Measurements of the HDO/H2O Isotopic Ratio in the Asian Summer Monsoon

International audienceThe Asian Summer Monsoon (ASM) is one of the world's largest weather systems, and forms one of the main pathways by which water vapor enters the UTLS. Uplift in the region lofts highly polluted air from South Asia, making the region an important driver of both stratospheric chemistry and the stratospheric radiation budget. Uplifted air tends to be confined by the monsoon anticyclone, but may enter the stratosphere through uplift within the anticyclone, or via large scale shedding events along its edges. We report here on in situ measurements in the monsoon UTLS of water vapor and its isotopic composition (the ratio of HDO/H2O), an important tracer of uplift processes and of convective activity in general. Measurements were made by the Chicago Water Isotope Spectrometer (ChiWIS) in both the StratoClim (2017) and ACCLIP (2022) campaigns, at monsoon center and in monsoon outflow, respectively. We use these measurements to diagnose the importance of overshooting convection in water transport by the Asian monsoon, characterize the extent to which convection-driven water vapor perturbations propagate to higher altitudes and contribute to the overall stratospheric water budget, and explore cirrus properties in the ASM region