Drift in the uppermost part of the ocean

Abstract

Lagrangian drift velocities within the uppermost meter of the ocean mostly depend on the local wind forcing, turbulent mixing, and waves. While the interior part of the Ekman layer has been extensively studied using drogued drifters, the drift at - or very close to - the surface is less investigated. The wind response of surface currents on time scales from 1 h to 10 days is analyzed using two types of satellite-tracked drifters: (i) spherical floats on the surface and (ii) drifters with a drogue centered at 70 cm depth. The response of drifting objects to wind and wave forcing is highly dependent on the vertical position, even within the upper meter of the ocean. The surface drifters are wind coherent for both cyclonic and anticyclonic subinertial frequencies. In contrast, the subsurface drift responds primarily to anticyclonic forcing that resonates with the intrinsic ocean dynamics.