Simulations, reanalyses, processes

The ocean is a complex system that cannot be understood by the mere theoretical thinking, or the mere examination of observations. It is necessary to simulate explicitly its behaviour using models as accurate as possible (simulations), or to reconstruct its time evolution by assimilation of all available obsrvations (reanalyses). The study and interpretation of these simulations and reanalyses is thus an new problem by itself, that requires analyzing these huge amounts of data, to better describe and therefore better understand the functionning of the ocean.

Snapshot of sea surface elevation (with respect to the reference geoid), as simulated by the DRAKKAR global ocean configuration (at a 1/4 resolution) of the NEMO model. Snapshot of temperature at 180~m depth in the Labrador sea, as simulated by a regional CLIPPER configuration (at 1/15 resolution) using the AGRIF. mesh refinement tool.

On the one hand, the DRAKKAR project gives the framework of the MEOM numerical simulations of the ocean. Our objectives are the study of the ocean global circulation (with a special focus on the North Atlantic and Nordic Seas), and the understanding of the mechanisms explaining the variability of these regions for the last 50 years (a period of intense industrical activity, with fast increase of the CO2 concentration in the atmosphere). A special interest is given to the exchanges between gyres or basins, and to the impact of specific regions on the global ocean circulation. Meridional exchanges mainly occur in the turbulent frontal regions, separating the large scale circulation cells, or accross the Northern Straits in the Atlantic. The dynamics of these regions is dominated by strong scale interactions, imposing to study altogether time scale ranging from days to decades, and spatial scales ranging from mesoscale to basin scale.

Meridional section (longitude 30W) of the North Atlantic mean salinity (year 1970-2000) as simulated by the DRAKKAR global ocean configuration (at a 1/4 resolution) of the NEMO model. Mean overturning circulation (in Sv) in the North Atlantic (year 1970-2000) as simulated by the DRAKKAR global ocean configuration (at a 1/4 resolution) of the NEMO model. Surface chlorophyle concentration in June, as simulated by a 1/3 resolution coupled circulation and ecosystem model of the North Atlantic.

On the other hand, the MEOM team is involved in the scientific study of ocean reanalyses, with a special focus on the following problems:

Temperature snapshot in the Gulf Stream region, as reconstructed by assimilation of altimetry and sea surface temperature observations, in a CLIPPER 1/3 model of the North Atlantic. The three-dimensional field is cut along 2 isosurfaces: the surface (situated in the warm vein in yellow and red) along which velocity is 0.9 m/s, and the surface (in green) along which temperature is 10C. Snapshot of temperature and sea surface elevation along the equator in the Tropical Pacific, as reconstructed by assimilation of altimetry and TAO temperature profiles in a global low resolution (2x1/2 in that zone) configuration of the NEMO model. In a normal situation (no el niño event), the sea surface elevation is higher and the thermocline deeper in the Western part of the basin. [Animation]