Parameterization of surface wind-driven currents in the Black Sea using drifters, wind, and altimetry data

Abstract

The original method is presented for parameterization of surface wind-driven currents in the Black Sea using drifters, altimetry, and wind data. Buoys velocities for the cases with small time variability of the altimetry-derived geostrophic currents were parameterized as a function of the amplitude coefficient b and rotation angle a between wind and residual current direction at drifter drogue depth ∼ 15 m. The results show that the variability of a and b for different cases is very high: angle a changes from 10 to 90° to the right, amplitude coefficient b varies from 0.01 to 0.03. At the same time, it is shown that amplitude coefficient b and rotation angle a on 15 m depth are not independent parameters and there is a robust dependence between them. Using quasi-Ekman theory and the revealed dependence, we can determine parameterization for wind-driven currents exactly on the surface. As a result, we found that wind-driven currents at z = 0 m are directed on b 0 = 13° to the right of wind direction with amplitudes equal to k = 2.8 % of wind velocity. It is important that these parameters did not depend on Ekman layer depth and can be used under different ocean conditions. This parameterization is used to compute the total surface currents and determine the trajectories of oil slick propagation observed on satellite images. Comparison shows that the presented method can be successfully used to predict floating objects trajectories basing on the satellite data.