cldfrac_tot_UPP is zero at the first time step

[maxhbalsmeier]

Hi,
I am using a regional MPAS domain with 3 km resolution for NWP. I am using the variable cldfrac_tot_UPP to obtain the total cloud cover in percent.
However, I noticed that this variable is zero at all grid points at the very first time step.
Before I go into more details about how to reproduce this issue, I would like to ask: is this expected behaviour?

 

[Ming Chen]

Yes this is an expected behavior. cldfrac_tot_UPP is a diagnostic variable that is calculated based on cldfrc. At the initial time, both are set to zero.

 

[maxhbalsmeier]

Thank you for your reply. I noticed the same is the case with the CLDFRA variable in WRF.
This seems like a small imperfection since in the real-world, clouds are clearly present at the first time step. I imagine that it would be possible to call the diagnostics once before writing the first output.
Do you think this would be a useful code modification?

 

[Ming Chen]

I agree that clouds may exist at the initial time of model run. MPAS doesn't calculate cldfra in the first time step because it is based on other physical variables like qc,qi, rh etc. Some of these variables are not available at the beginning of model run. For this reason, I don't think it is practical to diagnose cldfra at the initial time.

 

[maxhbalsmeier]

In that case it is probably indeed too large of a code change to solve a minor inconvenience.

 

[Ming Chen]

Codes for MPAS initiiazation need to be modified to include all the required variables for CLDFRA calculation.