Interfacial Mixing by Horizontal Vortices and Shear Turbulence

Summary

In this paper the entrainment rates of shear flows and turbulent Taylor vortices are considered in the light of the mixed-layer deepening in oceans, seas and lakes. The entrainment by Taylor vortices can be considered to represent a model for entrainment by continuously driven horizontal vortices such as Langmuir circulation. When the forcing is related to the surface wind stress, the interfacial entrainment by Langmuir vortices can be estimated from the experimental results on turbulent Taylor vortices, and compared with the entrainment rates in pure shear-flows. The results indicate that mixing by Langmuir vortices is important for all Richardson numbers, Ri _∗ (based on wind-induced surface stress velocity), and that for Ri _∗ > 80 Langmuir vortices dominate the mixed-layer deepening.