GEOS-Chem vertical grids
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On this page we provide information about the various vertical grids used in GEOS-Chem. We also invite you to visit our GEOS-Chem horizontal grids wiki page.
Comparisons of vertical grids used by GEOS-Chem
The table below compares the level structure of the various grids used by GEOS-Chem.
GEOS-Chem v11-02 aka 12.0.0 and later versions only support the GEOS-FP and MERRA-2 met field products from NASA/GMAO. All other met field products mentioned below have been de-supported.
| Description | Comparison |
|---|---|
| Vertical grids up to 3 km: | 
|
| Vertical grids up to 10 km: | 
|
| Vertical grids up to 32 km: | 
|
| Vertical grids up to 80km: | 
|
--Bob Yantosca (talk) 20:47, 14 November 2016 (UTC)
Vertical grids for GEOS-FP and MERRA-2
The GEOS-FP and MERRA-2 met field products from GMAO share the same vertical grid.
NOTE: The GEOS-5 and MERRA met field products are placed on the same vertical grid as GEOS-FP and MERRA-2. But per request of NASA/GMAO, the GEOS-5 and MERRA met field products have been de-supported from GEOS-Chem v11-02 and later versions.
72-layer vertical grid
| Used by | These met field products are currenlty used by GEOS-Chem:
These met field products have been de-supported from GEOS-Chem v11-02 and later versions: |
|---|---|
| Number of layers |
|
| Indexing |
|
| Type of grid | |
| Hybrid Ap parameter [hPa] |
(surface) 0.000000d+00, 4.804826d-02, 6.593752d+00, 1.313480d+01, 1.961311d+01, 2.609201d+01, 3.257081d+01, 3.898201d+01, 4.533901d+01, 5.169611d+01, 5.805321d+01, 6.436264d+01, 7.062198d+01, 7.883422d+01, 8.909992d+01, 9.936521d+01, 1.091817d+02, 1.189586d+02, 1.286959d+02, 1.429100d+02, 1.562600d+02, 1.696090d+02, 1.816190d+02, 1.930970d+02, 2.032590d+02, 2.121500d+02, 2.187760d+02, 2.238980d+02, 2.243630d+02, 2.168650d+02, 2.011920d+02, 1.769300d+02, 1.503930d+02, 1.278370d+02, 1.086630d+02, 9.236572d+01, 7.851231d+01, 6.660341d+01, 5.638791d+01, 4.764391d+01, 4.017541d+01, 3.381001d+01, 2.836781d+01, 2.373041d+01, 1.979160d+01, 1.645710d+01, 1.364340d+01, 1.127690d+01, 9.292942d+00, 7.619842d+00, 6.216801d+00, 5.046801d+00, 4.076571d+00, 3.276431d+00, 2.620211d+00, 2.084970d+00, 1.650790d+00, 1.300510d+00, 1.019440d+00, 7.951341d-01, 6.167791d-01, 4.758061d-01, 3.650411d-01, 2.785261d-01, 2.113490d-01, 1.594950d-01, 1.197030d-01, 8.934502d-02, 6.600001d-02, 4.758501d-02, 3.270000d-02, 2.000000d-02, 1.000000d-02 (top of atmosphere) |
| Hybrid Bp parameter [1] |
(surface) 1.000000d+00, 9.849520d-01, 9.634060d-01, 9.418650d-01, 9.203870d-01, 8.989080d-01, 8.774290d-01, 8.560180d-01, 8.346609d-01, 8.133039d-01, 7.919469d-01, 7.706375d-01, 7.493782d-01, 7.211660d-01, 6.858999d-01, 6.506349d-01, 6.158184d-01, 5.810415d-01, 5.463042d-01, 4.945902d-01, 4.437402d-01, 3.928911d-01, 3.433811d-01, 2.944031d-01, 2.467411d-01, 2.003501d-01, 1.562241d-01, 1.136021d-01, 6.372006d-02, 2.801004d-02, 6.960025d-03, 8.175413d-09, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00 (top of atmosphere) |
| Pressures and altitudes for a column at atmospheric sea level, from surface upwards |
L Eta Edge Eta Mid Altitude Pressure
(unitless) (unitless) (km) (hPa)
========================================================
0.000000 80.581 0.010
72 0.000005 78.146 0.015
0.000010 76.357 0.020
71 0.000016 74.594 0.026
0.000022 73.180 0.033
70 0.000030 71.812 0.040
0.000037 70.657 0.048
69 0.000046 69.440 0.057
0.000055 68.392 0.066
68 0.000067 67.243 0.078
0.000078 66.245 0.089
67 0.000093 65.115 0.105
