Case study of a moisture intrusion over the Arctic with the ICON model: resolution dependence of its representation

Abstract. The Arctic is warming faster than the global average and any other region. One important factor for this is the poleward atmospheric transport of heat and moisture, which contributes directly to the surface and air warming. In this case study, the atmospheric circulation and spatio-temporal structure of a moisture intrusion event is assessed, which occurred during the 5th to 7th June 2017 over the Nordic Seas during an intensive measurement campaign over Svalbard. This analysis focuses on high-spatial resolution simulations with the ICON (ICOsahedral Non-hydrostatic) model which is put in context with coarser resolution runs as well the ERA5 reanalysis. A variety of observations including passive microwave satellite measurements is used for evaluation. The global operational ICON forecasts from the German Weather Service DWD at 13 km horizontal resolution are used to drive high resolution Limited Area Mode (LAM) ICON simulations over the Arctic with 6 km and 3 km horizontal resolutions. The results show the skillfull capacity of the ICON-LAM model to represent the observed spatio-temporal structure of the selected moisture intrusion event and its signature in the temperature, humidity and wind profiles, and surface radiation. The high resolution simulations offer a higher accuracy than the global simulations and the ERA5 reanalysis, compared to observations. This is especially demonstrated in the representation of the changing vertical structure of specific humidity and wind associated with the moisture intrusion passing Ny-Alesund (western Svalbard). Namely, the humidity increase in 1–2 km height topped by a dry layer and the development of a low-level wind jet is best represented by the 3 km simulation. The study also demonstrates that such moisture intrusions can have a strong impact on the radiative and turbulent heat fluxes at the surface. A drastic decrease of downward shortwave radiation by ca. 500 W m−2 and an increase of downward longwave radiation by ca. 100 W m−2 within 3 hours are determined, which highlight the importance of both moisture and clouds associated with this event for the surface energy budget.