Langmuir Turbulence in Algebraic Reynolds Stress Models (Invited Presentation)

The algebraic Reynolds stress model (ARSM) for second moment closure (SMC) is modified for Langmuir turbulence by the introduction of the Craik-Leibovich (CL) vortex force in the momentum equation, representing the interaction of turbulence with the surface wave Stokes drift. In addition to CL production of turbulent kinetic energy (TKE), new terms appear in the ARSM for TKE anisotropy and for vertical fluxes of momentum. The former is consistent with the observed elevation of vertical TKE with surface waves in the ocean, and the latter requires that a component of the vertical flux of momentum be directed down the gradient of the Stokes drift. An inhomogeneous near-surface pressure-strain closure is also necessary to represent the redirection of Langmuir jet downwelling into the transverse surface recirculation of counter-rotating vortex rolls, and an associated reduction in the generation of momentum flux restores downwind Eulerian shear within the top few meters. SMC model results are compared with observations and LES solutions.