Water Vapour Isotope Signals during an Atmospheric River Event: Model Simulations and Observations from TROPOMI and TCCON

The Arctic is warming at more than twice the global average, a phenomenon known as Arctic amplification. In consistency with this rapid warming, a pronounced moistening trend is observed over the past 30-40 years. While the region's atmospheric humidity is increasing, it remains unclear whether this increased moisture originates primarily from local sources such as enhanced evaporation from ice-free ocean surfaces or is transported from lower latitudes. Atmospheric rivers (ARs) play a central role in the poleward moisture transport and play a critical role in Arctic climate processes.

During phase change processes, such as evaporation and condensation, the heavy stable isotopes of water accumulate in the condensed phase. As a result, the isotopic composition of water vapour act as an integrated tracer of an air parcel’s condensation (or phase change) history, providing information on moisture sources and transport pathway that can help to improve our understanding of moisture processes during transport into and within the Arctic.

In this study, we investigate the isotopic composition of water vapour during an event that occurred in March 2021 where an AR made landfall in Northern Scandinavia. We analyse data from the isotope-enabled COSMO model (COSMO-iso) and evaluate them against observations from the TROPOMI satellite instrument and TCCON ground based stations to diagnose the isotopic signals associated with the AR. The comparison indicates that TROPOMI observations capture more detailed spatial structures and more distinct features than COSMO-Iso model output. Histogram analyses further show systematic differences in isotope abundances in the model compared to TROPOMI. Ground-based TCCON observations provide an independent reference to assess the consistency of both the model simulations and satellite retrievals during the event.