Tidal downscaling in a 3D (structured) circulation model: a new approach based on tailored 2D (unstructured) simulations

Florence Toublanc (LEGOS/CNES, France)

CoAuthors

Nadia Ayoub (CNRS - LEGOS, France); Florent Lyard (CNRS - LEGOS, France); Patrick Marsaleix (CNRS - LA, France); Thomas Duhaut (CNRS - LA, France); Damien Allain (Celad - LEGOS, France)

Event: 2016 Ocean Surface Topography Science Team Meeting

Session: Tides, internal tides and high-frequency processes

Presentation type: Type Poster

Modelling the 3D ocean circulation in coastal areas requires an accurate representation of the tidal dynamics. This is particularly true in the Bay of Biscay, where tides are highly energetic over the shelf, with tidal ranges reaching 6m at the coast. Although tidal dynamics are dominated by semi-diurnal constituents, nonlinear interactions occurring between these constituents and the topography result in the generation of overtides such as M4. Downscaling the tidal dynamics in a coastal model from a larger scale solution raises several methodological issues, especially in terms of currents. In particular, the choice of the large scale solution is crucial; the impact of likely inconsistencies in bathymetry and grid resolutions between the large scale model and the coastal one should be evaluated.
In this study, we propose a new approach to tidal downscaling for coastal modelling by using two numerical models, T-UGO and SYMPHONIE, on the same rectangular mesh and bathymetry at the nodes. The unstructured grid model T-UGO 2D spectral model is adapted to perform these simulations, and provide tidal boundary conditions to the 3D circulation model SYMPHONIE. The latter is set-up on a variable mesh grid that allows us to represent the different physical processes, including tides, that influence the dynamics of the bay, from the deep plain scale to the estuarine scale. The horizontal grid resolution varies between approximately 3km at the oceanic open boundary and less than 300m in the Gironde estuary and the Pertuis Charentais. Three types of tidal boundary conditions are tested for the SYMPHONIE model: the FES2012 atlas, T-UGO 2D spectral simulations, and SYMPHONIE 2D clamped simulations. Complex errors, taking into account both the amplitude and the phase of the M2 tidal constituent, are reduced by more than 75% with a regional forcing (SYMPHONIE or T-UGO 2D), compared to a global forcing (FES2012).

 

Poster show times:

RoomStart DateEnd Date
Grande Halle Thu, Nov 03 2016,11:00 Thu, Nov 03 2016,18:00
Florence Toublanc
LEGOS/CNES
France
florence.toublanc@legos.obs-mip.fr