GEM offers the possibilities of running global uniform (up to version 4), global YinYang (starting version 4) and limited area (LAM) grids. Have a look at the grid types.
The grid is specified in the file 'gem_settings.nml' in the namelist 'grid'. This GEM grid specification parameters link explains how to define the parameters. Alternatively, see below.
You have to set variables for the
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The only thing left now when setting up a LAM grid is to specify where the limited area is located on the rotated grid. Once does that by adjusting the following 4 parameters:
| Grd_iref | : | reference point in limited area region, x-grid coordinate | |
| Grd_jref | : | reference point in limited area region, y-grid coordinate | |
| Grd_latr | : | location of reference point in "grid latitude" | |
| Grd_lonr | : | location of reference point in "grid longitude" |
In the image above, the top left square represents the LAM area. Let's call it "LAM grid". Its size is given by 'Grd_ni' and 'Grd_nj'. The larger square on the lower right represents the rotated grid on the whole globe. Let's call it "global grid". It is defined by 'Grd_xlat1' , 'Grd_xlon1', 'Grd_xlat2', and 'Grd_xlon2' (for the rotation) and 'Grd_dx' and 'Grd_dy' (for the resolution).
Now one needs to decide where the "LAM grid" should be located on the "global grid". To do that one need to choose on grid point on the "LAM grid".
Click here to find out how to set blending and pilot area (halo).
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