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| Titel |
Modelling the spreading of the Western Mediterranean Deep Water formed during winter 2004-2005 : role of deep eddies |
| VerfasserIn |
Jonathan Beuvier, Cindy Lebeaupin-Brossier, Romain Bourdallé-Badie, Florence Sevault, Samuel Somot, Karine Béranger, Yann Drillet, Nicolas Ferry, Florent Lyard |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047258
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| Zusammenfassung |
| Our modelling study focuses on the role of deep processes responsible of the spreading of Western Mediterranean Deep Water (WMDW). The case study concerns the spectacular event that occured during winter 2004-2005. This event was characterized by a very extended convection area and a high formation rate of unusually warm and salty WMDW. The spreading of this water mass was relatively short according to measurements showing new WMDW characteristics throughout the western Mediterranean, towards the Gibraltar and Sardinia straits (Schroeder et al. 2008).
We use the free-surface NEMO OGCM (Madec 2008) in a regional configuration of the Mediterranean Sea with a 1/12° resolution (MED12) developped within the framework of the SiMED project funded by Mercator Océan. This model is eddy-resolving. The exchanges with the Atlantic Ocean are modelled with a relaxation to the Levitus (2005) climatology. The initial conditions for temperature and salinity come from the Medatlas-II database (Rixen et al. 2005). Climatological runoff and Black Sea inputs are used (Beuvier et al. 2010). The ocean model is forced during the period 1998-2008 by the atmospheric fields derived from the ARPERA fluxes and winds (Herrmann et al. 2010). The bottom friction is quadratic and function of the horizontal speed and the mean tide energy E.
Three companion simulations were carried out by modifying E and the scheme to conserve the water volume in the model:
- the control simulation EXP0 is characterized by a constant E and the excess of Mediterranean evaporation is put as rain in the Atlantic area at each time step,
- the simulation EXP1 differs from EXP0 by only E, which is estimated from a tide model,
- the simulation EXP2 differs from EXP1 by applying in the Atlantic Ocean a relaxation of the sea surface height towards a climatological estimate from GLORYS-1 simulation (Ferry et al. 2010).
The simulations reproduce the exceptionnal convection event of the winter 2004-2005 and the spreading of a new water mass in the western Mediterranean. Several diagnostics (surface circulation, variations of the heat and salt contents in the north-western Mediterranean, heat and water budgets in the Gulf of Lions area, spatial extent of the convection area, thermohaline characteristics and WMDW formation rate) are compared to observations. The spreading is investigated with lagrangian diagnostics, pointing out the importance of deep eddies. The comparison of the sensitivity simulations also highlights the effects of the boundary conditions. The most important volume of WMDW is indeed formed in EXP2, allowing a more substantial spreading of this water mass in the western Mediterranean. |
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