Note about the "NE" variable. This is the name of a Fortran variable and also used in CIME XML files to refer to cubed sphere grids. It is meaningless jargon to most people. For written documents we recommend referring to grids by their resolution in km. For the quasi-uniform cubed-sphere grid, average grid spacing at the equator is a good measure of the resolutions.
For cubed sphere grids (CAM-SE Grid Overview ), NE is the number of spectral elements along each cube face. Thus the total number of elements N = 6 NE^2.
For regionally refined grids, internally in the code NE=0 and the number of elements N is read in from the Exodus RRM mesh file. RRM grids can be any quadrilateral tiling of the sphere and may not be based on cubed-sphere grids.
For any spectral element grid with N elements, the number of unique points (physics columns) is (np-1)^2 * N + 2, where each element contains a np x np tensor product of Gauss-Lobatto points.
NE | name | Resolution degrees | Resolution at equator (km) | Resolution at equator (miles) | N elements | N columns | factor over ne30 N columns | grid file size | map file size |
---|---|---|---|---|---|---|---|---|---|
4 | ultra low | 7.5 | 835 | 520 | 96 | 866 | |||
11 | 2.7 | 304 | 190 | 726 | 6536 | ||||
16 | 1.9 | 210 | 130 | 1536 | 13826 | ||||
30 | low | 1.0 | 110 | 70 | 5400 | 48602 | 1x | ||
120 | high | 0.25 | 28 | 17.25 | 86400 | 777602 | 16x | ||
240 | 0.125 | 14 | 8.65 | 345600 | 3110402 (3.1M) | 64x | |||
256 | 0.1171875 | 13 | 8.1 | 393216 | 3538946 (3.5M) | 73x | |||
512 | 0.05859 | 6.5 | 4 | 1572864 (1.57M) | 14155778 (14.16M) | 291x | |||
1024 | ultra high | 0.029297 | 3.25 | 2 | 6291456 (6.29M) | 56623106 (56.6M) | 1165x | ||
2048 | 0.014648 | 1.63 | 1 | 25165824 (25.2M) | 226492418 (226.5M) | 4660x | |||
3600 | 0.0083333 | 0.925 | 0.58 | 77760000 (77.76M) | 699840002 (688.85M) | 14400x | |||
*All reported resolutions are average distances based on a third order cubed sphere spectral element domain using 4x4 Gauss-Labotto points (np=4).
...
For quick reference, one RRM grid being tested ne0np4_northamericax4v1
has 14454 elements and 130088 physics columns.
Now that we are moving to the physgrid I think it could be useful to have a table that compares various aspects of typical pg2 and np4 grids.
Formulas:
dynamics grid (i.e. GLL) number of unique columns = (NP-1)^2 * 6 * NE^2 + 2
FV physics grid (i.e. physgrid) number of columns = NE^2 * 6 * NPG^2
Approximate resolution of GLL grid = 360 / ( 4 * NE * (NP-1) )
Approximate resolution of FV physics grid = 360 / ( 4 * NE * NPG )
NP is normally 4 (ex. ne30np4)
NPG is normally 2 (ex. ne30pg2)
NE | ncol (np4) | ncol (pg2) | approx physics grid spacing [deg] (np4) | approx physics grid spacing [deg] (pg2) |
---|---|---|---|---|
4 | 866 | 384 | 7.50 | 11.25 |
8 | 3,458 | 1,536 | 3.75 | 5.63 |
11 | 6,536 | 2,904 | 2.73 | 4.09 |
16 | 13,826 | 6,144 | 1.88 | 2.81 |
30 | 48,602 | 21,600 | 1.00 | 1.50 |
45 | 109,352 | 48,600 | 0.67 | 1.00 |
60 | 194,402 | 86,400 | 0.50 | 0.75 |
120 | 777,602 | 345,600 | 0.25 | 0.38 |
256 | 3,538,946 | 1,572,864 | 0.12 | 0.18 |
512 | 14,155,778 | 6,291,456 | 0.06 | 0.09 |
1024 | 56,623,106 | 25,165,824 | 0.03 | 0.04 |
2048 | 226,492,418 | 100,663,296 | 0.01 | 0.02 |