Measurements of the viscous tangential stress in the airflow above wind waves

The stress and drag at the surface of the ocean are crucial parameters for both short term forecasting and the modeling of long‐term global climate trends. However, the partition between viscous, turbulent, and wave stresses, and in particular the effects of airflow separation are not well understood. We present direct measurements of the velocity in the airflow above wind‐generated waves. We observe intermittent separation of the viscous sublayer past the crest of the wind waves leading to dramatic along‐wave variability in the surface viscous tangential stress. These results hold for wind speeds that would normally be considered low to moderate. These viscous stress measurements in the airflow above the wavy surface, and within the separated region are, to the best of the authors' knowledge, the first of this kind.