0.000108 64.130 0.120
66 0.000128 63.004 0.140
0.000148 62.021 0.159
65 0.000173 60.902 0.185
0.000199 59.924 0.211
64 0.000232 58.816 0.245
0.000265 57.846 0.279
63 0.000308 56.752 0.322
0.000350 55.794 0.365
62 0.000405 54.717 0.420
0.000460 53.773 0.476
61 0.000529 52.716 0.546
0.000599 51.788 0.617
60 0.000687 50.754 0.706
0.000775 49.844 0.795
59 0.000886 48.835 0.907
0.000996 47.946 1.019
58 0.001135 46.962 1.160
0.001274 46.092 1.301
57 0.001446 45.134 1.476
0.001619 44.286 1.651
56 0.001834 43.355 1.868
0.002048 42.529 2.085
55 0.002312 41.627 2.353
0.002576 40.825 2.620
54 0.002900 39.951 2.948
0.003224 39.173 3.276
53 0.003619 38.328 3.677
0.004013 37.574 4.077
52 0.004492 36.759 4.562
0.004971 36.030 5.047
51 0.005548 35.244 5.632
0.006126 34.539 6.217
50 0.006818 33.782 6.918
0.007510 33.101 7.620
49 0.008336 32.372 8.456
0.009162 31.716 9.293
48 0.010141 31.015 10.285
0.011120 30.382 11.277
47 0.012287 29.701 12.460
0.013455 29.085 13.643
46 0.014844 28.423 15.050
0.016232 27.824 16.457
45 0.017878 27.180 18.124
0.019523 26.596 19.792
44 0.021467 25.971 21.761
0.023410 25.402 23.730
43 0.025699 24.794 26.049
0.027987 24.240 28.368
42 0.030673 23.648 31.089
0.033358 23.108 33.810
41 0.036499 22.531 36.993
0.039641 22.004 40.175
40 0.043326 21.438 43.910
0.047011 20.920 47.644
39 0.051326 20.364 52.016
0.055641 19.855 56.388
38 0.060682 19.309 61.496
0.065723 18.807 66.603
37 0.071600 18.269 72.558
0.077477 17.773 78.512
36 0.084313 17.243 85.439
0.091149 16.753 92.366
35 0.099191 16.222 100.514
0.107233 15.731 108.663
34 0.116695 15.198 118.250
0.126157 14.706 127.837
33 0.137287 14.170 139.115
0.148418 13.674 150.393
32 0.161513 13.134 163.661
0.174608 12.633 176.930
31 0.190061 12.086 192.587
0.205513 11.578 208.244
30 0.223772 11.021 226.745
0.242032 10.504 245.246
29 0.263587 9.936 267.087
0.285142 9.409 288.927
28 0.309854 8.846 313.966
0.334566 8.320 339.005
27 0.353349 7.943 358.038
0.372133 7.582 377.070
26 0.390927 7.237 396.112
0.409720 6.905 415.155
25 0.428528 6.585 434.212
0.447337 6.277 453.269
24 0.466153 5.980 472.335
0.484970 5.692 491.401
23 0.503795 5.413 510.475
0.522620 5.142 529.550
22 0.541449 4.879 548.628
0.560278 4.623 567.706
21 0.579115 4.375 586.793
0.597953 4.132 605.880
20 0.616790 3.896 624.967
0.635628 3.665 644.054
19 0.654471 3.439 663.146
0.673314 3.219 682.239
18 0.685878 3.074 694.969
0.698442 2.932 707.699
17 0.711006 2.792 720.429
0.723570 2.654 733.160
16 0.736134 2.517 745.890
0.748698 2.382 758.621
15 0.761265 2.249 771.354
0.773832 2.118 784.088
14 0.786400 1.988 796.822
0.798967 1.860 809.556
13 0.809021 1.759 819.743
0.819075 1.659 829.929
12 0.826616 1.584 837.570
0.834157 1.510 845.211
11 0.841698 1.436 852.852
0.849239 1.363 860.493
10 0.856781 1.290 868.135
0.864323 1.218 875.776
9 0.871864 1.146 883.418
0.879406 1.075 891.059
8 0.886948 1.004 898.701
0.894489 0.934 906.342
7 0.902031 0.864 913.984
0.909573 0.795 921.626
6 0.917116 0.726 929.268
0.924658 0.657 936.911
5 0.932200 0.589 944.553
0.939743 0.521 952.195
4 0.947285 0.454 959.837
0.954828 0.387 967.480
3 0.962370 0.320 975.122
0.969913 0.254 982.765
2 0.977456 0.189 990.408
0.984999 0.123 998.051
1 0.992500 0.058 1005.650
1.000000 -0.006 1013.250
|
--Bob Yantosca (talk) 19:51, 14 November 2016 (UTC)
47-layer reduced vertical grid
In order to save computational resources, GEOS-Chem "Classic" can collapse the 72 layer grid down to a 47-layer grid "on-the-fly". Groups of 2 and 4 layers are lumped together starting at ~70 hPa. See the table below for more information.
