Geopotential naming issue

[grantfirl]

Description

@mdtoyNOAA reported that the variables in fv3atm and ccpp-physics with the standard name of geopotential are not actually geopotential in the familiar sense. That is, by typical convention, geopotential is defined relative to MSL, but according to https://github.com/ufs-community/ccpp-physics/blob/ufs/dev/physics/tools/get_phi_fv3.F90, the variable with the standard name of geopotential in the UFS is relative to the local surface. In effect, what is being stored in the variable called geopotential is really the geopotential minus the surface geopotential. Although it may be awkward to change the geopotential standard name (and any others currently based of this within the UFS) to geopotential_minus_surface_geopotential, it is more accurate and could avoid confusion/mistakes for any physics schemes that need the TRUE, classically-defined value of geopotential.

Steps to Reproduce

Inspect the creation of the variables given standard names of geopotential and observe how they are calculated relative to the local surface. I.e. the lowest model interface value (corresponding to the physical surface) is given a value of zero, regardless of its relation to MSL.

Additional Context

See the definition of geopotential here: https://glossary.ametsoc.org/wiki/Geopotential. Notice that z=0 is referencing MSL, not z=0 referencing the local surface.

Output

N/A

[mdtoyNOAA]

Perhaps "height_above_ground_times_gravity"?