Update descriptions of dcEdge and dvEdge

[xylar]

The existing descriptions were not clear to developers.

[xylar]

@mark-petersen, @proteanplanet, @matthewhoffman, as representatives form each affected component, could you let me know if you're okay with these changes to the descriptions of dcEdge and dvEdge?

<var name="dvEdge" type="real" dimensions="nEdges" units="m"
    description="The great circle distance between vertices bordering a given edge.  It is the length of the edge on the primal mesh."
/>
<var name="dcEdge" type="real" dimensions="nEdges" units="m"
    description="The great circle distance between cell centers bordering a given edge.  It is the length of the edge on the dual mesh."
/>

[matthewhoffman]

@xylar , thanks for tackling this. If we are adjusting these definitions, I would prefer some additional elaboration:

dvEdge:
The distance (great circle distance for spherical meshes, Euclidean distance for planar meshes) between the two vertices (defined by verticesOnEdge) located at the endpoints of a given edge. It is the length of the edge on the primal mesh.

dcEdge
The distance (great circle distance for spherical meshes, Euclidean distance for planar meshes) between the centers of the two cells (defined by cellsOnEdge) neighboring a given edge. It is the length of the edge on the primal mesh.

[xylar]

The second one should be "dual", rather than "primal", right?

[xylar]

Good point about planar vs. spherical.

[matthewhoffman]

The second one should be "dual", rather than "primal", right?

Yes, oops, good catch. Copy-and-paste error. :)

[xylar]

@matthewhoffman, could you take a careful look at the update I just made? I want to make sure it's what you wanted.

[xylar]

Taking @mark-petersen off as he's away.

[matthewhoffman]

@xylar , I read it carefully out loud twice, and it looks good.

[proteanplanet]

Looks great. Thank you.

[xylar]

I need to update the respective E3SM namelist files using https://github.com/MPAS-Dev/MPAS-Tools/blob/master/source_code_processing/e3sm_namelist_file_generator/generate_e3sm_namelist_files.py

[xylar]

Never mind, there's nothing to update with generate_e3sm_namelist_files.py. Moving to E3SM...

[xylar]

Closing in favor of E3SM-Project#6427