NOTE: The GEOS-5 and MERRA met field products are placed on the same vertical grid as GEOS-FP and MERRA-2. But per request of NASA/GMAO, the GEOS-5 and MERRA met field products have been de-supported from GEOS-Chem v11-02 and later versions.
| Used by | These met field products are currently used by GEOS-Chem:
These met field products have been de-supported from GEOS-Chem v11-02 and later versions: |
|---|---|
| Number of layers |
|
| Indexing |
|
| Type of grid | |
| Lumping of vertical levels |
47-level reduced vertical grid Bottom Bottom # levels edge of edge prs lumped level (hPa) together PTOP 0.010 47 0.066 4 46 0.211 4 45 0.617 4 44 1.651 4 43 4.077 4 42 9.293 4 41 19.792 4 40 28.368 2 39 40.175 2 38 56.388 2 37 78.512 2 %%%% START LUMPING LEVELS ABOVE HERE %%%%% 36 92.366 35 108.663 34 127.837 33 150.393 32 176.930 %%%% FIXED-PRESSURE LEVELS BEGIN HERE %%%% |
| Hybrid Ap parameter [hPa] |
(surface) 0.000000d+00, 4.804826d-02, 6.593752d+00, 1.313480d+01, 1.961311d+01, 2.609201d+01, 3.257081d+01, 3.898201d+01, 4.533901d+01, 5.169611d+01, 5.805321d+01, 6.436264d+01, 7.062198d+01, 7.883422d+01, 8.909992d+01, 9.936521d+01, 1.091817d+02, 1.189586d+02, 1.286959d+02, 1.429100d+02, 1.562600d+02, 1.696090d+02, 1.816190d+02, 1.930970d+02, 2.032590d+02, 2.121500d+02, 2.187760d+02, 2.238980d+02, 2.243630d+02, 2.168650d+02, 2.011920d+02, 1.769300d+02, 1.503930d+02, 1.278370d+02, 1.086630d+02, 9.236572d+01, 7.851231d+01, 5.638791d+01, 4.017541d+01, 2.836781d+01, 1.979160d+01, 9.292942d+00, 4.076571d+00, 1.650790d+00, 6.167791d-01, 2.113490d-01, 6.600001d-02, 1.000000d-02 (top of atmosphere) |
| Hybrid Bp parameter [1] |
(surface) 1.000000d+00, 9.849520d-01, 9.634060d-01, 9.418650d-01, 9.203870d-01, 8.989080d-01, 8.774290d-01, 8.560180d-01, 8.346609d-01, 8.133039d-01, 7.919469d-01, 7.706375d-01, 7.493782d-01, 7.211660d-01, 6.858999d-01, 6.506349d-01, 6.158184d-01, 5.810415d-01, 5.463042d-01, 4.945902d-01, 4.437402d-01, 3.928911d-01, 3.433811d-01, 2.944031d-01, 2.467411d-01, 2.003501d-01, 1.562241d-01, 1.136021d-01, 6.372006d-02, 2.801004d-02, 6.960025d-03, 8.175413d-09, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00, 0.000000d+00 (top of atmosphere) |
| Pressures and altitudes for a column at atmospheric sea level, from surface upwards |
L Eta Edge Eta Mid Altitude Pressure
(unitless) (unitless) (km) (hPa)
========================================================
0.000000 80.581 0.010
47 0.000028 72.180 0.038
0.000055 68.392 0.066
46 0.000127 63.053 0.139
0.000199 59.924 0.211
45 0.000399 54.834 0.414
0.000599 51.788 0.617
44 0.001109 47.135 1.134
0.001619 44.286 1.651
43 0.002816 40.166 2.864
0.004013 37.574 4.077
42 0.006588 34.024 6.685
0.009162 31.716 9.293
41 0.014342 28.654 14.542
0.019523 26.596 19.792
40 0.023755 25.307 24.080
0.027987 24.240 28.368
39 0.033814 23.020 34.272
0.039641 22.004 40.175
38 0.047641 20.836 48.282
0.055641 19.855 56.388
37 0.066559 18.727 67.450
0.077477 17.773 78.512
36 0.084313 17.243 85.439
0.091149 16.753 92.366
35 0.099191 16.222 100.514
0.107233 15.731 108.663
34 0.116695 15.198 118.250
0.126157 14.706 127.837
33 0.137287 14.170 139.115
0.148418 13.674 150.393
32 0.161513 13.134 163.661
0.174608 12.633 176.930
31 0.190061 12.086 192.587
0.205513 11.578 208.244
30 0.223772 11.021 226.745
0.242032 10.504 245.246
29 0.263587 9.936 267.087
0.285142 9.409 288.927
28 0.309854 8.846 313.966
0.334566 8.320 339.005
27 0.353349 7.943 358.038
0.372133 7.582 377.070
26 0.390927 7.237 396.112
0.409720 6.905 415.155
25 0.428528 6.585 434.212
0.447337 6.277 453.269
24 0.466153 5.980 472.335
0.484970 5.692 491.401
23 0.503795 5.413 510.475
0.522620 5.142 529.550
22 0.541449 4.879 548.628
0.560278 4.623 567.706
21 0.579115 4.375 586.793
0.597953 4.132 605.880
20 0.616790 3.896 624.967
0.635628 3.665 644.054
19 0.654471 3.439 663.146
0.673314 3.219 682.239
18 0.685878 3.074 694.969
0.698442 2.932 707.699
17 0.711006 2.792 720.429
0.723570 2.654 733.160
16 0.736134 2.517 745.890
0.748698 2.382 758.621
15 0.761265 2.249 771.354
0.773832 2.118 784.088
14 0.786400 1.988 796.822
0.798967 1.860 809.556
13 0.809021 1.759 819.743
0.819075 1.659 829.929
12 0.826616 1.584 837.570
0.834157 1.510 845.211
11 0.841698 1.436 852.852
0.849239 1.363 860.493
10 0.856781 1.290 868.135
0.864323 1.218 875.776
9 0.871864 1.146 883.418
0.879406 1.075 891.059
8 0.886948 1.004 898.701
0.894489 0.934 906.342
7 0.902031 0.864 913.984
0.909573 0.795 921.626
6 0.917116 0.726 929.268
0.924658 0.657 936.911
5 0.932200 0.589 944.553
0.939743 0.521 952.195
4 0.947285 0.454 959.837
0.954828 0.387 967.480
3 0.962370 0.320 975.122
0.969913 0.254 982.765
2 0.977456 0.189 990.408
0.984999 0.123 998.051
1 0.992500 0.058 1005.650
1.000000 -0.006 1013.250
|
--Bob Yantosca (talk) 19:33, 14 November 2016 (UTC)
Reference section for vertical grids
In this section we provide more general information about the vertical grids used by GEOS-Chem.
