PBL Stratiform Cloud Inhomogeneities Thermally Induced by the Orography: A Parameterization for Climate Models

Abstract

Abstract This paper proposes a parameterization for use in climate models of the orographic variance and associated thermal circulation's impact on the macroscopic behavior of planetary boundary layer (PBL) stratiform clouds. Orographically induced inhomogeneities in the PBL cloud field can significantly alter the area-averaged cloud-radiative properties and consequently the PBL evolution. Current climate models do not include this effect. The design of the parameterization is based on a systematic set of experiments in which a cloud system resolving model (CSRM) explicitly simulates the diurnally varying interactions between PBL clouds and the orography for a variety of configurations. Analyses of the results suggest that the orographic effect on PBL clouds is parameterizable to a large extent due to a quasi equilibrium between cloud-radiative, turbulent, and mesoscale processes. Parameterizability holds in the range of parameters for which stratiform clouds play a dominant role in the PBL dynamics (clou...