Cloud fraction limit to 0.9 in module_mp_thompson_cldfra3

[saulo.freitas]

Hi,
The routine cal_cldfrac3 limits the maximum value of cloud fraction to 0.9 (see line 134). Is there a plausible reason for that, or is this just a mistype?

Thanks,

Saulo Freitas

 

[Ming Chen]

Saulo,
Please see whether you can find information in the paper:
hompson, Gregory, Paul R. Field, Roy M. Rasmussen, William D. Hall, 2008: Explicit Forecasts of Winter Precipitation Using an Improved Bulk Microphysics Scheme. Part II: Implementation of a New Snow Parameterization. Mon. Wea. Rev., 136, 5095–5115.
doi:10.1175/2008MWR2387.1

 

[Ming Chen]

Hi Saulo,
I explore this issue a bit more. What I found is that, based on some NCEP-EMC tests, the icloud3 option made far too many clouds when compared to observations. I guess this could be the reason that cal_cldfrac3 limits the maximum value of cloud fraction to 0.9. However, I didn't find any publications that specifically address this issue.
I believe you can tune the model behavior by modifying the maximum value of cloud fraction at line 134. Hope this is helpful for you.

 

[saulo.freitas]

Hi Ming,
Thanks for your comments! I also found in my experiments that this formulation overestimates the cloud fraction, which results in poor energy balance on the surface in the Amazon basin.
Regards,
Saulo

 

[haiqingsong]

Hi Ming,
Thanks for your comments! I also found in my experiments that this formulation overestimates the cloud fraction, which results in poor energy balance on the surface in the Amazon basin.
Regards,
Saulo

When cal_cldfrac3 limits the maximum value of cloud fraction from 0.9 to a Smaller values, WRF will overestimates the cloud fraction to a lesser extent ？

 

[Ming Chen]

@haiqingsong

This is what is expected. However, I have to say that it may be case-dependent. if your case still shows large overestimation, you may need to further reduce the maximum cldfra value.