International audienceWe present a new and fast method for blending altimetry and surface drifters data in the Eastern Levantine Mediterranean. The method is based on a vari-ational assimilation approach for which the velocity is corrected by matching real drifters positions with those predicted by a simple advection model, while taking into account the wind effect. The velocity correction is done in a time-continuous fashion by assimilating at once a whole trajectory of drifters using a sliding time window. Except for the wind component, the velocity is constrained to be divergence free. We show that with few drifters, our method improves the the estimation of velocity in two typical situations: an eddy between the Lebanese coast and Cyprus, and velocities along the Lebanese coast

Blending drifters and altimetric data to estimate surface currents: Application in the Levantine Mediterranean and objective validation with different data types

“…Variational methods that take into account the temporal variation within the optimization are called 4D-Var (Kamachi and O'Brien, 1995;Mead, 2005;Nodet, 2006;Carrier et al, 2014;Muscarella et al, 2015). A more detailed review of various assimilation methodologies can be found in Issa et al (2016).…”

“…From the application point of view, merging altimetry and in-situ data for a better estimation of the sea surface circulation has previously had several successful applications: for example in the Gulf of Mexico (Carrier et al, 2014;Muscarella et al, 2015;Berta et al, 2015), the Black Sea (Kubryakov and Stanichny, 2011;Stanichny et al, 2016), the North Pacific (Uchida and Imawaki, 2003), and the Mediterranean Sea (Taillandier et al, 2006;Menna et al, 2012;Issa et al, 2016), each of them using different methodologies for merging.…”

“…The variational assimilation algorithm used by Issa et al (2016) proved its efficiency in the Eastern Levantine Mediterranean region, specifically along the Lebanese coast and in the region between Lebanon and Cyprus. Sensitivity analyses showed that the velocity estimation can be improved significantly even with only a small number of drifters.…”

“…The contribution of the current work is two-fold: (i) a further extension of the application of the previous algorithm by Issa et al (2016) in the Levantine Mediterranean and (ii) an objective validation of the algorithm, using reliable tools/data independent of the algorithm itself. In particular, we use four different types of independent data: first, a current meter moored off Libya is used to validate the algorithm results in terms of velocity intensity and direction.…”

Reconstructing Large- and Mesoscale Dynamics in the Black Sea Region from Satellite Imagery and Altimetry Data—A Comparison of Two Methods

“…Third, altimetry-derived velocities are geostrophic and represent only a part, also very important, of the current velocity [31]. Wind-driven currents are another important part of the surface currents, and should be additionally described using different assumptions [32][33][34][35] to reconstruct total surface currents on the basis of satellite altimetry. Such an approach was used, for example, to simulate drift trajectories or oil spill propagation [34,36], and it was shown that it may perform better than the data assimilative models in [36].…”