Cube-based atmospheric GCMs at CSIRO
Two cube-based atmospheric GCMs have been developed at CSIRO, the Conformal-Cubic Atmospheric Model (CCAM) and, more recently, the Variable Cubic Atmospheric Model (VCAM). The design of the dynamical cores of both models will be described and compared. CCAM is formulated on the conformal-cubic grid, and employs 2-time-level semi-Lagrangian semi-implicit numerics. On the other hand, VCAM is cast on the highly-uniform equiangular gnomonic-cubic grid and employs a split-explicit flux-conserving approach, which provides benefits for modelling trace gases. Both models use reversible staggering for the wind components (McGregor, MWR, 2005) to produce good wave dispersion behaviour. The models use the same physics package. CCAM includes the Miller-White nonhydrostatic treatment, whereas VCAM is presently an hydrostatic model.
Both models use an efficient MPI message-passing strategy. Although VCAM avoids the message-passing overheads necessitated by the Helmholtz solver of CCAM, it instead has some minor overheads related to more frequent calls to the wind staggering/unstaggering routines. Timings will be shown for simulations utilising up to 288 processors.
Comparative model performance will be shown for idealized advection tests, the Held-Suarez test case, aquaplanet simulations, and for AMIP simulations.