Sigma grid definition
The sigma grid is a purely terrain-following coordinate. The following met data products are defined on the sigma grid:
- GMAO GEOS-3 (NOTE: Now obsolete)
- GCAP/GISS meteroloogy
- NOTE: GCAP met is really a hybrid grid, but it is defined as if it were a pure sigma grid (i.e. PTOP=150 hPa, and negative sigma edges at higher levels.
The sigma grid is defined as follows:
P(I,J,L) - PTOP
σ(L)= ------------------------
Psurface(I,J) - PTOP
where:
I,J,L are the longitude, latitude, level indices of the grid box P(I,J,L) is the pressure at a level edge or level center at grid box (I,J,L) Psurface(I,J) is the surface pressure at grid box (I,J) PTOP is the pressure at the top of the atmosphere
σ(L) always varies between 0 and 1, with 1 being the surface and 0 being the atmosphere top. Therefore you can think of σ(L) as the "fraction" of the atmosphere (measured from the top down) at which you are located.
The σ(L) therefore are independent of (I,J). The sigma values are typically fixed for a given met field type. Knowing the sigma value allows you to compute the center or edge pressures as follows:
Pedge(I,J,L) = σedge(L) * [ Psurface(I,J) - PTOP ] + PTOP Pcenter(I,J,L) = σcenter(L) * [ Psurface(I,J) - PTOP ] + PTOP
Any sigma grid can also be computed with the hybrid grid equation:
Pedge(I,J,L) = Ap(L) + [ Bp(L) * ( Psurface(I,J) - PTOP ) ] Pcenter(I,J,L) = [ Pedge(I,J,L) + Pedge(I,J,L+1) ] / 2
where
Psurface(I,J) = the "true" surface pressure at lon,lat (I,J) Ap(L) = PTOP = model top pressure Bp(L) = σedge(L) = bottom sigma edge of level L
Hybrid grid definition
Earlier versions of the GMAO met data products used a pure-sigma grid definition. The problem with a sigma-grid is that you still see the signature of the mountains at the very top of the atmosphere. This was the case in GEOS-3 and this caused a lot of noise in the stratospheric winds, which led to poor STE.
The improvement on the sigma grid is the hybrid (or η) grid. This grid is defined with A and B coefficients, which are specified by the makers of the met data products (e.g. GMAO).
The following met data products use the hybrid grid formulation:
- GMAO GEOS-FP (currently used in GEOS-Chem)
- GMAO MERRA-2 (currently used in GEOS-Chem)
- GMAO GEOS-4 (de-supported in GEOS-Chem v11-02)
- GMAO GEOS-5 (de-supported in GEOS-Chem v11-02)
- GMAO MERRA (de-supported in GEOS-Chem v11-02)
The pressure at the bottom edge of grid box (I,J,L) is defined as follows:
Pedge(I,J,L) = Ap(L) + [ Bp(L) * Psurface(I,J) ]
Pcenter(I,J,L) = [ Pedge(I,J,L) + Pedge(I,J,L+1) ] / 2
where
I,J,L are the lon, lat, level indices of the grid box
Psurface(I,J) is the "true" surface pressure at lon,lat (I,J)
Ap(L) has the same units as surface pressure [hPa]
Bp(L) is a unitless constant given at level edges
The Ap(L) and Bp(L) for each met field type are listed in the GEOS-Chem source code file pressure_mod.f.
The hybrid grid formula in more depth
Rebecca Buchholz wrote:
- I'm having trouble conceptualising exactly how GEOS-Chem deals with the vertical grid. I'm using the GEOS-5 reduced vertical resolution of 47 eta levels. I've seen the AMS definition of eta.
