Prospective new tool for user to easily modify ocn/lnd mask in their CESM cases

[slevis-lmwg]

In this list of CSSI use-cases, only case 2 can be handled solely by the new fsurdat_modifier tool that allows users to modify existing fsurdat files (#1448). In cases with active land where users want to replace ocean with land, users must modify two more files. E.g. in the 1-degree gx1v7 resolution:

mesh_mask = /glade/p/cesmdata/cseg/inputdata/share/meshes/gx1v7_151008_ESMFmesh.nc
mesh_atm = /glade/p/cesmdata/cseg/inputdata/share/meshes/fv0.9x1.25_141008_polemod_ESMFmesh.nc
mesh_lnd = /glade/p/cesmdata/cseg/inputdata/share/meshes/fv0.9x1.25_141008_polemod_ESMFmesh.nc

To discuss (@mvertens @billsacks @ekluzek others?):

• Where should this tool reside?
• From discussion with @mvertens I got the sense that it may be non-trivial to modify the mesh-mask file.

[slevis-lmwg]

Followed up with @mvertens

• We agreed that I can develop this tool in CTSM. If it needs to move for whatever reason later, we will figure it out then.
• @mvertens reminded me that all components are on the same grid in F cases. This means I can work on this tool and not worry about ocean-model displaced-pole grids for now. Later we can address displaced-pole grids as needed.