Author: Paul Ullrich Email: [email protected]

Copyright 2000-2014 Paul Ullrich

This file is distributed as part of the Tempest source code package. Permission is granted to use, copy, modify and distribute this source code and its documentation under the terms of the GNU General Public License. This software is provided "as is" without express or implied warranty.

This software constitutes the beta release of TempestRemap, a conservative, consistent and monotone remapping package for arbitrary grid geometry with support for finite volumes and finite elements. There is still quite a bit of work to be done, but any feedback is appreciated on the software in its current form.

If you choose to use this software in your work, please cite our papers:

Paul A. Ullrich and Mark A. Taylor, 2015: Arbitrary-Order Conservative and Consistent Remapping and a Theory of Linear Maps: Part I. Mon. Wea. Rev., 143, 2419–2440. doi: http://dx.doi.org/10.1175/MWR-D-14-00343.1

Paul A. Ullrich, Dharshi Devendran and Hans Johansen, 2015: Arbitrary-Order Conservative and Consistent Remapping and a Theory of Linear Maps: Part II. Submitted to Mon. Wea. Rev.

The software can be obtained from the GITHub repository via git:

git clone https://github.com/paullric/tempestgecore.git

You will likely need to edit the first couple lines of the Makefile to customize the NetCDF paths and change any compiler flags. Once you have modified the Makefile, build the code:

make all

The remapping process requires multiple stages. First you will need an Exodus file (file extension .g) for your input mesh and your output mesh. This can either be done via the SQuadGen mesh utility, or via the three GenerateMesh executables that come with TempestRemap.

For a cubed-sphere mesh:

./GenerateCSMesh --res --alt --file .g

For a latitude-longitude mesh:

./GenerateRLLMesh --lon --lat --file .g

For a geodesic mesh:

./GenerateICOMesh --res --dual --file .g

Once your input and output meshes are generated, you will need to generate the overlap mesh (that is, the mesh obtained by placing the input and output mesh overtop one another and recalculating intersections). This can be done as follows:

./GenerateOverlapMesh --a .g --b .g --out .g

Once the overlap mesh is generated, you can now generate the weight file, which the contains information on remapping from one mesh to the other. The type of offline map desired is specified by --in_type and --out_type, which can be one of the following:

fv - Finite volume mesh, with degrees of freedom stored as volume averages cgll - Continuous finite element method (such as spectral element) dgll - Discontinuous finite element method (such as discontinuous Galerkin)

Offline map generation is then performed as follows:

For finite volume to finite volume remapping:

./GenerateOfflineMap --in_mesh .g --out_mesh .g --ov_mesh .g --in_np --out_map .nc

Monotone remapping in this case can be achieved with --in_np 1.

For finite element to finite volume remapping:

./GenerateOfflineMap --in_mesh .g --out_mesh .g --ov_mesh .g --in_type [cgll|dgll] --out_type fv --in_np --out_map .nc

Monotone remapping in this case can be achieved with argument --mono.

For finite volume to finite element remapping:

./GenerateOfflineMap --in_mesh .g --out_mesh .g --ov_mesh .g --in_type fv --out_type [cgll|dgll] --in_np --out_np --out_map .nc

Monotone remapping in this case requires --mono and --in_np 1.

For finite element to finite element remapping:

./GenerateOfflineMap --in_mesh .g --out_mesh .g --ov_mesh .g --in_type [cgll|dgll] --out_type [cgll|dgll] --in_np --out_np --out_map .nc

Monotone remapping in this case requires --in_np 1 and --out_np 1.

In each case, the linear weights file will then be written to .nc in SCRIP format (although it’s a bare-bones version of SCRIP format at the moment and I’m not sure it’ll work with SCRIP utilities). Now that the map is generated you can apply it to your data files:

The offline map can be applied using the ApplyOfflineMap utility:

./ApplyOfflineMap --map .nc --var --in_data .nc --out_data .nc

The remapped fields should then appear in .nc. Note that if your output mesh is rectilinear, such as a latitude-longitude mesh, the data will automatically be arranged with horizontal spatial dimensions lat and lon.

Please let me know if you have any problems / bugs / comments / feature requests.