GEOS-Chem vertical grids: Difference between revisions

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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|''GEOS-Chem horizontal grids'' wiki page]].


On this page we provide information about the various vertical grids used in GEOS-Chem.
== Comparisons of vertical grids used by GEOS-Chem ==


== Vertical grid for GEOS-5, GEOS-FP, MERRA, and MERRA-2 ==
The table below compares the level structure of the various grids used by GEOS-Chem.


The [[GEOS-5]], [[GEOS-FP]], [[MERRA]], and [[MERRA-2]] met field products from GMAO all share the same vertical grid.
<span style="color:red">'''''[[GEOS-Chem 12#12.0.0|GEOS-Chem 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.'''''</span>
 
{| border=1 cellspacing=0 cellpadding=5  
|-valign="top"
!bgcolor="#CCCCCC" width="300px"|Description
!bgcolor="#CCCCCC" width="700px"|Comparison
 
|-valign="top"
|Vertical grids up to 3 km:
#[[#GCAP vertical grid|GCAP]]
#[[#GEOS-3 vertical grid|GEOS-3]]
#[[#Vertical grids for GEOS-4|GEOS-4]] and
#[[#Vertical grids for GEOS-5, GEOS-FP, MERRA, and MERRA-2|GEOS-5 / GEOS-FP / MERRA / MERRA2]]
|[[Image:Levels3km.png]]
 
|-valign="top"
|Vertical grids up to 10 km:
#[[#GCAP vertical grid|GCAP]]
#[[#GEOS-3 vertical grid|GEOS-3]]
#[[#Vertical grids for GEOS-4|GEOS-4]] and
#[[#Vertical grids for GEOS-5, GEOS-FP, MERRA, and MERRA-2|GEOS-5 / GEOS-FP / MERRA / MERRA2]]
|[[Image:Levels10km.png]]
 
|-valign="top"
|Vertical grids up to 32 km:
#[[#GCAP vertical grid|GCAP]]
#[[#GEOS-3 vertical grid|GEOS-3]]
#[[#Vertical grids for GEOS-4|GEOS-4]] and
#[[#Vertical grids for GEOS-5, GEOS-FP, MERRA, and MERRA-2|GEOS-5 / GEOS-FP / MERRA / MERRA2]]
|[[Image:Levels32km.png]]
 
|-valign="top"
|Vertical grids up to 80km:
#[[#GCAP vertical grid|GCAP]]
#[[#GEOS-3 vertical grid|GEOS-3]]
#[[#Vertical grids for GEOS-4|GEOS-4]] and
#[[#Vertical grids for GEOS-5, GEOS-FP, MERRA, and MERRA-2|GEOS-5 / GEOS-FP / MERRA / MERRA2]]
|[[Image:Levels80km.png]]
 
|}
 
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|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.
 
<span style="color:red">'''''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.'''''</span>


=== 72-layer vertical grid ===
=== 72-layer vertical grid ===
Line 13: Line 60:
|-valign="top"
|-valign="top"
!width="200px" bgcolor="#CCCCCC"|Used by  
!width="200px" bgcolor="#CCCCCC"|Used by  
|width="800px"|
|width="800px"|These met field products are currenlty used by GEOS-Chem:
*[[GEOS-FP|GMAO GEOS-5 "forward processing" (aka GEOS-FP)]]
*[[MERRA-2|GMAO MERRA-2 reanalysis product]]
 
These met field products have been de-supported from [[GEOS-Chem v11-02]] and later versions:
*[[GEOS-5|GMAO GEOS-5]]
*[[GEOS-5|GMAO GEOS-5]]
*[[GEOS-FP|GMAO GEOS-5 "forward processing" (aka GEOS-FP)]]
*[[MERRA|GMAO MERRA reanalysis product]]
*[[MERRA|GMAO MERRA reanalysis product]]
*[[MERRA-2|GMAO MERRA-2 reanalysis product]]


|-valign="top"
|-valign="top"
Line 234: Line 283:


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.
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.
<span style="color:red">'''''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.'''''</span>


