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This page is devoted to instruction in NCO’s regridding operator, 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:


Floating-point mask variables (grid_imask) in SCRIP files---they are non-standard and may break some software. TempestRemap's GenerateOverlapMesh program, for example, breaks (as of this writing, 20210428) when asked to ingest a SCRIP grid-file with a floating point mask. This problem can occur when using grid-files from TR's old ConvertExodusToSCRIP program which outputs output floating point masks. The new TR program, ConvertMeshToSCRIP, appears to have fixed this problem (as of this writing in 20240110). Also, users often create masks from floating-point variables (as described in the next section) and inadvertently leave the mask as a floating point variable. The solution to the problem of floating-point masks can be as simple as a straightforward conversion of the mask to an integer: