MPAS
Description
MPAS (Model for Prediction Across Scales) uses a spherical centroidal
Voronoi tessellation: a quasi-uniform mesh of polygonal cells (almost all
hexagons, with exactly 12 pentagons inherited from the icosahedral seed).
Cells are described not by (i, j) block-structured indices but by edge-
and vertex-of-cell adjacency tables loaded from a NetCDF mesh file:
| Table | Meaning |
|---|---|
cells_on_cell[c, k] | k-th neighbor of cell c |
edges_on_cell[c, k] | k-th edge of cell c |
n_edges_on_cell[c] | number of edges (5 or 6) |
dv_edge[e] | edge length (distance between Voronoi vertices) |
dc_edge[e] | dual-edge length (distance between cell centers) |
area_cell[c] | cell area |
Discretization rules on this family use indirect indexing (reduction and
indirect selectors — see discretizations/SELECTOR_KINDS.md) since
neighbor count varies per cell.
Visualization
x1.642, x1.10242, x1.40962) are derived from
successively-bisected icosahedral seeds and have the characteristic
12 pentagons + (n − 12) hexagons.Trait coverage
Registered against AbstractUnstructuredGrid. The neighbor_indices API
returns ragged adjacency arrays; bulk fields like area_cell and the per-edge
geometry are loaded once from the source NetCDF and exposed as flat arrays
keyed by cell / edge / vertex index.
Canonical fixtures
discretizations/grids/mpas/x1.642.esm— 642 cells (~480 km)discretizations/grids/mpas/x1.2562.esm— 2562 cellsdiscretizations/grids/mpas/x1.10242.esm— 10242 cells (~120 km)
Mesh files themselves live outside the repo (the .esm is a manifest;
the loader resolves meshes/mpas/*.grid.nc at bind time per GRIDS_API.md §10).
See also
nn_diffusion_mpas- Skamarock et al. (2012), MWR 140
- Thuburn et al. (2009), JCP 228; Ringler et al. (2010), JCP 229