Entrainment and Dilution in Tropical Deep Convection

Abstract:

Many studies suggest that cumulus entrainment should be larger than typical values used in convective parameterizations. However, artificially increasing the entrainment rate does not make convective parameterizations more realistic. This paradox highlights a lack of understanding and oversimplified representations of entrainment processes. A series of high-resolution simulations of deep convection initiated with a warm humid bubble are compared to a more conventional radiative-convective equilibrium simulation. Entrainment rates are diagnosed with the direct measurement method and the analysis does support an inverse relationship between entrainment and cloud radius, as is often assumed in plume models. A method for quantifying a cloud dilution rate associated with entrainment is presented. Dilution and entrainment are found to generally not be synonymous. Dilution is found to have a weak inverse relationship to cloud core radius, inadvertently supporting the simplifying assumptions of conventional parameterizations. Additional sensitivity experiments and suggestions for parameterization development are discussed.