SYMPHONIE-NH is the non-hydrostatic ocean model following the Boussinesq hydrostatic SYMPHONIE-2010 model developed by the Sirocco system team (CNRS & Toulouse University). Both are using an Arakawa type finite difference method for the C grid. The R&D team generally gives priority to a physically based approach of modelling (global conservation of the mechanical energy, consistency of pressure and density, accuracy of the bottom pressure torque,...) that tends to favour low order and robust numerical schemes. The principal equations of the physical engine are detailed in Auclair et al (2011), Marsaleix et al ( 2006, 2008, 2009). Most of the physical and numerical options (Non-Hydrostatic, free surface, generalised coordinates combined to an ALE method,...) are particularly suitable for the coastal area.
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November 2010 :



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Fukushima Forecast Bulletin
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            SIROCCO has performed, at the request of the International Atomic Energy Agency (IAEA), simulations using the 3D SIROCCO ocean circulation model to investigate the dispersion in seawater of radionuclides emitted by the Fukushima nuclear plant. The model uses a stretched horizontal grid with a variable horizontal resolution, from 600m x 600m at the nearest grid point from Fukushima, to 5km x 5km offshore. The initial fields (T,S,U,V,SSH) and the lateral open boundary conditions are provided by the Mercator PSY4V1R3 system (one field per day, horizontal resolution 1/12 x 1/12 ). At the sea surface, the ocean model is forced by the meteorological fluxes delivered every 3hours by ECMWF. The tidal forcing at the lateral open boundaries is provided by the T-UGO model, implemented for this purpose by the SIROCCO team on the Japanese Pacific coast.

             We strongly recommend to the visitors of this site to read carefully the description of our modelling system.

             Animations of various variables characterizing the ocean state are presented : surface temperature, salinity and current beginning on March 9, two days before the tsunami. The animation finishes by a few days of forecast (see our Protocol of Simulation).

Temperature, salinity, currents

Dispersion of radionuclides in the sea

        The Fukushima nuclear plant has injected in the atmosphere and in the seawater radionuclides at different times and in variable quantities. A model of dispersion needs a good knowledge of the source terms to be able to correctly calculate the dispersion. Of course, very few information is available to build elaborate scenarios of radionuclides emssion. Besides, the evolution of dispersion in the sea also requires to know very well the behaviour of the radionuclides, for example the fraction which is dissolved in the seawater, the particulate fraction and its associated sedimentation velocity. Even if we knew all this information, radionuclides can aggregate with marine particles and then their sedimentation velocity can evolve. Finally, the oceanic currents computed by our model are not the reality: they are the result of mathematical equations too simple to fully represent the complexity of nature. The wind which strongly drives the oceanic currents is also a forecast whose accuracy is not known.

      We do not know how much radionuclides have been injected, when they have been injected and how they behave once they reach the sea. That is why we do not claim that our simulations are able to provide an accurate quantification of radioactivity in the sea. However, in order to build our scenarios, special attention has been paid to the measurements of Cesium 137 concentration taken several times every day by TEPCO at 30 and 300m in front of the nuclear plant.

      Two sources of radionuclides are considered. One corresponds to a direct emission in the sea in front of the nuclear plant (migration of water contaminated by the reactors), the other one corresponds to fallout of atmospheric particles. In the first case, we introduce a flux at the grid point corresponding to the nuclear plant. This flux is adjusted to produce a concentration close to the values of Cesium 137 measured (see our page of validation ). In the last case, we used 1-h outputs of the atmospheric transport model Polyphemus/Polair3D (0.25 horizontal resolution) (pers. comm. Marc Bocquet & Victor Winiarek, Ecole des Ponts ParisTech/CEREA).
For each source (direct release and atmospheric), we consider two cases: one corresponds to dissolved elements, the other one to particles that fall into the sea with a velocity of 10meters per day. Obviously dispersion in the first case will happen at larger scale than for the second case for which deposition of particles on the sea floor reduces the dispersion. Deposition of particles is cumulated over time and will be mapped later on.


        In the coastal zone, wind plays an important role on the dispersion of tracers by inducing alongshore currents directed northward or southward (function of the wind direction). Offshore, the local action of wind on currents is concentrated in the surface layer adding a drift on the right of the wind to the large scale currents.
Wind animation



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REAL TIME FORECAST in North-Western Mediterranean (CASCADE projet)

REAL TIME FORECAST of the Pacific coast of Japan

PhD proposition: Budget of biogenic elements on the Gulf of Lion shelf and offshore transport. More details

Energy transfers in internal tide generation, propagation and dissipation in the deep ocean
Floor J.W., Auclair F., Marsaleix P., 2011 Ocean Modelling

The energy transfers associated with internal tide (IT) generation by a semi-diurnal surface tidal wave impinging on a supercritical meridionally uniform deep ocean ridge on the f-plane, and subsequent IT-propagation are analysed using the Boussinesq, free-surface, terrain-following ocean model Symphonie. The energy diagnostics are explicitly based on the numerical formulation of the governing equations, permitting a globally conservative, high-precision analysis of all physical and numerical/artificial energy transfers in a sub-domain with open lateral boundaries. The net primary energy balances are quantified using a moving average of length two tidal periods in a simplified control simulation using a single time-step, minimal diffusion, and a no-slip sea floor. This provides the basis for analysis of enhanced vertical and horizontal diffusion and a free-slip bottom boundary condition. After a four tidal period spin-up, the tidally averaged (net) primary energy balance in the generation region, extending ±20 km from the ridge crest, shows that the surface tidal wave loses approximately C = 720 W/m or 0.3% of the mean surface tidal energy flux (2.506 × 105 W/m) in traversing the ridge. This corresponds mainly to the barotropic-to-baroclinic energy conversion due to stratified flow interaction with sloping topography. Combined with a normalised net advective flux of baroclinic potential energy of 0.9 × C this causes a net local baroclinic potential energy gain of 0.72 × C and a conversion into baroclinic kinetic energy through the baroclinic buoyancy term of 1.18 × C. Tidally averaged, about 1.14 × C is radiated into the abyssal ocean through the total baroclinic flux of internal pressure associated with the IT- and background density field. This total baroclinic pressure flux is therefore not only determined by the classic linear surface-to-internal tide conversion, but also by the net advection of baroclinic (background) potential energy, indicating the importance of local processes other than linear IT-motion. In the propagation region (PR), integrated over the areas between 20 and 40 km from the ridge crest, the barotropic and baroclinic tide are decoupled. The net incoming total baroclinic pressure flux is balanced by local potential energy gain and outward baroclinic flux of potential energy associated with the total baroclinic density. The primary net energy balances are robust to changes in the vertical diffusion coefficient, whereas relatively weak horizontal diffusion significantly reduces the outward IT energy flux. Diapycnal mixing due to vertical diffusion causes an available potential energy loss of about 1% of the total domain-averaged potential energy gain, which matches to within 0.5%, for km linearly distributed grid-levels and constant background density ?0, vertical diffusivity (KV) and buoyancy frequency (N).

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