Seasonal ATLAS

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Seasonal ATLAS Powered By Docstoc
					                                  Seasonal Atlas of

                    the Western Mediterranean Sea

                             from climatologies and

high resolution numerical models of Mercator



                                      by FLORE MOUNIER1,2,

      Karine Béranger1,2, Romain Bourdalle-Badie3, Yann Drillet3 & Laure Siefridt3




1
    LODYC, Tour 26, 4e étage, boite 100, 4 Place Jussieu, 75252 Paris Cedex 05, France

                        mounier@lodyc.jussieu.fr, beranger@lodyc.jussieu.fr
          2
              ENSTA, UME, Chemin de la Hunière, 91761 Palaiseau Cedex, France
               3
                   CERFACS, Mercator Project, Gustave Coriolis, Toulouse, France

                     bourdall@cerfacs.fr, drillet@cerfacs.fr,,siefridt@cerfacs.fr
Introduction

Results from modelling projects and climatological databases for the Mediterranean
Sea are now available. This atlas has been designed as a flexible tool to compare
outputs from general circulation models with climatologies derived from observations.
It has been implemented for PAM and MED16 present simulations (see part I) but it
will be used for further simulations.

Basically, in the Western Mediterranean Sea, three major water masses are identified
according to their formation sites:

      - one in the upper layer, the Modified Atlantic Water (MAW) which originates
       from the Strait of Gibraltar;
      - another one at mid-depth, the thick layer of the Levantine Intermediate Water
       (LIW), that propagates from the eastern basin to the western basin;
      - and finally one at the bottom, which is a reservoir filled by Western
       Mediterranean Deep Water (WMDW) which are produced during the winter
       season in the Gulf of Lions.

This atlas allows to compare views of seasonal horizontal distributions of properties
at significant levels of these water masses : temperature, salinity, velocities, eddy
Kinetic Energy. The barotropic stream function is also available. Seasonal vertical
distributions of temperature and salinity are shown for 11 preselected sections.

Part I provides a description of the four simulations and Part II shortly describes the
two climatologies. Part III describes useful information concerning the positions of the
vertical sections and the descriptions of the figures.




I. Simulations from high resolution models of Mercator



A very high resolution model of the Mediterranean Sea has been developed in the
context of the MERCATOR project (Bahurel et al., 2002; www.mercator.com.fr). The
PAM model (the Atlantic-Mediterranean Prototype, in French 'Prototype Atlantique
Méditerranée'; Drillet et al., 2000; Béranger et al., 2001; Siefridt et al., 2002) uses a
1/16°coshorizontal grid mesh (the latitude), and 43 z-levels on the vertical. The
horizontal grid is stretched at Gibraltar in order to better fit the coast line (Blanchet
and Siefridt, 1998). The topography is based on the 1/30° bathymetry (Smith and
Sandwell, 1997) averaged onto the 1/16° grid. The numerical model is an extended
version of the primitive equation numerical model OPA (Ocean PArallel, Madec et al.,
1997) with the rigid lid approximation. The horizontal diffusion is parameterised by a
biharmonic operator. On the vertical, the mixing is parameterised by a turbulent
kinetic energy scheme. The model has been forced by daily atmospheric fluxes from
ECMWF analyses over the period March 1998 to June 2002. This choice was
motivated by the relatively fine resolution of the fluxes allowed from March 1998 at
the ECMWF centre (0.5° per 0.5°, TL319 grid). It is know that the resolution of the
atmospheric forcings can play a major role to simulate some circulation patterns
(Horton et al., 1994; Lascaratos and Hatziapostolou, 2001). The fluxes are applied
using the flux correction method (Barnier et al., 1995) with a retroaction coefficient .
In the retroaction term, the model sea surface temperature (SST) is relaxed to the
climatological SST. Freshwater fluxes (Evaporation, Precipitation, River runoffs) are
put as a virtual salt flux, with an added term that relaxes the model sea surface
salinity (SSS) toward the climatological SSS. For the Mediterranean Sea, runoffs of
31 rivers (Vörösmarty et al., UNESCO, 1996) are incorporated using an upstream
scheme at the river mouth. The Black Sea discharge is modelled using the estimates
of Stanev et al. (2000). The Atlantic Ocean initial state was provided by the seasonal
climatology of Reynaud et al. (1998) . The simulations PAM-20 and PAM-21 (see
below), which have been incorporated in this atlas have been computed at the
ECMWF centre (Drillet et al., 2000).

