Atmospheric moisture strongly controls Earth’s radiative budget and transports energy through latent heat. Uncertainties in the atmospheric moisture transport pathways have large effects on climate modelling and prediction. Isotopologues of water offer further insights into the water cycle due to fractionation processes on phase changes. High-quality measurements of the vertical distribution of water vapour isotopologues are urgently needed, e.g. to investigate the relative importance of different vertical moisture transport mechanisms, to improve models, and to validate remote sensing observations by satellite borne instruments, including the TROPOMI instrument onboard ESA’s Sentinel 5P satellite.

To date, profile measurements are costly and thus sparse. In this project, a novel instrument to measure profiles of water vapour isotopologues from ground to the upper troposphere on a small balloon-borne platform will be developed. The system will sample air in flasks at different altitudes, which will be analyzed with a cavity ringdown spectroscopy instrument after landing and recovery. The flask sampler is based on an existing and proven flask sampling technology currently used on drones, which is adapted to lower pressures and lower water vapour mixing ratios present at higher altitudes up to the tropopause. The instrument will be deployed in a field campaign at Sodankylä with concurrent measurements by the Fourier transform spectrometer within the Total Carbon Column Observing Network (TCCON).