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One only needs to specify the core/free number of points in y-direction (Grd_nj) as well as the "overlap" in degrees (Grd_overlap). The model will calculate the number of points in x-direction as well as the size of the grid boxes automatically from that.
| Grd_nj | : | core/free number of grid points in y-direction Including the overlap!!!=> Number of points covering 90°+2*Grd_overlap | 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!
The overlap is needed because the two LAM grids will give different answers in the overlap region and the larger the overlap region the easier it is for the solver to find the common solution.The minimum overlap (degrees) should be 3 to 8 times the grid resolution (delta Y degrees).
To specify a Yin-Yang grid one should only specify 'Grd_nj' and 'Grd_overlap'. 'Grd_ni' will get calculated automatically using the following equation:
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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). An overlap is needed because the two LAM grids will give different answers in the overlap region and the larger the overlap region the easier it is for the solver to find the common solution.The minimum overlap (degrees) should be 3 to 8 times the grid resolution (delta Y degrees)
Example for a 0.25° YinYang grid
1. First calculate the size of the overlap when covering 8 times the grid resolution:
Grd_overlap = 8 * 0.25° = 2°
2. Calculate the number of points in y-direction:
Grd_nj = (90° + 2*2°) / 0.25° = 376
To learn more about Yin-Yang grids have a look at the following wiki page: Yin-Yang grid
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