Long-term turbulent flux measurements over Arctic fjords in Svalbard

Long-term measurements on a 20 m tower combined with shorter measuring campaigns are used to study processes involved in air-ice-sea interactions in the Arctic, with a special emphasis on fjord systems in Svalbard.

The boundary layer in the Arctic is poorly understood compared to boundary layers at lower latitudes. The main reasons for this are the practical problems of measuring in a remote and very cold environment and this is especially true for the marine boundary layer. Air-ice-sea interactions in the Arctic have been studied in several short field experiments, but long-term measurements are still rare.

In the Arctic, temperature differences between the ocean and the atmosphere can be extreme and lead to large heat fluxes in areas where not restricted by a sea ice cover. A special case of air-ice-sea interactions takes place in fjords, i.e., narrow inlets of the sea often surrounded by complex topography consisting of mountains, valleys and glaciers. Distinctive meteorological conditions apply in the fjord systems due to these features and the boundary layer is influenced also by possible sea ice and oceanographic phenomena such as polynyas, i.e., openings enclosed by sea ice. Svalbard, an archipelago in the Arctic Ocean, provides an excellent location for long-term monitoring of turbulent fluxes, especially over fjords.

In January 2008, long-term meteorological measurements on a 20 m tower on the coastline of Isfjorden, Svalbard (78° 15' N, 15° 28' E), will be started. Isfjorden covers an area of 3,084 km² and is orientated in southwest-northeast direction. At the measuring site, situated close to shoreline on the southern coast, there is an over fjord fetch of approximately 25-40 km. The sea ice cover in Isfjorden is seasonal and in a normal sea ice year consists of fast ice in the inner part of the fjord and mostly open water with frazil ice and thin ice in the mouth area. The measurement site located in the middle of the fjord enables the study of turbulent fluxes during different sea ice conditions. Slow response wind speed and wind direction sensors are placed at four levels and temperature and humidity sensors at two levels on the mast. In addition, a sonic anemometer placed on the mast measures turbulence at a rate of 20 Hz. This set up offers a unique possibility to study the air-ice-sea interaction in fjords on a continuous basis. An additional, shorter measuring campaign will also take place in April 2008 in Storfjorden, a larger fjord situated southeast from Isfjorden, in order to study differences between dissimilar fjords.

The main purpose with this study is to gain a better understanding of the processes involved in air-ice-sea interactions with special emphasis on phenomena typical for Arctic fjords, such as influence of sea ice, fetch and topography on the turbulence structure. Results from the first winter season with measurements will be presented.