The second model MED16 uses the Mediterranean the configuration of the PAM
model but on a smaller domain. MED16 has been extracted from the PAM model and
the exchanges with the Atlantic Ocean are modelled by an Atlantic box (bufferzone).
The simulations MED16-05 and MED16-07 (see below) have been done at the IDRIS
centre (Béranger, 2001; Béranger et al., 2002).



1. PAM simulations



In the PAM model, the diffusivity coefficients are taken equal to -3.109 m2.s-1 for the
tracers and equal to –9.109 m2.s-1 for the velocities. A free slip condition is used and
the time step is 900s. Only the major Mediterranean rivers (large runoff) are
represented according to MED16.



PAM-20

- Duration of the simulation : about 5 years

- Initial state in the Mediterranean Sea : MODB5 seasonal climatology

- Atmospheric forcing : the PAM model has been forced, during 16 months by the
daily fluxes averaged over the period March 1998 to February 2001, and then by
interannual fluxes from March 1998 to February 2001

- Retroaction term for SST : the model SST is relaxed to the weekly SST of Reynolds
estimated from satellite data, with a constant coefficient equal to –20 W.m-2

- Relaxation term for SSS : the model SSS is relaxed to the MODB5 climatological
SSS with a constant coefficient equivalent to =–20 W.m-2 .
PAM-21

- Duration of the simulation : about 5 years

- Initial state in the Mediterranean Sea : MEDATLAS-II seasonal climatology (that
comes from an averaged of monthly means)

- Atmospheric forcing : the PAM model has been forced, during 16 months by the
daily fluxes averaged over the period March 1998 to February 2001, and then by
interannual fluxes from March 1998 to June 2002

- Retroaction term for SST : constant coefficient equal to -40 W.m-2, using
Reynolds SST

-Relaxation term for SSS : constant coefficient equivalent to -40 W.m-2, using
MEDATLAS-II climatological SSS.



MED16 simulations

          1.

In the MED16 model, the diffusivity coefficients are taken equal to -4.109 m2.s-1 for
tracers and velocities. A no slip condition is used at the coast. The time step is 600s.



MED16-05

- Duration of the simulation : 11 years

- Initial state : MODB5 seasonal climatology

- Atmospheric forcing : daily air-sea surface fluxes applied in a yearly perpetual mode
(period March 1998 to February 1999)

- Retroaction term for SST : constant coefficient equal to -40 W.m-2 using
Reynolds SST

- Relaxation term for SSS : constant coefficient equivalent to -40 W.m-2 using
MODB5 climatological SSS.
MED16-07

- Duration of the simulation : 13 years

- Initial state in the Mediterranean Sea: MEDATLAS-II monthly climatology

- From year 1 to year 8 :

          - Amospheric forcing : daily fluxes applied in a yearly perpetual mode (year
          2000). The net heat flux has been corrected by a factor of 1.12 to allow the
          heat budget to be equal to –7 W.m-2 over the Mediterranean Sea, a value
          commonly known (Béthoux, 1980)

          - Retroaction term for SST : the model SST is relaxed to the climatological
          SST with a coefficient . ranges from –10 in winter to –40 W.m-2 in
          summer. Spatial means of this retroaction term have been applied over a
          box of half a degree

          - Relaxation term for SSS : the model SSS is relaxed to the MEDATLAS-II
          climatological SSS with a coefficient equivalent to =–40 W.m-2. Spatial
          means of this relaxation term have been applied over a box of half a
          degree

- From year 9 to year 13 :

          - Atmospheric forcing: daily fluxes over the period March 1998 to June
          2002. No correction of the net heat flux budget was applied (balance
          around -30 W.m-2). The net evaporation budget is about 700 mm.yr-1, a
          value in agreement with the compilation of Boukthir and Barnier (2000)

          - Retroaction term for SST : the model SST is relaxed to the weekly SST of
          Reynolds (2 and spatial means) from March 1998 to December 2000, and
          then to the daily SST of Reynolds (2 and spatial means) from January
          2001 to May 2002

          - Relaxation term for SSS : the model SSS is relaxed to the MEDATLAS-II
          climatological SSS with a coefficient equivalent to = –40 W.m-2 (spatial
          means).




