cam6_4_173: fix energy bug in physics-dynamics coupling

[PeterHjortLauritzen]

Closes #1551 - Bug in physics tendency scaling
Closes #1553 - RRTMGP diagnostic net_flx bug
Closes #1550 - ZM scheme no longer conserving energy

[PeterHjortLauritzen]

Please note that we need to make these changes in CAM-SIMA as well!

[jimmielin]

Thanks @PeterHjortLauritzen! I checked and the same issue is present in CAM-SIMA.

As I understand from reading your fix, my proposed fix for CAM-SIMA is to create a registry variable saving cp_or_cv_dycore_at_start_of_physics_timestep (to avoid saving it into a temp variable) with the value computed in d_p_coupling, where it calls cam_thermo_water_update to update cp_or_cv_dycore. This value computed at the beginning of the physics timestep is the one that should always be provided to the energy checker/fixer.

When thermo_water_uptake is called within physics, updating cp_or_cv_dycore, its only intended use is for tot_energy_phys diagnostics.

Is that understanding correct? If yes then I can start drafting the equivalent fix in CAM-SIMA which will look different since we don't have physpkg.

[PeterHjortLauritzen]

Yes in current CAM! Once we move towards a true variable latent heat formulation in physics we would update cp_pr_cv after each parameterization ...

[nusbaume]

Thanks @PeterHjortLauritzen!