Non-linear aspects of the tidal dynamics in the Sylt-Rømø Bight,south-eastern North Sea

Abstract. This study investigates the tidal dynamics in the Sylt-Romo bight with a focus on the non-linear processes. The FESOM-C model was used as the numerical tool, which works with triangular, rectangular or mixed meshes and is equipped with a wetting/drying option. As the model's success at resolving currents largely depends on the quality of the bathymetric data, we have created a new bathymetric map for an area based on recent studies of Lister Deep, Lister Ley, and the Hojer and Romo Deep areas. This new bathymetric product made it feasible to work with high resolution grids (up to 2 m in the wetting/drying zone). As a result, we were able to study the tidal energy transformation and the role of higher harmonics in the domain in detail. For the first time, the tidal ellipses, maximum tidally-induced velocities, energy fluxes and residual circulation maps were constructed and analysed for the entire bight. Additionally, tidal asymmetry maps were introduced and constructed. The full analysis was performed on two grids with different structures and showed a convergence of the obtained results as well as fulfillment of the energy balance. A great deal of attention has been paid to the selection of open boundary conditions, model verification against available tide gauges, and recent ADCP data. The obtained results are necessary and useful benchmarks for further studies in the area, including baroclinic and sediment dynamics tasks.