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General
project presentation |
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Scientific
program |
CLIPPER is a project of high resolution modelling of
the Atlantic Ocean Circulation, either forced by air-sea fluxes or coupled
with an atmospheric model. The project has been named after the tall ships
that used to cross the Atlantic Ocean from Europe to the Cape Horn or the
Cape of Good Hope, the image of a Clipper in full sail raising more
enthusiasm than obscure acronyms (in the project team, at least). In
2000-2001, the project has performed a prognostic simulation of the
ocean circulation in the whole Atlantic Basin (from Iceland to Antarctica)
with a high-resolution (1/6° at the equator) primitive equation
model. This experiment covers the period 1979-2000, forced by ECMWF
winds and fluxes. It resolves the very energetic mesoscale dynamics, and
thus explicitly simulates its contribution to the large scale ocean
circulation in the Atlantic.
Scientific results are found in the "CLIPPER
reports" and "CLIPPER publications" directories.
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A
contribution to WOCE |
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CLIPPER is a contribution to
WOCE (World Ocean Circulation Experiment). In summary, the goals of WOCE
are to improve our understanding of the ocean circulation, of the role
of the ocean in the Earth's climate, and to improve modelling of the
global ocean circulation and eventually lead to skill in climate
prediction. During the field phase of the program (1990-97), the French
contribution to WOCE has been concentrated in the Equatorial and South
Atlantic Ocean, with hydrographic sections carried out within the
programs CITHER and CIVA, with the float program SAMBA in the Brazil
Basin, and with intense surveys of ocean flows (including current meters
moorings) in the region of the confluence of the Brazil and Malvinas
Currents (the CONFLUENCE project), in fracture zones in the mid-Atlantic
Ridge (the ROMANCHE experiment), and in the western tropical Atlantic (the
ETAMBOT program). This field program has been accompanied by a modelling
program in the South Atlantic, the MOCA project.
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CLIPPER
and WOCE aims |
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The final term of WOCE is the
Analysis, Interpretation, Modelling and Synthesis (AIMS) phase which
will last to the year 2002. As a contribution to WOCE-AIMS, the CLIPPER
project uses prognostic modelling and data assimilation to provide
a four dimensional picture of the ocean circulation in the Atlantic
which will contribute to the interpretation of observations collected by
the field program. A high resolution model is needed because of the high
resolution of the WOCE data, and the emphasis of the French program on
the Western and Eastern boundaries of the South Atlantic (regions were
narrow currents are found). A second objective of CLIPPER is to help
understand the role of local processes or features (such as mesoscale
eddies, boundary currents, bottom topography) in shaping the ocean
circulation at basin scale, its variability and its interactions with
the atmosphere.
Finally, CLIPPER contributes to the development and mastery of the ocean
models that will be used (in coupled mode with atmospheric models) for
climate prediction studies during CLIVAR, and of the modelling tools (high
resolution ocean models and data assimilation techniques) required by
the emerging operational oceanography.
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The
CLIPPER project team |
The CLIPPER numerical experiments are carried out by a
project team, made of scientists and engineers from 4 laboratories in France:
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LEGI
Grenoble
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LPO
Brest
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LEGOS
Toulouse
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LODYC
Paris
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Scientists and engineers
participating to the project team in 2001 are listed below :
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Laboratory
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Name |
Position |
Email |
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LEGOS (Toulouse)
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C. Le Provost |
CNRS scientist |
cleprovos@pontos.cst.cnes.fr |
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LEGI (Grenoble)
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B. Barnier |
CNRS scientist |
barnier@hmg.inpg.fr.fr |
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LEGI (Grenoble)
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J. M. Molines |
CNRS ITA |
molines@hmg.inpg.fr.fr |
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LEGI (Grenoble)
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A. P. de Miranda |
ADR |
miranda@hmg.inpg.fr |
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LEGI (Grenoble)
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J. Fagot |
ADR |
Josiane.Fagot@hmg.inpg.fr |
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LODYC (Paris)
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G. Madec |
CNRS scientist |
gm@lodyc.jussieu.fr |
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LPO (Brest)
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A. M. Treguier |
CNRS scientist |
treguier@ifremer.fr |
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LPO (Brest)
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Sylvain Michel |
UBO ITA |
smichel@ifremer.fr |
There are PhD and post-doctoral students working with
the CLIPPER team scientists (not listed here).
Besides the project
team, a number of scientists in the French oceanographic community have
participated in the definition of the various model configurations, and
are using the model output for their research (ongoing efforts are listed in the
CLIPPER final report, 2001).
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Organisation
of the project team |
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Project Scientific Coordinator
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Anne Marie Tréguier (LPO-Brest)
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Project Technical Coordinator
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Jean-Marc Molines (LEGI-Grenoble)
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Project Financial Coordinator
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Bernard Barnier (LEGI-Grenoble)
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Project Secretary
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Josiane Brasseur (LEGI-Grenoble)
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Co-ordination with the MERCATOR Project
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Christian Le Provost (LEGOS-Toulouse)
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Support |
The project is
supported by CNRS/INSU, IFREMER, CNES, SHOM, and Météo-France. Calculations
are performed at IDRIS, the super computer centre of CNRS in Orsay.
