Modelled and observed phenomena's in a marginal ice zone

The boundary layer over a marginal ice zone was studied during a four week measuring campaign in the Bay of Bothnia, February-March 1998. During the field campaign radio sonde measurements were performed four times a day at six station in the area. Two stations were located at the coastline were there was open water (Sundsvall and Merikarvia). Two stations were situated with solid ice as upstream fetch for onshore winds (Kallax and Kokkola). Kokkola and Merikarvia are located on the Finnish west coast, and Sundsvall and Kallax are located on the Swedish east coast. A research vessel, Aranda, was situated in the ice outside the Finnish west coast. At the sixth site, situated close to the city Umeå on the Swedish east coast, the onshore conditions varied during the campaign. The fetch with ice varied from approximately a kilometre to more than 10 km. However the conditions of the ice varied also. At the end of the period the ice closest to the site was solid ice of a depth of more than 10 cm while at distances beyond 1 km from the site there was new ice which had a thickness of the order 0-2 cm. In addition to the radio sounding surface measurements were performed at three of the stations; Arranda, Umeå and Kokkola. At all sites turbulent fluctuations of the three wind components and virtual temperature were measured with a sonic anemometer at one height. At the sites profile measurements and radiation measurements were also performed.

During the experiment the ice outside Umeå was broken and open water appeared close to the coast during several occasions. As the water was much warmer than the air meso-scale circulation systems were developed. The different thermal structures of the different ices caused some interesting phenomena's in combination with the open water. The phenomena's observed were ice breeze, internal boundary layer and low level jets. Investigation on the occurrence and structure of the phenomena's has been performed. The phenomena observed were simulated with a meso scale model using different boundary conditions and ice distribution in order to study the sensitivity of the ice and snow conditions on the phenomena observed. The simulations were performed with different energy balance scheme for snow and ice areas in order to find an optimum algorithm.