Dear RegCNET Colleagues,
Alex and I followed up on this thread offline, and we realized that both fcmax and cftotmax must be set to 1 in the namelist in order for the maximum cloud fraction to reach 1.
The fcmax variable is the maximum volume of a grid cell occupied by cloud (i.e., it is 3D), whereas cftotmax is the maximum area of a column occupied by cloud (as far as radiation is concerned; it is 2D). Both of these variables need to be set because of the cloud overlap assumption that RegCM 4.3 uses:
totcf(n) = d_half * ( totcf(n) + maxval(cld(n,:)) ) [line 920 of mod_rad_radiation.F90 in RegCM 4.3.5.6]
The RegCM 4.3/4.4 reference manuals note that this assumption is used. Users of previous RegCM versions should keep this change in mind, if they aren't aware of it already, since it differs from the overlap assumption used in previous version of RegCM.
With Kind Regards,
-Travis-