Impacts of an Altimetric Wave Data Assimilation Scheme and Currents-Wave Coupling in an Operational Wave System: The New Copernicus Marine IBI Wave Forecast Service

The Copernicus Marine IBI-MFC (Iberia–Biscay–Ireland Monitoring and Forecasting Centre) has delivered operational wave forecasts since 2017. The operational application is based on a MFWAM model (Meteo-France WAve Model) set-up, running at a 1/20º grid (5-km). The research presented here was conducted to improve the accuracy of the IBI-MFC wave model products, by means of (i) including a new wave data assimilation scheme and (ii) developing a new coupled ocean-wave modelling framework. Evaluation of these set-up upgrades, in terms of improvements in IBI wave model system capabilities, is here presented. All the model sensitivity test runs, performed for the year 2018, are assessed over the whole IBI domain, using the available in-situ (from 49 mooring buoys) and independent satellite wave observation. The results show that the most relevant improvement is due to the data assimilation, while the impact of surface ocean currents, although less significant, also improves the wave model qualification over the IBI area. The demonstrated benefit, related to the herein proposed upgrades, supported the IBI-MFC decision to evolve its operational wave system, using (since the March 2020 Copernicus Marine Release) the resulting wave model set-up, with data assimilation and currents-wave coupling for operational purposes.

Stokes drift

During its periodic motion, a particle floating at the free surface of a water wave experiences a net drift velocity in the direction of wave propagation, known as the Stokes drift (Stokes 1847 Trans. Camb. Philos. Soc.8, 441-455). More generally, the Stokes drift velocity is the difference between the average Lagrangian flow velocity of a fluid parcel and the average Eulerian flow velocity of the fluid. This paper reviews progress in fundamental and applied research on the induced mean flow associated with surface gravity waves since the first description of the Stokes drift, now 170 years ago. After briefly reviewing the fundamental physical processes, most of which have been established for decades, the review addresses progress in laboratory and field observations of the Stokes drift. Despite more than a century of experimental studies, laboratory studies of the mean circulation set up by waves in a laboratory flume remain somewhat contentious. In the field, rapid advances are expected due to increasingly small and cheap sensors and transmitters, making widespread use of small surface-following drifters possible. We also discuss remote sensing of the Stokes drift from high-frequency radar. Finally, the paper discusses the three main areas of application of the Stokes drift: in the coastal zone, in Eulerian models of the upper ocean layer and in the modelling of tracer transport, such as oil and plastic pollution. Future climate models will probably involve full coupling of ocean and atmosphere systems, in which the wave model provides consistent forcing on the ocean surface boundary layer. Together with the advent of new space-borne instruments that can measure surface Stokes drift, such models hold the promise of quantifying the impact of wave effects on the global atmosphere-ocean system and hopefully contribute to improved climate projections.This article is part of the theme issue 'Nonlinear water waves'.