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| Grd_overlap | : | Overlap in degrees(!) The overlap size should be at least 3 times the resolution of the grid resolution. In general, for higher resolution grids (ie: 0.25° or finer), an overlap of 8 times would be better for the solver. | |
| Grd_nj | : | Core/Free number of grid points in y-direction |
Note that there is no blending/merging area, also called Davies sponge, in Yin-Yang grids, which means that the free area is the same as the core area!
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This means the overlap is 3 times larger on the left and right border of each LAM grid than at the top and bottom! This is done because the solver needs the grids to be 3 times larger in x- than in y-direction (minus 1 point).
Example
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to setup a 0.25°
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Yin-Yang grid
1. First calculate the size of the overlap when covering 8 times the grid resolution:
Grd_overlap = 8 * 0.25° = 2°
2. Then calculate the resulting total number (including 2 times the overlap) of core/free points in y-direction + 1 point:
Grd_nj = (90° + 2*2°) / 0.25° + 1 = 376 377
That's itall!
FYI, Grd_nj does not have to match the FFT criteria.
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