- I can see the first fraction is the sigma definition (which follows terrain). Is the second fraction essentially a scaling by the pressure at altitude relative to pressure at sea surface? I'm not sure how it fits in with the GEOS-Chem definition, i.e. when rearranging the equation, what becomes A_p and B_p.
- The manual and wiki pages indicate GEOS-5 is a hybrid pressure-sigma grid. Are the first 31 levels pure sigma levels in both the reduced vertical 47 and native 72 level GEOS-5 fields? Does this mean GEOS-5 doesn't use the above eta definition of the levels - only sigma definition? Does GEOS-Chem then change the sigma levels to eta levels?
Bob Yantosca replied:
- Maybe we have used “eta” as a synonym for “hybrid” grid. Basically it refers to a grid that transitions smoothly from a sigma terrain-following coordinate near the surface to fixed pressure levels in the upper atmosphere.
- Older met fields (e.g. GEOS-3) came on pure-sigma grids. However, the problem is that with a pure-sigma grid, you still see some signal of the mountains even at the top of the atmosphere. This makes the upper-atmosphere winds very noisy and it messes up the strat-trop exchange. (Or so GMAO tells us.)
- The way I like to think of it is we specify the pressure at the bottom edge of grid box (I,J,L) with this formula:
Pedge(I,J,L) = Ap(L) + [ Bp(L) * Psurface(I,J) ]
- where Ap(L) and Bp(L) are specified by GMAO. Then you specify the pressures at the center of grid box (I,J,L) with this formula:
Pcenter(I,J,L) = [ Pedge(I,J,L) + Pedge(I,J,L+1) ] / 2
- i.e. it’s an average of the pressure at both edges.
- Note that the Pedge(I,J,L) and Pcenter(I,J,L) vary w/ the topography up until about 170 hPa. That is where the first fixed-pressure levels occur. Skyward of that, then Pedge(I,J,L) and Pcenter(I,J,L) will be constant for all longitudes and latitudes (I,J).
- Once you have computed Pedge(I,J,L) and Pcenter(I,J,L), you can construct an ETA coordinate such as:
ETAedge(I,J,L) = [ Pedge(I,J,L) – Ptop ] / [ Psurface – Ptop ] ETAcenter(I,J,L) = [ Pcenter(I,J,L) – Ptop ] / [ Psurface – Ptop ]
- but for the purposes of GEOS-Chem, we don’t really use the ETA values. We use the pressures computed from the Ap(L) and Bp(L) values.
- The most important thing to note is that the thicknesses of the grid boxes near the surface vary with the surface pressure. When you come to a mountain, the levels all kind of bunch together and get small. When you are over flat land or ocean, the levels widen out.
- Also note that a pure-sigma grid (like GEOS-3) can also be expressed using the same type of hybrid formulation:
Pedge(I,J,L) = Ap(L) + [ Bp(L) * ( Psurface(I,J) – PTOP ) ]
where
Ap(L) = PTOP (for all L) Bp(L) = Sigma_Edge(L) = the bottom sigma edge for level L
- In GeosUtil/pressure_mod.f we use the same hybrid formula but we use the Ap(L) and Bp(L) that pertain to each grid (GEOS-3, GEOS-4, GEOS-5, GCAP, etc). That simplifies the coding.
--Bob Y. 15:58, 6 April 2011 (EDT)
Ordering of the vertical levels
In the GMAO met field files
The "raw" GMAO met data files—which we cut and/or regrid for input into GEOS-Chem—store data from the top of the atmopshere downward.
| GMAO data product |
Grid type |
Surface level |
Top-of- atmosphere level |
Top-of- atmosphere pressure | |
|---|---|---|---|---|---|
| GEOS-3 | Pure sigma | Level 48 | Level 1 | 0.01 hPa | |
| GEOS-4 | Hybrid | Level 55 | Level 1 | 0.01 hPa | |
| GEOS-5.2.0 GEOS-FP MERRA MERRA-2 |
Hybrid | Level 72 | Level 1 | 0.01 hPa |
--Bob Yantosca (talk) 20:51, 14 November 2016 (UTC)
GEOS-Chem
GEOS-Chem labels vertical levels starting from the surface and then moving upward—exactly in the opposite way as in the GMAO met field files.
| GMAO data product |
Grid type |
Surface level |
Top-of- atmosphere level: Full grid |
Top-of- atmosphere level: Reduced grid |
Top-of atmosphere pressure |
|---|---|---|---|---|---|
| GEOS-3 | Pure sigma | Level 1 | Level 48 | Level 30 | 0.01 hPa |
| GEOS-4 | Hybrid | Level 1 | Level 55 | Level 30 | 0.01 hPa |
| GEOS-5.2.0 GEOS-FP MERRA MERRA-2 |
Hybrid | Level 1 | Level 72 | Level 47 | 0.01 hPa |
GEOS-Chem denotes the surface by L=1 because there are special processes (i.e. emissions, deposition, etc) that always happen at the surface level. The coding would be much more difficult if we kept L=1 for the atmosphere top and let the index of the surface vary. Also, in many instances it is more natural to think of processes as extending upward from the surface rather than as downward from the atmosphere top.