II. Climatologies



Two climatologies have been used for the initial state of the models. The MODB5
seasonal climatology of Brasseur et al. (1996) and the monthly climatology of the
MEDATLAS/MEDAR group (2002). These climatologies have been interpolated onto
the Mediterranean grid of the PAM-MED16 models. These interpolated fields are
showed in this atlas. More informatiosn are available at the following WWW
locations :

MEDATLAS:           http://modb.oce.ulg.ac.be/Medar/medar.html
and                 http://www.ifremer.fr/sismer/program/medar/


MODB                 http://modb.oce.ulg.ac.be/atlas/atlas.html




III. Useful informations



1. Atlas interface

Access to the data can be done by two different ways:

- Through the html interface by selecting a figure with a click on the mouse, a quick
look of a low resolution which size is adjusted user’s screen size

- By downloading the figure (jpeg format), a high resolution figure can be obtained.

The atlas is organised in two parts given on the main page of the interface : model
results and climatologies. For both, figures for the four seasons are proposed (winter
= January to March). A selection of sections (Part III.1) is proposed for each
parameter.




2. Sections available in the atlas

- Horizontal sections are located at surface and 400 meter depth levels.

- A full line and a name on the following figure indicate vertical sections. Their
detailed positions are given in Tab.1. The vertical fields are characterised by a colour
scale that does not change neither with seasons nor with sections. On the other
hand, the contour scales change according to season and section to follow easily the
major water masses through the whole basin.
                                Begin                             End
    Section         Longitude           Latitude      Longitude         Latitude
     MED1            -5.65°E            35.78°N        -5.90°E          36.15°N
    MED3-4            3.09°E            36.08°N         3.09°E          41.78°N
     MED5             1.55°E            39.10°N         2.41°E          39.55°N
     MED8             9.16°E            37.10°N         9.16°E          39.16°N
     MED9             9.47°E            42.98°N         9.47°E          44.42°N
     MED10            9.59°E            42.43°N       11.16°E           42.43°N
     MED11           11.09°E            37.05°N       12.53°E           37.99°N
     MED26            0.28°E            36.04°N         0.28°E          38.73°N
     MED27            4.34°E            39.84°N         16°E            39.84°N
     MED28            0.16°E            38.63°N         1.28°E          38.92°N
     MED29           6.28°E          36.85°N            6.28°E          42.98°N
Tab.1: Geographical coordinates of the vertical sections presented in the atlas.

   3.
   4.
3. Figures



Model results: temperature, salinity, velocity, barotropic stream function,
and eddy kinetic energy

For each parameter, the same section (Tab.1) is plotted for the four simulations, and
is indicated at the top of the figure, with the chosen season, the location of the model
results inside the figure, and, the name of the chosen parameter. The same palette is
used for the four figures.

For example, for the potential temperature in winter at the vertical section med1, the title of the figure
is :

' Section : med1 / Season: Winter / MED16-05 (top-left), MED16-07 (top-right), PAM-20 (bottom-left),
PAM-21 (bottom-right) / Temperature '

The winter temperature of MED16-05 is put at the top-left in the figure, the winter temperature of
MED16-07 is put at the top-right in the figure, the winter temperature of PAM-20 is put at the bottom-
left in the figure, and the winter temperature of PAM-21 is put at the bottom-right in the figure.

    
    


Climatological fields: temperature and salinity

Temperature and salinity of the two climatologies have been plotted on the same
page. Figures are organised as follows : At the top of the page, the name of the
section is indicated with the chosen season, the location of the climatological results
inside the figure, and, the names of the chosen parameters. One common palette is
used per parameter.

For example, in winter at the vertical section med1, the title is :

Section : med1 / Season: Winter / MEDATLAS-II (left), MODB5 (right), Temperature (top), salinity
(bottom)

The winter temperature of MEDATLAS-II is put at the top-left in the figure, the winter temperature of
MODB5 is put at the top-right in the figure, the winter salinity of MEDATLAS-II is put at the bottom-left
in the figure, and the winter salinity of MODB5 is put at the bottom-right in the figure.




