Observations of summer turbulent surface fluxes in a High Arctic fjord

Abstract

AbstractThe summer atmospheric boundary layer over a fjord in the High Arctic has been investigated during three consecutive years (2008–2010). Measurements of turbulent surface layer fluxes of momentum and sensible heat using a sonic anemometer and slow‐response instruments were taken from a tower on the coast of Isfjorden, Svalbard, and analysed for seasonal variability and differing fetch conditions. The results resembled the atmospheric boundary layer characteristics previously found for ice‐free winter conditions. The momentum flux was usually directed downwards, but for low wind speeds there was a possible contribution of swell, giving an upward directed momentum flux. The cross‐wind component of the momentum flux sometimes contributed significantly to the total flux. The sensible heat flux was very dependent on the origin of air, whether it had a long over‐water fetch, or originated from land areas with or without glaciers. In addition to non‐stationarity of the flow due to the influence of the fjord's shape and its surrounding topography, low wind speeds questioned the validity of the Monin–Obukhov similarity theory, whereas the over‐water fetch and off‐wind angle were of minor importance. Moreover, some results, especially the off‐wind angle, were very sensitive to how the raw data were treated, in particular which coordinate rotation method was employed, the double rotation or the planar fit method.