The GEOS-Chem routines (in GeosUtil/pressure_mod.f):
GET_PEDGE( I, J, L )GET_PCENTER( I, J, L )
return the pressures in hPa at the edge and center, respectively, of grid box (I,J,L).
--Bob Yantosca (talk) 20:18, 14 November 2016 (UTC)
Vertical grids and GAMAP
Ray Nassar wrote:
- Appendix 3 of the GEOS-Chem online manual describes the different GEOS vertical grids.
- These are based on a sigma/eta co-ordinate system, therefore equivalent altitudes can only be approximately defined by specifying a surface pressure. For example, altitudes for the GEOS-4 vertical grid and the reduced vertical grid are both shown in the online manual using a surface pressure of 1000 hPa (although the page incorrectly states that 1010 hPa was used).
- Please note: Using the GAMAP software package, the altitudes provided in plot titles for the first 12 GEOS-4 levels differ from those specified in the GEOS-Chem online manual due to the specification of a different surface pressure. A correction for this apparent error can be found in the GAMAP bugs and fixes section of this wiki.
Bob Yantosca wrote:
- GAMAP v2-15 fixes many of the inconsistencies in the computation of the pressure and ETA coordinates for hybrid grids that were noted in previous GAMAP versions. If you are using an older version of GAMAP, then you should update.
- For example:
IDL> a = ctm_grid( ctm_type( 'gcap', res=4 ) )
--Bob Yantosca (talk) 20:14, 14 November 2016 (UTC)
For more information
Please see the following resources for more information about vertical grids:
--Bob Yantosca (talk) 20:16, 14 November 2016 (UTC)
Obsolete information
The following sections correspond to vertical grids that have been de-supported in the most recent versions of GEOS-Chem. We shall keep this information here for reference.
GCAP vertical grid
The original GCAP functionality in GEOS-Chem "Classic" is more or less obsolete. Most people use the ICECAP version of GEOS-Chem for climate-chemistry applications. We shall leave this information here for reference.
GCAP Native Vertical Grid (23 layers)
L Sig Edge Sig Mid Altitude Pressure
(unitless) (unitless) (km) (hPa)
=======================================================
0.000000 89.247 0.002
23 0.000000 77.507 0.017
0.000000 73.489 0.031
22 0.000000 66.346 0.088
0.000000 62.725 0.145
21 0.000000 57.209 0.303
0.000000 54.014 0.461
20 0.000000 48.400 0.960
0.000000 45.215 1.460
19 0.000000 39.712 3.045
0.000000 36.651 4.630
18 0.000000 33.388 7.315
0.000000 31.209 10.000
17 0.000000 28.959 13.900
0.000000 27.300 17.800
16 0.000000 25.141 24.700
0.000000 23.543 31.600
15 0.000000 21.439 43.900
0.000000 19.876 56.200
14 0.000000 18.387 71.200
0.000000 17.187 86.200
13 0.000000 16.154 101.600
0.000000 15.265 117.000
12 0.000000 14.431 133.500
0.000000 13.690 150.000
11 0.000000 12.825 171.737
0.000000 12.056 193.473
10 0.000000 11.192 220.903
0.000000 10.421 248.332
9 0.000000 9.524 284.042
0.000000 8.721 319.752
8 0.000000 7.580 377.198
0.000000 6.578 434.645
7 0.000000 5.424 509.687
0.000000 4.401 584.730
6 0.000000 3.509 657.185
0.000000 2.692 729.641
5 0.000000 2.098 786.052
0.000000 1.536 842.463
4 0.000000 1.215 876.103
0.000000 0.903 909.743
3 0.000000 0.692 933.032
0.000000 0.485 956.321
2 0.000000 0.344 972.365
0.000000 0.206 988.408
1 0.000000 0.099 1000.829
0.000000 -0.006 1013.250
--Bob Yantosca (talk) 20:12, 14 November 2016 (UTC)
GEOS-3 vertical grid
GEOS-Chem no longer supports GEOS-3 meteorology. We shall keep this information here for future reference.
GEOS-3 is a pure-sigma grid, unlike the hybrid grids used in later met field products such as GEOS-4, GEOS-5, etc.) The vertical levels are lumped together in sigma-space as follows:
Original Sigma Lumped
levels edges, levels
on the original on the
48-L grid 48-L grid 30-L grid
============== 0.000000 ==============
48
0.000018
47
0.000048 30
46
0.000092
45
============== 0.000155 ==============
44
0.000245
43
0.000370 29
42
0.000540
41
============== 0.000765 ==============
40
0.001060
39
0.001440 28
38
0.001900
37
============== 0.002530 ==============
36
0.003300
35
0.004280 27
34
0.005500
33
============== 0.007040 ==============
32
0.008975
31
0.011405 26
30
0.014480
29
============== 0.018380 ==============
28
0.023330 25
27
============== 0.029600 ==============
26
0.037540 24
25
============== 0.047610 ==============
24
0.060350 23
23
============== 0.076480 ==============
--Bob Yantosca (talk) 20:04, 14 November 2016 (UTC)
GEOS-4 55-layer vertical grid
NOTE: Per request of NASA/GMAO, the GEOS-4 met fields have been de-supported in GEOS-Chem v11-02 and later versions.