    
Useful information




Horizontal sections

TEMPERATURE                     Isotherms every 0.05°C
VELOCITY                   One vector of five is plotted (m.s-1)
SALINITY                       Isohalines every 0.1 psu
EDDY KINETIC ENERGY           Isoclines every 0.5 cm2.s-2
BAROTROPIC STREAM FUNCTION       Isoclines every 1.5 Sv




Vertical sections

                       Annual
                EDDY KINETIC ENERGY
            Section   Isoclines in cm2.s-2
                      every 0.5 up to 5
              MED1
                      then every 5
                      every 1 up to 10
             MED3-4
                      then every 2.5
                      every 1 up to 10
              MED5
                      then every 2.5
             MED8     every 2
             MED9     every 0.5
             MED10    every 0.5
             MED11    every 1
                      every 0.5 up to 5
             MED26
                      then every 2
             MED27    every 2
             MED28    every 1
                      every 1 up to 10
             MED29
                      then every 5
                     Winter & Autumn
                TEMPERATURE                   SALINITY
Section
                 Isotherms in ° C          Isohalines in psu
                                      from 36.3 to 37.5 by 0.2
          from 12.7 to 13.6 by 0.05
MED1                                  then every 0.05 until 38.2
          then every 0.4
                                      then every 0.025
       from 12.4 to 13 by 0.05
                                      from 36.3 to 38.2 by 0.1
MED3-4 then every 0.1 until 13.3
                                      then every 0.025
       then every 0.5
          from 13 to 13.3 by 0.025    from 36.3 to 37.5 by 0.2
MED5      then every 0.1 until 13.5   then every 0.05 until 38.2
          then every 0.2              then every 0.025
          from 12.4 to 14 by 0.1      from 37 to 38.6 by 0.1
MED8
          then every 0.4              then every 0.05
      12.7
                                      from 37 to 37.9 by 0.2
 MED9 from 12.8 to 14.3 by 0.05
                                      then every 0.05
      then every 0.4
      12.7
                                      from 37.3 to 37.9 by
MED10 from 12.8 to 14.3 by 0.05
                                      0.05     then every 0.1
      then every 0.4
      12.7
      13.2                            from 37.3 to 38.6 by 0.1
MED11
      from 13.7 to 15 by 0.05         then every 0.025
      then every 0.25
      from 12.7 to 13.3 by 0.05       from 36.3 to 37.5 by 0.2
MED26 then every 0.1 until 14         then every 0.05 until 38.2
      then every 0.4                  then every 0.025
                                      from 37 to 38.4 by 0.2
      from 12.7 to 13.6 by 0.05
MED27                                 then every 0.05 until 38.6
      then every 0.2
                                      then every 0.025
          from 12.7 to 13.6 by 0.05   from 37 to 37.5 by 0.1
MED28
          then every 0.4              from 38.2 to 38.7 by 0.025
          from 12.7 to 13.6 by 0.05   from 37 to 38.4 by 0.1
MED29
          then every 0.4              then every 0.02
                    Spring & Summer
               TEMPERATURE                    SALINITY
section
                Isotherms in °C            Isohalines in psu
          from 12.8 to 13.9 by 0.1
                                      from 35.5 to 38 by 0.5
MED1      then every 0.2 until 15
                                      then every 0.1
          then every 0.4
       from 12.4 to 13 by 0.05        from 36.2 to 38.3 by 0.2
MED3-4 then every 0.1 until 13.3      then every 0.025 until 38.7
       then every 0.5                 then every 0.1
          from 12.9 to 13.3 by 0.05   from 37 to 38.1 by 0.5
MED5
          then every 0.5              then every 0.025 from 38.2
                                      from 37 to 38.4 by 0.2
          from 12.4 to 14 by 0.1
MED8                                  then every 0.05 until 38.5
          then every 0.4
                                      then every 0.025
          12.7
MED9      from 12.8 to 14 by 0.1      every 0.04 from 37.3
          then every 0.4
          from 13 to 13.6 by 0.1      from 37.3 to 38.5 by 0.1
MED10
          then every 0.1              then every 0.025
          from 13.7 to 15 by 0.05     from 37.3 to 37.9 by 0.1
MED11
          then every 0.1              then every 0.2
                                      38.2 to 38.4 by 0.1
MED26 every 0.05 from 12.7            then 38.425
                                      then every 0.01
                                      38.4
                                      38.45
MED27 every 0.1 from 12.7
                                      38.525
                                      then every 0.05
          from 12.7 to 13.2 by 0.05   from 37 to 38.225 by 0.2
MED28
          then every 0.4              then every 0.05
          from 12.7 to 13.6 by 0.1    from 37 to 38.422 by 0.2
MED29
          then every 0.4              then every 0.02
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