The Impact of Surfactants on the Airflow Above Wind Waves

Abstract We investigate phase‐dependent features of the airflow above wind waves on slick‐free and slick‐covered water surfaces and relate them to small‐scale wave structures. Three surfactants with different viscoelastic properties were deployed in a wind‐wave tank, with wind speeds between and . In slick‐free conditions, the airflow exhibits pronounced phase‐locked asymmetries, including reduced wind speeds extending from the leeward side of wave crests across the troughs. Small‐scale roughness patterns, likely associated with capillary waves trailing the crests, modulate the airflow in subsequent wave phases. In contrast, surfactants suppress high‐frequency slope roughness, resulting in increased shear near the surface under nearly all conditions, suggesting a more closely attached boundary layer. Strength and persistence of these effects vary with surfactant type and wind speed, influencing both wave growth and air–sea momentum exchange.