The oceanic boundary layer driven by wave breaking with stochastic variability. Part 1. Direct numerical simulations

摘要: We devise a stochastic model for the effects of breaking waves and fit its distribution functions to laboratory field data. This is used represent space–time structure momentum energy forcing oceanic boundary layer in turbulence-resolving simulations. The aptness this breaker evaluated direct numerical simulation (DNS) an otherwise quiescent fluid driven by isolated wave, results are good agreement with measurements. faithfully reproduces bulk features event: mean kinetic decays at rate approaching $t^{-1}$ , long-lived vortex (eddy) generated close water surface. long lifetime (more than 50 wave periods) makes it effective energizing surface region layers. Next, comparison several different DNS idealized layers (i.e. constant current (as Couette flow), stress, or mixture stress plus breakers) elucidates importance intermittent transmission underlying currents. A small amount active breaking, about 1.6% total area any instant time, significantly alters instantaneous flow patterns as well ensemble statistics. Near vigorous downwelling–upwelling pattern develops head tail each three-dimensional breaker. enhances vertical velocity variance generates both negative- positive-signed flux. Analysis scalar profiles shows that effectively increases roughness $z_o$ more factor 30; our simulations $z_o/\lambda \,{\approx}\, 0.04$ 0.06, where $\lambda$ wavelength wave. Compared current, extra mixing from breakers eddy viscosity 10 near Breaking alter usual balance production dissipation turbulent (TKE) budget; pressure transports work important sources sinks budget. also show no breaking) differ fundamental ways. additional freedom provided constant-stress condition permits finite variances surface, so flows mimic weakly statistically homogeneous waves.