Vertical mixing by Langmuir circulations

Wind and surface wave frequently induce Langmuir circulations (LC) in the u pper ocean, and the LC contribute to mixing materials down from the surface . In this paper we analyze large-eddy simulation (LES) cases based on surfa ce-wave-averaged, dynamical equations and show that the effect of the LC is a great increase in the vertical mixing efficiency for both material prope rties and momentum. We provide new confirmation that the previously propose d K-profile parameterization (KPP) model accurately characterizes the turbu lent transport in a weakly convective, wind-driven boundary layer,vith stab le interior stratification. We also propose a modest generalization of KPP for the regime of weakly convective Langmuir turbulence. This makes the KPP turbulent flux profiles match those in the LES case with LC present fairly well, especially so for material properties being transported downwards fr om the ocean surface. However, some open issues remain about how well the p resent LES and KPP formulations represent Langmuir turbulence, in part beca use wave-breaking effects are not yet included. (C) 2001 Elsevier Science L td, All rights reserved.