The Sea Surface Current Response to Wave and Wind: Numerical Modeling and Observations from Lagrangian Drifters

Motivated by data of the sea surface currents collected from 62 Lagrangian (iSphere and CODE-type) drifters, we investigate the wind-wave-current-turbulence interactions at the sea surface under different forcing conditions based on a one-dimensional (1D) water-column mixing model, implemented along the pathway of each drifter. To realistically account for the influence of surface gravity waves on drift velocities, the wind and wave data from the NORA10 hindcast along the trajectory of each drifter is used to specify the forcing in a dynamical model for the surface currents. The vertical mixing is modified further to include the effects of wave-current and wave-turbulence interactions, i.e. Coriolis-Stokes forcing, wave breaking, non-breaking waves, and Langmuir turbulence. The main objective is to study the roles of surface gravity waves and the misalignment between the wind and wave fields on the variability of the surface currents. We further study the spectral relationships between the measured surface current from drifters, wind, and the numerically predicted current. A rotary spectral analysis shows coherency between surface current and wind above the inertial frequency. Furthermore, the amount of estimated energy along the trajectory of each drifter to the upper ocean Ekman layer is closely linked to the quality of the total surface current decomposition into the quasi-Eulerian current and wave-induced Stokes drift. It is also specific concern how the reconstructed surface velocities from the 1D wave-modified model outputs along with the drifter data can improve the prediction of Lagrangian transport in coastal flows.