Olson land map

From Geos-chem
Revision as of 20:59, 21 March 2012 by Bmy (Talk | contribs) (Structure of the vegtype.global file)

Jump to: navigation, search

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.

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.

File:Olson1992.png

--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:

  1. owe14d.0.5: Olson land map file at 0.5° x 0.5° resolution
  2. lai_all.dat: leaf area index data at 1° x 1° resolution

and created these files as output:

  1. vegtype.global: Olson land map indices, on the GEOS-Chem grid
  2. 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:

  1. GEOS-Chem grid box longitude index (I)
  2. GEOS-Chem Grid box latitude index (J)
  3. Number of Olson land types (at 0.5° x 0.5° resolution) that fit inside the GEOS-Chem grid box (I,J)
  4. List of indices of all Olson land types that fit inside the GEOS-Chem grid box (I,J)
  5. 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

  1. GEOS-Chem grid box (20,13) contains only 1 Olson land type, (type 0=ice), which covers 100% (1000 mils) of the box.
  2. Ditto for GEOS-Chem grid box (21,13)
  3. GEOS-Chem grid box (22,13) contains 5 Olson land types (0=ice, 41=shrub/grass, 24=deciduous/conifer, 31=agricultural, 67=coastal), which cover 81.1%, 2.5%, 6.2%, 7.6%, and 2.6% of the box, respectively.
  4. GEOS-Chem grid box (23,13) contains 4 Olson land types (41, 24, 52=steppe, 31), which cover 13.7%, 17.5%, 65.0%, and 3.8% of the box, respectively.
  5. GEOS-Chem grid box (24,13) contains 5 Olson land types (52, 8=desert, 0, 41, 31), which cover 58.9%, 6.2%, 29.8%, 2.5% and 2.6% of the box, respectively.

This information is read into the following GEOS-Chem arrays:

Modifications for the grid-independent model

References

  1. 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
  2. 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.
  3. 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.

Known issues