Dynamical core

Atmosphere dynamical core 

CCAM employs a non-hydrostatic, semi-implicit, semi-Lagrangian dynamical core.  The use of a semi-Lagrangian dynamical core allows for larger time-steps which is useful for simulating the regional atmospheric dynamics over climate time-scales.  The dynamical core also produces a credible kinetic energy spectra (see below), which is a measure of the quality of the dynamical core. 

The design of the CCAM dynamical core is documented in mcgregor2005_overview.pdf.  An important feature of CCAM is its reversibly staggered grid that allows CCAM to transform between Arakawa C and A grids and then transform back again while restoring the winds to their original state.  The reversibly staggered grid approach improves the dispersive properties of the simulation. 

The non-hydrostatic model is based on the Miller-White approach.  The Miller-White equation is included by modifying the Helmholtz equation, which allows CCAM to generate a non-hydrostatic solution without a noticeable increase in computation.

Ocean dynamical core

CCAM also supports an ocean dynamical core.  The ocean dynamical core also uses semi-implicit, semi-Lagrangian methods.  However, it is currently hydrostatic (valid to 1km resolution), is based on sigma-z coordinates and assumes a Boussinesq fluid.  Unlike other ocean dynamical cores, the CCAM ocean model exploits the reversibly staggered grid to improve the ocean dispersive properties.  Since the atmosphere and ocean grids are co-located, then coupling between the atmosphere and ocean is computationally highly efficient.  As a result the coupling between the atmosphere and ocean models occurs every time-step.