Dr. John McGregor (CSIRO Atmospheric Research):
The conformal-cubic atmospheric model (CCAM) has been developed at CAR
over recent years. The grid was devised by Rancic, and is appealing
because of its quasi-uniformity, orthogonality and isotropy.
Besides having an unusual grid, CCAM possesses a number of attractive
features in its dynamical formulation. Perhaps the most significant of
these is a reversible staggering procedure for the winds, available
because of the cyclic nature of the grid. This procedure provides
similarly good dispersion properties to a spectral or
vorticity/divergence formulation.
CCAM is a two-time-level, semi-Lagrangian, semi-implicit model, allowing
large advective time steps. For vertical advection, the TVD scheme is
found to treat the tropopause best.
Regional climate modelling at CAR is carried out with a
variable-resolution version of CCAM. Compared to the traditional
limited-area modelling approach, this method possesses no lateral
boundaries and thus avoids any boundary reflection problems. This
downscaling technique also avoids potential problems due to different
temperature and moisture biases of the host and fine-scale climate
models. A selection of regional climate applications will be shown. Some
weather forecasting applications will also be shown.
A recent realization is that the various dynamics treatments developed
for CCAM can also be applied to the non-orthogonal gnomonic-cubic grid.
The reformulation will allow greater uniformity of resolution, and
straightforward incorporation of conserving advection schemes for trace
gases and chemical species.