Stable boundary layers commonly form during Arctic polar night, but their correct representation poses a major challenge for numerical weather prediction (NWP) systems. To perform detailed model verification by probing the lower boundary layer, airborne fiber-optic distributed sensing (FODS), tethered sonde and ground-based eddy-covariance measurements are carried out during contrasting synoptic forcings in a fjord-valley system in Svalbard. The FODS-derived turbulent potential energy and static stability profiles are used to investigate the spatial and temporal evolution of different inversion types. The observed vertical temperature and wind speed profiles are compared to two configurations of the HARMONIE-AROME system with different horizontal resolutions of 2.5 km and 0.5 km. The higher-resolved model captures cold pool and low level jet formation during weak synoptic forcing, resulting in a well-represented vertical temperature profile, while the coarser model exhibits a warm bias in near-surface temperatures up to 8 K. During changing background flow, the higher-resolved model is more sensitive to misrepresented wind directions. The results indicate the importance of the ratio between nominal model resolution and valley width to represent stable boundary layer features. Kinetic and potential energy spectra are examined for the two model configurations to derive the effective resolutions. The higher-resolved model has also a higher effective resolution, but is more diffusive than the coarser model. Our results underline the substantial benefit of spatially resolving FODS measurements for model verification studies and underline the importance of model and topography resolution for accurate representation of stable boundary layers in complex terrain.

Accurately simulating the interactions between the components of a coupled Earth modelling system (atmosphere, sea-ice, and wave) on a kilometer-scale resolution is a new challenge in operational numerical weather prediction. It is difficult due to the complexity of interactive mechanisms, the limited accuracy of model components and scarcity of observations available for assessing relevant coupled processes. This study presents a newly developed convective-scale atmosphere-wave coupled forecasting system for the European Arctic. The HARMONIE-AROME configuration of the ALADIN-HIRLAM numerical weather prediction system is coupled to the spectral wave model WAVEWATCH III using the OASIS3 model coupling toolkit. We analyze the impact of representing the kilometer-scale atmosphere-wave interactions through coupled and uncoupled forecasts on a model domain with 2.5 km spatial resolution. In order to assess the coupled model’s accuracy and uncertainties we compare 48-hour model forecasts against satellite observational products such as Advanced Scatterometer 10 m wind speed, and altimeter based significant wave height. The fully coupled atmosphere-wave model results closely match both satellite-based wind speed and significant wave height observations as well as surface pressure and wind speed measurements from selected coastal station observation sites. Furthermore, the coupled model contains smaller standard deviation of errors in both 10m wind speed and significant wave height parameters when compared to the uncoupled model forecasts. Atmosphere and wave coupling reduces the short term forecast error variability of 10m wind speed and significant wave height with the greatest benefit occurring for high wind and wave conditions.