Articles | Volume 13, issue 2
https://doi.org/10.5194/os-13-289-2017
https://doi.org/10.5194/os-13-289-2017
Research article
 | 
13 Apr 2017
Research article |  | 13 Apr 2017

An atmosphere–wave regional coupled model: improving predictions of wave heights and surface winds in the southern North Sea

Kathrin Wahle, Joanna Staneva, Wolfgang Koch, Luciana Fenoglio-Marc, Ha T. M. Ho-Hagemann, and Emil V. Stanev

Abstract. The coupling of models is a commonly used approach when addressing the complex interactions between different components of earth systems. We demonstrate that this approach can result in a reduction of errors in wave forecasting, especially in dynamically complicated coastal ocean areas, such as the southern part of the North Sea – the German Bight. Here, we study the effects of coupling of an atmospheric model (COSMO) and a wind wave model (WAM), which is enabled by implementing wave-induced drag in the atmospheric model. The numerical simulations use a regional North Sea coupled wave–atmosphere model as well as a nested-grid high-resolution German Bight wave model. Using one atmospheric and two wind wave models simultaneously allows for study of the individual and combined effects of two-way coupling and grid resolution. This approach proved to be particularly important under severe storm conditions as the German Bight is a very shallow and dynamically complex coastal area exposed to storm floods. The two-way coupling leads to a reduction of both surface wind speeds and simulated wave heights. In this study, the sensitivity of atmospheric parameters, such as wind speed and atmospheric pressure, to the wave-induced drag, in particular under storm conditions, and the impact of two-way coupling on the wave model performance, is quantified. Comparisons between data from in situ and satellite altimeter observations indicate that two-way coupling improves the simulation of wind and wave parameters of the model and justify its implementation for both operational and climate simulations.

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Short summary
Reduction of wave forecasting errors is a challenge, especially in dynamically complicated coastal ocean areas such as the southern part of the North Sea area. We study the effects of coupling between an atmospheric and two nested-grid wind wave models. Comparisons with data from in situ and satellite altimeter observations indicate that two-way coupling improves the simulation of wind and wave parameters of the model and justifies its implementation for both operational and climate simulation.