Stable Isotopes in Hailstones. Part I: The Isotopic Cloud Model

Abstract

Equations describing the isotopic balance between five water species (vapor, cloud water, rainwater, cloud ice and graupel)have been incorporated into a one-dimensional steady-state cloud model. The isotope contents of the various water substances were calculated as a function of height. From these profiles, the isotopic concentration δH of the water accreted by hailstones growing in this model cloud is determined. The results are compared with those obtained from the adiabatic model (δAM). The differences are substantial. A sensitivity study shows that the δH profiles for two different soundings are dependent on the changes in the droplet-size distributions, which influence the conversion of cloud water to rainwater, and, to a lesser degree, on entrainment. If a reasonable concentration of raindrops is allowed, the results are remarkably stable if all the other adjustable parameters are varied. The application of the model to isotopic data of hailstones and its comparison with the adiabatic model in Part II shows that it gives realistic results.