Portal de Periódicos da CAPES

Effects of wave averaging on estimates of fluid mixing in the surf zone

2011; American Geophysical Union; Volume: 116; Issue: C4 Linguagem: Inglês

10.1029/2010jc006678

2156-2202

Joseph D. Geiman, James T. Kirby, Ad Reniers, Jamie MacMahan,

Tropical and Extratropical Cyclones Research

[1] Irrotational surface gravity waves approach the beach and break at a relatively high frequency, while vorticity generated by each new wave breaking event strongly interacts with the existing vorticity distribution at relatively low frequencies, leading to a surf zone that is energetic over a wide range of temporal scales. This poses a challenge to any surf zone model to accurately resolve all relevant scales. One approach to sidestep this issue is to use a short-wave-averaged model, where fast-scale wave effects are included as forcing terms for the mean current. This is in contrast to Boussinesq wave-resolving models, where each individual wave is resolved along with any ambient current. In general, these two models will predict different current fields for the same wave and bathymetric input and therefore predict different mixing behavior of the flow. Using Lagrangian methods, we compare wave-averaged and wave-resolving model results to data from the RCEX experiment, which mapped the rip current circulation over a rip-channeled bathymetry using nearshore surface drifters. Absolute and pair dispersion estimates, including the finite size Lyapunov exponent, based on virtual trajectories are shown to be consistent with field observations, except for scales less than 5 m, where field drifters predict greater pair dispersion than both models because of either unresolved subgrid processes or GPS error. A simple Lagrangian stochastic model is able to reproduce some of this short time and length scale diffusivity found in the observational data.