12° global configuration (ORCA12)

• Earth's sphericity: local gravity directed towards the centre of the Earth
• Relatively shallow water: ocean depth small in relation to the Earth's radius
• Hydrostatic: equilibrium between the vertical pressure gradiant and the floatability
• Boussinesq values: variations in density are not taken into account apart from their contribution to floatability
• Incompressibility: the three-dimensional divergence of the velocity field is considered to be nil
• 1.5 order closure turbulence scheme
• Non-linear equation of state couples the two active trace indices (temperature and salinity)
• Linearised and filtered free surface
• Nested with LIM sea ice model

• Model state variables : temperature, salinity, zonal and meridian velocity, free surface elevation and vertical diffusivity coefficient
• Sea ice variables: thickness ice, ice production, ice concentration, ice temperature, ice/sea interface flux, zonal and meridional ice velocity
• Atmospheric forcing: zonal and meridional wind stress, penetrating heat flux, solar flux, non solar flux, salt flux, snow flux, precipitation and runoff minus evaporation budget
• Diagnostic variables: mixed layer depth (density diagnostic), mass transport by density class through sections, meridional heat transport

• Diffusion: laplacian isopycnal operator (100 m2/s)
• Viscosity : bilaplacian horizontal operator (-1 E10 m2/s)
• Energy and enstrophy conserving advection scheme
• TKE (turbulent kinetic energy) vertical mixing model
• Partial slip lateral boundary friction condition
• Non linear bottom friction
• Partial step vertical coordinate

A restoring zone is applied in the Gulf of Cadiz.

1/12° ORCA grid on the whole domain, i.e. 3 to 10 Km. Number of points : 4322 x3059

ORCA12 resolution (Km)

50 levels. From 1 m at the surface, to 450 m at the bottom

ORCA12 vertical resolution (see black diamonds)

Bulk formulation (CLIO). The monthly climatological flow of the 120 main rivers is taken into account in the evaporation minus precipitation budget. The fresh water budget water is made in interannual mode. A parameterization of the penetrating heat flux is used.

ECMWF (2000-2005) daily operational analysis. Zonal and meridional wind stress components, wind module, relative humidity, cloud coverage, rain, air temperature.

Monthly Levitus temperature and salinity from Levitus 98

Combination between: ETOPO2, for open ocean, BEDMAP (Lythe et al., 2001), for Antarctic and GEBCO (IOC, 2003) for continental shelves

ORCA12 Bathymetry (m)

• 414 Gigabytes of memory
• 90 000 CPU hours
• 1 Terabyte of output (daily output)

2008