A new parameterization of marine stratocumulus and shallow cumulus clouds for climate models.

摘要

A new parameterization of marine stratocumulus and shallow cumulus clouds is presented. The parameterization consists of a mass flux cumulus convection scheme coupled to a 1.5 order Turbulence Closure Model (TCM) with an entrainment closure for convective boundary layers. The mass flux scheme is based on a buoyancy sorting entrainment-detrainment plume model, where detrainment is linked to the expulsion from the updraft of negatively buoyant parcels generated by lateral mixing. Model performance is verified using single column model simulations at relatively high vertical resolution of stratocumulus-capped, cumulus-capped, and transitional marine boundary layers. Mixing rates, cloud cover and vertical flux profiles, as deduced from previously published large eddy simulation (LES) studies, are well reproduced by the parameterization. The parameterization is implemented in a mesoscale model, and regional climate simulations are presented for a northern hemisphere summer for domains including regions of the northeast and southeast Pacific Ocean. Inclusion of the parameterization of shallow convection significantly improves the simulated cloud fields and vertical structure of trade cumulus regimes.