Observations and Modelling of the Atmospheric Boundary Layer Over Sea-Ice in a Svalbard Fjord |
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| Authors: | Eeva Mäkiranta Timo Vihma Anna Sjöblom Esa-Matti Tastula |
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| Institution: | (1) Physics Department, Mangalagangotri, Mangalore University, Mangalore, India;(2) Indira Gandhi Centre for Atomic Research, Kalpakkam, India |
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| Abstract: | 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)
× 10−4 m, whereas that for cross-fjord directions was (5.4 ± 2.8) × 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. |
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