Diapositive 1

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Observing the ocean variability in the Western
Mediterranean Sea by using coastal
multi-satellite data and Models M. Bouffard(1,),
L. Roblou(2), Y. Ménard(3), P. Marsaleix(4), and
P. De Mey(1) (1)LEGOS, Toulouse, France (2)
Noveltis , France (3) C.N.E.S., Toulouse,
France (4)L.A., Toulouse, France
(1,)bouffard_at_notos.cst.cnes.fr

• Symphonie a coastal ocean model
• Symphonie is basically a three-dimensional
  primitive equation model of the coastal ocean.
• The three components of the current, free surface
  elevation, temperature and salinity are computed
  on a C grid. A generalized sigma coordinate is
  used. The turbulence closure is achieved through
  a prognostic equation for the turbulent kinetic
  energy and a diagnostic equation for the mixing
  and dissipation length scales. A leap frog scheme
  is used for the time stepping. Calculus costs are
  limited thanks to a time splitting technique that
  permits to compute the vertical shear of the
  current and its depth-averaged components
  separately with appropriate time steps. Radiation
  conditions combined to restoring terms to the
  large-scale circulation are applied at the open
  boundaries
• Geophysical coordinates -1,74E 10,95 E /
  38,26 N 45,61 N
• Horizontal resolution 3 km 3 km
• Lateral Boundary conditions MFSTEP OGCM
• Surface Boundary conditions Aladin Weather
  Forecast

Abstract The spatial and temporal resolution of
satellite altimetry is usually well adapted to
the sampling of the sea surface topography of the
open ocean. However, the coastal ocean dynamics
are much more complex, being characterized by a
wide range of spatial and temporal scales, which
are more difficult to observe with a single
altimetric satellite. Thus a coastal
multi-satellite altimetric data set
(Topex/Poseidon, Jason1, Envisat, GFO) has been
derived from routine geophysical data products
using a new processing software dedicated to
coastal zone applications. Particular attention
has been paid to the tide and inverse barometer
corrections, which have been applied to
altimetric data, using a high-resolution 2D
gravity wave model (MOG2D). In addition, we
developed an orbit error reduction method, which
is a key point for improving altimetric products,
based on a crossover minimization technique. We
then compared this data set with sea surface
anomalies built from the 3D coastal model
Symphonie ( run from 2001 to 2003 ).

• MOG2D model
• (Lynch and Gray (1979), adapted by Greenberg and
  Lyard)
• barotropic, free surface, non-linear and
  time-stepping model
• solves the continuity and momentum equations in
  a single wave equation
• implemented on a finite element grid (2D)
• gt finer resolution on steeper and shallower
  bathymetric zone
• adequate for studying the high frequency response
  to meteorological forcing (Carrere Lyard, 2003)

O Orbit and large scale error reduction -
Firts step Large-scale time-dependant errors
filtering - Second step
Crossover minimization technique
MOG2D finite element grid
Along track mean ( Topex - track9 )/ Time
. GFO/ Symphonie
Conclusion This work emphasizes the potential of
multi-satellite altimetry to validate coastal 3D
hydrodynamical model thanks to the use of
altimetric products dedicated to coastal zone
applications. Indeed a first step is to improve
the capability of modelling and forecasting the
coastal ocean dynamics through the development of
observation systems and their integration into
coastal circulation models through data
assimilation techniques. Thus, the next step will
be to assimilate altimetric and tide gauges data
in the 3 D Symphonie model and to evaluate the
impact of different satellite configurations.
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