CFL violation CAM T42

[lehner@climate_unibe_ch]

Hello

I'm using CCSM3 T42gx1v3 and my simulation fails after several hundred years due to a CFL violation in CAM.

I saw an older reply of to a post on the same topic, however, the problem wasn't solved there.

As recommended by the forum, I changed 'dtime' in cam.buildnml_prestage.csh from 1200 to 900, I changed 'dt' in csim.buildnml_prestage.csh from 3600 to 4800, and I changed 'dtime' in clm.buildnml_prestage.csh from 1200 to 900. Then I built new. According to the code found in ../models/cpl/cpl6/main.F90 communication frequency between coupler and component should be the same (every 18th timestep, before every 24th timestep) for atm, ice and land. However, when running the model I encounter the following error message:

(main) verify acceptable coupling intervals, check for dead components
(main) -------------------------------------------------------------------------
ERROR: unacceptable ncpl_[ail] = 18 18 24
(shr_sys_abort) WARNING: calling shr_mpi_abort() and stopping

Apparently, the coupling interval in the land component wasn't changed. Does anyone know how to make sure the three components atm, ice and land have the same coupling intervals?

Your help would be greatly appreciated!

 

[lehner@climate_unibe_ch]

After several fruitless attempts to change the time step in CAM, CLM and CPL (apparently the time stepping of these three components has to be synchronized) I changed the sub-cycling timestep 'ndyn_dt' in the CSIM namelist and this worked.

However, it would be nice to know, what piece was missing in my quest for shortening the timestep in CAM.