Olson land map
On this page we discuss the land map from Jennifer Olson that is currently used by the GEOS-Chem Dry deposition and Soil NOx emissions modules.
Contents
Overview
Description of land map
The GEOS-Chem Dry deposition and Soil NOx emissions modules rely on the Olson (1992) land map. This map specifies 74 different land types on the 0.5° x 0.5° "generic" grid, which is defined by:
Lon centers = -179.75, -179.25, -178.75, -178.25, ... 178.25, 178.75, 179.25, 179.75 Lat centers = -89.75, -89.25, -88.75, -88.25, ... 88.25, 88.75, 89.25, 89.75
The individual Olson land types and their respective indices are as follows:
0 Water 25 Deciduous 50 Desert 1 Urban 26 Deciduous 51 Desert 2 Shrub 27 Conifer 52 Steppe 3 --- 28 Dwarf forest 53 Tundra 4 --- 29 Trop. broadleaf 54 rainforest 5 --- 30 Agricultural 55 mixed wood/open 6 Trop. evergreen 31 Agricultural 56 mixed wood/open 7 --- 32 Dec. woodland 57 mixed wood/open 8 Desert 33 Trop. rainforest 58 mixed wood/open 9 --- 34 --- 59 mixed wood/open 10 --- 35 --- 60 conifers 11 --- 36 Rice paddies 61 conifers 12 --- 37 agric 62 conifers 13 --- 38 agric 63 Wooded tundra 14 --- 39 agric. 64 Moor 15 --- 40 shrub/grass 65 coastal 16 Scrub 41 shrub/grass 66 coastal 17 Ice 42 shrub/grass 67 coastal 18 --- 43 shrub/grass 68 coastal 19 --- 44 shrub/grass 69 desert 20 Conifer 45 wetland 70 ice 21 Conifer 46 scrub 71 salt flats 22 Conifer 47 scrub 72 wetland 23 Conifer/Deciduous 48 scrub 73 water 24 Deciduous/Conifer 49 scrub
Here is a plot of the Olson 1992 land map at 0.5° x 0.5° resolution. Only one land type is assigned to an 0.5° x 0.5° grid box.
--Bob Y. 15:56, 21 March 2012 (EDT)
Preparation of input files for GEOS-Chem
The raw Olson land map data are stored in the file owe14d.0.5 (which is now archived in Bob Yantosca's disk space). This was an ASCII file containing 20 integer values per line (Fortran format '(20i4)').
The IDL routine REGRIDH_LAI (which is distributed as part of the GAMAP package) was used to prepare the Olson land map for input into GEOS-Chem. REGRIDH_LAI read these files as input:
- owe14d.0.5: Olson land map file at 0.5° x 0.5° resolution
- lai_all.dat: leaf area index data at 1° x 1° resolution
and created these files as output:
- vegtype.global: Olson land map indices, on the GEOS-Chem grid
- laiMM.global: leaf area index files, on the GEOS-Chem grid (MM = 01 .. 12)
Therefore, REGRIDH_LAI had to be called several times in order to create the proper vegtype.global files for each different GEOS-Chem grid configuration. (4° x 5°, 2° x 2.5°, and the 0.5° x 0.666° nested grids).
NOTE: The original leaf area index data has now been supplanted by those from the MODIS satellite instrument.
Structure of the vegtype.global file
As mentioned above, each GEOS-Chem grid configuration required its own vegtype.global file. The vegtype.global file contained the following information:
- GEOS-Chem grid box longitude index (I)
- GEOS-Chem Grid box latitude index (J)
- Number of Olson land types (at 0.5° x 0.5° resolution) that fit inside the GEOS-Chem grid box (I,J)
- List of indices of all Olson land types that fit inside the GEOS-Chem grid box (I,J)
- Fraction (in mils) of the GEOS-Chem grid box covered by each Olson land type
Each of these quantities was represented as an integer value (with 20 integer values per line). Therefore, a quick look at the 4° x 5° vegtype.global file would reveal the following text:
... 20 13 1 01000 21 13 1 01000 22 13 5 0 41 24 31 67 811 25 62 76 26 23 13 4 41 24 52 31 137 175 650 38 24 13 5 52 8 0 41 31 589 62 298 25 26 ... etc.
From the snippet of the file above, we would read that
| GEOS-Chem grid box | has this many Olson land types | with indices | which cover this % of the box |
|---|---|---|---|
| (20,13) | 1 | 0 | 100% |
| (21,13) | 1 | 0 | 100% |
| (22,13) | 5 | 0, 41, 24, 31, 67 | 81.1%, 2.5%, 6.2%, 7.6%, 2.6%, respectively |
| (23,13) | 4 | 41, 24, 52, 31 | 13.7%, 17.5%, 65.0%, 3.8%, respectively |
| (24,13) | 5 | 52, 8, 0, 41, 31 | 58.9%, 6.2%, 29.8%, 2.5% and 2.6%, respectively |
GEOS-Chem routine rdland.F reads the information from the vegtype.global into the following arrays:
| Array | Quantity | Where used |
|---|---|---|
| IREG( I, J ) | Number of Olson land types per GEOS-Chem grid box (i.e. Column #2 in the table above) |
Soil NOx emissions |
| ILAND( I, J, 1:IREG(I,J) ) | List of Olson land type indices per each GEOS-Chem grid box (i.e. Column #3 in the table above) |
Soil NOx emissions |
| IUSE( I, J, 1:IREG(I,J) ) | Fraction (in mils) of the GEOS-Chem grid box covered by each Olson land type (i.e. Column #4 in the table above) |
Soil NOx emissions |
| IJREG( IJLOOP ) | Same data as in IREG, but with 1 spatial dimension | Dry deposition |
| ILAND( IJLOOP, 1:IJREG(I,J) ) | Same data as in ILAND, but with 1 spatial dimension | Dry deposition |
| IJUSE( IJLOOP, 1:IJREG(I,J) ) | Same data as in IUSE, but with 1 spatial dimension | Dry deposition |
| FRCLND( I, J ) | Fraction of each GEOS-Chem grid box that is not water (computed from IUSE) | Several locations |
NOTE: The reason why there are two sets of arrays (IREG, ILAND, IUSE) and (IJREG, IJLAND, IJUSE) is purely historical baggage. This usage dates back to the original Harvard/GISS CTM, from which we obtained the GEOS-Chem dry deposition and soil NOx emissions modules.
--Bob Y. 17:24, 21 March 2012 (EDT)
Modifications for the grid-independent model
References
- Bey I., D. J. Jacob, R. M. Yantosca, J. A. Logan, B. Field, A. M. Fiore, Q. Li, H. Liu, L. J. Mickley, and M. Schultz, Global modeling of tropospheric chemistry with assimilated meteorology: Model description and evaluation, J. Geophys. Res., 106, 23,073-23,096, 2001
- Olson, J, World Ecosystems (WE1.4): Digital raster data on a 10 minute geographic 1080 x 2160 grid, in Global Ecosystems Database, version 1.0, Disc A, edited by NOAA Natl. Geophys. Data Center, Boulder, Colorado, 1992.
- Wang, Y., D.J. Jacob, and J.A. Logan, Global simulation of tropospheric O3-NOx-hydrocarbon chemistry, 1. Model formulation, J. Geophys. Res., 103, D9, 10,713-10,726, 1998.
