Entrainment and detrainment required to explain updraft properties and work dissipation

Abstract

A one-dimensional thermodynamic entrainment-detrainment model is used to determine updraftvirtual temperature excess, updraft velocity, and other updraft properties from sounding data.The model correctly predicts most updraft properties and explains how work of buoyancy isdissipated. The unique feature of the model is that fractional entrainment and detrainment areboth functions of the virtual temperature excess of the updraft and independent of updraft massor diameter. The updraft temperature and composition are rigorously determined before updraftvelocity is considered. The entrainment and detrainment functions allow the flows in and outof the updraft to vary in a physically realistic way and are used from the base of the soundingto cloud top. The model limits the growth of cumulus under conditions of dry air aloft. Themodel shows that entrainment inhibits deep convection. The model predicts higher intensityfor continental than for oceanic updrafts. High humidity at the bottom of the atmospheredecreases the intensity of the updrafts because it lowers the condensation level, the level atwhich evaporative cooling comes into play. High humidity aloft increases the intensity of theupdrafts because it reduced evaporative cooling.