How is CLDICE related to CLOUD in CAM4?

[deepashree_dutta@student_unsw_edu_au]

Hi all,

I am using CESM1.2.2 and analyzing the cloud outputs from CAM4. I'm confused about the variables related to cloud liquid and ice content, especially CLDICE and CLDLIQ variables.
How is CLDICE (Grid box averaged cloud ice amount) calculated and how is it related to cloud fraction in the model (is CLDICE = CLOUD x Ice content present?)

Thanks in advance for any suggestion,
Deepashree

 

[brianpm]

CLDLIQ and CLDICE are the prognostic variables in CAM4 (as in CAM5 and CAM6). So the model determines the tendencies of these (i.e., d(CLDICE)/dt, d(CLDLIQ)/dt)) based on various physical processes. The cloud fraction, CLOUD, is then a diagnostic quantity. In CAM4 cloud fraction is mainly determined from the relative humidity with partitioning between liquid and ice that is temperature dependent. There is also a convective cloud fraction, a stability-based stratus fraction, and a freeze-dry condition that can all modify CLOUD (and CLDTOT, CLDHGH, CLDMED, CLDLOW). The liquid and ice water contents are used to determine the cloud optical properties. I think CAM4 uses the cloud fraction determined in $CAM/src/physics/cam/cloud_fraction.F90. The optical properties are calculated in the radiation scheme (trace it back from radiation_tend in $CAM/src/physics/camrt/radiation.F90).

 

[deepashree_dutta@student_unsw_edu_au]

Thank you so much Brain!