Coupled Modeling of Air-Sea Processes in the Iroise Sea at High Horizontal Resolution

Our understanding of coastal processes and capability to predict marine variables that describe ocean, atmosphere, and sea state conditions are key for environmental protection, exploitation of marine energies, fisheries and more. In an effort to improve current operational coastal services, the French "Ministère de l’Environnement, de l’Energie et de la Mer" funded the AMICO (Actions de Modélisation Intégrée Côtière Opérationnelle) project within the framework of the COPERNICUS program. The first phase of the project consisted in developing a generic fully coupled Ocean-Atmosphere-Waves numerical system. In this second phase we exploit the system to tease out best practices for operational use.

Here we will present results based on high resolution (500-1500 m) coupled simulations of the Iroise Sea (French Brittany). Using an adapted OASIS-MCT interface, the ocean Model for Applications at Regional Scale (MARS3D), the third generation wind and wave model WaveWatchIII (WW3), and the non-hydrostatic mesoscale atmospheric model of the French research community (MesoNH) were coupled. The Iroise Sea offers an excellent study area with a multitude of physical processes spanning several spatio-temporal scales (strong tidal currents, an intense seasonal SST front, and long fetch waves) which allow to shed insights on air-sea interactions and importance of various aspects of dynamical coupling. After demonstrating how crucial the quality of the atmospheric forcing is for improving modeled ocean hydrodynamics and vice versa, we explore whether 2-way atmosphere-wave-ocean coupling is necessary, in what environments and conditions. The necessity to include wave dynamics will be evaluated and their representation in the coupled framework will be discussed. We will focus on two sub regions with contrasting dynamics: the Ouessant SST front and the Fromveur Passage where tidal currents are strong. The simulations were run for a period of low to moderate winds as observed during the FroMVar (Front de Marée Variable) field campaign at the beginning of September 2011. Data collected during FroMVar (scanfish, ADCP, wave buoy, radio soundings, eddy covariance fluxes) will be used to ascertain model accuracy.