The Sensitivity of Atmospheric Water Isotope to Entrainment and Precipitation Efficiency

An analytical model based on the bulk-plume convective water budget and isotopic fractionation is derived for water vapor (H2O) and one of its heavy isotopes (HDO) in radiative convective equilibrium. We investigate joint changes in water vapor and water isotope variables within the convective plume and its environment under changes in the entrainment rate and precipitation efficiency. We find a surprisingly small sensitivity of δD profiles to entrainment rate and precipitation efficiency. We provide a mechanistic explanation of these relationships that establishes a theoretical range for δD in convective cloud plumes and their immediate environments.