Abstract. Targeting a long-term effort towards a variable-resolution (VR) global weather and climate model, this study systematically configures and evaluates
an unstructured mesh atmospheric model based on the multiresolution approach. The model performance is examined from dry dynamics to simple physics and full
physics scenarios. In the dry baroclinic wave test, the VR model reproduces comparable fine-scale structures in the refined regions as a
fine-resolution quasi-uniform (QU) mesh model. The mesh transition zone does not adversely affect the wave pattern. Regional kinetic energy spectra
show that the fine-scale resolving ability improves as the fine resolution increases. Compared to a QU counterpart that has equivalent degrees of
freedom, the VR model tends to increase the global errors, but the errors can be reduced when the resolution of the coarse region is
increased. The performance over the coarse region is generally close to that of a low-resolution QU counterpart. Two multi-region refinement
approaches, the hierarchical and polycentric refinement modes, further validate the model performance under the multiresolution
refinement. Activating hyperdiffusion for horizontal velocity is helpful with respect to VR modeling. An idealized tropical cyclone test is further
used to examine its ability to resolve fine-scale structures. In the simple physics environment, the VR model can have the tropical cyclone stably
pass the transition zone in various configurations. A series of sensitivity tests examines the model performance in a hierarchical refinement
mode. The simulations exhibit consistency even when the VR mesh is slightly perturbed by one of the three parameters that control the density
function. The tropical cyclone, starting from the second refinement region and passing through the inner transition zone, gets intensified and covers
a smaller area in the refined regions. Such variations are consistent with the behavior that one may observe when uniformly refining the QU
mesh. In the full physics environment with a highly variable mesh that reaches sub-10 km resolution, the VR model also produces a reasonable
evolution for the tropical cyclone. The explicit diffusion shows its usefulness in terms of suppressing some unrealistic isolated-scale structures
that are far away from the initial vortex and does not adversely affect the physically important object. The fine-scale structure is determined
mainly by the fine-resolution area, although the systems may have larger differences before they move into the fine-resolution area. Altogether,
this work demonstrates that the multiresolution configuration is a reliable and economic alternative to high-resolution global modeling. The adverse
impact due to mesh transition and the coarse region can be controlled well.
Vorticity-Divergence semi-Lagrangian Global Atmospheric Model
SL-AV20: Dynamical Core
