About
POC:
The
POC group has been created in 2001 by scientists from LEGOS
and LA. One of the main objectives of POC is to study the oceanic
circulation at regional and coastal scales. The approach is
essentially... read
the following
g
ated.
Last 10 publications (full
list):
Le
Bars Y., Lyard F., Jeandel
C., Dardengo L., 2010. The AMANDES tidal model for the
Amazon estuary and shelf. Ocean Modelling, 31, 132-149, http://dx.doi.org/10.1016/j.ocemod.2009.11.001
Marsaleix P., Ulses C., Pairaud I., Herrmann M.J., Floor J.W.,
Estournel C., Auclair F., 2009. Open
boundary conditions for internal gravity wave modelling using
polarization relations. Ocean Modelling, 29,
27-42. http://dx.doi.org/10.1016/j.ocemod.2009.02.010
Marsaleix P., Auclair
F., Estournel C., 2009. Low-order
pressure gradient schemes in sigma coordinate models: The seamount
test revisited. Ocean Modelling http://dx.doi.org/10.1016/j.ocemod.2009.06.011
Herrmann, M., J. Bouffard,
and K. Beranger, 2009 Monitoring
open-ocean deep convection from space, Geophysical Research
Letters, doi:10.1029/2008GL036422
Hu Z.Y., Doglioli A.M., Petrenko A.A., Marsaleix
P., Dekeyser I., 2009.
Numerical simulations of eddies in the Gulf of Lion. Ocean
Modelling, 28, 203-208 http://dx.doi.org/10.1016/j.ocemod.2009.02.004
Durand, F., D. Shankar, F. Birol,
and S.S.C. Shenoi, 2009, Spatio-temporal structure of
the East India Coastal Current from satellite altimetry, Journal
of Geophysical Research, doi:10.1029/2008JC004807
Le
Hénaff M., De Mey P., Marsaleix P., 2009
Assessment of observational networks with the Representer Matrix
Spectra method-application to a 3D coastal model of the Bay
of Biscay. Ocean
Dynamics, 59, 3-20 http://dx.doi.org/10.1007/s10236-008-0144-7
Estournel
C., Auclair F, Lux M., Nguyen C., Marsaleix P., 2009.
"Scale
oriented" embedded modeling of the North-Western Mediterranean
in the frame of MFSTEP. Ocean Science, 5, 73-90
html
Rubio A., Barnier B., Jorda G., Espino M., Marsaleix
P., 2009 Origin and dynamics of mesoscale eddies
in the Catalan Sea (NW Mediterranean): Insight from a numerical
model study. Journal of Geophysical Research, 114, C06009,
doi:10.1029/2007JC004245
Fontana C., Grenz C., Pinazo C., Marsaleix
P., Diaz F, 2009.
Assimilation of SeaWiFS chlorophyll data into a 3D coupled physical
biogeochemical model applied to a freshwater influenced coastal
zone. Continental Shelf Research, 29, 1397-1409,
http://dx.doi.org/10.1016/j.csr.2009.03.005
POC
Publications from 2000
SYMPHONIE
Non-Hydrostatic:
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NH |
Francis
Auclair Cyril
Nguyen
A
non-hydrostatic version of the POC 3D free surface model Symphonie
has been developed. A prognostic equation for the vertical momentum
has been implemented resulting in the inversion of a classical
Poisson equation for the non-hydrostatic component of the pressure.
The animations show a comparison ofthe hydrostatic
and non-hydrostatic versions of Symphonie on the classical and
simple test case of the oscillations of a 10m-wide and 10m-deep
basin. The hydrostatic modeling shows long non-dispersive waves
while the non-hydrostatic version exhibits short, dispersive
waves as expected based on the dimension of the basin. In perfect
agreement with theory, the resulting period of the oscillations
is 1.5 larger in the non-hydrostatic version.
 Video:
Vertical velocity in a 2D vertical section.
Toulouse, April 2007.
Toulouse, january
2008. © Claudine Marsaleix
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The
AMANDES tidal model for the Amazon estuary and shelf
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Le
Bars Y., Lyard F., Jeandel
C., Dardengo L., (OM 2010)
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The
AMANDES project aims to study transports from the Andean mountains
to the Atlantic Ocean through the Amazon system. This requires
realistic estuarine modelling in this area strongly forced by
tides and river discharge. As none of the existing models for
this region would fit the actual needs of the project, a specific
new generation model has been implemented.
The model
is based on the hydrodynamic finite element model T-UGOm.
In a first step, we limit our investigations to tidal dynamics.
As the Amazon estuary is a very shallow macro-tidal area,
it is necessary to improve the available bathymetries and
to develop a precise bottom friction parametrisation.
In this
paper, we discuss the implementation of a high resolution
regional model. This allows us to develop a precise and accurate
tidal model: for instance, the overall root mean square error
on complex differences is reduced from 54 cm in a standard
model to 27 cm in our best model. Such precise and accurate
tidal modelling is a prerequisite for modelling particle transport.
http://dx.doi.org/10.1016/j.ocemod.2009.11.001
Photographs:
POC linux
cluster
Assessment
of observational networks with the Representer Matrix
Spectra method-application to a 3D coastal model of the
Bay of Biscay
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Le
Hénaff M., De Mey P.,
Marsaleix P.
