OCEAN FORECAST FORCED BY THE WEATHER SKIRON MODEL

The system produces a daily 5-day forecast of 3D ocean temperatures, salinity and current velocities on a routine basis. The model has been implemented in the Sicily Strait area with a horizontal resolution of 1/32° and 30 sigma layers.

The model is forced by an interactive air-sea module through a high resolution (10 km horizontal resolution) weather prediction model (SKIRON), developed at the Atmospheric Modeling & Weather Forecasting Group of the Athens University (Kallos et al., J.Geoph.Res., 2005). The coupling between the ocean and the atmospheric model assumes that the net shortwave radiation and the downward infrared radiation at the sea surface is provided directly by the atmospheric model at 1-hour interval while momentum, turbulent heat fluxes and freshwater are calculated by the bulk formulae through the simulated sea surface temperature.

The lateral open boundary conditions are defined through an off-line one way nesting technique (Sorgente et al., Annales Geophysicae, 2003) with the coarse forecasting system of the whole Mediterranean basin sea circulation (Pinardi et al., Annales Geophysicae, 2003).

The sub-regional model is initialized every day through the downscaling and optimization of coarse resolution fields (temperature, salinity and current velocity), in order to remove the spurious external gravity waves during the spin-up phase. Details can be found in Gabersek et al, Ocean Science, 2007.

The forecast fields are available available every day at about 09:00 AM UTC as daily means.

The numerical simulation system of the coastal wave field provides a daily forecast, to maximum 5 days, of the wave height & direction in the Sicily Strait area at steps of 3 hours. The core of the forecasting system is the SHYFEM, a finite element hydrodynamic numerical model that has been already validated and calibrated in previous studies (Ferrarin et al., 2004, Cucco et al., 2006). Such a model well reproduces the tide and wind induced water circulation in the study area where it is applied in its 2D version in order to reproduce the wave height & direction. Numerical simulations are carried out over a computational domain that represents the area between 8.95°' and 17.1° of longitude E and, 30° and 39.5° of latitude N, by means of a finite element staggered grid. The numerical grid consists nodes and triangular elements with different spatial resolutions varying from 10m, for the smallest coastal areas, to few kms off-shore. The model considers the off-shore perimeter of the computational domain as open boundary. The model is forced by an astronomic tide imposed at the open boundary and by a wind intensity and direction imposed as surface boundary condition. Meteorological data are provided by means of the SKIRON high resolution atmospheric numerical model.