EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Tidal asymmetry in the Sylt-Romo Bight, south-eastern North Sea

Vera Fofonova, Alexey Androsov, Lasse Sander, Ivan Kuznetsov, Felipe Amorim, H. Christian Hass, Finn Mielck, and Karen Helen Wiltshire
Vera Fofonova et al.
  • The Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany (


The study is dedicated to the tidal dynamics in the Sylt-Rømø 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 grids 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 Højer and Rømø 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. 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 results as well as fulfillment of the energy balance. The tidal residual circulation and asymmetric tidal cycles largely define the circulation pattern, transport and accumulation of sediment and the distribution of bedforms in the bight, therefore the results are necessary and useful benchmarks for further studies in the area, including baroclinic and sediment dynamics investigations.

How to cite: Fofonova, V., Androsov, A., Sander, L., Kuznetsov, I., Amorim, F., Hass, H. C., Mielck, F., and Wiltshire, K. H.: Tidal asymmetry in the Sylt-Romo Bight, south-eastern North Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1359,, 2019

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Presentation version 1 – uploaded on 26 Apr 2020
  • CC1: Comment on EGU2020-1359, Joice Cagliari, 04 May 2020

    Dear authors,

    How the bedform peculiarities added to your results?


    • AC1: Reply to CC1, Vera Fofonova, 04 May 2020

      Dear Joice,

      That is a very good question as soon as the bedform peculiarities influence the penetration of the tidal signal, however the tidal waves in turn modify bedforms. In our case we used a 'constant' bathymetry data of very high quality (the spatial resolution is about 2-50 meters)  and fixed bottom friction coefficient (however, we have chosen it based on observations available). With a such approximation we were able to predict the bedform peculiarities shown on slide 5. 


      • CC2: Reply to AC1, Joice Cagliari, 04 May 2020

        Thank you Vera. Bedforms of slide 5 are really interesting. Let me ask you another questions. What do you mean by tidal residual circulation? Is it the difference between flood and ebb flows?

        • AC2: Reply to CC2, Vera Fofonova, 05 May 2020

          Dear Joice,

          It is a residual circulation  of the summary tide for the full tidal cycle -29.5 days  (lunar cycle in relation to the Earth, from the New Moon to the New Moon). Thank you for the question!

          Kind regards, Vera