Abstract
The contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a high-resolution configuration of the Geestacht COAstal model SysTem (GCOAST), implemented in the Northeast Atlantic, the North Sea and the Baltic Sea which are considered as connected basins. The GCOAST system accounts for wave-ocean interactions and the ocean circulation relies on the NEMO (Nucleus for European Modelling of the Ocean) ocean model, while ocean-wave simulations are performed using the spectral wave model WAM. The objective is to demonstrate the contribution of wave-induced processes to sea level at different temporal and spatial scales of variability. When comparing the ocean-wave coupled experiment with in situ data, a significant reduction of the errors (up to 40% in the North Sea) is observed, compared with the reference. Spectral analysis shows that the reduction of the errors is mainly due to an improved representation of sea-level variability at temporal scales up to 12 h. Investigating the representation of sea-level extremes in the experiments, significant contributions (> 20%) due to wave-induced processes are observed both over continental shelf areas and in the Atlantic, associated with different patterns of variability. Sensitivity experiments to the impact of the different wave-induced processes show a major impact of wave-modified surface stress over the shelf areas in the North Sea and in the Baltic Sea. In the Atlantic, the signature of wave-induced processes is driven by the interaction of wave-modified momentum flux and turbulent mixing, and it shows its impact to the occurrence of mesoscale features of the ocean circulation. Wave-induced energy fluxes also have a role (10%) in the modulation of surge at the shelf break.
Highlights
Sea level is considered as a key indicator of climate variability and change (e.g. Church et al 2013; Stocker et al 2013; von Schuckmann et al 2018; Oppenheimer et al 2019), as it integrates the response of different components of the Earth’s system (Storto et al 2019a) interacting at different temporal and spatial scales
Sea-state contribution to sea-level variability was investigated by means of ocean-wave coupled simulations over a 9-year period (2010–2018)
Four different experiments were designed by varying the wave-induced processes considered in the numerical simulations
Summary
Sea level is considered as a key indicator of climate variability and change (e.g. Church et al 2013; Stocker et al 2013; von Schuckmann et al 2018; Oppenheimer et al 2019), as it integrates the response of different components of the Earth’s system (Storto et al 2019a) interacting at different temporal and spatial scales. Arns et al (2017) underscored the need of considering the changing non-linear interactions between tides, waves, and surges caused by sea-level rise for coastal risk assessments and coastal protection design. The objective of the present work was to assess the contribution of wave-induced processes to sea-level variability and non-tidal residuals (hereafter surge) using a two-way coupled waves-circulation model, based on a high-resolution (∼3.5 km) configuration of the GCOAST system, which considers the Northeast Atlantic, North Sea and Baltic Sea as connected basins. The paper is structured as follows: after this introduction, Section 2 describes the ocean-wave coupled modelling system used in this study, the experimental set-up designed to investigate sea-state contributions to sea-level variability, and the observation datasets used to assess the skill of the OGCM simulations.
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