ATM Grid Resolution Summary

Atmosphere Grid Trivia. 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

common name

Resolution degrees

Resolution at equator (km)

Resolution at equator (miles)

N elements

N columns

factor over ne30 N columns

NE

common name

Resolution degrees

Resolution at equator (km)

Resolution at equator (miles)

N elements

N columns

factor over ne30 N columns

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).

**Standard vertical resolution for E3SM is 72 vertical levels.

For cubed sphere grids with np=4:

Resolution degrees = 360/4/NE/3 Resolution km = 40075/4/NE/3 Resolution miles = 24901/4/NE/3 Number elements = NE*NE*6 Number columns = 54*NE*NE + 2

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.e. pg2) it is useful to have a table that compares various aspects of typical pg2 and np4 grids. 

For the formulas, note that NP is normally 4 (ex. ne30np4) and NPG is normally 2 (ex. ne30pg2)

NE

np4 # physics columns
(NP-1)^2 * 6 * NE^2 + 2

pg2 # physics columns
NE^2 * 6 * NPG^2

np4 approx grid spacing
[degrees]
360 / ( 4 * NE * (NP-1) )

pg2 approx grid spacing
[degrees]
360 / ( 4 * NE * NPG )

np4 approx grid spacing
[km]
40075 / ( 4 * NE * (NP-1) )

pg2 approx grid spacing
[km]
40075 / ( 4 * NE * NPG )

NE

np4 # physics columns
(NP-1)^2 * 6 * NE^2 + 2

pg2 # physics columns
NE^2 * 6 * NPG^2

np4 approx grid spacing
[degrees]
360 / ( 4 * NE * (NP-1) )

pg2 approx grid spacing
[degrees]
360 / ( 4 * NE * NPG )

np4 approx grid spacing
[km]
40075 / ( 4 * NE * (NP-1) )

pg2 approx grid spacing
[km]
40075 / ( 4 * NE * NPG )

4

866

384

7.50

11.25

834.9

1252.3

8

3,458

1,536

3.75

5.63

417.4

626.2

11

6,536

2,904

2.73

4.09

303.6

455.4

16

13,826

6,144

1.88

2.81

208.7

313.1

30

48,602

21,600

1.00

1.50

111.3

167.0

45

109,352

48,600

0.67

1.00

74.2

111.3

60

194,402

86,400

0.50

0.75

55.7

83.5

120

777,602

345,600

0.25

0.38

27.8

41.7

256

3,538,946

1,572,864

0.12

0.18

13.0

19.6

512

14,155,778

6,291,456

0.06

0.09

6.5

9.8

1024

56,623,106

25,165,824

0.03

0.04

3.3

4.9

2048

226,492,418

100,663,296

0.01

0.02

1.6

2.4