README -- describes contents of HEMCO/MODIS_XLAI/v2017-07 directory
13 Feb 2019
GEOS-Chem Support Team
geos-chem-support@g.harvard.edu


Overview:
===============================================================================

These files were processed from the data files:

   ExtData/CHEM_INPUTS/MODIS_LAI_201707/For_Olson_2001/
   YYYY/MODIS.LAIv.V5.generic.025x025.YYYY.nc

in order to separate out the LAI values corresponding to the 73 land types
(0..72) of the 2001 Olson Land Map into separate netCDF variables.  This
facilitates regridding by HEMCO, as each landtype can then be multiplied by
mask denoting the grid boxes where each land type is present.

The files listed below were created by running the script called
"make_XMODIS.run" in the scripts/ folder.  This is the driver script for
the NCL program make_XMODIS_for_GCHP.ncl.  (NOTE: If you are going to
reprocess the data, edit the paths to the folders in which the input data
files are found on your system in make_MODIS_for_GCHP.ncl).

Jenny Fisher describes how this data differs from the MODIS LAI files
version 2012-04:

   The summary version of the issue is:
   
      - Several years back, Mike got a version of the raw MODIS LAI files
        from BU on a 0.25°x0.25° grid. These had some sort of projection
        error that led to the weird behaviour I saw over Australia
        (offsetting along the southern coasts of Australia, w/ some SW ocean
        grid boxes having LAI > 0 and some SE land boxes having LAI = 0).
      - Mike processed those files to a 0.5°x0.5° version for input to
        GEOS-Chem. This was NOT just regridding the original files, but also
        making some adjustments following Muller et al. 2008*.
      - These were the files in the archive for some unknown period of time.
        Eventually (for HEMCO? Or 0.25x0.3125? or both?) someone must have
        regridded these 0.5°x0.5° files back to 0.25°x0.25°.
      - In the meantime, Eloise received an updated version of the raw MODIS
        LAI files from BU on a 0.25°x0.25° grid. These did not have the
        projection error.
      - Eloise Marais has not applied the same type of processing Mike did -
        so what I have now are just the raw data converted to HEMCO format.
   
   After all of this, my recommendation for moving forward is that we
   replace the existing files currently used in GEOS-Chem with the
   versions from Eloise.
   

Files:
===============================================================================

YYYY = 2005..2011; MM = 01..12

YYYY/MODIS_XLAI.025x025.YYYYMM.nc

   -- Monthly MODIS leaf area indices, separated so that the LAI values
      corresponding to each land type is contained in a separate netCDF
      variable.

      Resolution  : 0.25 x 0.25 GENERIC grid (1440 x 720 grid boxes)
      Units       : cm2 leaf / cm2 grid box
      Timestamps: : Monthly, YYYY/01/01 through YYYY/12/01,
                    where YYYY is the year listed in the file name
      Compression : Level 1 (nccopy -d1)
      Chunking    : nccopy -c lon/1440,lat/720,time/1

The files have this structure:

      dimensions:
              time = 1 ;
              lat = 720 ;
              lon = 1440 ;
      variables:
              float XLAI00(time, lat, lon) ;
                      XLAI00:gamap_category = "MODIS" ;
                      XLAI00:units = "cm2 cm-2" ;
                      XLAI00:long_name = "MODIS leaf area index" ;
                      XLAI00:_FillValue = 9.96921e+36f ;
                      XLAI00:_Storage = "chunked" ;
                      XLAI00:_ChunkSizes = 1, 720, 1440 ;
                      XLAI00:_DeflateLevel = 1 ;
              float XLAI01(time, lat, lon) ;
                      XLAI01:gamap_category = "MODIS" ;
                      XLAI01:units = "cm2 cm-2" ;
                      XLAI01:long_name = "MODIS leaf area index" ;
                      XLAI01:_FillValue = 9.96921e+36f ;
                      XLAI01:_Storage = "chunked" ;
                      XLAI01:_ChunkSizes = 1, 720, 1440 ;
                      XLAI01:_DeflateLevel = 1 ;
              ... etc ...
              float XLAI72(time, lat, lon) ;
                      XLAI72:gamap_category = "MODIS" ;
                      XLAI72:units = "cm2 cm-2" ;
                      XLAI72:long_name = "MODIS leaf area index" ;
                      XLAI72:_FillValue = 9.96921e+36f ;
                      XLAI72:_Storage = "chunked" ;
                      XLAI72:_ChunkSizes = 1, 720, 1440 ;
                      XLAI72:_DeflateLevel = 1 ;

where XLAI00 are the MODIS LAI values corresponding to Olson land type 0,
      XLAI01 are the MODIS LAI values corresponding to Olson land type 1,
      and so forth.