Last updated on August 29, 2012.

Specification of COCO

Current version: 4.9

Model equations and coordinate system

Boussinesq and hydrostatic
Explicit free surface
Generalized curvilinear horizontal coordinate (tripolar coordinate is available)
Z-sigma hybrid vertical coordinate
Multi-category sea ice with elastic-visco-plastic rheology and 1-layer thermodynamics

Discretization

Finite-difference with the Arakawa B horizontal staggered grid
Staggered time stepping (velocities are defined at different time levels from tracers by a half of model time step)
Partial step bottom topography representation (Adcroft et al., 1997, MWR)
Barotropic-baroclinic mode split for horizontal velocity
Time split in solving the barotropic mode

Numerical algorithms and physical parameterizations in standard use

Momentum advection

The second-order, energy-conserving algorhitm for coarse resolution.
A pseudo-enstropy preserving scheme with up-/down-sloping advection (Ishizaki and Motoi, 1999, JAOT) for eddy-resolving cases.

Tracer advection

QUICKEST (Leonard, 1979) for vertical advection and UTOPIA (Leonard et al., 1993: multidimensional QUICKEST) for horizontal advection.
A second order moment preserving scheme (Prather, 1986, JGR) is also available.

Vertical convection

Convective adjustment.

Vertical mixing

Two equation closure based on a generic length scale concept (Umlauf and Burchard, 2003, JMR).

Background vertical profiles are prescribed for vertical viscosity and diffusion. The background viscosity coefficient is 1.0x10^4 m^2/s at all levels in most application. The background vertical diffusion coefficient of Tsujino et al.'s (2000, JPO) type III is often used. The background vertical diffusion coefficient is lowered at low latitudes by following the functional form of Gregg et al., (2003, Nature).

Lateral mixing of momentum

The constant coefficient harmonic viscosity for coarse resolution.
The shear-dependent coefficient (Smagorinsky, 1963, MWR) biharmonic viscosity for eddy-resolving/permitting resolution.

Lateral mixing of tracer

The constant coefficient harmonic isopycnal diffusion (Cox, 1987) and layer thickness diffusion (Gent and McWilliams, 1990, JPO) for coarse resolution.
The constant coefficient biharmonic horizontal diffusion for eddy-resolving/permitting resolution.