


SYMPHONIENH is the
nonhydrostatic ocean model following the Boussinesq hydrostatic
SYMPHONIE2010 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 (NonHydrostatic, free surface, generalised coordinates
combined to an ALE method,...) are particularly suitable for
the coastal area.


Webcontributors:
get the background page 



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 TUGO
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 1h 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.
Wind
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
Animations



DOWNLOAD
the last
SYMPHONIE release
REAL
TIME FORECAST in NorthWestern 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 semidiurnal surface tidal wave impinging
on a supercritical meridionally uniform deep ocean ridge on the
fplane, and subsequent ITpropagation are analysed using the Boussinesq,
freesurface, terrainfollowing ocean model Symphonie. The energy
diagnostics are explicitly based on the numerical formulation of
the governing equations, permitting a globally conservative, highprecision
analysis of all physical and numerical/artificial energy transfers
in a subdomain 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 timestep,
minimal diffusion, and a noslip sea floor. This provides the basis
for analysis of enhanced vertical and horizontal diffusion and a
freeslip bottom boundary condition. After a four tidal period spinup,
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 barotropictobaroclinic
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
surfacetointernal tide conversion, but also by the net advection
of baroclinic (background) potential energy, indicating the importance
of local processes other than linear ITmotion. 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
domainaveraged potential energy gain, which matches to within 0.5%,
for km linearly distributed gridlevels and constant background
density ?0, vertical diffusivity (KV) and buoyancy frequency (N).
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INSU
LA
LEGOS
OMP
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