Effects of wave averaging on estimates of fluid mixing in the surf zone
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 ra...
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| Published in: | Journal of Geophysical Research Vol. 116; no. C4 |
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| Main Authors: | , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Washington
Blackwell Publishing Ltd
01-04-2011
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | 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.
Key Points
Wave‐resolving/averaged models perform similarly for rip channel bathymetry
Delft3D generates more coherent, large‐scale rip current eddies
Funwave generates less coherent eddies, which mix small scales more efficiently |
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| Bibliography: | istex:5C6F6568C2EF6D792082BB18D954D6498ECDE79A ark:/67375/WNG-BTS3VFF8-Z ArticleID:2010JC006678 Tab-delimited Table 1.Tab-delimited Table 2. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0148-0227 2169-9275 2156-2202 2169-9291 |
| DOI: | 10.1029/2010JC006678 |