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LAM grid

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'.

Global grid

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).

Set location of LAM grid on global grid

Now one needs to decide where the "LAM grid" should be located on the "global grid".

Imagine the "LAM grid" is a piece of paper and you want to pin it in a certain location on a global map. First you would put a pin in the piece of paper in the "reference point", defined by 'Grd_iref' and 'Grd_jref'. Then you would pin it at a certain location on the "global grid", defined by 'Grd_lon1' and 'Grd_lat1' (in longitude and latitude of the rotated grid!).

First one needs to choose any one grid point on the "LAM grid" by setting 'Grd_iref' and 'Grd_jref'. This point is called the "reference point". I find it easiest to choose the middle point of the grid. Meaning set 'Grd_iref'  to 'Grd_ni/2' and 'Grd_jref'  to 'Grd_nj/2'. But you have to put the values!

Then one needs to set where this "reference point" should be located on the "global grid". The location is given by setting 'Grd_lonr' and 'Grd_latr' to the longitude and latitude of the reference point, in longitude and latitude with respect to the rotated grid. If one chose the middle point of the LAM grid to be the reference point and chose the center point of the global grid (set by 'Grd_lon1' and 'Grd_lat1'), then one should set:

    Grd_lonr  =  180.0,   Grd_latr  =  0.0. 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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