The Summer Atmospheric Boundary Layer in a Fjord in Svalbard

The summer atmospheric boundary layer in a High Arctic fjord has been investigated during three consecutive years (2008-2010). Measurements of momentum and sensible heat fluxes using a sonic anemometer and slow response instruments were taken in a 30-m tower over Isfjorden, close to the settlement Longyearbyen in Svalbard at 78°N, and analysed in terms of seasonal and spatial variability.

The momentum flux is usually directed downwards, but for low wind speeds there is a possible contribution of swell giving an upward directed momentum flux. For high wind speeds, the cross-wind component of the momentum flux also becomes significant. The sensible heat flux is very dependent on the origin of air, whether it has a long over water fetch, or comes from an area with high mountains or glaciers.

In addition to the shape of the fjord and its surrounding topography influencing the flow field, non-stationarity, and large off-wind angles contribute to question the validity of the Monin-Obukhov similarity theory during some conditions. Moreover, the results are very sensitive to how the raw data is treated, in particular which rotation method is used, the double rotation method or the planar fit method.