CESM1.1.z - Limitations with different coupling frequencies for different models.

[aliceb]

Affected Releases - CESM1.1.zFixed in CESM1.2.1(Bugzilla 1740) CESM allows different coupling frequencies for different models. However, there are some limitations. The coupling frequencies are set via the env_run.xml variables *_NCPL. Generally, the atmosphere, land, and ice model coupling frequencies should match. The ocean model coupling frequency should be equal to or less than the atm coupling frequency. And the runoff model coupling frequency should be greater or equal to the atm coupling frequency and less than or equal to the ocean coupling frequency. The known problem is that there are no checks at setup or run-time that these constraints are met. If they are not met, there can be problems with the simulation. In summary, users should ensure that the following is true,

ATM_NCPL = LND_NCPL = ICE_NCPL >= ROF_NCPL >= OCN_NCPL

especially for fully active configurations.