Abstract
Abstract. The isotopic compositions of water vapour and its condensates have long been used as tracers of the global hydrological cycle, but may also be useful for understanding processes within individual convective clouds. We review here the representation of processes that alter water isotopic compositions during processing of air in convective updrafts and present a unified model for water vapour isotopic evolution within undiluted deep convective cores, with a special focus on the out-of-equilibrium conditions of mixed-phase zones where metastable liquid water and ice coexist. We use our model to show that a combination of water isotopologue measurements can constrain critical convective parameters, including degree of supersaturation, supercooled water content and glaciation temperature. Important isotopic processes in updrafts include kinetic effects that are a consequence of diffusive growth or decay of cloud particles within a supersaturated or subsaturated environment; isotopic re-equilibration between vapour and supercooled droplets, which buffers isotopic distillation; and differing mechanisms of glaciation (droplet freezing vs. the Wegener–Bergeron–Findeisen process). As all of these processes are related to updraft strength, particle size distribution and the retention of supercooled water, isotopic measurements can serve as a probe of in-cloud conditions of importance to convective processes. We study the sensitivity of the profile of water vapour isotopic composition to differing model assumptions and show how measurements of isotopic composition at cloud base and cloud top alone may be sufficient to retrieve key cloud parameters.
Highlights
Tion of water isotopologue measurements can constrain crit- references ), a second motivation is to obtain othical convective parameters, including degree of supersaturation, supercooled water content and glaciation temperature
We first describe the various classes of water species involved (Sect. 3.1), present a simple representation of the microphysics and thermodynamics of rising air parcels, considering light water alone (Sect. 3.2), and apply the previously established isotope physics to extract the evolution of the isotopic ratio of water vapour Rv (Sect. 3.3)
This work revisits the basic processes setting the isotopic composition of water vapour in a rising unmixed air parcel, with a consistent and physically-based treatment of microphysics and thermodynamics over vapour, liquid water and cloud ice
Summary
It is useful to review the basic physics of isotopes partitioning at microphysical scales and its connection with the macroscopic description. 2.1) and review both equilibrium isotopic partitioning 2.2) and the additional fractionation induced by the kinetics of particle growth/decay Additional material on kinetic effects is included in appendices: Appendix A reviews the growth and loss rates of droplets and ice crystals that is the basis of the isotopic kinetic effects and Appendix B provides the full derivation of kinetic fractionation factors. We follow closely the derivations of Jouzel et al (1975) and Jouzel and Merlivat (1984), but emphasize the differences between fractionation of ice and liquid water and highlight interpretations that are specific to the context of deep convection. Reviews covering similar material include Gedzelman and Arnold (1994) and Blossey et al (2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
