MEDRYS1: A New Mediterranean Sea Reanalysis Over 1992-2013
Mathieu Hamon1, Jonathan Beuvier1,2, Jean-Michel Lellouche1, Eric Greiner 3, Antoinette Alias2, Thomas
Arsouze4, Mounir Benkiran3, Karine Béranger4, Yann Drillet1, Florence Sevault2, Samuel Somot2
1
Mercator Océan, 8-10 rue Hermès, Parc Technologique du Canal, 31520 Ramonville Saint-Agne, FRANCE
2
CNRM-GAME, Météo-France/CNRS, 42 avenue Coriolis, 31057 Toulouse Cedex, FRANCE
3
CLS, 8-10 rue Hermès, Parc Technologique du Canal, 31520 Ramonville Saint-Agne, FRANCE
4
UME, ENSTA-ParisTech, 828 Boulevard des Maréchaux, 91762 Palaiseau Cedex, FRANCE
The French research community on the Mediterranean Sea and the French operational ocean
forecasting center Mercator Océan are gathering their skills and expertises in physical oceanography,
ocean modelling, atmospheric forcings and data assimilation, to carry out a MEDiterranean Sea
ReanalYsiS (MEDRYS) at high resolution for the period 1992-present. The reanalysis is used to have a
realistic description of the ocean state over the recent decades and it will help to understand the longterm water cycle over the Mediterranean basin in terms of variability and trends. This work is done
under the framework of the LEFE/GMMC project SiMED-2 (Simulating the general circulation in the
Mediterranean Sea at meso-scale).
The ocean model used is NEMOMED12 [1; 2; 3; 4], a Mediterranean configuration of NEMO [5], with
a 1/12° (~ 7 km) horizontal resolution and 75 vertical z-levels with partial steps. It is forced by the 3hourly atmospheric fluxes coming from an ALADIN-Climate simulation at 12 km of resolution [6],
driven by the ERA-Interim atmospheric reanalysis. The exchanges with the Atlantic Ocean are
performed through a buffer zone, with a damping on 3D θ-S and on sea level towards the ORA-S4
oceanic reanalysis [7].
This model configuration is used to carry a 34-year free simulation over the period 1979-2013. This
free simulation is the initial state of the reanalysis in October 1992. It is also used to compute
anomalies from which the data assimilation scheme derives required characteristic covariances of the
ocean model.
MEDRYS1 uses the current Mercator Océan operational data assimilation system [8]. It uses a reduced
order Kalman filter with a 3D multivariate modal decomposition of the forecast error. A 3D-Var
scheme corrects biases in temperature and salinity for the slowly evolving large-scale. In addition,
some modifications dedicated to the Mediterranean area (more specific Post-Glacial-Rebound
corrections, new model-equivalent for the Sea Level Anomaly for example) have been introduced.
Temperature and salinity vertical profiles from the newly released CORA4 database, altimeter data and
satellite SST and are jointly assimilated.
We assess here the ability of a MEDRYS1 to reproduce the general circulation and the water masses in
the Mediterranean Sea. We present the misfit between the reanalysis and the assimilated observations,
as well as differences between the reanalysis and its twin free simulation. We show diagnostics on the
surface circulation variability, heat and salt contents and deep water formation over the whole period of
the reanalysis.
[1] Lebeaupin Brossier, C., K. Béranger, C. Deltel, P. Drobinski, The Mediterranean response to
different space-time resolution atmospheric forcings using perpetual mode sensitivity simulations,
Ocean Modelling, 36, 1-25, doi:10.16/j.ocemod.2010.10.008 (2011)
[2] Lebeaupin Brossier, C., K. Béranger, P. Drobinski, Sensitivity of the northwestern Mediterranean
Sea coastal and thermohaline circulation simulated by the 1/12°-resolution ocean model NEMOMED12 to the spatial and temporal resolution of atmospheric forcing, Ocean Modelling, 43-44, 94-107,
doi:10.1016/j.ocemod.2011.12.007 (2012)
[3] Beuvier, J., K. Béranger, C. Lebeaupin-Brossier, S. Somot, F. Sevault, Y. Drillet, R. BourdalléBadie, N. Ferry, and F. Lyard, Spreading of the Western Mediterranean Deep Water after winter 2005:
time-scales and deep cyclone transport, Journal of Geophysical Research, 117, C07022,
doi:10.1029/2011JC007679 (2012a)
[4] Beuvier, J., C. Lebeaupin-Brossier, K. Béranger, T. Arsouze, R. Bourdallé-Badie, C. Deltel, Y.
Drillet, P. Drobinski, N. Ferry, F. Lyard, F. Sevault, and S. Somot, MED12, oceanic component for the
modeling of the regional Mediterranean Earth System, Mercator Ocean Quaterly Newsletter, 46,
Octobre 2012, 60-66 (2012b)
[5] Madec, G., and the NEMO Team, NEMO ocean engine. Note du Pôle de modélisation, Institut
Pierre-Simon Laplace (IPSL), France, n° 27, ISSN n° 1288-1619 (2008)
[6] Herrmann, M., S. Somot, S. Calmanti, C. Dubois, and F. Sevault, Representation of spatial and
temporal variability of daily wind speed and of intense wind events over the Mediterranean Sea using
dynamical downscaling: impact of the regional climate model configuration, Natural Hazard Earth
System Sciences, 11, 1983-2011 (2011)
[7] Balmaseda, M.A., Mogensen, K., and Weaver, A., Evaluation of the ECMWF Ocean Reanalysis
ORAS4, Quaterly Journal of the Royal Meteorological Society, 139(674), 1132-1161,
doi:10.1002/qj.2063 (2012)
[8] Lellouche, J.-M., Le Galloudec, O., Drévillon, M., Régnier, C., Greiner, E., Garric, G., Ferry, N.,
Desportes, C., Testut, C.-E., Bricaud, C., Bourdallé-Badie, R., Tranchant, B., Benkiran, M., Drillet, Y.,
Daudin, A., and De Nicola, C., Evaluation of global monitoring and forecasting systems at Mercator
Océan, Ocean Science, 9(1), 57-81, doi:10.5194/os-9-57-2013 (2013)