Factors Controlling Rapid Stratocumulus Cloud Thinning

Abstract

he relationship between the inversion stability and the liquid water path (LWP) tendency of a vertically well-mixed, adiabatic stratocumulus cloud layer is investigated in this study through the analysis of the budget equation for the LWP. The LWP budget is mainly determined by the turbulent fluxes of heat and moisture at the top and the base of the cloud layer, as well as by the source terms due to radiation and precipitation. Through substitution of the inversion stability parameter ? into the budget equation, it immediately follows that the LWP tendency will become negative for increasing values of ? due to the entrainment of increasingly dry air. Large ? values are therefore associated with strong cloud thinning. Using the steady-state solution for the LWP, an equilibrium value ?eq is formulated, beyond which the stratocumulus cloud will thin. The Second Dynamics and Chemistry of Marine Stratocumulus field study (DYCOMS-II) is used to illustrate that, depending mainly on the magnitude of the moisture flux at cloud base, stratocumulus clouds can persist well within the buoyancy reversal regime.