Observations and Modelling of the Atmospheric Boundary Layer Over Sea-Ice in a Svalbard Fjord

Sonic anemometer and profile mast measurements made in Wahlenbergfjorden, Svalbard Arctic archipelago, in May 2006 and April 2007 were employed to study the atmospheric boundary layer over sea-ice. The turbulent surface fluxes of momentum and sensible heat were calculated using eddy correlation and gradient methods. The results showed that the literature-based universal functions underestimated turbulent mixing in strongly stable conditions. The validity of the Monin-Obukhov similarity theory was questionable for cross-fjord flow directions and in the presence of mesoscale variability or topographic effects. The aerodynamic roughness length showed a dependence on the wind direction. The mean roughness length for along-fjord wind directions was (2.4 +/- 2.6) x 10(-4) m, whereas that for cross-fjord directions was (5.4 +/- 2.8) x 10(-3) m. The thermal stratification and turbulent fluxes were affected by the synoptic situation with large differences between the 2 years. Channelling effects and drainage flows occurred especially during a weak large-scale flow. The study periods were simulated applying the Weather Research and Forecasting (WRF) model with 1-km horizontal resolution in the finest domain. The results for the 2-m air temperature and friction velocity were good, but the model failed to reproduce the spatial variability in wind direction between measurement sites 3 km apart. The model suggested that wind shear above the stable boundary layer provided a non-local source for the turbulence observed.