Improving the representation of subtropical boundary layer clouds in the NASA GEOS model with the Eddy-Di usivity/Mass-Flux parameterization

A systematic underestimation of subtropical planetary boundary layer (PBL) stratocumulusclouds by the GEOS model has been signicantly improved by a new Eddy-Diusivity/Mass-Flux (EDMF) parameterization. The EDMF parameterization representsthe subgrid-scale transport in the dry and moist parts of the PBL in a unied mannerand it combines an adjusted eddy-diusivity PBL scheme from GEOS with a stochasticmulti-plume mass-ux model. The new EDMF version of the GEOS model is rst comparedagainst the CONTROL version in a single-column model (SCM) framework for twobenchmark cases representing subtropical stratocumulus and shallow cumulus clouds, andvalidated against large eddy simulations. Global simulations are performed and comparedagainst observations and reanalysis data. The results show that the EDMF version of theGEOS model produces more realistic subtropical PBL clouds. Noteworthy, the EDMF improvementsrst detected in the SCM framework translate into similar improvements of theglobal GEOS model.