Articles | Volume 22, issue 13
Research article
 | Highlight paper
11 Jul 2022
Research article | Highlight paper |  | 11 Jul 2022

Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model

Andries Jan de Vries, Franziska Aemisegger, Stephan Pfahl, and Heini Wernli

Model code and software

The NCAR Command Language (Version 6.5.0) NCAR

Executive editor
Tropical convective clouds distribute water vapour across the tropical tropopause layer (TTL), which affects the radiative budget in both the troposphere below and the stratosphere above. Water isotopes can be used as tracers to conclude on the history of water vapour in these altitudes, i.e. whether it went through phase change processes and was part of ice or liquid clouds before. de Vries and coworkers used an innovative modelling scheme capable of simulating convection together with the phase-change processes producing the isotopic signatures to simulate tropical ice clouds and compare their simulations to respective observations. By this, they were able to disentangle processes of convective updraft versus cirrus cloud formation in tropical cloud systems and demonstrate how the isotopic fractionation of water vapour does help to distinguish respective processes. Over all, this paper is innovative and a considerable step forward in studies of convection and transport of water vapour into the upper tropospher/lower startosphere (UTLS).
Short summary
The Earth's water cycle contains the common H2O molecule but also the less abundant, heavier HDO. We use their different physical properties to study tropical ice clouds in model simulations of the West African monsoon. Isotope signals reveal different processes through which ice clouds form and decay in deep-convective and widespread cirrus. Previously observed variations in upper-tropospheric vapour isotopes are explained by microphysical processes in convective updraughts and downdraughts.
Final-revised paper