{| border=1 cellspacing=0 cellpadding=5  
{| border=1 cellspacing=0 cellpadding=5  
Line 239: Line 290:
|-valign="top"
|-valign="top"
!width="200px" bgcolor="#CCCCCC"|Used by  
!width="200px" bgcolor="#CCCCCC"|Used by  
|width="800px"|
|width="800px"|These met field products are currently used by GEOS-Chem:
*[[GEOS-FP|GMAO GEOS-5 "forward processing" (aka GEOS-FP)]]
*[[MERRA-2|GMAO MERRA-2 reanalysis product]]
 
These met field products have been de-supported from [[GEOS-Chem v11-02]] and later versions:
*[[GEOS-5|GMAO GEOS-5]]
*[[GEOS-5|GMAO GEOS-5]]
*[[GEOS-FP|GMAO GEOS-5 "forward processing" (aka GEOS-FP)]]
*[[MERRA|GMAO MERRA reanalysis product]]
*[[MERRA|GMAO MERRA reanalysis product]]
*[[MERRA-2|GMAO MERRA-2 reanalysis product]]


|-valign="top"
|-valign="top"
Line 423: Line 476:
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 19:33, 14 November 2016 (UTC)
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 19:33, 14 November 2016 (UTC)


== GEOS-4 vertical grid ==
== Reference section for vertical grids ==
 
=== 55-layer vertical grid ===
 
{| border=1 cellspacing=0 cellpadding=5
 
|-valign="top"
!width="200px" bgcolor="#CCCCCC"|Used by
|width="800px"|
*[[GMAO GEOS-4]]
 
|-valign="top"
!bgcolor="#CCCCCC"|Number of layers
|
*55 centers
*56 edges
 
|-valign="top"
!bgcolor="#CCCCCC"|Indexing
|
*Surface upwards (in GEOS-Chem "Classic"); L=1 is the surface
*Surface upwards (in met field files read in by GEOS-Chem); L=1 is the surface
*Top down (in GMAO "raw" data files); L=1 is the atmosphere top
 
|-valign="top"
!bgcolor="#CCCCCC"|Type of grid
|
*[[#Hybrid grid definition|Hybrid sigma-pressure]]
 
|-valign="top"
! bgcolor="#CCCCCC"|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)
|-valign="top"
!bgcolor="#CCCCCC"|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)
 
|-valign="top"
!bgcolor="#CCCCCC"|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
|}
 
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 19:50, 14 November 2016 (UTC)
 
=== 30-level reduced vertical grid ===
 
In order to save computational resources, GEOS-Chem "Classic" can collapse the [[GMAO GEOS-4|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.
 
{| border=1 cellspacing=0 cellpadding=5
 
|-valign="top"
!width="200px" bgcolor="#CCCCCC"|Used by
|width="800px"|
*[[GMAO GEOS-4]]
 
|-valign="top"
! bgcolor="#CCCCCC"|Number of layers
|
*30 centers
*31 edges
 
|-valign="top"
!bgcolor="#CCCCCC"|Indexing
|
*Surface upwards (in GEOS-Chem "Classic"); L=1 is the surface
 
|-valign="top"
!bgcolor="#CCCCCC"|Type of grid
|
*[[#Hybrid grid definition|Hybrid sigma-pressure]]
 
|-valign="top"
!bgcolor="#CCCCCC"|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 %%%%
 
|-valign="top"
! bgcolor="#CCCCCC"|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)
 
|-valign="top"
! bgcolor="#CCCCCC"|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)
 
|-valign="top"
! bgcolor="#CCCCCC"|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
|}
 
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 20:02, 14 November 2016 (UTC)
 
== GCAP vertical grid ==
 
== Obsolete grids ==
 
=== GEOS-3 ===
 
<span style="color:red">'''''GEOS-Chem no longer supports GEOS-3 meteorology.  We shall keep this information here for future reference.'''''</span>
 
GEOS-3 is a pure-sigma grid (unlike the hybrid grids used in GEOS-4, GEOS-5, and MERRA).  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 ==============
 
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 20:04, 14 November 2016 (UTC)


== Reference ==
In this section we provide more general information about the vertical grids used by GEOS-Chem.


