Compare A-Grid and C-Grid Shallow-Water Model Solver on Icosahedral Grids

Solving shallow water model on icosahedral grids on sphere is an indispensable step for a few weather and climate models (e.g. NICAM (Nonhydrostatic ICosahedral Atmospheric Model) and MPAS (Model for Prediction Across Scales)). A notable difference among these solvers are the way variables are staggered on the pentagonal-hexagonal cells (Arakawa staggering schemes), for example the unstaggered A-grid with mass and velocity at cell centers versus the staggered C-grid with mass at center and normal velocity on cell edges. A single software dwarf is designed to accommodate both A-grid and C-grid schemes, reproducing published results for NICAM and MPAS, respectively. We will compare the numerical accuracy, stability, conservation law, and computational cost between these two methods using long time integration (~ 100 days) at high spatial resolution (> G8, 30-km globally). We focus on the scaling relationship, i.e. dependence of numerical accuracy as well as energy and enstropy conservation on the spatial resolution. Discussion will be given to grid point noise and computational modes. We derive analytic formula for numerical discretization errors of spatial operators (e.g. gradient and vorticity) for the A-grid approach. The parallelization of this software on CPU and GPU shall be discussed in a separate presentation (abstract ID: 350600).

References

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