Harald Sodemann – Evaluating regional model biases in the European Arctic using paired stable water isotope observations

CESOC kindly invites you to a talk given by Prof. Harald Sodemann, Professor, Meteorology (Numerical Modelling, Atmospheric Water Cycle), at the University of Bergen and Mercator Fellow in the TR172  “Arctic Amplification” with the title:

Evaluating regional model biases in the European Arctic using paired stable water isotope observations

Date: 24 July 2025,
Time: 14:00 CEST
Location: University of Cologne

It will also be streamed via zoom:
for online participation, please contact info@cesoc.net

Abstract:

Svalbard is located within the major entry pathway of relatively warm, mid-latitude air masses into the polar region. The stable water isotope composition in atmospheric water vapour and precipitation is a sensitive indicator of the accumulated condensation history of air masses on their way into the Arctic. The progressive loss of heavy isotopes with precipitation results in the well-known latitude gradient of stable isotopes in precipitation. Here we evaluate how well a simulation with the isotope-enabled regional model COSMO-iso driven by ECHAM6 nudged to ERA5 reanalyses represents the increasing depletion with higher latitude measurement location. We thereby make use of a data set of time-resolved precipitation and vapour isotope measurements collected during the ISLAS campaigns from 2020 to 2022 using research aircraft and station measurements from Ny-Ålesund, Longyearbyen, Tromsø, Andøya, Bergen, and Finse, all located along the European entry pathway for mid-latitude air masses into the Arctic. Results show that the time variations are well represented at all three measurements sites. While the sub-Arctic and the mid-latitude sites show a small low-bias in the simulated isotope depletion for δ18O and δD in precipitation, the indicator for non-equilibrium fractionation d-excess shows a high bias of more than 10 permil. Comparison with measurements taken on Svalbard during the ISLAS campaigns show a substantial increase in scatter with no consistent bias for δ18O and δD, whereas the d-excess has a consistent low bias. Vapour measurements confirm the results the from precipitation comparison. An investigation of the thermodynamic environment within and below clouds from in-situ and remote sensing observations points to an important role of the saturation adjustment in the microphysics scheme that prevents highly ice super-saturated environments in clouds that are conducive to low values of the d-excess. The operational model AROME-Arctic allows for more wide-spread regions of ice super-saturation, but does currently not include water isotopes. We conclude that paired precipitation-vapour water isotope measurements are a valuable diagnostic for model evaluation for mixed-phase cloud microphysics in the Arctic.

Bio: https://www4.uib.no/en/find-employees/Harald.Sodemann