This page is under construction...explanation and links will be added in the coming days and weeks...feedback welcome!
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The new grids and mapfiles address these problems, which have always existed in ACME and its predecessors (CESM, CCSM, CCM), and therefore cannot be too severe. The numerical flaws explained above can be thought of as fuzziness at the level of a few tenths of a degree in geo-referencing regridded data to the native model grid. These location errors produce only small (<< 1%) errors in regional or global statistics. So, why migrate? One aim is that diagnostics and observational evaluations with regridded data (often much more intuitive to visually evaluate than native SE grids) produce the same answers (to double precision whenever possible) as statistics computed on the native model grid. Without migration, agreement between native and regridded statistics beyond single precision is a matter of luck and coincidence, not determinism and reproducibility. As ACME grids shift to ~1/4 degree and finer, it becomes even more important to exploit the full double precision accuracy that software can guarantee when supplied with accurate grids.
Names of ACME gridfiles and mapfiles are date-stamped. The new grid and mapfiles were produced on or after 20150724. Cubed-sphere gridfiles produced before 20150724 are still considered good. Most other atmosphere gridfiles produced before 20150724 contain the flaws mentioned above. Gridfile flaws propagate to mapfiles so in most cases mapfiles must be updated too.
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| Old (flawed) Gridfile | New (corrected) | Generation: |
|---|---|---|
| 129x256_SCRIP.20150901.nc | ncks --rgr grd_ttl='FV-scalar grid 129x256' --rgr grid=${DATA}/grids/129x256_SCRIP.20150901.nc --rgr lat_nbr=129 --rgr lon_nbr=256 --rgr lat_typ=fv --rgr lon_typ=grn_ctr ~zender/nco/data/in.nc ~/foo |
ncks -O -D 7 --rgr grd_ttl='FV-scalar grid 801x1600' --rgr grid=${DATA}/grids/801x1600_SCRIP.20150901.nc --rgr lat_nbr=801 --rgr lon_nbr=1600 --rgr lat_typ=fv --rgr lon_typ=grn_ctr ~zender/nco/data/in.nc ~/foo.nc
| .nc | ||
| 257x512_SCRIP.130510.nc | 257x512_SCRIP.20150901.nc | ncks --rgr grd_ttl='FV-scalar grid 257x512' --rgr grid=${DATA}/grids/257x512_SCRIP.20150901.nc --rgr lat_nbr=257 --rgr lon_nbr=512 --rgr lat_typ=fv --rgr lon_typ=grn_ctr ~zender/nco/data/in.nc ~/foo.nc |
ncks --rgr grd_ttl='FV-scalar grid 801x1600' --rgr grid=${DATA}/grids/801x1600_SCRIP.20150901.nc --rgr lat_nbr=801 --rgr lon_nbr=1600 --rgr lat_typ=fv --rgr lon_typ=grn_ctr ~zender/nco/data/in.nc ~/foo.nc |
Note that ACME gridfiles and mapfiles are date-stamped. The new grid and mapfiles were produced on or after 20150724. Cubed-sphere gridfiles produced before 20150724 are still considered good. Most other atmosphere gridfiles produced before 20150724 contain the flaws mentioned above. Gridfile flaws propagate to mapfiles so in most cases mapfiles must be updated too:
Other (non-ACME) Gridfiles:
| Old (flawed) Gridfiles | New (corrected) | Generation: | |
|---|---|---|---|
| map_ne30np4_to_fv129x256_aave.150418 | t42_SCRIP.20150901.nc | map_ne30np4_to_fv129x256_aave.20150901.nc | |
| map_ne30np4_to_fv257x512_bilin.150418.nc | |||
| map_ne120np4_to_fv257x512_aave.150418.nc | map_ne120np4_to_fv257x512_aave.20150901.nc | ||
| map_ne120np4_to_fv801x1600_bilin.150418.nc |
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ncks --rgr grd_ttl='T42 Gaussian grid' --rgr grid=${DATA}/grids/t42_SCRIP.20150901.nc --rgr lat_nbr=64 --rgr lon_nbr=128 --rgr lat_typ=gss --rgr lon_typ=Grn_ctr ~zender/nco/data/in.nc ~/foo.nc | ||
| t62_SCRIP.20150901.nc | ncks --rgr grd_ttl='T62 Gaussian grid' --rgr grid=${DATA}/grids/t62_SCRIP.20150901.nc --rgr lat_nbr=94 --rgr lon_nbr=192 --rgr lat_typ=gss --rgr lon_typ=Grn_ctr ~zender/nco/data/in.nc ~/foo.nc | |
| ncks --rgr grd_ttl='T85 Gaussian grid' --rgr grid=${DATA}/grids/t85_SCRIP.20150901.nc --rgr lat_nbr=128 --rgr lon_nbr=256 --rgr lat_typ=gss --rgr lon_typ=Grn_ctr ~zender/nco/data/in.nc ~/foo.nc |
Generating Gridfiles:
The netCDF Operator ncks generates accurate and complete SCRIP-format gridfiles for select grid types, including equi-angular, FV, and Gaussian rectangular latitude/longitude grids. Full documentation is at http://nco.sf.net/nco.html#grid. Options pertinent to the grid geometry and metadata are passed to NCO via key-value pairs prefixed by "--rgr". Pass at least six key-value pair arguments to create a fully explicitly specified, well-annotated grid. The six arguments, and their corresponding keys, are: grid title (grd_ttl), grid filename (grid), number of latitudes (lat_nbr), number of longitudes (lon_nbr), latitude grid type (lat_typ), and longitude grid type (lon_typ). Four other arguments (the NSEW bounding box) are necessary to construct regular regional (non-global) grids, but for now we focus on global grids.
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