Tracing Moist Diabatic Processes with Water Isotopes: Overview of NAWDICiso’s Multi-Platform Observations

Moist diabatic processes – such as air-sea fluxes, turbulent mixing, cloud microphysics – are key drivers of midlatitude high-impact weather. These processes affect the atmospheric temperature distribution and stability, thereby directly modifying mesoscale circulation patterns. Mesoscale structures, in turn, tend to be the most hazardous features within midlatitude weather systems and are closely linked to forecast uncertainties. We refer to these features as mesoscale moisture-cycling structures (MOCs): anomalies in moisture and wind fields on scales of approximately 1-50 km, embedded within midlatitude weather systems such as extratropical cyclones, their fronts and airstreams. It remains a major challenge to correctly represent moist diabatic processes and their impact on MOCs in numerical weather models.

Recent airborne field campaigns in tropical and polar regions have demonstrated the power of water isotope observations to quantify and disentangle the role of different diabatic processes. Building on this approach, NAWDICiso, i.e. the isotopic component of the North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC, January – March 2026) aimed at conducting multi-platform observations of water vapour isotopes on two aircrafts (French ATR-42 operated by Safire and German Cessna F406 D-ILAB operated by TU Braunschweig) and at ground-based stations in Brittany (operated at the KITcube together with KIT), Ireland as well as within a European-wide precipitation sampling network to survey the downstream impact of North Atlantic cyclones. This intensive measurement period enables us to capture the imprint of diabatic processes on MOCs through simultaneous observations of stable water isotopes in water vapour and precipitation. Here, we present a first overview of the collected data and selected case studies from the NAWDICiso observation network. These measurements, combined with km-scale resolution isotope and tagging-enabled numerical model simulations, provide the basis for identifying and characterising moist diabatic processes within MOCs. Ultimately, these observations deliver unprecedented three-dimensional insights into MOCs in midlatitude weather systems, which are essential for improving forecasts of the development, intensification, and surface impacts of these weather systems.