(Ocean Dynamics)
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The
development of coastal ocean modeling in the recent years
has allowed an improved representation of the associated complex
physics. Such models have become more realistic, to the point
that they can now be used to design observation networks in
coastal areas, with the idea that a "good" network
is a network that controls model state error. To test this
ability without performing data assimilation, we set up a
technique called Representer Matrix Spectra (RMS) technique
that combines the model state and observation error covariance
matrices into a single scaled representer matrix. Examination
of the spectrum and the eigenvectors of that matrix informs
us on which model state error modes a network can detect and
constrain amidst the observation error background. We applied
our technique to a 3D coastal model in the Bay of Biscay,
with a focus on mesoscale activity, and tested the performance
of various altimetry networks and an in situ array deployment
strategy. It appears that a single nadir altimeter is not
efficient enough at capturing coastal mesoscale physics, while
a wide swath altimeter would do a much better job. Testing
various local in situ array configurations confirms that adding
a current meter to a vertical temperature measurement array
improves the detection of secondary variability modes, while
shifting the array higher on the shelf break would obviously
enhance the model constraint along the coast. The RMS technique
is easily set up and used as a "black box," but
the utility of its results is maximized by previous knowledge
of model state error physics. The technique provides both
quantitative (eigenvalues) and qualitative (eigenvectors)
tools to study and compare various network options. The qualitative
approach is essential to discard possibly inconsistent modes.
http://dx.doi.org/10.1007/s10236-008-0144-7
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| Monitoring
open-ocean deep convection from space |
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| Herrmann,
M., J. Bouffard,
and
K. Beranger
(GRL 2009) |
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Deep convection (DC) is a key-process
of the oceanic circulation, costly to monitor in-situ and under
the influence of climate change. Our study is a first step toward
monitoring DC from space: we investigate the feasibility of
observing its variability using improved satellite altimetry.
An oceanic simulation of the Mediterranean circulation was performed
for the 1999-2007 period. DC interannual variability is realistically
modelled, and the sea surface elevation (SSE) is in agreement
with altimetry data. Numerical results show a strong correlation
between the annual DC characteristics and the winter SSE. From
that, we propose a method to monitor DC interannual variability
and long term evolution using altimetry data. Our method, applied
to the longest available altimetry series, represents correctly
the interannual variability of DC in the Northwestern Mediterranean
between 1994 and 2007. doi:10.1029/2008GL036422
Exploiting
the potential of an improved multi mission altimetric
dataset over the coastal ocean
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| Bouffard,
J.,
S.
Vignudelli, P. Cipollini, and Y. Menard, (GRL 2008) |
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Until
now, most satellite altimetry studies of the coastal ocean have
been based on along-track data from a single mission, whereas
up to four missions were operative in 2002–2005. Here,
to monitor the coastal ocean we have applied specialized corrections
and dedicated processing strategies to compute a multimission
data set at a mean distance of 32 km of the coast. The resulting
altimetric data set is compared with sea level data from three
in situ stations over a coastal zone of the northwestern Mediterranean.
The mean rms difference between this data set and the sea level
stations is 2.9 cm against 3.7 cm when using the AVISO altimetric
product. Comparison of altimeter-derived geostrophic velocities
with a mooring also shows that the spatial and temporal variability
of the surface current field is well reproduced. The agreement
with in situ measurements extends to intraseasonal time scales
showing a significant improvement compared to previous studies
in the 50 km coastal-band.
doi:10.1029/2008GL033488
Modeling
the deep convection in the northwestern Mediterranean
Sea using an eddy-permitting and an eddy-resolving model:
Case study of winter 1986-1987
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Herrmann,
M. J.,
S. Somot, F. Sevault, C. Estournel, and M. Deque (JGR 2008)
In
the Northwestern Mediterranean sea, winter 1986-87 was particularly
cold, inducing a strong open-ocean convection event. In order
to investigate the impact of numerical models spatial resolution
on the convection representation and the effects of deep convection
on the Northwestern Mediterranean circulation, we perform
two numerical three-dimensional simulations (eddy-permitting
vs. eddy-resolving). Models are forced at the surface by the
ERA40 atmospheric fluxes, with a simple heat flux correction
to better mimic the observed value. We examine the characteristics
of the deep convection (mixed layer, water masses characteristics
, convection zone and mesoscale structures), and perform temporal
analysis of this event in terms of kinetic energy, buoyancy
equilibrium and deep water (DW) evolution. The convection
characteristics are represented similarly on a global scale
by both models and are in good agreement with observations,
except for the size of the convection region. However, the
eddy-resolving model reproduces better the mesoscale structures,
whose role in the DW formation, mixing and transport is shown
to be essential. The boundary circulation and the overturning
are enhanced during the convection event. 66% of the DW spreading
is due to the bleeding effect into the Catalan sea during
the convection event, whereas 33% is due to the mesoscale
structures southwestward advection after the event. 60% of
the restratification with respect of the water column initial
structure occurs before July 1987 and is due to light water
advection. Afterwards, restratification is due to the mixing,
and is not complete before next year convection.
http://dx.doi.org/10.1029/2006JC003991
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