=== Sigma grid ===
=== Sigma grid definition ===


The sigma grid is a purely terrain-following coordinate.  The following met data products are defined on the sigma grid:
The sigma grid is a purely terrain-following coordinate.  The following met data products are defined on the sigma grid:
Line 878: Line 529:
The following met data products use the hybrid grid formulation:
The following met data products use the hybrid grid formulation:


#[[GMAO GEOS-4]]
#[[GEOS-FP|GMAO GEOS-FP]] (currently used in GEOS-Chem)
#[[GEOS-5|GMAO GEOS-5]]
#[[MERRA-2|GMAO MERRA-2]] (currently used in GEOS-Chem)
#[[MERRA|GMAO MERRA]]
#[[GMAO GEOS-4]] (de-supported in GEOS-Chem v11-02)
#[[MERRA-2|GMAO MERRA-2]]
#[[GEOS-5|GMAO GEOS-5]] (de-supported in GEOS-Chem v11-02)
#[[GEOS-FP|GMAO GEOS-FP]]
#[[MERRA|GMAO MERRA]] (de-supported in GEOS-Chem v11-02)


The pressure at the bottom edge of grid box <tt>(I,J,L)</tt> is defined as follows:
The pressure at the bottom edge of grid box <tt>(I,J,L)</tt> is defined as follows:
Line 888: Line 539:
     P<sub>edge</sub>(I,J,L) = A<sub>p</sub>(L) + [ B<sub>p</sub>(L) * P<sub>surface</sub>(I,J) ]
     P<sub>edge</sub>(I,J,L) = A<sub>p</sub>(L) + [ B<sub>p</sub>(L) * P<sub>surface</sub>(I,J) ]
   
   
     P<sub>center</sub>(I,J,L) = [ P<sub>edge</sub>(I,J,L) + P<sub>edge</sub>(I,J,L) ] / 2
     P<sub>center</sub>(I,J,L) = [ P<sub>edge</sub>(I,J,L) + P<sub>edge</sub>(I,J,L+1) ] / 2
where
where


Line 948: Line 599:


