799 / 2024-09-19 13:54:08

The 3D dynamic structures of rip currents with a wave-current two-way coupling simulation

Rip currents,3D modelling,Wave-current interaction

Bathymetric rips are small-scale surf zone processes influenced by alongshore three-dimensional (3D) morphology. The generation of these rips results from wave-current-topography interactions. Rip currents represent a form of wave effects on current (WEC), which are driven by wave breaking and vortex force. Conversely, current effects on wave (CEW) can also modulate rip current behaviors, including wave refraction as waves propagate through spatially varying current fields and the increase in wave steepness due to localized wave height concentrations. Therefore, the wave-current interactions are a major factor that dictates the generation and evolution of rip currents. In this study, we utilize the Coastal and Regional Ocean Community Model (CROCO) to conduct two simulations with idealized bathymetry: one with CEW and the other without. The results reveal the 3D structure of rip currents, which are not well examined in the previous studies, particularly those based on the Boussinesq-type equation. Specifically, the flow field features a surface-intensified, depth-dependency structure where a counter-rotating vertical overturning cell is present in the rip trough/channel. The vorticity budget analysis further demonstrates that such vertical structure is mainly caused by the advection, stretching, and tilting of the vortex instead of local wave forcing or bottom friction. The CEW, on the other hand, reduces the intensity of rip currents, leading to a more localized and confined rip current structure. Thus, CEW alters the vertical distribution of velocity and enhances the asymmetry of the rip current’s structure, which could have implications for sediment transport and mixing within the surf zone.