Partitioning of cloud liquid water into precip, detrained vapor & liquid

   rn_ptop      rn_frac_top of parcel liquid water converted to precip 
                for cloud top pressures above rn_ptop
                [real, default: rn_ptop = 500.0E2 Pascals]

   rn_pbot      rn_frac_bot of parcel liquid water converted to precip 
                for cloud top pressures below rn_pbot  
                (linear profile in between)
                [real, default: rn_pbot = 800.0E2 Pascals]

   rn_frac_bot  Frac