--[[User:Bmy|Bob Y.]] 15:58, 6 April 2011 (EDT)
--[[User:Bmy|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&mdash;which we cut and/or regrid for input into GEOS-Chem&mdash;store data from the top of the atmopshere downward.
{| border=1 cellspacing=0 cellpadding=5
|-valign="top" bgcolor="#CCCCCC"
!width="120px"|GMAO data<br>product
!width="120px"|Grid<br>type
!width="100px"|Surface<br> level
!width="100px"|Top-of-<br>atmosphere level
!width="100px"|
!width="100px"|Top-of-<br>atmosphere pressure
|-valign="top" align="center"
|[[Overview of GMAO met data products#GEOS-3|GEOS-3]]
|Pure sigma
|Level 48
|Level 1
|
|0.01 hPa
|-valign="top" align="center"
|[[GMAO GEOS-4|GEOS-4]]
|Hybrid
|Level 55
|Level 1
|
|0.01 hPa
|-valign="top" align="center"
|[[GEOS-5|GEOS-5.2.0]]<br>[[GEOS-FP]]<br>[[MERRA]]<br>[[MERRA-2]]
|Hybrid
|Level 72
|Level 1
|
|0.01 hPa
|}
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 20:51, 14 November 2016 (UTC)
==== GEOS-Chem ====
GEOS-Chem labels vertical levels starting from the surface and then moving upward&mdash;exactly in the opposite way as in the GMAO met field files.
{| border=1 cellspacing=0 cellpadding=5
|-valign="top" bgcolor="#CCCCCC"
!width="120px"|GMAO data<br>product
!width="120px"|Grid<br>type
!width="100px"|Surface<br> level
!width="100px"|Top-of-<br>atmosphere level:<br>Full grid
!width="100px"|Top-of-<br>atmosphere level:<br>[[#Collapsing of the vertical levels in GEOS-Chem|Reduced grid]]
!width="100px"|Top-of<br>atmosphere pressure
|-valign="top" align="center"
|[[Overview of GMAO met data products#GEOS-3|GEOS-3]]
|Pure sigma
|Level 1
|Level 48
|Level 30
|0.01 hPa
|-valign="top" align="center"
|[[GMAO GEOS-4|GEOS-4]]
|Hybrid
|Level 1
|Level 55
|Level 30
|0.01 hPa
|-valign="top" align="center"
|[[GEOS-5|GEOS-5.2.0]]<br>[[GEOS-FP]]<br>[[MERRA]]<br>[[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 <tt>GeosUtil/pressure_mod.f</tt>):
* <code>GET_PEDGE( I, J, L )</code>
* <code>GET_PCENTER( I, J, L )</code>
return the pressures in hPa at the edge and center, respectively, of grid box <tt>(I,J,L)</tt>.
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 20:18, 14 November 2016 (UTC)
=== Vertical grids and GAMAP ===
'''''[mailto:Ray.Nassar@ec.gc.ca Ray Nassar] wrote:'''''
:[The different GEOS vertical grids] 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 [http://acmg.seas.harvard.edu/gamap/ 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.  [[GAMAP_bugs_and_fixes#GAMAP_plot_titles_showing_.22incorrect.22_altitudes_for_plots|A correction for this apparent error]] can be found in the GAMAP bugs and fixes section of this wiki.
'''''[mailto:yantosca@seas.harvard.edu Bob Yantosca] wrote:'''''
:[http://acmg.seas.harvard.edu/gamap/ 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 ) )
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 20:14, 14 November 2016 (UTC)
=== For more information ===
Please see the following resources for more information about vertical grids:
# [http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/vertical_grids.pdf ''Overview of vertical grids'' by Bob Yantosca] (PDF)
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 20:16, 14 November 2016 (UTC)

Latest revision as of 15:03, 19 June 2019

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 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:
  1. GCAP
  2. GEOS-3
  3. GEOS-4 and
  4. GEOS-5 / GEOS-FP / MERRA / MERRA2
 Levels3km.png
Vertical grids up to 10 km:
  1. GCAP
  2. GEOS-3
  3. GEOS-4 and
  4. GEOS-5 / GEOS-FP / MERRA / MERRA2
 Levels10km.png
Vertical grids up to 32 km:
  1. GCAP
  2. GEOS-3
  3. GEOS-4 and
  4. GEOS-5 / GEOS-FP / MERRA / MERRA2
 Levels32km.png
Vertical grids up to 80km:
  1. GCAP
  2. GEOS-3
  3. GEOS-4 and
  4. GEOS-5 / GEOS-FP / MERRA / MERRA2
 Levels80km.png

--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
  • 72 centers
  • 73 edges
Indexing
  • Surface upwards (in GEOS-Chem "Classic"); L=1 is the surface
  • Surface upwards (in met field files read in by GEOS-Chem); L=1 is the surface
  • Top down (in GMAO "raw" data files); L=1 is the atmosphere top
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
  • 47 centers
  • 48 edges
Indexing
  • Surface upwards (in GEOS-Chem "Classic"); L=1 is the surface
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:

  1. GMAO GEOS-3 (NOTE: Now obsolete)
  2. 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:

  1. GMAO GEOS-FP (currently used in GEOS-Chem)
  2. GMAO MERRA-2 (currently used in GEOS-Chem)
  3. GMAO GEOS-4 (de-supported in GEOS-Chem v11-02)
  4. GMAO GEOS-5 (de-supported in GEOS-Chem v11-02)
  5. 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:

[The different GEOS vertical grids] 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:

  1. Overview of vertical grids by Bob Yantosca (PDF)

--Bob Yantosca (talk) 20:16, 14 November 2016 (UTC)

Retrieved from "https://wiki.seas.harvard.edu/geos-chem/index.php?title=GEOS-Chem_vertical_grids&oldid=42846"