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- global uniform
- global YinYang (two LAM grids, each covering a little more than half the globe, overlapping like a tennis ball)
- regional LAM (Limited Area Model) grids
For LAM grids we distinguish three main regions:
- model grid (whole grid, including halo/pilot region)
- core grid (model grid minus halo/pilot region but including blending/merging area/Davies sponge)
- free grid (inner area)
The pilot region or halo contains only the driving interpolated to the model grid. The model need this region to check where the air comes from but the dynamics do not do any calculations in this region.
In the blending/merging area, also called Davies sponge, the model results get merged with the driving data, giving more weight to the driving data on the outside and more to the model results on the inside, following a cos2 curve. This is also the grid specified in the gem_settings.nml.
The free area contains only the model results. Usually, this is the grid used for the model output.
Grids of GEM version 4 and up are horizontally (Arakawa C-grid) and vertically staggered.