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Overview
of the various model configurations |
CLIPPER
uses the primitive equation code OPA8.1
maintained by Gurvan Madec (LODYC-Paris)
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Modelling
strategy |
The CLIPPER team has developed 4 model
configurations based on the same code, the primitive equation parallel code OPA.
The code has been developed at LODYC. The 8.1 version is used for CLIPPER. The
model solves the primitive equations (with rigid lid assumption). Second order
difference schemes are used on a C-grid.
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Configuration
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Name
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Boundaries
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Number of points
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Grid size
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Atlantic Low Resolution
(Mercator 1 degree)
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ATL1
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lon : 98.5W to 30E
lat : 75S to 70N
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131x218
42 levels
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min : 28 km
max : 111 km
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Medium Resolution Atlantic
(Mercator 1/3 degree)
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ATL3
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lon : 98.5W to 30E
lat : 75S to 70N
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387x649
42 levels
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min : 9.6 km
max : 37 km
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North Atlantic
(Mercator 1/3 degree)
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NATL
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lon : 98.5W to 20E
lat : 20S to 70N
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358x361
42 levels
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min : 12.6 km
max : 37 km
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High Resolution Atlantic
(Mercator 1/6 degree)
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ATL6
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lon : 98.5W to 30E
lat : 75S to 70N
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773x1296
42 levels
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min :4.8 km
max :18.5 km
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The grids are based on isotropic
Mercator grids. The maximum grid size is at the Equator, and the grid is refined
following the convergence of meridians. The refinement of the grid going
polewards is consitent with the decrease of the first baroclinic Rossby radius,
but does not follow it closely.
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The
low resolution configuration (1 degree) |
This configuration (ATL1) covers the
whole Atlantic ocean. The aim of this configuration within the CLIPPER project
was mainly to test the forcing fields and open boundary conditions over long
periods (20 years) to allow corrections to be made. This configuration has been
used to study interannual variability (forced by the NCEP reanalysis, PhD thesis
of J.O. Beissmann, LEGI, Grenoble). It has also served as a basis for
variational assimilation (PhD thesis of C. Deltel, LPO, Brest).
ATL1 has the same parameterisation as the other configurations, excepted for the
horizontal mixing which is harmonic rather than biharmonic due to low spatial
resolution. An isopycnal mixing of tracers, associated eventually with a
representation of potential vorticity mixing following Gent et al. (1995) is
supplied as an option in the OPA code.
This configuration runs on a workstation .
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The
medium resolution (1/3°) configuration ATL3 |
The configuration ATL3 has an
isotropic Mercator grid with resolution of 1/3° at the equator. The grid is
modified locally near the straits of Gibraltar to provide a higher resolution.
The aim of this configuration was to validate the model, forcing and boundary
conditions in an eddy-permitting configuration before performing the high
resolution experiment. A 22 years experiment has been run, forced by the
climatology of the ECMWF reanalysis ERA15. A detailed analysis of the solution
and boundary conditions has been performed (Treguier et al, 2001, in
"CLIPPER publications"). A subdomain of ATL3 covering the South
Atlantic has been used for model comparisons and assimilation studies (Penduff
et al, 2001). The ATL3 configuration is more costly than ATL1 but still
manageable. The memory required is 4.2 Gbytes and the configuration runs on 53
processors on a T3E.
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The
North Atlantic (1/3°) configuration NATL3 |
A first North Atlantic configuration
close to the one used in the DYNAMO project has been implemented to test the
code, initial conditions and forcing fields. This first configuration has a
closed boundary in the south. Differences with the DYNAMO experiments include
the parameterisation of vertical mixing by a turbulent closure, the
representation of strait of Gibraltar with a refined grid, the use of the ECMWF
reanalysis to force the model, and the new initial conditions for T and S.
This configuration serves as the basis for the first operational prototype PSYS
of the operational oceanography MERCATOR project (www.mercator.com.fr).
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The
high resolution (1/6°) configuration ATL6 |
The ATL6 configuration is the major
focus of the CLIPPER project. It has an isotropic Mercator grid with resolution
of 1/6° at the equator. The model has four open boundaries at the northern
limit of the domain (70°N), at 8°W in the Gulf of Cadiz, at the Drake passage
(68°W) and between Africa and Antarctica at 30°E. The locally modified grid
near the straits of Gibraltar used in the ATL3 configuration was not
satisfactory concerning the properties of the Mediterranean outflow, and has
been successfully replaced by an open boundary at 8°E. A 8 year spin-up has
been performed, and the simulation of the WOCE years, from 1979 to 2000 has been
carried-out with daily forcing from ECMWF.
Simulations with ATL6 are computationally heavy. The memory required is 16.2
Gbytes and the configuration runs on 140 processors on a T3E with a time step of
1080 sec. One year of simulation requires 5000 hours of cpu on this machine.
Five day means are stored every five days, and the storage of one year of
simulation amounts to 72 Gb.
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ATL6 bottom topography. Heavy red lines
indicate the
location of open boundaries. |
Splitting of the computational domain on
140 T3E processors |
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