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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Using the mbtempest tool
The mbtempest tool exposes the algorithms and interfaces to invoke TempestRemap through MOAB to generate remapping weights for combinations of discretizations and unstructured meshes defined on a source grid to a target grid. Most of the options supported by TempestRemap tools are provided in this unified interface with one key difference: the entire workflow makes use of MPI parallelism. This implies that the overlap mesh computation that would normally use the GenerateOverlapMesh tool in TempestRemap would be replaced by the MOAB's parallel implementation of an advancing front intersection computation. This intersection mesh can subsequently be written out to file as an intermediate step or used by mbtempest to generate the remapping weights needed to project a solution field from source to target component grid. Prescriptions to preserve conservation of scalar/flux data and to impose monotonicity constraints are also available as options to pass to the mbtempest tool.
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We are currently working on a Python script to convert the MOAB h5m file to a SCRIP file to be consumed in E3SM directly. As a future task, we will also be investing effort into writing a SCRIP file in parallel through a custom I/O interface using PNetCDF.
Machines with mbtempest tool installed
Anvil soon....
Building your own version of the mbtempest tool
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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.