How does coupler works in CESM2 (CAM)?

[FuchengY]

What version of the code are you using?
CESM2.2.2 on Derecho


Have you made any changes to files in the source tree?
Yes. I revised physpkg.F90 to output climate before and after coupling within one model step.


Describe every step you took leading up to the problem:
I am running an AMIP-type simulation.
I revised physpkg.F90 by adding lines like:
call outfld('T_bCP',state%t,pcols,lchnk)
at the end of subroutine tphysbc, and:
call outfld('T_aCP',state%t,pcols,lchnk)
near the begining of subroutine tphysac.


Describe your problem or question:
Hello,

I want to see how temperature (and other variables) changes due to coupling so I output the climate before and after coupling in the sequence of integration. However, the temperature (the lowest level in sigma-p coordinate) seems identical (the difference is exactly 0 in MATLAB) in two outputs, suggesting that coupling does not change temperature. It is quite odd. I also tested other processes, such as convection scheme, and I can see tempeature changing before and after those processes.

Do I misunderstand the coupling in CESM? Could anyone help me? I have attached the revised file.

 

[FuchengY]

What version of the code are you using?
CESM2.2.2 on Derecho


Have you made any changes to files in the source tree?
Yes. I revised physpkg.F90 to output climate before and after coupling within one model step.


Describe every step you took leading up to the problem:
I am running an AMIP-type simulation.
I revised physpkg.F90 by adding lines like:
call outfld('T_bCP',state%t,pcols,lchnk)
at the end of subroutine tphysbc, and:
call outfld('T_aCP',state%t,pcols,lchnk)
near the begining of subroutine tphysac.


Describe your problem or question:
Hello,

I want to see how temperature (and other variables) changes due to coupling so I output the climate before and after coupling in the sequence of integration. However, the temperature (the lowest level in sigma-p coordinate) seems identical (the difference is exactly 0 in MATLAB) in two outputs, suggesting that coupling does not change temperature. It is quite odd. I also tested other processes, such as convection scheme, and I can see tempeature changing before and after those processes.

Do I misunderstand the coupling in CESM? Could anyone help me? I have attached the revised file.

In my understanding, the dynamic core, moist processes (including convection and stratiform), radiation, coupling, other processes (including vertical diffusion and gravity wave drag) are conducted one by one in one model step.

 

[FuchengY]

After reading more codes, I think I understand how coupler works. The coupling only updates variables at surface, which will be used as boundary condition in dynamic core. The atmopshere does not change due to coupling.