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Regionally refined grids require no special steps when using the physgrid because the regional refinement happens at the element level, and the physgrid only changes the physics column arrangement within the element. 

Steps to Interpolate

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Between Grids

There's nothing special about these steps, just thought I'd post them a basic example in case someone is looking for a basic exampleneeding to convert between grids for comparison purposes.

In this particular example I'm interpolating from ne30np4 to ne30pg3 using the default initial condition file for an aquaplanet case.. 

${tempest_root}/bin/GenerateOverlapMesh --a ${grid_data_root}/ne30.g --b ${grid_data_root}/ne30pg3.g --out ${grid_output_root}/tmp_overlap_mesh.nc

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ncremap -4 -m ${grid_data_root}/tmp_mapping_weights.nc /project/projectdirs/acme/inputdata/atm/cam/inic/homme/cami_aquaplanet_ne30np4_L72_c190215.nc ${data_output_root}/cami_aquaplanet_ne30pg3_L72.nc ${input_file_name} ${output_file_name}