Observations of Turbulence Mixing and Vorticity in a Littoral Surface Boundary Layer

Abstract Measurements of small-scale vorticity, turbulence velocity, and dissipation rates of turbulence kinetic energy e were taken in a littoral fetch-limited surface wave boundary layer. Drifters deployed on the surface formed convergence streaks with ∼1-m horizontal spacing within a few minutes. In the interior, however, no organized pattern of velocity, vorticity, or turbulence mixing intensity was found at a similar horizontal spatial scale. The turbulent Langmuir number La was 0.6–1.3, much larger than the 0.3 of the typical open ocean, suggesting comparable importance of wind-driven turbulence and Langmuir circulation. Observed e are explained by the wind-driven shear turbulence. The production rate of turbulence kinetic energy associated with the vortex force is about 10−7 W kg−1, slightly smaller than that generated by the wind-driven turbulence. The rms values of the streakwise component of vorticity σζ|| and the vertical component of vorticity σζz have a similar magnitude of ∼0.02 s−1. Vertica...