| Used by | |
|---|---|
| Number of layers |
|
| Indexing |
|
| Type of grid | |
| Hybrid A parameter [hPa] |
(surface) 0.00000, 0.000000, 12.704939, 35.465965, 66.098427, 101.671654, 138.744400, 173.403183, 198.737839, 215.417526, 223.884689, 224.362869, 216.864929, 201.192093, 176.929993, 150.393005, 127.837006, 108.663429, 92.365662, 78.512299, 66.603378, 56.387939, 47.643932, 40.175419, 33.809956, 28.367815, 23.730362, 19.791553, 16.457071, 13.643393, 11.276889, 9.292943, 7.619839, 6.216800, 5.046805, 4.076567, 3.276433, 2.620212, 2.084972, 1.650792, 1.300508, 1.019442, 0.795134, 0.616779, 0.475806, 0.365041, 0.278526, 0.211349, 0.159495, 0.119703, 0.089345, 0.066000, 0.047585, 0.032700, 0.020000, 0.010000 (top of atmosphere) |
| Hybrid B parameter [1] |
(surface) 1.000000, 0.985110, 0.943290, 0.867830, 0.764920, 0.642710, 0.510460, 0.378440, 0.270330, 0.183300, 0.115030, 0.063720, 0.028010, 0.006960, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000 (top of atmosphere) |
| Pressures and altitudes for a column at atmospheric sea level, from surface upwards |
L Eta Edge Eta Mid Altitude Pressure
(unitless) (unitless) (km) (hPa)
========================================================
0.000000 80.581 0.010
55 0.000005 78.146 0.015
0.000010 76.357 0.020
54 0.000016 74.594 0.026
0.000022 73.180 0.033
53 0.000030 71.812 0.040
0.000037 70.657 0.048
52 0.000046 69.440 0.057
0.000055 68.392 0.066
51 0.000067 67.243 0.078
0.000078 66.245 0.089
50 0.000093 65.115 0.105
0.000108 64.130 0.120
49 0.000128 63.004 0.140
0.000148 62.021 0.159
48 0.000173 60.902 0.185
0.000199 59.924 0.211
47 0.000232 58.816 0.245
0.000265 57.846 0.279
46 0.000308 56.752 0.322
0.000350 55.794 0.365
45 0.000405 54.717 0.420
0.000460 53.773 0.476
44 0.000529 52.716 0.546
0.000599 51.788 0.617
43 0.000687 50.754 0.706
0.000775 49.844 0.795
42 0.000886 48.835 0.907
0.000996 47.946 1.019
41 0.001135 46.962 1.160
0.001274 46.092 1.301
40 0.001446 45.134 1.476
0.001619 44.286 1.651
39 0.001834 43.355 1.868
0.002048 42.529 2.085
38 0.002312 41.627 2.353
0.002576 40.825 2.620
37 0.002900 39.951 2.948
0.003224 39.173 3.276
36 0.003619 38.328 3.677
0.004013 37.574 4.077
35 0.004492 36.759 4.562
0.004971 36.030 5.047
34 0.005548 35.244 5.632
0.006126 34.539 6.217
33 0.006818 33.782 6.918
0.007510 33.101 7.620
32 0.008336 32.372 8.456
0.009162 31.716 9.293
31 0.010141 31.015 10.285
0.011120 30.383 11.277
30 0.012287 29.701 12.460
0.013455 29.085 13.643
29 0.014844 28.423 15.050
0.016232 27.824 16.457
28 0.017878 27.180 18.124
0.019523 26.596 19.792
27 0.021467 25.971 21.761
0.023410 25.402 23.730
26 0.025699 24.794 26.049
0.027987 24.240 28.368
25 0.030673 23.648 31.089
0.033358 23.108 33.810
24 0.036499 22.531 36.993
0.039641 22.004 40.175
23 0.043326 21.438 43.910
0.047012 20.920 47.644
22 0.051326 20.364 52.016
0.055641 19.855 56.388
21 0.060682 19.309 61.496
0.065723 18.807 66.603
20 0.071600 18.269 72.558
0.077477 17.773 78.512
19 0.084313 17.243 85.439
0.091149 16.753 92.366
18 0.099191 16.222 100.515
0.107234 15.731 108.663
17 0.116695 15.198 118.250
0.126157 14.706 127.837
16 0.137287 14.170 139.115
0.148418 13.674 150.393
15 0.161513 13.134 163.661
0.174608 12.633 176.930
14 0.190061 12.086 192.587
0.205513 11.578 208.244
13 0.223772 11.021 226.745
0.242032 10.504 245.246
12 0.263587 9.936 267.087
0.285142 9.409 288.927
11 0.310561 8.830 314.683
0.335980 8.291 340.439
10 0.365938 7.700 370.793
0.395895 7.148 401.146
9 0.431179 6.541 436.898
0.466464 5.975 472.650
8 0.508017 5.351 514.754
0.549571 4.768 556.857
7 0.598479 4.125 606.413
0.647387 3.523 655.968
6 0.695218 2.969 704.433
0.743050 2.443 752.898
5 0.786601 1.986 797.026
0.830152 1.549 841.154
4 0.866492 1.197 877.974
0.902831 0.857 914.795
3 0.929330 0.615 941.644
0.955828 0.378 968.494
2 0.970469 0.249 983.328
0.985110 0.122 998.163
1 0.992555 0.058 1005.706
1.000000 -0.006 1013.250
|
--Bob Yantosca (talk) 19:50, 14 November 2016 (UTC)
GEOS-4 30-level reduced vertical grid
NOTE: Per request of NASA/GMAO, the GEOS-4 met fields have been de-supported in GEOS-Chem v11-02 and later versions.
