Mercator Ocean is the French center for analysis and forecasting of the global ocean and is based in Ramonville Saint-Agne, near Toulouse. Since May 2015, Mercator Ocean is entrusted by the European Commission to implement and operate the Copernicus Marine Environment Monitoring Service (CMEMS).
Mercator Ocean is a privately-owned non-profit company. It provides a service of general interest to France and Europe as a whole. The organisation was founded and is funded by the five major French institutions involved in operational oceanography: CNRS (National Center of Scientific Research), Ifremer (French Research Institute for Exploitation of the Sea), IRD (Institute of Research for Development), Météo-France and SHOM (Hydrographic and Oceanographic Service of the French Navy).
Mercator Ocean describes analyses and forecasts Ocean conditions at the surface or at depth, on a global scale or for a specific zone, in real-time or delayed mode. The numerical models and systems developed by Mercator Ocean are able to describe the physical state of the ocean at any given time for the following parameters: temperature, salinity, sea surface height, ice thickness, currents and biochemistry tracers.
Operational systems descriptions
Mercator operates its first system in 2001, based on OPA ocean model (OPA is now the “blue” component of NEMO). Now, Mercator Ocean operates global forecasting systems and produces global and regional reanalysis, all based on NEMO ocean model, coupled to a data assimilation system:
- The global forecasting system is based on NEMO’s “blue” component OPA and its “white” component LIM2 and is running on the ORCA grid at 1/4° resolution 1/12° ;
- The biogeochemical forecasting system is based on the passive tracers transport module TOP and the PISCES biogeochemical model and are running on the 1/4° resolution ORCA grid;
- Global physical reanalysis GLORYS and biogeochemical reanalysis are running the ORCA grid at 1/4° resolution;
- Mercator is also developing regional forecasting systems and reanalysis, like the Ireland-Biscay-Iberian (IBI) configuration at 1/36° resolution.
Interests in NEMO OGCM
In order to improve the operational systems, Mercator’s ocean modellers are working on several aspects of the NEMO model:
Improvement of the vertical physics: vertical mixing parametrization, light penetration scheme, ocean/waves interaction;
Improvement of the surface boundary condition: development of an Atmospheric Boundary Layer (space and time downscaling of the atmospheric forcing ) and upgrade of Sea ice to the multi category LIM3 sea ice model;
Tide forcing: the tide is already used in regional reanalysis and operational forecasting system, main objective is now to improve configuration including tide and to move to global configuration for short term forecast but also for long inter-annual reanalysis;
Horizontal coordinate: increase the resolution of the global and regional forecasting system: at global scale an operational system at ~2 km resolution could be envisaged and at regional scale the resolution could be less than 1km.
Vertical coordinate: Using a z~ ALE vertical coordinates could reduce spurious numerical mixing and using a generalized vertical coordinate could improve water masses representation;
Numerical schemes: To use NEMO model at higher resolutions, higher order advection scheme are needed, with a limited CPU cost;
AGRIF is the two-way nesting tool available in NEMO, it has been developed since several years and is currently used for R&D activities, to test and validate some numerical approaches. It will be used to define the next version of the global high resolution operational forecasting system, especially to define precisely the optimal resolution and the numerical schemes adapted to this resolution. The option consisting in AGRIF zooms in strategic areas in a global configuration will be also investigate.;
The ensemble approach is essential in operational oceanography to move to an ensemble data assimilation method which will allow a much better representation of the error covariances and to move from a deterministic to an ensemble forecast. NEMO already includes stochastic parametrization, perturbation method and technical solution to perform ensemble simulation. The huge numerical coast and the huge quantity of model output generated by such method will imply new development to optimize the method to perturb the model and to optimize the IO library.