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).
...
These commands will generate the remapping weights by computing the intersection mesh through advancing front intersection algorithm in MOAB and then using TempestRemap to generate the weights in parallel. The computed matrix weights are then written out in parallel in the h5m format (specified through option -f). . The user can also specify the field discretization type and order by using the -m and -o options. Currently, the -m option can take fv, cgll, dgll as valid options and -o is any non-zero, positive integer representing the order of the spectral or FV discretization for climate problems.
Additionally, the GLOBAL_ID tag is used as an identifier to uniquely represent degrees-of-freedom (DoF) for element-based discretizations such as FV or vertex-based lower order discretizations such as FD. These options can be specified with -g options for mbtempest. However, complex discretizations should provide the unique DoF numbering in special element-based MOAB tags. In the above example (3), the GLOBAL_DOFS tag represents the SE DoF ids for the source mesh and the GLOBAL_ID tag represents that DoF ids for the target mesh, since we are computing remapping weights from SE to FV.
Note on DoF IDs for SE meshes
...
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.
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.