In order to save computational resources, GEOS-Chem "Classic" can collapse the GEOS-4 55 layer grid down to a 30-layer grid "on-the-fly". Groups of 2 and 4 layers are lumped together starting at ~70 hPa. See the table below for more information.
| Used by | |
|---|---|
| Number of layers |
|
| Indexing |
|
| Type of grid | |
| Lumping of vertical levels |
GEOS-4 30-level reduced vertical grid Bottom Bottom # levels edge of edge prs lumped level (hPa) together PTOP 0.010 30 0.066 4 29 0.211 4 28 0.617 4 27 1.651 4 26 4.077 4 25 9.293 4 24 19.792 4 23 28.368 2 22 40.175 2 21 56.388 2 20 78.512 2 %%%% START LUMPING LEVELS ABOVE HERE %%%%% 19 92.366 18 108.663 17 127.837 16 150.393 15 176.930 %%%% FIXED-PRESSURE LEVELS BEGIN HERE %%%% |
| Hybrid Ap parameter [hPa] |
(surface) 0.000000, 0.000000, 12.704939, 35.465965, 66.098427, 101.671654, 138.744400, 173.403183, 198.737839, 215.417526, 223.884689, 224.362869, 216.864929, 201.192093, 176.929993, 150.393005, 127.837006, 108.663429, 92.365662, 78.512299, 56.387939, 40.175419, 28.367815, 19.791553, 9.292943, 4.076567, 1.650792, 0.616779, 0.211349, 0.066000, 0.010000 (top of atmosphere) |
| Hybrid Bp parameter [1] |
(surface) 1.000000, 0.985110, 0.943290, 0.867830, 0.764920, 0.642710, 0.510460, 0.378440, 0.270330, 0.183300, 0.115030, 0.063720, 0.028010, 0.006960, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000 (top of atmosphere) |
| Pressures and altitudes for a column at atmospheric sea level, from surface upwards |
L Eta Edge Eta Mid Altitude Pressure
(unitless) (unitless) (km) (hPa)
=======================================================
0.000000 80.581 0.010
30 0.000028 72.180 0.038
0.000055 68.392 0.066
29 0.000127 63.053 0.139
0.000199 59.924 0.211
28 0.000399 54.834 0.414
0.000599 51.788 0.617
27 0.001109 47.135 1.134
0.001619 44.286 1.651
26 0.002816 40.166 2.864
0.004013 37.574 4.077
25 0.006588 34.024 6.685
0.009162 31.716 9.293
24 0.014342 28.654 14.542
0.019523 26.596 19.792
23 0.023755 25.307 24.080
0.027987 24.240 28.368
22 0.033814 23.020 34.272
0.039641 22.004 40.175
21 0.047641 20.836 48.282
0.055641 19.855 56.388
20 0.066559 18.727 67.450
0.077477 17.773 78.512
19 0.084313 17.243 85.439
0.091149 16.753 92.366
18 0.099191 16.222 100.515
0.107234 15.731 108.663
17 0.116695 15.198 118.250
0.126157 14.706 127.837
16 0.137287 14.170 139.115
0.148418 13.674 150.393
15 0.161513 13.134 163.661
0.174608 12.633 176.930
14 0.190061 12.086 192.587
0.205513 11.578 208.244
13 0.223772 11.021 226.745
0.242032 10.504 245.246
12 0.263587 9.936 267.087
0.285142 9.409 288.927
11 0.310561 8.830 314.683
0.335980 8.291 340.439
10 0.365938 7.700 370.793
0.395895 7.148 401.146
9 0.431179 6.541 436.898
0.466464 5.975 472.650
8 0.508017 5.351 514.754
0.549571 4.768 556.857
7 0.598479 4.125 606.413
0.647387 3.523 655.968
6 0.695218 2.969 704.433
0.743050 2.443 752.898
5 0.786601 1.986 797.026
0.830152 1.549 841.154
4 0.866492 1.197 877.974
0.902831 0.857 914.795
3 0.929330 0.615 941.644
0.955828 0.378 968.494
2 0.970469 0.249 983.328
0.985110 0.122 998.163
1 0.992555 0.058 1005.706
1.000000 -0.006 1013.250
|
--Bob Yantosca (talk) 20:02, 14 November 2016 (UTC)