Entrainment processes in the diurnal cycle of deep convection over land

Abstract

AbstractIn this article we show that entrainment during the developing stages of deep convection over land is much higher than convection at equilibrium. A series of idealised cloud‐resolving model simulations are performed for a range of environmental conditions, and these show that the interaction with the environment via the entrainment and detrainment rates gradually decreases as the day progresses, reverting to the values found at equilibrium. The entrainment and detrainment rates are themselves found to depend on the environmental humidity and stability, and are also strongly linked to cloud size, suggesting that the representation of the horizontal growth of clouds in convective parametrizations is important for the representation of the diurnal cycle. We propose a simple new entrainment and detrainment formulation to take account of these findings, and show that this improves the representation of developing convection in a single‐column model, providing a more gradual transition towards deep convection. Copyright © 2011 British Crown copyright, the Met Office. Published by John Wiley & Sons Ltd.