NCL: Weight files used to regrid POP Ocean Model data

Interpolation of rectilinear lat/lon grids to POP lat/lon grids and POP lat/lon grids to rectilinear lat/lon grids requires CESM validated weight files. These weight files are freely available for download from the CESM4 subversion repository. You may be required to register on the CESM4.0 website to obtain a guest login and password for the CESM4.0 subversion repository.

All validated weight files may be downloaded by pointing your browser directly at:

     https://svn-ccsm-inputdata.cgd.ucar.edu/trunk/ncl/

and download the desired file(s) by right-clicking on the file and selecting "Save As" or "Download Linked File as".

Also, individual files (here, map_gx1v6_to_1x1d_bilin_da_100716.nc) via:

     svn export https://svn-ccsm-inputdata.cgd.ucar.edu/trunk/ncl/map_gx1v6_to_1x1d_bilin_da_100716.nc

The following will download all the weight files:

     svn export https://svn-ccsm-inputdata.cgd.ucar.edu/trunk/ncl

Generally, you do not want to do this. There are many files.

Currently, bilinear interpolation weight files are available for the most common model configurations and rectilinear grids. Bilinear interpolation is adequate for most common usages (eg, graphics). Conservative interpolation weight files will be addressed on a case-by-case basis.

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If you can not find a weight file in the svn repository and, if you have a login on a CISL compute server, additional weight files may be available in the following directories:

    /glade/p/cesm/cseg/ncl
or
    /glade/p/cesm/cseg/inputdata/cpl/cpl6

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NCL's ESMF regridding functions can be used to generate weight files: See Example 24. The advantage is a custom weight file can be generated. For example, generate a weight file that will conservatively regrid the POP data to (say) a 1x2 grid.

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Users may generate their own weight files via the SCRIP (Spherical Coordinate Remapping and Interpolation Package) software. This uses the fortran-90 language.

An alternate implementation of the SCRIP package is available via the Climate Data Operators (CDO) . The CDO are implementated from the unix/linux command line.

NOTE: The NCL development team does not support either implementation of the SCRIP software.

REFERENCES

Jones, Philip W. (1999): First and Second Order Conservative
Remapping Schemes for Grids in Spherical Coordinates.
Monthly Weather Review: v127 pp 2204-2210.

Jones, Philip W. (1998): A User's Guide for SCRIP: A Spherical
Coordinate Remapping and Interpolation Package. Version 1.2.
Los Alamos National Laboratory.