☠️ CAM-SE vertical coordinate difference across model version

[hkershaw-brown]

💀 Skeleton issue for CAM-SE vertical coordinate.

Placeholder, stay tuned for more detail.

[kdraeder]

This issue arose because of #662.
I believe that the root of the issue is that recent CAM-SE models (in CESM2[.?.?])
separate the total pressure into the dry mass pressure and pressure due to moisture fields.
The model output does not signal whether the pressure it provides is full or dry mass,
so the current cam-se/model_mod_nml contains a variable for telling model mod which it is.

If the dry mass pressure is provided, the model_mod (usually? always?) needs to calculate the total pressure
by adding the moisture pressures to the dry pressure. I believe that there is some question
about the correct way to do that. #662 deals with part of that; which moisture fields
are, andor should be, included in the state vector and are available for use by the total pressure calculation.

It may be related to comments in cam-se/model_mod.f90:

! Note that other tracers in the dry mass cam/se have a dry mixing ratio, not specific mixing ratio (although
! Peter plans to change this for consistency).
!SENote: The following should all be 0, but A's at levels 2, 3, 4, and 5 are not.
! This is confirmed in the caminput.nc file and is a PROBLEM.
! Some tests on the A and B coefficients
!do k = 1, nlevels
   !write(*, *) k, (grid_data%hyai%vals(k) + grid_data%hyai%vals(k+1))/2.0_r8 - grid_data%hyam%vals(k)
   !write(*, *) k, (grid_data%hybi%vals(k) + grid_data%hybi%vals(k+1))/2.0_r8 - grid_data%hybm%vals(k)
!enddo