As part of the efforts in the CMDV project, interfaces to integrate the MOAB unstructured mesh library with the TempestRemap remapping tool have been undertaken. Detailed information on the algorithmic and implementation aspects of this effort have been written in a manuscript submitted to Geoscientific Model Development [1]. This work has led to the development of a new offline remapping tool called mbtempest, which exposes the functionality to compute the supermesh or intersection mesh between two unstructured source and target component grids, in addition to using this supermesh for computing the remapping weights to project solutions between the grids. This functionality is part of the critical worflow with E3SM, where the generated remapping weights in the offline step are consumed by MCT at runtime to seamlessly transfer solution data between components (atm↔ocn, atm↔lnd, etc).
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For RRM grids or non-standard SE grids, the recommended workflow is to run HOMME to get the resolution of the grid required to generate the mapping file, and then store the DoF IDs as a GLOBAL_DOFS tag in MOAB, before being written to disk. This eliminates the need to get a consistent match when generating the weights in the MOAB mbtempest offline workflow since the tag in the file will be loaded in parallel along with the mesh during the setup phase of the tool.
Update: An extension to the mbconvert tool was implemented so as to add metadata information while converting an exodus mesh to MOAB h5m format. An example execution with options to write out the DoF IDs into a "GLOBAL_DOFS" tag looks like below.
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tools/mbconvert -B -i GLOBAL_DOFS -r 4 outOCTGridHOMME.g outOCTGridHOMME.h5m |
Here, the option -B indicates that TempestRemap is used to load the input mesh, option -i indicates the global DoF tag name and -r specifies the SE order of the field discretization. Using the outOCTGridHOMME.h5m file, now mbtempest can be launched without any other workflow changes.
Converting parallel h5m file to SCRIP file for E3SM
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If steps (a)-(g) pass successfully, the MOAB libraries and tools, along with interfaces for TempestRemap will be installed in $INSTALL_PREFIX/moab directory. The offline remapping weight computation tool, mbtempest, will also be installed during this process and can then be used standalone to generate the weight files as needed.
References
1 Mahadevan, V. S., Grindeanu, I., Jacob, R., and Sarich, J.: Improving climate model coupling through a complete mesh representation: a case study with E3SM (v1) and MOAB (v5.x), Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-280, in review, 2018.