This page is devoted to instruction in ncremap. It describes steps necessary to create grids, and to regrid datasets between different grids with ncremap. Some of the simpler regridding options supported by ncclimo are also described at Generate, Regrid, and Split Climatologies (climo files) with ncclimo. This page describes those features in more detail, and other, more boutique features often useful for custom regridding solutions.
The Zen of Regridding
Most modern climate/weather-related research requires a regridding step in its workflow. The plethora of geometric and spectral grids on which model and observational data are stored ensures that regridding is usually necessary to scientific insight, especially the focused and variable resolution studies that E3SM models conduct. Why does such a common procedure seem so complex? Because a mind-boggling number of options are required to support advanced regridding features that many users never need. To defer that complexity, this HOWTO begins with solutions to the prototypical regridding problem, without mentioning any other options. It demonstrates how to solve that problem simply, including the minimal software installation required. Once the basic regridding vocabulary has been introduced, we solve the prototype problem when one or more inputs are "missing", or need to be created. The HOWTO ends with descriptions of different regridding modes and workflows that use features customized to particular models, observational datasets, and formats. The overall organization, including TBD sections (suggest others, or vote for prioritizing, below), is:
...
ncremap -P mwf -s ocean.RRS.30-10km_scrip_150722.nc -g t62_SCRIP.20150901.nc --nm_src=oRRS30to10 --nm_dst=T62 --dt_sng=20180901
produces the 12 10 ERWG map-files:
map_oRRS30to10_to_T62_aave.20180901.nc
map_oRRS30to10_to_T62_blin.20180901.nc
map_oRRS30to10_to_T62_ndtos.20180901.nc
map_oRRS30to10_to_T62_nstod.20180901.nc
map_oRRS30to10_to_T62_patc.20180901.nc
map_oRRS30to10_to_T62_tempest.20180901.nc
map_T62_to_oRRS30to10_aave.20180901.nc
map_T62_to_oRRS30to10_blin.20180901.nc
map_T62_to_oRRS30to10_ndtos.20180901.nc
map_T62_to_oRRS30to10_nstod.20180901.nc
map_T62_to_oRRS30to10_patc.20180901.nc
map_T62_to_oRRS30to10_tempest.20180901.nc
The ordering of source and destination grids is immaterial for ERWG maps since MWF-mode produces all map combinations. However, as described above in the TempestRemap section, the Tempest overlap-mesh generator must be called with the smaller grid preceding the larger grid. For this reason, always invoke MWF-mode with the smaller grid (i.e., the ocean) as the source, otherwise some Tempest map-file will fail to generate. The six optimized SE<->FV Tempest maps described above in the TempestRemap section will be generated when the destination grid has a ".g" suffix which ncremap interprets as indicating an Exodus-format SE grid (NB: this assumption is an implementation convenience that can be modified if necessary). For example,
ncremap -P mwf -s ocean.RRS.30-10km_scrip_150722.nc -g ne30.g --nm_src=oRRS30to10 --nm_dst=ne30np4 --dt_sng=20180901
produces the 6 TempestRemap map-files:
map_oRRS30to10_to_ne30np4_monotr.20180901.nc
map_oRRS30to10_to_ne30np4_highorder.20180901.nc
map_oRRS30to10_to_ne30np4_mono.20180901.nc
map_ne30np4_to_oRRS30to10_mono.20180901.nc
map_ne30np4_to_oRRS30to10_highorder.20180901.nc
map_ne30np4_to_oRRS30to10_intbilin.20180901.nc
...