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:
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The main difference between generating the timeseries for the Historical ensemble and the DECK PI experiment is the need to loop over the ensemble. Here the splitter command is not backgrounded so that one member experiment is processed at a time (to avoid overwhelming nodes with I/O and RAM demands). Set the input directory in the ensemble loop, and ensure the globbing pattern for filenames matches the naming convention used for all five members. Consider whether to output to member-specific directories or to a single, ensemble-wide directory. If the former, then nothing special need be done. If the latter, use the --fml_nm (family-name) option as above to avoid identical timeseries names (that will overwrite one another) and to create instead member-specific timeseries names like
CLDLOW_H1_185001_201412.nc
CLDLOW_H2_185001_201412.nc
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Epilogue: User-Suggested Examples
E3SM employs some the most advanced grid formulations used in ESM modeling today, and since regridding is a complex subject full of details, it is unlikely that the foregoing documentation already answers everyone's questions. Moreover, since some of the greatest E3SM innovations and optimization rely on even newer grid treatments, we are unlikely to ever stop needing to learn newer regridding techniques. If you read this far you know about ncremap's main capabilities, yet either you and U2 still haven't found what you're looking for, or you may have a hunch that one of those relevant-sounding-though-undocumented (at least in Confluence) options that appears with ncremap --help, is for.In that spirit, we welcome user requests for annotated examples for their real-world regridding issues. Fire away!