Sea-state contributions to sea-level variability in the European Seas

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.

Understanding Sea Level Processes During Western Mediterranean Storm Gloria

“…Waves can also contribute to extreme sea levels recorded by tide gauges, at hourly timescales, as already proposed by Charnock (1955); Stewart (1974). In fact, several studies have paid attention to this topic in recent years (Bertin et al, 2015;Melet et al, 2018;Bonaduce et al, 2020). The following wave-induced processes could affect sea level during a storm surge: (i) Stokes-Coriolis drift and consequent mass transport (Stokes, 1847;Hasselmann, 1970); (ii) wave induced effect on the wind stress, due to momentum exchange (Staneva et al, 2017); and (iii) wave setup (Longuet-Higgins and Stewart, 1962;Bowen et al, 1968).…”

Towards a pan-European coastal flood awareness system: Skill of extreme sea-level forecasts from the Copernicus Marine Service

“…The IBI and NWS models offer the most complete coupling, while BAL and MED models only account for the Stokes Drift and the wave drag effects respectively and could therefore be limiting the water-level representation capabilities of these models. Several recent studies have reported on the significant impact of the wave coupling on water-levels around the European Northwest Shelf and Baltic regions, in particular during extreme events, which may increase coastal extreme sea-levels by several decimeters (Staneva et al, 2016;Staneva et al, 2017;Lewis et al, 2019;Bonaduce et al, 2020;Staneva et al, 2021).These studies argue that, on the shelf, the strongest impact is induced by the sea-state dependent sea-surface roughness, which can be importantly enhanced during growing, young sea states (Bertin et al, 2015, Pineau-Guillou et al, 2020. This process is currently lacking in the BAL model.…”

Detecting anomalous sea-level states in North Sea tide gauge data using of autoassociative Neural Network

“…For the experiments discussed later in this study, we use only the ocean circulation part based on the Nucleus for European Modelling of the Ocean (NEMO v3.6;Madec, 2017, Staneva et al, 2017, Bonaduce et al, 2020 with 3.5 km horizontal resolution as an ocean component of the Geesthacht Coupled cOAstal model SysTem (GCOAST). The NEMO setup used within the GCOAST system has an eddy-resolving spatial resolution of ∼3.5 km, and uses an explicit free-surface formulation (Madec 2017;Staneva et al 2021, Bonaduce et al, 2020. The model area covers the Baltic Sea, the Danish Straits, the North Sea and part of the northeast Atlantic Ocean.…”