Observations of mean and wave orbital flows in the upper centimeters of the ocean surface layer

The near-surface current response to wind forcing and wave-induced motions is a topic of fundamental interest within air-sea interaction. However, obtaining measurements of fluid velocity close to an undulating boundary presents a unique observational challenge. Here we describe first-of-their-kind thermal and polarimetric camera-based observations of wave orbital velocities and mean shear flows in the upper centimeters of the ocean surface layer, gathered aboard the "laboratory at sea" R/P FLIP. Measurements reveal a well defined logarithmic layer as seen in laboratory measurements and described by classical surface layer theory. Measured orbital velocity magnitudes are generally found to agree well with the prescriptions of linear wave theory, with departures at high levels of wind forcing attributed to the effects of microscale wave breaking. Measurements of wave characteristics and near-surface current during heavy rain indicate an acceleration of current near the sea surface. These phenomena are broadly important to the processes of upper-ocean mixing and global ocean-atmosphere interaction.