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Total cloud fraction (definition & calculation method)

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Dear WRF community,

I am writing for a question about total cloud fraction.

(1) How to get total cloud fraction from wrfout_d0* files? The CLDFRA variable is a multi-dimension with bottom_top levels. The function wrf_user_getvar(*,"cfrac",-1) can get low,mid,high levels cloud fraction. But, how to get the total cloud fraction? The mean value of low,mid,high or different bottom_top levels?

(2) What is the exact definition of total cloud fraction? In many papers, the total cloud fraction is one single value for a grid cell.


cloud fraction in WRF refers to the percentage area of a grid covered by cloud. People use different methods to obtain total cloud fraction.
We usually use UPP column max method to determine the total cloud fraction.