The Time-Dependent Vertical Structure of Mixed-Layer Currents

The vertical structure of ocean boundary layer flow is of first-order importance to a wide-variety of phenomenon, however measurement challenges continue to limit the availability of upper ocean velocity data. Here we report on a unique long record of moored high-resolution velocity observations spanning the upper 30 m at 10°S, 10°W. Frequency-domain analysis reveals that the vertical structure of wind-coherent currents is consistent with a simple time-dependent Ekman model. The role of stratification in limiting the penetration of wind-driven momentum is particularly evident in the near-inertial band. The effects of surface waves and horizontal buoyancy gradients on the observed near-surface currents are also considered in light of recent theoretical advances on the frictional dynamics of the ocean surface boundary layer.