Glacio-meteorological investigations on Vatnajokull, Iceland, Summer 1996:: An overview

We give an overview of a glacio-meteorological experiment carried out in the summer (melt season) of 1996 on the largest European ice cap, Vatnajokull, Iceland (area 8000 km(2); altitude range: from sea level to about 2000 m). The main goal was to understand how the energy used in the melting of snow and ice is delivered to the surface. Many meteorological stations were operated simultaneously on the ice cap, at almost all of which profile measurements were made. Cable balloons and radiosondes were used to probe the vertical structure of the boundary layer. It appears that the flow near the surface is katabatic most of the time, with the height of the wind maximum varying between a few metres and a few tens of metres. It is only during the passage of intense storms that the katabatic wind in the melt zone disappears. Global radiation increases significantly with altitude. Surface albedo varies enormously in space and time, with very low values (approximate to 0.1) being found at many places because of the melt out of volcanic ash layers. If we consider the total melt in the period 22 May-31 August 1996, we conclude that radiation typically provides two-thirds of the melt energy, and turbulent exchange of heat one-third. At locations high on the glacier, turbulent exchange becomes less significant.